Search

The persistence of motivational alterations, including apathy, in older HIV-1 seropositive individuals, despite treatment with combination antiretroviral therapy, necessitates the development of innovative adjunctive therapeutics. S-Equol (SE), a selective estrogen receptor β agonist, has been implicated as a neuroprotective and/or neurorestorative therapeutic for HIV-1 associated neurocognitive disorders (HAND); its therapeutic utility for apathy, however, has yet to be systematically evaluated. Thus, beginning at approximately seven to nine months of age, HIV-1 transgenic (Tg) and control animals were treated with either a daily oral dose of SE (0.2 mg) or vehicle and assessed in a series of tasks to evaluate goal-directed behavior. First, at the genotypic level, apathetic behavior in older HIV-1 Tg rats treated with vehicle was characterized by a diminished reinforcing efficacy of, and sensitivity to, sucrose and enhanced drug seeking for cocaine relative to control animals treated with vehicle. Second, treatment with SE ameliorated alterations in goal-directed behaviors and reduced drug seeking behavior in HIV-1 Tg rats. Following a history of cocaine self-administration, HIV-1 Tg animals treated with vehicle exhibited prominent decreases in dendritic branching and a shift towards longer dendritic spines with decreased head diameter; synaptic dysfunction that was partially restored by SE treatment. Taken together, SE restored motivated behavior in the HIV-1 Tg rat, expanding the potential clinical utility of SE to include both neurocognitive and affective alterations.

An environmental barrier-coated Sylramic-iBN/pyrolytic carbon/chemical vapor infiltration silicon carbide ceramic matrix composite was characterized in a harsh combustion environment under two conditions; (i) with a coating surface temperature of 1480℃, and (ii) with a combustion flame distance of 120 mm (constant flux). Three coating systems were evaluated; Coating “A” (ytterbium silicate using hafnium–silicate bond), Coating “B” (ytterbium silicate using alumina bond), and Coating “C” (ytterbium–silica compounds using alumina bond). All three coatings survived with essentially no mass loss up to 25 h when tested at 1480℃. At a flame distance of 120 mm coatings “A” and “B” experienced extensive degradation and strength loss while coating “C” had practically no degradation in retained strength. Coating “C” outperformed the other two coatings exposed to the harsh combustion environment. It performed best in terms of material loss, thermal barrier capability, and residual tensile strength.

Motivational alterations, such as apathy, in HIV-1+ individuals are associated with decreased performance on tasks involving frontal-subcortical circuitry. We used the HIV-1 transgenic (Tg) rat to assess effect of long-term HIV-1 protein exposure on motivated behavior using sucrose (1–30%, w/v) and cocaine (0.01–1.0 mg/kg/infusion) maintained responding with fixed-ratio (FR) and progressive-ratio (PR) schedules of reinforcement. For sucrose-reinforced responding, HIV-1 Tg rats displayed no change in EC50 relative to controls, suggesting no change in sucrose reinforcement but had a downward shifted concentration-response curves, suggesting a decrease in response vigor. Cocaine-maintained responding was attenuated in HIV-1 Tg rats (FR1 0.33 mg/kg/infusion and PR 1.0 mg/kg/infusion). Dose-response tests (PR) revealed that HIV-1 Tg animals responded significantly less than F344 control rats and failed to earn significantly more infusions of cocaine as the unit dose increased. When choosing between cocaine and sucrose, control rats initially chose sucrose but with time shifted to a cocaine preference. In contrast, HIV-1 disrupted choice behaviors. DAT function was altered in the striatum of HIV-1 Tg rats; however, prior cocaine self-administration produced a unique effect on dopamine homeostasis in the HIV-1 Tg striatum. These findings of altered goal directed behaviors may determine neurobiological mechanisms of apathy in HIV-1+ patients.

Fatigue behavior of Sylramic-iBN/BN/CVI SiC CMC was investigated under tension–tension fatigue using a test facility which simulated simultaneously both loading and combustion conditions of hot-section components of gas turbine engines. Combustion environment was created using a high-velocity oxygen fuel gun to impinge combustion flame on one side of specimen subjected to fatigue to simulate the real situation. The flame-impinged surface of specimen was heated to average temperature of 1250, 1350, or 1480 °C. Ultimate tensile strength of CMC was about 270 MPa at 1480 °C under combustion environment. Fatigue life diagram was established at stress ratio of 0.1 and frequency of 1 Hz. The CMC survived up to 25 h at 46 and 33 % of ultimate tensile strength under combustion at 1250 and 1350 °C, respectively. However, it could not survive 25 h at 1480 °C under combustion fatigue environment even with no stress on the specimen due to degradation/erosion of the material. Microscopic analysis of fracture surface showed oxidation of BN interface, which was more on flame side than other side. Fracture surfaces showed oxide formation over matrix, fibers, and/or fiber/matrix interphase causing embrittlement and thereafter failure of CMC.

Purposes: This work consists of studying the interseed and tissue composition effects for two model iodine seeds: the IBt Interseed‐125 and the 6711 model seed. Materials & Methods: Three seeds were modeled with the MCNP MC code in a water sphere to evaluate the interseed effect. The dose calculated at different distances from the centre was compared to the dose summed when the seeds were simulated separately. The tissue composition effect was studied calculating the radial dose function for different tissues. Before carrying out post‐implant studies, the absolute dose calculated by MC was compared to experiment results: with LiF TLDs in an acrylic breast phantom and with an EBT Gafchromic film placed in a water tank. Afterwards, the TG‐43 approximation effects were studied for a prostate and breast post‐implant. Results and Discussion: The interseed effect study shows that this effect is more important for model 6711 (15%) than for IBt (10%) due to the silver rod in 6711. For both seed models the variations of the radial dose function as a function of the tissue composition are quasi similar. The absolute dose comparisons between MC calculations and experiments give good agreement (inferior to 3% in general). For the prostate and breast post‐implant studies, a 10% difference between MC calculations and the TG‐43 is found for both models of seeds. Conclusion: This study shows that the differences in dose distributions between TG43 and MC are quite similar for the two models of seeds and are about 10% for the studied post‐implant treatments.

International audience; Cystic fibrosis is caused by a mutation in the gene for the cystic fibrosis transmembrane conductance regulator (CFTR) protein. N-butyl 1-deoxynojirimycin (N-Bu DNJ), a clinical candidate for the treatment of cystic fibrosis, is able to act as a CFTR corrector by overcoming the processing defect of the mutant protein. To explore the potential of multivalency on CFTR correction activity, a library of twelve DNJ click clusters with valencies ranging from 3 to 14 were synthesized. Significantly, the trivalent analogues were found to be up to 225-fold more potent than N-Bu DNJ and up to 1000-fold more potent than the corresponding monovalent models. These results provide the first description of a multivalent effect for correcting protein folding defects in cells and should have application for the treatment of a number of protein folding disorders. Preliminary mechanistic studies indicated that CFTR correction activity enhancement was not due to a multivalent effect in ER-glucosidase inhibition or to a different mode of action of the multivalent iminosugars.

Filamentous actin protein (F-actin) plays a major role in spinogenesis, synaptic plasticity, and synaptic stability. Changes in dendritic F-actin rich structures suggest alterations in synaptic integrity and connectivity. Here we provide a detailed protocol for culturing primary rat cortical neurons, Phalloidin staining for F-actin puncta, and subsequent quantification techniques. First, the frontal cortex of E18 rat embryos are dissociated into low-density cell culture, then the neurons grown in vitro for at least 12-14 days. Following experimental treatment, the cortical neurons are stained with AlexaFluor 488 Phalloidin (to label the dendritic F-actin puncta) and microtubule-associated protein 2 (MAP2; to validate the neuronal cells and dendritic integrity). Finally, specialized software is used to analyze and quantify randomly selected neuronal dendrites. F-actin rich structures are identified on second order dendritic branches (length range 25-75 µm) with continuous MAP2 immunofluorescence. The protocol presented here will be a useful method for investigating changes in dendritic synapse structures subsequent to experimental treatments.

In order to generate new data for vitamin D content for the Canadian Nutrient File, a method for the quantification of vitamin D3 and 25(OH)D3 in foodstuffs has been modified and improved. Vitamin D3 was quantified using reverse phase liquid chromatography (LC) with UV-diode array detector (UV-DAD), while 25(OH)D3 was measured by triple quadrupole mass spectrometry (APCI MS/MS). Quantification was by internal standards (IS) using vitamin D2 and 25(OH)D2. A Certified Reference Material (CRM-421 containing vitamin D3) and a control sample (internally generated reference material of ground pork containing both vitamin D3 and 25(OH)D3) were used as validation and quality control tools. Limit of detection for both compounds was 0.04 μg/100 g. Accuracy for vitamin D in the CRM-421 was 99% (0.142 mg/kg for a target of 0.143, n = 10). Recovery of vitamin D3 in ground pork was 97% (88% absolute recovery). For 25(OH)D3, a recovery of 94% (73% absolute recovery) was obtained. Using this method, data for vitamin D3 and 25(OH)D3 content in a variety of foods (pork, beef, eggs, poultry, fish, and dinners) have been generated.

Defining the impact on health of exposure to a low-dose pesticide mixture via food intake is a topical question since epidemiological studies suggest that this may increase the risk of pathologies and particularly haematopoietic malignancies. Here we investigated on the haematopoietic system of mice, the effect of a mixture of six pesticides frequently ingested through the intake of fruits and vegetables produced in France (alachlor, captan, diazinon, endosulfan, maneb, mancozeb). The mixture was administered repeatedly by gavage to mice for 4 weeks at levels derived from the human Acceptable Daily Intake (ADI) level adapted to the mean weight of mice. Using a NMR-based metabonomic approach, we show that this treatment led to specific gender-linked variations in the level of hepatic metabolites involved in oxidative stress and in the regulation of glucose metabolism, indicating a metabolic signature for this repeated administration. Interestingly, exposure to the low-dose pesticide mixture induced significant changes in the blood cell counts with modifications in the clonogenic and differentiating capacities of haematopoietic progenitors showing abnormalities in the granulocytic and monocytic lineages in female and male mice, respectively. From a molecular point of view, the changes induced by the pesticide treatment correlated with modifications of the PI 3-kinase/Akt signalling pathway, the tyrosine kinase Pyk2 and the c-Myc transcription factor, which are involved in the balance between self-renewal and differentiation of haematopoietic stem cells. Our results point to a significant effect of a very low dose of a mixture of commonly used pesticides on mice metabolism and haematopoietic system with major differences between males and females.

Different processing approaches were adopted to obtain the best combination of strength and toughness. The approach that yielded superior properties was examined in detail to study the mechanical response of nanoscale calcium carbonate-reinforced high density polyethylene in conjunction with unreinforced high density polyethylene. The reinforcement of high density polyethylene with nanoscale calcium carbonate increases impact strength and is not accompanied by decrease in yield strength. The addition of nanoscale calcium carbonate to high density polyethylene alters the micromechanism of deformation from crazing-tearing in high density polyethylene to fibrillation in high density polyethylene-calcium carbonate nano-composite.

A new type of injector has been developed for gas chromatographic analysis. The injector has high volume and band compression (HVBC) capabilities useful for the analysis of complex samples. The injector consists essentially of a packed liner operated at room temperature while a narrow heated zone is used to axially scan the liner selectively desorbing the compounds of interest. The scanning speed, distance and temperature of the zone are precisely controlled. The liner is connected to an interface which can vent the solvent or any undesirable compounds, and transfer the analytes to an analytical column for separation and quantification. The injector is designed to be compatible with injection volumes from 1 to more than 250microL. At a low sample volume of 1microL, the injector has competitive performances compared to those of the "on-column" and "split/splitless" injectors for the fatty acid methyl esters and toxaphene compounds tested. For higher volumes, the system produces a linear response according to the injected volume. In this explorative study, the maximum volume injected seems to be limited by the saturation of the chromatographic system instead of being defined by the design of the injector. The HVBC injector can also be used to conduct "in situ" pretreatment of the sample before its transfer to the analytical column. For instance, a toxaphene sample was successively fractionated, using the HVBC injector, in six sub-fractions characterized by simpler chromatograms than the chromatogram of the original mixture. Finally, the ability of the HVBC injector to "freeze" the separation in time allowing the analyst to complete the analysis at a later time is also discussed.

Trypsin was immobilized using glutaraldehyde either by covalent attachment to aminopropyl controlled pore glass (CPG) or by direct crosslinking without a carrier. As peptide mapping is a comparative method, reproducibility of the analytical separation techniques (liquid chromatography, HPLC, and capillary zone electrophoresis, CZE) and the proteolyses resulting from both enzyme preparations were evaluated. Elution time reproducibilities of 0.3 and 0.6% were found for HPLC and CZE maps, respectively. Proteolysis reproducibility was tested for each trypsin preparation and compared with solution phase proteolysis. Sequence coverages of ca 65% were obtained from matrix‐assisted laser desorption/ionization−time‐of‐flight (MALDI‐TOF) mass spectral mapping for the two solid phase preparations.

Illicit drugs, such as cocaine, are known to increase the likelihood and severity of HIV-1 associated neurocognitive disorders (HAND). In the current studies synaptic integrity was assessed following exposure to low concentrations of the HIV-1 viral protein Tat 1-86B, with or without cocaine, by quantifying filamentous actin (F-actin) rich structures (i.e., puncta and dendritic spines) on neuronal dendrites in vitro. In addition, the synapse-protective effects of either R-Equol (RE) or S-Equol (SE; derivatives of the soy isoflavone, daidzein) were determined. Individually, neither low concentrations of HIV-1 Tat (10 nM) nor low concentrations of cocaine (1.6 μM) had any significant effect on F-actin puncta number; however, the same low concentrations of HIV-1 Tat + cocaine in combination significantly reduced dendritic synapses. This synaptic reduction was prevented by pre-treatment with either RE or SE, in an estrogen receptor beta dependent manner. In sum, targeted therapeutic intervention with SE may prevent HIV-1 + drug abuse synaptopathy, and thereby potentially influence the development of HAND.

TRPC6 plays important human physiological functions, notably in artery and arterioles constriction, in regulation of vascular volume and in bronchial muscle constriction. It is implicated in pulmonary hypertension, cardiovascular disease, and focal segmental glomerulosclerosis and seems to play a role in cancer development. Previously, we identified Guanabenz, an α2-adrenergic agonist used for hypertension treatment (Wytensin®), as an activator of calcium-dependent chloride channels (CaCC) in human Cystic Fibrosis (CF) nasal epithelial cells by transiently increasing [Ca2+]i via an influx of extracellular Ca2+. In this study, using assays to measure chloride channel activity, we show that guanabenz is an activator of CaCC in freshly dissociated human bronchial epithelial cells from three CF patients with various genotypes (F508del/F508del, F508del/R1066C, F508del/H1085R). We further characterised the effect of guanabenz and show that it is independent of α-adrenergic receptors, is inhibited by the TRPC family inhibitor SKF-96365 but not by the TRPV family inhibitor ruthenium red. Using western-blotting, Ca2+ measurements and iodide efflux assay, we found that TRPC1 siRNA has no effect on guanabenz induced responses whereas TRPC6 siRNA prevented the guanabenz-dependent Ca2+ influx and the CaCC-dependent activity stimulated by guanabenz. In conclusion, we show that TRPC6 channel is pivotal for the activation of CaCC by guanabenz through a α2-adrenergic-independent pathway in human airway epithelial cells. We suggest propose a functional coupling between TRPC6 and CaCC and guanabenz as a potential TRPC6 activator for exploring TRPC6 and CaCC channel functions and corresponding channelopathies.

The synthesis of eleven 1-deoxynojirimycin (DNJ) derivatives presenting either a monofluoro, difluoro, thiolated or unsaturated N-alkyl chain of various length is described. Exploiting the unsaturated moiety on the nitrogen, fluorine has been introduced through a HF/SbF5 superacid catalysed hydrofluorination and thiol-ene click chemistry allowed introduction of sulfur. The synthetic derivatives have been tested for their ability to inhibit glycosidases and correct F508del-CFTR. Two of the unsaturated iminosugars exhibited potency similar to Miglustat as F508del-CFTR correctors. The thioalkyl iminosugars as well as the corresponding alkyl iminosugars demonstrated low micromolar α-glucosidases and trehalases inhibition. Introduction of fluorine abolished F508del-CFTR correction and trehalase inhibition.

Thermoanalytical techniques are currently used for the analysis of additives contained in polymers that cannot be easily dissolved, extracted, or hydrolyzed. With these techniques, the polymers are heated to liberate the additives trapped in the polymer matrix. If the polymer is heated slowly, up to its thermal degradation, the technique is called temperature-programmed pyrolysis (TPPy). For TPPy experiments, mass spectrometry is generally used as the detection method. The ionization sources commonly used in mass spectrometry, such as CI and EI, can cause fragmentation during the ionization process. Fragmentation decreases the sensitivity of the molecular ions and increases the risks of interferences with the compounds coming from the matrix. An energy-tunable ionization technique, called metastable atom bombardment (MAB), is proposed for TPPy/MS experiments. With this ionization source, the energy of ionization depends on the metastable gas used. With low-energy metastable gases such as Xe or N(2), fragmentation is reduced compared to CI, whereas with medium-energy metastable gases such as Ar or Kr, the fragmentation is similar to that observed with CI. TPPy/MAB-MS was performed on an unknown polyurethane-based car paint. The detection of molecular ions and characteristic fragments with MAB(N(2)) led to the identification of two light stabilizers: Bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate (BPPS) and 2-(2H-benzotriazol-2-yl)-4,6- di-tert-pentylphenol (PTPP). Using MAB(Ar) to simulate CI, the molecular ion and one of the two characteristic fragments of BPPS were not detected, thus confirming the advantage of using MAB(N(2)) ionization for TPPy/MS experiments.

Polyurethanes are widely used in the formulation of car paints. During thermal degradation, such polymeric systems can generate a wide range of combustion products, including isocyanates. Their relative yield depends greatly on the specific combustion conditions selected (e.g. temperature, ventilation, fuel load) and sampling condition chosen (non-aged versus aged atmospheres). The extent that the analytes found by utilizing specific laboratory-scale conditions can potentially induce adverse health effects in humans is contingent upon further variables; their discussion is beyond the scope of this investigation. Thus, in order to evaluate potential hazards for workers potentially exposed to combustion products in car repair shops and to develop proper sampling strategies, it is important to understand the principal mechanisms involved in thermal degradation, with particular attention being paid to the isocyanate profile following combustion of these complex systems. A DIN 53436 laboratory scale furnace was used to thermally degrade the polymer under inert and oxidative atmospheres. Isocyanates in the gaseous effluent were analyzed using impinger flasks containing 1-(2-methoxyphenyl)piperazine (MOPIP) as derivatizing reagent. The derivatives were analyzed using high performance liquid chromatography hyphenated with tandem mass spectrometry (HPLC/MS/MS). During these experiments, isocyanic acid, aliphatic isocyanates, alkenyl isocyanates and many structural isomers of these compounds were analyzed.

Rapid detection and identification of bacteria and other microorganisms has become a field where new analytical methods are needed. An approach, based on the use of pyrolysis coupled to mass spectrometry (Py-MS), for the detection and identification of bacteria in urine and other aqueous samples is described. In this procedure, the sample is placed on a direct insertion probe and pyrolysis is conducted directly into the ion source of the mass spectrometer. Ionization is achieved with a metastable atom bombardment source (MAB). In contrast to electron ionization, this novel ionization source, by providing discrete ionization energies, allows selective ionization and control over fragmentation. The MAB source is coupled to a time-of-flight (Tof) mass analyzer that provides high sensitivity and fast spectral acquisition. Experiments conducted with a number of uropathogenic bacteria, such as Escherichia coli, Citrobacter freundii, Proteus mirabilis and Pseudomonas aeruginosa, reveal that they provide discernable fingerprints when analyzed in urine samples by Py-MAB-Tof. Results can be obtained in minutes and the sensitivity is such that 104 bacteria on the pyrolysis probe are required for analysis.

Polyurethanes are widely used in the manufacture of commercial products such as foams and paints. During combustion, these polymers can generate isocyanates, which induce adverse health effects. Polymer pyrolysis (Py) hyphenated with mass spectrometry (MS) allows the investigation of polymer thermal degradation over time/temperature. A diphenylmethanediisocyanate (MDI) polyurethane foam was analyzed with electron ionization (EI) and metastable atom bombardment (MAB) ionization at a pyrolysis temperature of 400 °C. The recently introduced MAB ionization source uses discrete energy stored in metastable atoms of gases to ionize the analytes. This characteristic allows modulation of the ionization energy by simply changing the ionization gas. The extensive fragmentation of molecular ions observed using EI 70 eV is not totally eliminated with EI 10 eV. However, only molecular ions are observed with MAB using N2 as the ionization gas. Temperature gradients were used to separate the products generated during the thermal degradation of a 1,6-hexamethylenediisocyanate (HDI) polyurethane paint. The analysis of mass spectra was facilitated owing to a selective desorption of pyrolysis products. Furthermore, changing the MAB ionization gas allows elucidation of the structure of the pyrolysis products by controlling the extent of their fragmentation. During these experiments, isocyanic acid, methyleneisocyanate, ethyleneisocyanate, propylisocyanate and butylisocyanate were detected.

International audience; The glycosidase inhibitory properties of synthetic C-alkyl and N-alkyl six-membered iminosugars have been extensively studied leading to therapeutic candidates. The related seven-membered iminocyclitols have been less examined despite the report of promising structures. Using an in house ring enlargement/C-alkylation as well as cross-metathesis methodologies as the key steps, we have undertaken the synthesis and biological evaluation of a library of fourteen 2C- and eight N-alkyl tetrahydroxylated azepanes starting from an easily available glucopyranose-derived azidolactol. Four, six, nine and twelve carbon atom alkyl chains have been introduced. The study of two distinct D-gluco and L-ido stereochemistries for the tetrol pattern as well as R and S configurations for the C-2 carbon bearing the C-alkyl chain is reported. We observed that C-alkylation of the L-ido tetrahydroxylated azepane converts it from an alpha-L-fucosidase to a beta-glucosidase and beta-galactosidase inhibitor while N-alkylation of the D-gluco iminosugar significantly improves its inhibition profile leading to potent beta-glucosidase, beta-galactosidase, alpha-L-rhamnosidase and beta-glucuronidase inhibitors whatever the stereochemistry of the alkyl chain. Interestingly, the N-alkyl chain length usually parallels the azepane inhibitor potency as exemplified by the identification of a potent glucocerebrosidase inhibitor (K-i 1 mu M) bearing a twelve carbon atom chain. Additionally, several C-alkyl azepanes demonstrated promising F508del-CFTR correction unlike the parent tetrahydroxyazepanes. None of the C-alkyl and N-alkyl azepanes did inhibit ER alpha-glucosidases I or II.

The authors have evaluated the emulsification of oil of varying viscosities for concentrated o/w emulsions (>60%). Rushton type impellers and baffled mixing vessels were used. The emulsions were prepared in the transition regime (80

Future surgical strategies to restore neurological function in peripheral nerve loss may involve replacement of nerve tissue with cultured Schwann cells using biodegradable guiding implants. Random copolymers of trimethylene carbonate and epsilon caprolactone (P(epsilonCL-TMC), 50: 50) have been synthesized by ring opening polymerization using rare earth alkoxides as initiator. Their potential use as nerve guide repairs has been assessed through indirect and direct in vitro biocompatibility tests and in vivo soft tissue response to EDI subclass macrophages. In vitro, we exposed monolayers of human skin fibroblasts and an established continuous cell line (Hela) to liquid extracts (either pure or diluted in the culture medium) of epsilonCL-TMC copolymer including positive (phenol) and negative controls. Then, colorimetric assays (Neutral red and MTT) were performed. The extracts of epsilonCL-TMC induced no significant cytotoxic effect. We also exposed in vitro Schwann cells to pieces of P(epsilonCL-TMC) and P(LA-GA) copolymers. We evaluated cell attachment at 1 and 3 h by measuring the activity of the lysosomal enzyme (N-acetyl-beta-hexosaminidase) and cell proliferation at 1, 3, 6 and 9 days by measuring the cell metabolic activity (MTT assay). Values for attachment slightly decreased between 1 and 3 h but were significantly higher than on agars (negative control). Cells plated on epsilonCL-TMC showed a rate of proliferation comparable with that of normalized controls and higher than on PGA-PLA at day 9. Finally, we evaluated in vivo the soft tissue response after implantation of cylindrical tubes of P(epsilonCL-TMC) and P(LA-GA) copolymers with an immunohistochemistry staining procedure for the newly recruited ED1 macrophages. An image analysis system automatically measured the optical density of labelled positive ED1 cells at 9, 21 and 60 days after implantation. epsilonCL-TMC copolymer showed a mild soft tissue reaction with no adverse chronic inflammatory reaction. These data allowed us to consider this conduit as a potential effective substitute in nerve repair. El sevier Science Ltd. All rights reserved.

Flow cytometry was used to quantify apoptotic and necrotic polymorphonuclear (PMN) cells in an exudate generated by biomaterials, and the results were compared with determinations of spontaneous apoptosis and necrosis in PMN cells from the bloodstream. The exudate formed inside cylindrical tubes subcutaneously implanted in the dorsal region of rats was collected over a 1-week period. A rapid and simple staining procedure based on the spectral properties of the bisbenzemide Hoechst 33342 was used to identify apoptotic PMN cells. Quantification of permeabilized PMN cells stained by propidium iodide was possible in the same unfixed specimens. The percentages of apoptotic and permeabilized PMN cells in peripheral rat blood were low (1.8 ±0 0.5% and 1.7 ± 0.7%, respectively), similar to results found in humans. In exudates generated by polyvinyl chloride (PVC), the percentages of apoptotic and permeabilized PMN cells were higher than in the blood. The percentage of PMN cells undergoing apoptosis progressively increased with time and reached a maximum at day 2 (27% ± 6%). The percentage of permeabilized cells progressively increased with time and was much higher than the percentage of apoptotic cells on days 4 and 8. Apoptosis and necrosis of PMN cells at day 2 were inhibited when tubes were filled with 10% serum. Selective inhibition of apoptosis with a caspase inhibitor in vivo indicated that apoptosis and necrosis are two separate pathways leading to the death of PMN cells in the exudate. At day 2, polyurethane (PU) was associated with a lower rate of apoptosis than PVC or a random copolymer of trimethylene carbonate (TMC) and ϵcaprolactone (ECL). Apoptosis was interpreted as an organized cell removal process that limits inflammation. Apoptosis was the natural route of PMN cell death at the early stage of inflammation. © 1999 John Wiley & Sons, Inc. J Biomed Mater Res, 44, 429–435, 1999.

The effect of analyte surface concentration on the observed extent of beam-induced dehalogenation in liquid secondary ion mass spectrometry (LSIMS) was investigated using a three-pronged approach. The thrust of the experiments was to vary directly and indirectly the analyte surface concentration and monitor the extent of dehalogenation. These experimental approaches consisted of the use of an anionic surfactant as a doping agent, synthetically modifying the hydrophobicity of a model analyte, and changing matrix surface tension through suitable matrix liquid selection. The results obtained show that increased analyte surface concentration leads to an increased extent of dehalogenation. These results are in agreement with the postulate that beam-induced reactions occur mainly at or near the surface, where the concentration of reactive species generated by the interaction of the bombarding particles and the sample is highest. It is proposed that this relationship is applicable to other phenomena in fast atom bombardment (FAB)/LSIMS. Copyright © 1998 John Wiley & Sons, Ltd.

978-5-94588-165-5; International audience; During atmospheric reentry, a plasma is formed ahead of the surface of the vehicle and the excited particle present in the plasma produces ra-diative heating §uxes to the surface of the vehicle. A high-temperature air plasma torch operating at atmospheric pressure was used to experimentally reproduce atmospheric reentry conditions. A high-resolution and absolute intensity emission spectrum (full width at half maximum (FWHM) = 0.064 nm) was obtained from 200 to 450 nm and then compared with computational results provided by the SPECAIR code [1]. This paper discusses the comparison of the two spectra over this wavelength range in order to con¦rm the validity of the calculation and provide direction to improve the calculated spectrum.

HIV-1 infects the brain and, despite antiretroviral therapy, many infected individuals suffer from HIV-1-associated neurocognitive disorders (HAND). HAND is associated with dendritic simplification and synaptic loss. Prevention of synaptodendritic damage may ameliorate or forestall neurocognitive decline in latent HIV-1 infections. The HIV-1 transactivating protein (Tat) is produced during viral latency in the brain and may cause synaptodendritic damage. This study examined the integrity of the dendritic network after exposure to HIV-1 Tat by labeling filamentous actin (F-actin)-rich structures (puncta) in primary neuronal cultures. After 24 h of treatment, HIV-1 Tat was associated with the dendritic arbor and produced a significant reduction of F-actin-labeled dendritic puncta as well as loss of dendrites. Pre-treatment with either of two plant-derived phytoestrogen compounds (daidzein and liquiritigenin), significantly reduced synaptodendritic damage following HIV-1 Tat treatment. In addition, 6 days after HIV-1 Tat treatment, treatment with either daidzein, or liquiritigenin enhanced recovery, via the estrogen receptor, from HIV-1 Tat-induced synaptodendritic damage. These results suggest that either liquiritigenin or daidzein may not only attenuate acute synaptodendritic injury in HIV-1 but may also promote recovery from synaptodendritic damage. The HIV-1 transactivating protein (Tat) is produced during viral latency in the brain. Treatment with either daidzein or liquiritigenin restored the loss of synaptic connectivity produced by HIV-1 Tat. This neurorestoration was mediated by estrogen receptors (ER). These results suggest that plant-derived phytoestrogens may promote recovery from HIV-1-induced synaptodendritic damage.

In the acidic stream (pH 2.2–4) of the Carnoules Pb-(Zn) mine, Gard, France, very high As contents (from 9 to 20%) can be accumulated as ferric arsenate and arsenate-sulphate precipitates in rapidly growing bacteria-made structures. The main bacterial forms are rod-shaped and sheathed, their sheath is made of Fe-As-rich material and is coated with ferric arsenate colloidal particles or may be partially included in authigenic crystals. Living forms ofThiobacillus-type bacteria have been recognized in the precipitates. The cyclic development of bacterial colonies alternating with sand deposition and erosive episodes results in the formation of As-rich ferruginous accretions. These laminated and dome-shaped bacterial constructions are similar to those of stromatolites. The extremely high contents of solute As in upstream flow (250 mg/1) are lowered by 2–3 order of magnitude downstream. Lead is also precipitated and concentrated in this FeAs-rich bacterial stromatolite (2500 ppm Pb). This accumulation and concentration of As and heavy metals via direct or induced microbial action limits pollution downflow. But seasonal storms could erode these FeAsPb-rich deposits and drastically increase pollution. The accumulation of ferric arsenate by bacterial stromatolites suggests that possible microbial remediation strategies may be used in acid mine drainage environments.

Upon investigation of the clustering behavior of a series of alkyl quaternary ammonium bromides (MBr) in liquid secondary ion mass spectrometry (LSIMS), only the dimer ion, M 2 Br + , was of significant abundance in the resultant mass spectra. The ion abundance of the dimer grows relative to that of the molecular ion, M + , with increasing analyte concentration in LSIMS until a concentration is reached where the ion abundance ratio M 2 Br + /M + remains constant upon subsequent analyte addition. The relationship between the M 2 Br + /M + ion abundance ratio and analyte concentration can be explained in terms of the solution equilibrium between these species, where the plateau region of the plot corresponds to the presence of an analyte monolayer at the liquid surface. The M 2 Br + /M + values obtained in this region provide relative dimer bond strengths for the alkyl quaternary ammonium salts, so the effect of different substituents on dimer stability can be assessed. Using this method, the importance of the electrostatic interaction on the dimer strength and the destabilizing effect of the hydrophobic interaction between long alkyl chains is revealed

A comparison has been made between different approaches for detecting low-level analytes in the TIC traces of sample mixtures analysed by different liquid chromatographic-mass spectrometric (LC-MS) techniques. The approaches studied were contour mapping or “eagle's view” and a background treatment software, TICFilt, recently developed. Typical pharmaceutical samples including standards and plasma containing common drugs such as propranolol, phenothiazine, acetaminophen have been analysed in LC-MS experiments using ionspray, atmospheric-pressure chemical ionization and direct liquid introduction interfaces. The data obtained were examined by contour mapping and treated by TICFilt in order to detect low level elution peaks. Contour mapping can be efficient at higher masses (> M r 250) where the background is generally weaker but cannot always detect elution peaks at lower masses where background contribution is important. Furthermore, it cannot distinguish actual peaks from spikes which are often present in these experiments. Background treatment algorithms such as TICFilt, however, can not only eliminate spikes from the TIC trace but also offer a peak detection efficiency for unknown compounds which is constant throughout the mass range and independent of the mobile phase composition and the ionization technique used. Furthermore, background treatment algorithms also provide mass spectra with enhanced spectral information which is important in the identification of unknown drug-related species.

Some cyclic acetals and derivatized monosaccharides which yielded anomalous [M − H] + in FAB/LSIMS were analyzed by electrospray ionization (ESI) to gain further information on the condensed phase processes suggested to be responsible for the formation of [M − H] + in FAB/LSIMS. For all compounds, [M + H] + was the only significant ion present in the molecular ion region in ESI. Since ionization in ESI is believed to reflect predominantly condensed phase equilibrium processes, the absence of [M − H] + in ESI suggests that these processes are not responsible for hydride abstraction in FAB/LSIMS and that processes other than the pre-formation of ions in solution have to be invoked. Fast atom/ion-induced processes are thus considered the most likely origin of [M − H] + in FAB/LSIMS and would explain the difference in ESI and FAB/LSIMS relative molecular ion intensities. The proposed occurrence of particle-induced ionization processes in the condensed phase in FAB/LSIMS is consistent with previous experimental evidence from this laboratory, and many chemical reactions which take place in FAB/LSIMS have been explained in like manner. The [M + H] + peak in ESI for the compounds studied is attributed to the presence of NH 4 + in solution as an impurity and the resulting condensed phase equilibrium processes. The presence of [M + NH 4 ] + in all ESI mass spectra is consistent with this interpretation. An [M + Na] + adduct is also observed in ESI for the derivatized monosaccharides which suggests that condensed phase equilibrium processes are responsible for this adduct when observed in FAB/LSIMS.

The design and the construction of an “in-source” thermospray-type capillary interface for LC-MS experiments on a bench-top quadrupole mass spectrometer is described. The interface consists of a small diameter fused capillary tube which is introduced directly into the CI source through the solid probe inlet and is oriented in the beam axis. In order to produce average linear velocities comparable to those used in conventional thermospray and compatible with the optimum operating conditions of capillary LC-MS systems, a fused-silica transfer capillary of 10 μm is used. Heating of the interface is provided by the ion source and ions are generated using external mode ionization (filament-on). The effect on performance of several operating parameters, such as source temperature, mobile phase composition, sampling distance in the source and flow-rate have been investigated. The results obtained in experiments conducted on the effect of interface temperature and flow-rate demonstrate that the system is very stable under optimal operating conditions which are compatible with the optimum performance of capillary liquid chromatography systems. The interface developed can be used with a series of mobile phases (normal and reversed) and the ionization features in terms of sensitivity are in all cases essentially comparable. The system yields reproducible results and allows picogram range sensitivity to be achieved in flow injection mass spectrometric or liquid chromatographic experiments involving low-molecular-mass polar organic compounds.

The ionization processes which take place in fast atom bombardment (FAB) mass spectrometry for perhydro-3a,6a,9a-triazaphenalene, a compound with strong proton affinity/basicity and hydride donor ability, are investigated. Chemical ionization (CI) and electrospray ionization (ESI) were also performed to facilitate elucidation of the FAB ionization mechanisms. At the onset of fast atom bombardment, protonation is favored over hydride abstraction, but upon continued bombardment the intensity of [M − H]+ increases relative to [M + H]+ and hydride abstraction becomes the dominant process. In CI, protonation is strongly favored with the relative intensity of [M − H]+ much lower than that obtained in FAB. Since the reactive ionic species in CI have greater gas phase hydride ion affinities than those proposed for FAB, hydride abstraction in FAB cannot be described predominantly in gas phase terms. A condensed phase ionization model for FAB, where protonation and hydride abstraction occur in solution, can instead explain the difference in relative molecular ion intensities obtained in FAB and CI. ESI data of perhydro-3a,6a,9a-triazaphenalene further enhances the condensed phase ionization model proposed for FAB, as the negligible presence of [M − H]+ suggests that beam-induced processes are responsible for the formation of this species in FAB. This interpretation would explain the increase in relative [M − H]+ intensity upon continued fast atom bombardment, through the accumulation of beam-induced reaction products in solution. The protonation of perhydro-3a,6a,9a-triazaphenalene in FAB is also proposed to occur predominantly through beam-induced processes, as equilibrium processes in solution should not account for the absolute ion intensities obtained in FAB. The presence of a strong [M + H]+ peak in ESI of perhydro-3a,6a,9a-triazaphenalene with methanol as solvent, is thought to be a consequence of the presence of NH4+ in solution and not to reflect the predominant formation of this species in FAB through equilibrium processes in solution. ESI work with ethylene glycol as solvent supports this interpretation.

The problem of artefact peaks, in spectra obtained from various tandem mass spectrometric scans on instruments of both forward and reverse geometry, is examined. The filtering conditions imposed by additional analyzers are investigated, in order to evaluate the potential of several different triple sector geometries to reduce specific interferences. No previous evaluation of the rejection ability for artefacts of different origins has been presented with respect to the various geometries. In order to gain a better insight into the origin of various artefacts, and to more easily explain their occurrence in certain geometries, a new graphical representation was developed in order to take into account the effects of three analyzer fields. This approach allows different linked scans to be projected within a cube, while also qualitatively proposing an explanation for the presence or absence of artefact peaks. New scans can also be conceived by means of this method, as is the case with a new selected mass ion kinetic energy (SMIKE) scan, which allows artefacts present in MIKE scans performed using reverse geometry instruments to be determined.

The possible presence of artefact peaks in mass-analyzed ion kinetic energy (MIKE) spectra has been recognized when such scans are performed using a two-sector instrument of reverse (BE) configuration. Since the presence of an artefact peak can be misleading when interpreting a spectrum, a new scan is proposed which allows these artefacts to be identified. This scan involves linking and scanning the two electrostatic sectors of an E1BE2 geometry instrument, while maintaining the magnet at the mass selected for the MIKE scan. This selected mass-analyzed ion kinetic energy (SMIKE) scan at E1=E2 results in a spectrum containing only artefact peaks that can be present in the corresponding MIKE spectrum.

The LSIMS beam-induced dehalogenation of several 4-halo-phenylalanine methyl esters (I, Br, Cl, F) was investigated and compared to that of atrazine using 12 different matrix compounds including diethyl phthalate for which the empirical electron affinity was known. The extent of dehalogenation, induced by a one-electron reduction process, is in agreement with the leaving group ability of the corresponding halogens (I >Br >Cl >F) and the dehalogenation inhibiting efficiency of the matrices. The latter is rationalized in terms of electron scavenging capacity and matrix structural features relating to that capacity. The extent of dehalogenation observed for 4-I-phenylalanine methyl ester is similar to that of atrazine, a chlorinated compound, which indicates that the halogen effect is not overwhelming in determining the extent of dehalogenation. The bracketing of matrix reduction potential was attempted based on the propensity of the matrices to induce M+· formation from analytes of known oxidation potentials. The ability of matrices to induce M+· formation parallels their dehalogenation and reduction inhibiting efficiencies. The last observation underlines the importance of matrix redox properties in effecting or inhibiting beam-induced processes, be they reductive or oxidative.

A glow discharge ion source has been constructed for the mass spectrometric analysis of organic compounds. Characterization of the source has been made by studying the effect of pressure and discharge current on ionic distributions by anodic ion sampling along the discharge axis. Ion and electron densities and electronic temperatures have been calculated by using the single Langmuir probe technique to correlate the extraction efficiency with measured ion distributions and gain some insight into the ionization of organic molecules. The spectra obtained for several classes of organic compounds show that formation of parent-molecular ions by proton transfer, resulting partly from the background water molecules, is a major low energy process while charge transfer, Penning ionization, and electron ionization are probably responsible for the fragmentation observed. The spectra result from the simultaneous occurrence of high and low energy reactions, and their structural information content is very high, yielding both molecular and extensive fragment ion information. The glow discharge ion source has proved to be essentially maintenance-free, easy to operate, stable, and can be used at reasonable mass resolution (up to 7000). The source also provides picogram range detection limits and has a linear response range of about six orders of magnitude, which makes it an interesting ion source for routine analysis. Preliminary work conducted with chromatographic interfaces indicates that its use can be easily extended to both gas and liquid chromatography.

The effect of experimental parameters such as time of irradiation, analyte concentration, primary beam density, matrix selection and matrix additives on the beam-induced dehalogenation of chlorpromazine in liquid secondary ion mass spectrometry (LSIMS) was investigated. It was found that dehalogenation of chlorpromazine in glycerol increased with increasing time of irradiation, analyte concentration and primary beam density. These results were compared with those obtained using 4-chlorophenylalanine ethyl ester and the differences observed were rationalized in terms of compound surface activity. Evidence is given that matrix selection is the key experimental parameter affecting the extent of beam-induced dehalogenation of chlorpromazine in LSIMS. Of the eleven matrices used, the greatest extent of dehalogenation was observed in glycerol. Sulfur-containing matrices consistently exhibited a lower extent of dehalogenation than oxygen-containing aliphatic matrices, implying that sulfur is implicated in mitigating the reduction process. Dehalogenation was totally inhibited in 2-hydroxyethyl disulfide, 4-hydroxybenzenesulfonic acid and 3-nitrobenzyl alcohol. Similarly, the use of matrix additives such as 3-nitrobenzyl alcohol and trifluoroacetic acid was found to be useful in inhibiting the extent of dehalogenation occurring in glycerol.

Several derivatized monosaccharides, the 2-deoxy-D-ribofuranoses, have been studied by liquid-assisted secondary ion mass spectrometry (LSIMS) in order to gain insight into the factors affecting ionization in FAB/LSIMS. Examination of the mass spectra for these compounds obtained in eight liquid matrices (diethanolamine, ethylene glycol, glycerol, 2-hydroxyethyl disulfide, 2-hydroxyphenethyl alcohol, 3-nitrobenzyl alcohol, sulfolane and thioglycerol) reveals that in all cases the anomalous [M – H]+ ion is the predominant species in the molecular ion region and that [M + Na]+ species are observed in the presence of Na+. The analysis of these compounds by chemical ionization with ammonia shows [M + H]+ as the major species while [M – H]+ is essentially absent. This indicates that the ionization processes occurring in the two techniques are not analogous. Thermodynamic considerations based on the gas-phase hydride ion affinities of the protonated matrices do not support a predominant gas-phase mechanism for the formation of [M – H]+ in LSIMS. However, it is possible using solvation energies to rationalize the formation of [M – H]+ in terms of condensed-phase ionization processes which take place either in the liquid matrix or in the dense selvedge region immediately above the surface where extensive solvation is present. Electrospray data obtained for one of the derivatized monosaccharides indicates that the [M – H]+ is not performed in the condensed phase in LSIMS and that it is the product of fast ion beam-induced processes. While the nature of the matrix is seen to have little effect on the intensities of [M – H]+ and [M + H]+ it is observed to be an important factor for the intensity of M+˙ for one of the monosaccharides. This effect can be related to the electron-scavenging properties of the matrices and reinforces the hypothesis that condensed phase processes are significant in ionization.

The monitoring of the chromatographic resolution for three pairs of analytes separated in different chromatographic systems using mobile phases with varying concentrations of viscous fast atom bombardment matrices showed that it exhibits a steady decrease with increasing matrix content in the mobile phase. The decrease in resolution is observed in the partition and ion-pair chromatographic modes at both low and high matrix contents in the eluent for both conventional and capillary chromatographic systems using precolumn addition of glycerol and thioglycerol. Careful examination of the normalized efficiency, capacity factor and selectivity terms contributing to the resolution allowed the identification of the sources of the decrease in resolution in the presence of a matrix in the eluent. Ale efficiency and capacity factor terms show decreases with increasing matrix content in all systems. Subtle variations in the selectivity term observed in the presence of a viscous matrix can increase or limit the decrease in resolution. The variations observed for the efficiency term show similar trends in all systems studied and appear to be independent of the analyte or the chromatographic mode. However, the variations in capacity factor and selectivity induced by the presence of the viscous matrix are dependent on the nature of the analyte, the type of chromatography and the nature of the matrix.

A series of experiments were conducted in order to evaluate the boundaries within which precolumn addition of viscous matrices can be systematically used in capillary LC—fast atom bombardment MS systems and to evaluate the broadening caused by components of the systems such as the column, the transfer capillary tube and the probe interface. The effect of the addition of a viscous matrix on the capillary system was studied by monitoring important chromatographic parameters such as capacity factors, selectivity, number of theoretical plates, peak width and resolution. The results obtained indicate that glycerol contents in the mobile phase higher than 5% have a deleterious effect on most chromatographic indicators. The overall effect of the presence of glycerol on the chromatographic system can be rationalized in terms of the modification of the analyte distribution between the mobile and stationary phases and changes in the kinetics of the system created by an increase in the viscosity of the mobile phase. Ale main contribution to band broadening in the system can be attributed to the interface and is related to the formation of a liquid droplet at the tip of the probe. Other contributions such as broadening in the column and in the transfer capillary affect the total variance of the chromatographic system but to a smaller extent.

The peak intensities observed in the molecular ion regions of fast-atom bombardment/liquid secondary ion mass spectra contain contributions from the parent ion species, its one- and two-electron reduction/oxidation products, and chemical background signal due to beam-induced damage. There are several solution and instrumental parameters that can affect the distribution of peak intensities in the molecular ion region. In this study, the analyte concentration and primary beam density and energy were varied systematically to investigate their effects on the measured peak intensities. A computer algorithm, Simbroc (Simulated Background and Reduction/Oxidation Calculations), was designed to deconvolute the observed intensities into their individual components so that the true effects of experimental parameters on redox extent and background levels could be evaluated. The algorithm is based on a comprehensive seven-variable mathematical model for experimental data simulation. The results obtained using the algorithm after its validation indicate that the primary beam energy does not significantly affect redox extent or background levels. Changes in analyte concentration and primary beam density tend to play a more important role in the generation of redox products and beam-induced damage. The background level generally increases as the analyte concentration is lowered for the peptide systems used in this study. An increase in the primary beam density often leads to higher background levels, although the effect is less detectable for samples that have a low (less than 3%) background signal. The apparent two-electron reduction is generally lower at the higher concentrations; however, the “true” reduction occurring for pentaphenylalanine does not show a significant concentration effect.

The initial use of an energy-tunable rare-gas metastable beam source generated by a corona discharge as an ionization source for mass spectrometry is reported. The metastable atom beam is produced external to the ion source and its excitation energy is controlled by the rare gas which is employed. The metastable beam source can be used routinely and provides sensitivities of the same order as those obtained by electron impact. Preliminary results involving the analysis of aromatic and aliphatic compounds with four different rare-gas metastable atom beams (krypton, argon, neon and helium) are presented in order to show the tunable fragmentation and selective ionization capabilities of the metastable source. Thus, this source can be used to gain fundamental information on the physical properties of polyatomic molecules as well as the Penning ionization process itself, and for analytical-type applications such as those encountered in LC-MS and desorption-ionization. Overall, the results presented support the potential of the metastable beam source as a new tool for a wide range of mass spectral experiments.

An Approach which allows the determination of the specific effects of experimental parameters on the extent of reduction observed in fast-atom bombardment/liquid-assisted secondary-ion mass spectrometry (FAB/LSIMS) has been developed. The methodology is based on the isolation of the different components-background, reduction extent, and isotopic abundances—which contribute to peak intensities in the molecular-ion cluster. The individual contributions of reduction and background are calculated by an algorithm SRBC (simulated reduction and background calculations) which utilizes a Monte-Carlo method to optimize the values obtained for these variables. This approach has been used to examine the effects of analyte concentration, primary-beam energy and beam density on the extent of reduction in FAB/SIMS experiments. The results obtained indicate that the beam energy has no significant effect on the apparent reduction, as measured by the experimental (A+2)/A isotope peak ratio, while analyte concentration and beam density effects are obseerved. However, background and reduction data generated by SRBC demonstrate that in some cases there is little effect of these parameters on the true reduction of the analyte and that the increase in apparent reduction with the variation in these parameters results mainly from an artefact created by an increase in the background signal at lower concentrations and higher beam densities.

The mass spectral behavior of a series of substituted 2-phenyl-1,3-dioxolanes has been studied by several ionization techniques in order to gain further insight into the basic ionization mechanisms occurring in the fast-atom bombardment mass spectrometry. The results obtained show that in chemical ionization, ions of the type [M+H]+ are predominant while [MH]+ ions are observed as important species in electron ionization and fast-atom bombardment. Comparison of the gas-phase hydride-ion affinities of thr chemical ionization reagent gases ammonia and isobutane with those of the loquid matrices glycerol and dithiothereitol/dithioerythritol indicates that the predomionant formation of the [MH]+ ion observed in fast-atom bombardment by hydride abstraction in the gas phase is improbable. Furthermore, comparison of the electron ionization behavior of the cyclic acetals with that observed under fast-atom bombardment suggests that the origin of [MH]+ in the latter is not related EI gas-phase processes.

A series of experiments were conducted in order to determine the effect of the precolumn addition of a viscous matrix such as thioglycerol on the chromatographic performance of liquid chromatographic-fast atom bombardment mass spectrometric (LC-FAB-MS) systems. In those experiments, the concentration of thioglycerol in a mobile phase consisting of acetonitrile-water-trifluoroacetic acid was varied and important chromatographic parameters such as retention times, capacity factors, number of theoretical plates, peak widths, resolution and impedance of separation were monitored for analytes such as met-enkephalin, leu-enkephalin and p-hydroxybenzoic acid. The results obtained indicate that for concentrations of thioglycerol in the mobile phase below 3% most chromatographic indicators are only slightly affected. However, for concentrations of the viscous matrix above that value the capacity factors are significantly decreased, indicating that thioglycerol is behaving as an efficient organic moderator, and peak broadening becomes important, having a detrimental effect on the performance of the system. Van Deemter plots obtained for the analytes at concentrations of thioglycerol in the mobile phase of 0-15% reveal that the major effect of thioglycerol is to reduce the mass transfer efficiency in the chromatographic system at high velocities and concentrations of thioglycerol above 3%. Comparison of the effects of viscous matrices such as thioglycerol and glycerol on the chromatographic performance of LC-FAB-MS systems indicates that the chromatographic efficiency is almost independent of the matrix concentration when the systems are operated near their optimum linear velocities and that high matrix contents and high linear velocities can be used with little decrease in efficiency if the systems are operated at higher temperatures.

Investigations into powder mixing in mixing vessels are surveyed, concentrating on practices used in different industries to distinguish this review from that given recently by Fan et al. [1]. The essential points to be examined for the treatment of solids mixing are reviewed and the definitions of the quality of a mixture, the mixing mechanisms, the possibilities for the choice of solid mixer, the experimental assessment of homogeneity and mixing indexes and the numerical simulation of mixing processes are reported.

The problem of acceptable accuracy in mass calibration for fast-atom bombardment (FAB) mass spectrometry has recently received some attention (K. Veekey, Rapid Commun. Mass Spectrom., 2, 213 (1988); Idem., Org. Mass Spectrom., 24, 183 (1989). We describe here a calibration method for negative-ionFAB, using gold cluster ions, which provides facile mass calibration over the range from can 200u to 10000u. Under suitable conditions, it is possible to use these ions as internal standards for accurate mass measurement.