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Two kinds of MS41-immobilized ionic liquids (ILs) based on dihydroimidazolium and pyridinium cation were prepared using a grafting method. The second immobilization of triflate salts on these materials led to the immobilization of metal-triflate complexes into ILs. The materials thus obtained were characterized by H-1 NMR, XRD, N-2-sorption measurements, TG-DTA, DRIFT, XPS, TEM, and ICP-AES. The catalysts were tested in acylation of amines and sulfonamides and proved highly active and selective. For both aromatic and aliphatic amines, acylation with carboxylic acids was possible. For sulfonamides, acylation was possible only with anhydrides. Recycling the catalysts was not accompanied by any leaching of ILs or metal triflate. (C) 2007 Elsevier Inc. All rights reserved.

Separation of metformin and glibenclamide was achieved within a single chromatographic run on a Zorbax CN column, under isocratic conditions, using acetonitrile and aqueous component (0.01 moles/L ammonium acetate adjusted at pH 3.5 with acetic acid) in volumetric ratio 1/1. Plasma sample preparation is based on protein precipitation by means of organic solvent addition. 1,3,5-Triazine-2,4,6-triamine (IS1) was used as internal standard for metformin, while gliquidone (IS2) played the same role for glibenclamide. Detection was performed with an ion trap mass analyzer, using atmospheric pressure chemical ionization (APCI). A single MS stage was used for detection of metformin and IS1, by extracting ion chromatograms corresponding to molecular ions. MS/MS detection in the SRM mode was used for glibenclamide (m/z transition from 494 to 369 Da) and IS2 (m/z transition from 528 to 403 Da). The method produces linear responses up to 2000 ng/mL for metformin and 400 ng/mL for glibenclamide, respectively. Low limits of quantification were found in the 40 ng/mL range for metformin and at the 4 ng/mL level for glibenclamide. Precision was characterized by relative standard deviations (RSD%) below 9%. The analytical method was successfully applied to a single dose, open-label, randomized, two-period, two-sequence, crossover bioequivalence study of two commercially available anti-diabetic combinations containing 400 mg metformin and 2.5 mg of glibenclamide per coated tablet.

A simple and fast method intended for large-scale bioequivalence studies for the determination of glibenclamide in plasma samples is presented. The chromatographic separation was achieved on a monolithic octadecyl chemically modified silicagel column and a mobile phase containing 42% aqueous 0.1% HCOOH solution (v/v) and 58% acetonitrile, at a flow rate of 1 mL/min, in isocratic conditions. Preparation of plasma samples was based on protein precipitation with acetonitrile. Gliquidone was used as internal standard. The target analytes were transferred into an ion trap mass analyzer via an atmospheric pressure chemical ionization interface. The precursor ions with mass 494 a.m.u. for glibenclamide and 528 a.m.u. for gliquidone were isolated, while in the second MS stage product ions 369 a.m.u. and 403 a.m.u., respectively, were monitored. The analytical process was characterized by a low limit of quantitation of 1.5 ng/mL. The mean recovery for glibenclamide was 98.1+/-2.8% over a concentration interval ranging from 1 to 500 ng/mL. Intra-day and inter-day precision calculated over 2-400 ng/mL concentration interval ranged from 15.4% to 3.4%. Inter-sequence accuracy expressed as % bias from theoretical concentration values over the concentration interval of 10-400 ng/mL fall within -13.9% and +14.6%. The method was applied for evaluation of the bioequivalence between two formulations containing 3.5mg glibenclamide per dose.

This review covers the most important aspects, focused on an actual topic in fundamental chromatographic research, which attempts to correlate the retentions of analytes in liquid chromatography with their structures, using various molecular descriptors/properties (hydrophobicity given by octanol/water partition coefficient, acidity/basicity constants, dipole moment, polarity parameters, molecular volume, and solubility). Some of these correlations are, however, based on retention mechanisms which are supposed to describe, thoroughly, the chromatographic process, such as the linear solvation energy relationship.

Enhancement of sensitivity for spectrometric detection in liquid chromatography is obtained when increased sample volumes are loaded into the chromatographic column. A new approach of injecting large volumes of solvents non‐miscible with the mobile phase is proposed. The paper focuses on the retention study of butylated hydroxyanisole (BHA) loaded into the chromatographic column dissolved in liquid alkanes (n‐hexane, n‐heptane, and iso‐octane, respectively) at volumes up to 600 µL. A simple model based on adsorption for explaining the experimental results is proposed. A clear insight of the process was possible by studying the migration of the solvent zone within the column, at different mobile phase compositions and different loaded volumes, by means of refractive index detection. The model allowed calculation of the number of solvent molecules saturating a C8 alkyl chain site within the stationary phase layer. Competition between the analyte and solvent molecules, together with the homogeneity ...

The ion‐pair (IP) mechanism was applied to achieve HPLC‐diode‐array detector (DAD) separation and determination of metformin and five related impurities (cyanoguanidine, 1‐methylbiguanidine, melamine, N,N‐dimethylmelamine, and 4,6‐diamino‐1,3,5‐triazin‐2‐yl guanidine). Sodium octanesulphonate (0.010 mol/L) at pH = 3 was used as an ion pair agent in the aqueous component of the mobile phase. Isocratic elution with 80% acetonitrile and 20% aqueous component was applied with a flow rate of 1.2 mL/min. A double end‐capped, 5 µm particle size Inertsil ODS‐2 stationary phase (250 mm length, 4.6 mm internal diameter column) was used. Limit of quantitation (LOQ), as absolute amount of analytes loaded to the column, in the 35–250 pg interval were obtained using detection at 218 nm. Retention data were used in estimating the thermodynamic parameters (enthalpy and entropy) corresponding to the mobile/stationary phase transfer. Correlations between experimental data and data predicted by means of basicity co...

Synthesis of amido-type surfactants derived from oleic and linoleic acid and triethylenetetramine was carried out in different solvents (dioxane, hexane, N,N -dimethyl-formamide) in the temperature range 70–190 °C using beta-zeolite as catalyst. The experimental data indicated the positive effect of catalyst in both amidation and formation of stable colloidal solutions. To cite this article: M. Musteaţa et al., C. R. Chimie 7 (2004).

A new method for the determination of 2-[(dimethylamino)methyl]cyclohexanone (DAMC) in Tramadol (as active substance or active ingredient in pharmaceutical formulations) is described. The method is based on the derivatisation of 2-[(dimethylamino)methyl]cyclohexanone with 2,4-dinitrophenylhydrazine (2,4-DNPH) in acidic conditions followed by a reversed-phase liquid chromatographic separation with UV detection. The method is simple, selective, quantitative and allows the determination of 2-[(dimethylamino)methyl]cyclohexanone at the low ppm level. The proposed method was validated with respect to selectivity, precision, linearity, accuracy and robustness.

The solvent and salting effects induced on the sample preparation procedure applied to plasma samples containing fenofibric acid and 4-chlorophenyl-4′-hydroxyphenyl methanone (internal standard) are evaluated. Sodium chloride addition during a deproteinization step using both methanol and phosphoric acid influences the recovery of the analytes as well as the selectivity of the process. The chromatographic method allows high sample volume injection (500 μl) with the focusing of both analytes in the stationary phase. The synthesized high porosity octadecylsilica material allows a fast elution gradient at 4 ml/min flow-rate and a complete analysis within 7 min. UV-detection is made at 295 nm and quantitation limit in the 20 ng/ml concentration level can be achieved. The method can be successfully applied for bioequivalence studies on fenofibrate, administrated as prodrug (fenofibric acid represents its main active metabolite) in pharmaceutical formulations. The main parameters used in studying the retention behavior of the internal standard and FEFA were also estimated.

Characterization of triglycerides in vegetable oils was achieved by silver-ion packed-column supercritical fluid chromatography (SI-pSFC) with mass spectrometric detection. Hyphenation was made using commercially available liquid chromatography-mass spectrometry (LC-MS) interfaces without any modification. A make-up fluid was delivered through a T-piece placed before or after the SFC restrictor by means of a high pressure pump. Atmospheric pressure chemical ionization (APCI) and coordination ion spray (CIS) with silver ions were used as ionization modes. Compared to UV detection, the sensitivity was increased by a factor of 100. Both ionization modes are generating similar structural information. Molecular ions [M-H]+ or [M-Ag(-)] are observed in the mass spectra with exception of the saturated triglycerides for which only CIS gives intense molecular ions. The position at which the fatty acids are esterified to the glycerol backbone can be elucidated by pSFC-APCI although it remains speculative whether this is valid for highly unsaturated triglycerides because reference compounds are not available to proof this.

Optimization of a liquid–liquid extraction procedure used for isolation of penicillin-V in human plasma samples and the subsequent HPLC–DAD analysis are reported. Some aspects related to the stability of penicillin-V in plasma and according to pH are also given. From seven tested solvents, the highest extraction yield was obtained with methyl- t -buthyl ether. Influence of the extraction parameters, such as pH of aqueous phase, sample/solvent volumetric ratio, and extraction duration, is discussed. HPLC separation was achieved on an Eclipse XDB-C8 column, using a mobile phase composed by aqueous phosphate buffer (pH=7.3), methanol and acetonitrile in the ratio 8:1:1. Quantitation limits of 50 ng/ml were obtained. The optimal sample preparation method and HPLC–DAD separations were used for a bioequivalence study, made on 36 volunteers.

The intact wax esters in jojoba oil were analyzed by microbore LC-MS. Neither atmospheric pressure chemical nor electrospray ionization (APCI and ESI) provided ions. Excellent ionization was obtained by adding post column Ag + ions. With this technique, called coordination ion spray MS (CIS-MS), the molecular ion could be unequivocally elucidated and, by applying a collision induced dissociation (CID) voltage of 290 V, the acidic and alcoholic part of the different wax esters could be identified. Ion formation and fragmentation are discussed. Unsaturation in the alcohol or acid chain is not a prerequisite for obtaining [M+Ag] + ions but fragmentation only occurs when the chains are unsaturated.

Quality of the analytical data obtained for large-scale and long term bioanalytical studies based on liquid chromatography depends on a number of experimental factors including the choice of sample preparation method. This review discusses this tedious part of bioanalytical studies, applied to large-scale samples and using liquid chromatography coupled with different detector types as core analytical technique. The main sample preparation methods included in this paper are protein precipitation, liquid-liquid extraction, solid-phase extraction, derivatization and their versions. They are discussed by analytical performances, fields of applications, advantages and disadvantages. The cited literature covers mainly the analytical achievements during the last decade, although several previous papers became more valuable in time and they are included in this review.

The therapeutic outcome of oximes used as reactivators of phosphorylated human acetylcholinesterase (AChE) is influenced, among other factors, by their biological distribution, their in vivo ability to achieve the nucleophilic attack and their affinity for the anionic center of the intact/inhibited AChE.An in silico evaluation of the molecular descriptors and biopharmaceutical properties of 454 set of oximes has been achieved. The available pharmacokinetic (PK) data was analyzed, in an attempt to illustrate their common characteristics and particularities. Based on the observed high water solubility and low permeability across biological barriers, we applied the officially adopted classification systems based on biopharmaceutical properties to identify the existing biopharmaceutical differences between the various oxime entities and to predict their in vivo fate.The structural differences of the organophosphorus compounds (OP) and the available oximes reactivators of OP-inhibited AChE generate distinct toxicokinetic or PK profiles. The tissue compartment specific distribution is one of the key elements for assessment of reactivating efficiency. The distribution through highly specialized barriers, such as blood-brain barrier remains a considerable challenge. The high solubility - low permeability biopharmaceutical profile of oximes can be used to suggest the possible involvement of active transport systems.

Appropriate substitution of acetonitrile (ACN) in mobile phases for reversed-phase liquid chromatography (RPLC) by low toxicity, ecologically friendly alternative solvents emerges as a greener approach in separation sciences. Ethyl lactate is considered as a green solvent in organic synthesis, industrial extraction processes and many other applicative fields. Its ability to substitute ACN in mobile phases for RPLC applications was barely investigated. The feasibility of such a replacement was tested for the separation of the mixture of 16 polycyclic aromatic hydrocarbons listed by the Environmental Protection Agency. The analytical approach was found to be achievable, with some compromises in terms of elution order, peak efficiency and UV detectability. Thermodynamic aspects of the chromatographic process were also comparatively assessed. Correlations between the elution order and some molecular descriptors were also discussed.

Determination of sub-ppm Triton concentrations in perfusable solutions using an off-line SPE-HPLC-DAD technique is described. Chromatographic separation is based on a two columns back flush set-up, in order to focus the analyte peak and for eliminating matrix interferences. SPE was mainly used for sample concentration.

An optimized method for determination of Metformin at ppb level in human plasma is described. Derivatization of Metformin with p-nitrobenzoyl chloride was carried out in a biphasic system. The derivative extracted in the organic layer (dichloromethane) was concentrated and analyzed by HPLC-DAD, using an isocratic elution (water/methanol mixture 65/35), monitored at 280 nm. Good selectivity against co-extracted matrix components was observed. A detection limit of 10 ppb Metformin in human plasma was reached.

The main parameters considered in optimizing the liquid extraction and quantitative assay were the yield, precision, limit of quantification, time required for extraction and concentration, and quantity of solvent. The influence on these parameters of the following factors was examined: nature of the extracting solvent, quantity of solvent, co-extraction solvent, and duration of stirring. Instead of equilibrium parameters of the involved thermodynamic system, a kinetic approach was preferred in terms of the effective partition 'constant', which is not really constant but a function of time and extraction conditions. The final selected method, considered to be rapid and simple, was applied to determine the pharmacokinetics of hydrochlorotiazide (HCT) after administration of Capozide (Bristol-Myers Squibb) tablets containing 50 mg Captopril and 25 mg HCT, to 4 healthy volunteers. The results obtained were in accordance with the pharmacokinetic parameters of HCT reported in the literature.

Two sample preparation methods were applied for the determination of Tolbutamide in the human plasma, at concentration levels ranging from 5 to 50 ppm. One method is based on the drug extraction into ethyl acetate. This solvent has never been used for Tolbutamide extraction from plasma matrix. The other method is a non-extraction one, based on the protein precipitation in presence of methanol. Both methods were successfully applied to in-vivo monitoring of plasma levels of Tolbutamide for a 24-hours period, as required for a pharmacokinetic study. The main parameters in both methods were optimized in order to achieve the acceptance criteria imposed by the bioavailability studies.

The enantiomeric forms of cyclohexanyl adenine and thymine nucleosides were obtained by separation of their diastereomeric esters with (R)-(-)methylmandelic acid. The four nucleoside analogues were appropriately protected, converted to their phosphoramidites and oligomerized. The resulting cyclohexanyl nucleic acids (CNAs) represent a new enantioselective Watson-Crick base-pairing system. Homochiral oligomers of equivalent chirality show Watson-Crick pairing, while those of opposite chirality (D-CNA and L-CNA) do not. No isochiral or heterochiral adenine-adenine or thymine-thymine base pairing is observed. Complex formation occurs only between oligomers in antiparallel orientations. D-CNA hybridizes with natural nucleic acids, and the strength of the interaction decreases in the order dsCNA>CNA:RNA> CNA:DNA. Thus, the D-cyclohexanyl nucleic acids are RNA-selective. L-CNA hybridizes either very weakly or not at all with natural nucleic acids, and the nature of this association is not clear. This study of CNAs leads us to hypothesize that a) the conformation of a single nucleoside analogue may be different from its conformation in an oligonucleotide and b) the conformational stress of a nucleotide analogue incorporated in an oligomer may contribute to the sequence-dependent thermal stability of oligonucleotide complexes. ispartof: Chemistry - a European Journal vol:5 issue:7 pages:2139-2150 status: published

The triglycerides in fish oil, and especially in Sardina pilchardus, were fractionated according to degree of unsaturation (DU) by silver-ion packed-column supercritical fluid chromatography. The collected fractions were analyzed by flow injection analysis in an electrospray mass spectrometer and by capillary electrochromatography on a 40 cm×0.1 mm i.d. fused silica column packed with 3-μm Hypersil ODS. In each DU fraction, the carbon number could be elucidated. The potential of this analytical schema is illustrated by the in depth analysis of the fractions containing 10, 11, and 12 double bonds. ©1999 John Wiley & Sons, Inc. J Micro Sep 11: 451–459, 1999

Determination of formaldehyde at sub-ppm level as impurity in acetals using HPLC-DAD is described. Automated on-line precolumn derivatization reaction with 2,4 dinitrophenylhydrazine has been used. Breakdown rates of some industrial scale used acetals (Methylal, Ethylal) to formaldehyde by hydrolysis in aqueous media, according to pH, are described.

Nitrated and hydroxylated polynuclear aromatic hydrocarbons (nitro- and hydroxy-PAHs) extracted from air particulates were fractionated from other micropollutants by semipreparative packed-column supercritical fluid chromatography on silicagel. Sample injection and fraction collection was automated by means of a Gilson 233 XL sample preparation station. The collected fractions were analyzed by capillary gas chromatography–mass spectrometry operated in the ion-monitoring mode. For some specific solutes, concentrations down to the 1 pg/m3 level could be measured. © 1998 John Wiley & Sons, Inc. J Micro Sep10: 89–97, 1998

The polysaccharide chiral stationary phases (CSPs) Chiralcel OD and Chiralpak AD, and the macrocyclic antibiotic CSPs Chirobiotic V and Chirobiotic T were evaluated in packed column subcritical fluid chromatography (pSFC) for the separation of different types of racemic compounds (β-blockers, β-agonists, benzodiazipines, non-steroidal anti-inflammatory drugs, barbiturates, free and derivatized amino acids, etc.). The same conditions and program could be applied to check the applicability and enantioselectivity of one of the CSPs for a given racemic mixture. The conditions are: temperature 30°C, pressure 200 bar, flow-rate 2 ml/min, carbon dioxide, modifier methanol containing 0.1% trifluoroacetic acid (TFAA) and 0.1% triethylamine (TEA) with a gradient from 5% (5 min) to 30% at 5%/min. A resolution of 0.4 under those conditions generally indicates that baseline separation can be realized on the CSP by fine-tuning the different parameters of the SFC separation. The best CSP for pSFC proved to be Chiralpak AD which provided separation for 70% of the 44 substances tested, followed by Chiralcel OD (66%), Chirobiotic T (50%) and Chirobiotic V (48%). For comparison, the enantio-selectivity in pSFC of the brush type CSPs Chirex 3022 with π-donor characteristics and Chirex 3005 with π-acceptor characteristics was also evaluated. As expected, these phases perform poorly under SFC conditions, on Chirex 3022 (34%) and on Chirex 3005 (20%).

Supercritical fluid chromatography was applied to evaluate the direct chiral discriminative properties of Chiralcel OJ, a tris(4-methylbenzoate) cellulose column towards frequently administered drugs. Two groups of acidic drugs, profen and barbiturate derivatives, and a few basic drugs of the benzodiazepine type were analysed. The effect on enantioselectivity of carbon dioxide when using methanol are acetonitrile as primary modifier was studied. Acetonitrile proved to be a good alternative for methanol, especially for the profen compounds that were not well resolved using methanol. The results were compared to normal phase chromatographic applications on the same column. SFC was not necessarily superior to high-performance liquid chromatography. Chirality 9:126–132, 1997. © 1997 Wiley-Liss, Inc.

The analysis of sterols in vegetable oils by off-line SFC followed by capillary GC-MS is described. The fractionation of the sterols from the complex oil matrix is achieved by SFC on aminopropyl silicagel in less than 8 minutes. Injection and collection of the sterol fraction is fully automated and time controlled. The sterols are analysed without derivatisation by capillary GC-MS. Identification is performed by full scan electron ionisation and quantitation is carried out by extracted ion chromatography at m/e 107, with cholesterol as internal standard. The analyses of the sterols from the sunflower oil and two olive oils illustrate the possibilities of the method.

The problem of sample diluent in bioanalytical LC–MS is reviewed with a special focus on large-volume injections and non-miscible solvents with mobile phase components. These issues are related to the sample preparation approach, which in many instances provides the sample diluent before injecting this into the chromatographic column. The sample volume influences the quantitation limit of the chromatographic method, while its nature may influence the retention process of the injected analytes. The literature reports a few papers that are focused on alternative sample diluents in bioanalytical LC–MS that are generally non-miscible with mobile phase. The principle of this approach and some of its current bioanalytical applications from literature are discussed. However, more applications and more publications from HPLC users and vendors are expected in this field, which could prove its analytical importance and potential in bioanalysis.

The liquid chromatographic behavior observed under bimodal retention conditions (reversed phase and hydrophilic interaction) offers a new basis for the determination of some derived lipophilicity indices. The experiments were carried out on a representative group (30 compounds) of pyridinium oximes, therapeutically tested in acetylcholinesterase reactivation, covering a large range of lipophilic character. The chromatographic behavior was observed on a mixed mode acting stationary phase, resulting from covalent functionalization of high purity spherical silica with long chain alkyl groups terminated by a polar environment created through the vicinal diol substitution at the lasting carbon atoms (Acclaim® Mixed Mode HILIC 1 column). Elution was achieved by combining different proportions of 5 mM ammonium formiate solutions in water and acetonitrile. The derived lipophilicity indices were compared with log P values resulting from different computational algorithms. The correlations between experimental and computed data sets are significant. To obtain a better insight on the transition from reversed phase to hydrophilic interaction retention mechanisms, the variation of the thermodynamic parameters determined through the van׳t Hoff approach was also discussed.

Background: Extreme efforts are made for the structural diversification of oximes used as AChE reactivators. Co-administration of different oximes should also be considered as a solution in therapy. Consequently, development of selective assays of oximes in biological matrices is of major importance. Results: Three chromatographic separation mechanisms were evaluated: hydrophilic-interaction LC; mixed reversed-phase/cation exchange (DUET); and reversed-phase ion pairing based on per-fluorinated agents. MS was used to identify and quantify oximes. Alternative preparation of whole blood and plasma samples were used based on protein precipitation through addition of acetonitrile or ionic liquids. Quality characteristics of the proposed analytical approaches are discussed. Conclusion: The reversed-phase ion pairing based on per-fluorinated agents chromatographic separation mechanism and positive ESI-MS/MS detection produced the best results for the assay of bis-quaternary pyridinium oximes. LLOQ in the tenths of nanogram per milliliter range are achievable.

The gas-like mass transfer and liquid-like solvating properties of supercritical fluids, together with considerations on automation, speed and cost, make supercritical fluids very attractive for application in coupled systems. A number of coupled systems in which supercritical fluids play a key role are described. Supercritical fluid extraction-capillary gas chromatography-mass spectrometry (SFE-cGC-MS) has been applied to the determination of pesticides in fruit juices. For the determination of polycyclic aromatic hydrocarbons, triazines, chlorophenols and phenoxy acids in water samples, the SFE-cGC-MS system was extended with a sample preparation station after SFE, allowing the addition of internal standards and derivation of the acidic solutes after SF extraction. The potential of on-line solid-phase extraction-supercritical fluid chromatography-diode array detection is illustrated with the determination of xanthines in iced tea and of traces of pesticides in water samples.

The more or less systematic studies on the specific activity of oximes as reactivators of acetylcholinesterase (AChE) inhibited by organophosphorus (OP) compounds provide a panoramic image of their pharmacological and toxicological profiles. Established structure-activity relationships are still unable to adequately predict their antidotal efficacy. However, the in vivo behavior of oximes is a direct consequence of their physico-chemical properties, considerably limiting the passive transport across the biological barriers.This paper discusses the efficacy of oximes from a biokinetic perspective. The non-homogenous distribution of oximes versus OP in tissues was considered and correlated with the highly variable AChE reactivation at both peripheral and central levels. The acute toxicity and formation of highly toxic phosphylated oximes are presented as possible sources for reduced therapeutic efficacy.Biokinetic of oximes is 'structure dependent', with variable, tissue-specific distribution and activity. The existing knowledge does not allow to state true limits for a minimum extent of AChE reactivation in different tissues granting the survival of intoxicated organisms. An increased penetration of biological barriers is not automatically equivalent to a high extent of reactivation or antidotal efficacy and most probably, induces significant risks because of the intrinsic toxicity of the oxime.

Substitution of acetonitrile (ACN) as organic modifier in mobile phases for liquid chromatography by mixtures of propylene carbonate (PC) and ethanol (EtOH) may be considered a greener approach for pharmaceutical applications. Such a replacement is achievable without any major compromise in terms of elution order, chromatographic retention, efficiency and peak symmetry. This has been equally demonstrated for reverse phase (RP), ion pair formation (IP) and hydrophilic interaction liquid chromatography (HILIC) separation modes. The impact on the sensitivity induced by the replacement between these organic solvents is discussed for UV-vis and mass spectrometric detection. A comparison between Van Deemter plots obtained under elution conditions based on ACN and PC/EtOH is presented. The alternative elution modes were also compared in terms of thermodynamic parameters, such as standard enthalpy (ΔH⁰) and entropic contributions to the partition between the mobile and the stationary phases, for some model compounds. Van't Hoff plots demonstrated that differences between the thermodynamic parameters are minor when shifting from ACN/water to PC/EtOH/water elution on an octadecyl chemically modified silicagel stationary phase. As long as large volume injection (LVI) of diluents non-miscible with the mobile phase is a recently developed topic having a high potential of greening the sample preparation procedures through elimination of the solvent evaporation stage, this feature was also assessed in the case of ACN replacement by PC/EtOH.

The decomposition of the pharmaceutical compound enalapril in aqueous solution using non-thermal plasma has been investigated. The plasma was generated in a dielectric barrier discharge reactor (DBD) in coaxial configuration, at the interface between gas (oxygen at atmospheric pressure and room temperature) and the solution which flows as a thin film on the surface of the inner electrode of the plasma reactor. The discharge was operated in pulsed mode, at low power, in order to prevent unnecessary heating. The evolution of the degradation process was continuously followed using liquid chromatography — mass spectrometry (LC-MS). Total organic carbon (TOC) and chemical oxygen demand (COD) analyses were used to determine the mineralization degree.

Micro-HPLC separation and UV detection of some metal thenoyltrifluoroacetonates has been achieved. Cyano, octadecyl, and HTT A modified silica gels were used as stationary phases. Data about separation and detection parameters optimization are also described.

The retention behavior of some flavonoids in reversed phase liquid chromatography (RPLC) was investigated using different chemistries of the modified silicagel based stationary phases. Highly end-capped octadecyl silicagel (ODS), polar embedded linker octadecyl silicagel (SB-18 Aqua), phenyl silicagel and pentafluorophenyl modified silicagel (PFP) were used as stationary phases. The mobile phase consisted in acetonitrile/acidified water mixtures, at different fractions of volume. The lipophilicity was estimated through different chromatographic descriptors, as it follows: log k(w), m log k, S, φ(0) and PC1/log k. The chromatographic behavior observed on the mentioned stationary phases was evaluated by means of various graphical profiles and correlation matrices. Additionally, new information about the characteristics of the stationary phases and their (dis)-similarities were provided through lipophilicity charts and by scatterplots of loadings obtained by applying principal component analysis (PCA) to retention data. Furthermore, the experimental lipophilicity indices estimated from retention data were correlated with the computed descriptors, at a high level of statistical significance.

Calibration data of LC-MS/MS rarely fit the pure least square regression model, especially for large concentration intervals. The response function of the MS instrument is corrected by weighted regression models or logarithms. The choice of a response linearization method is based on results produced through back-interpolation of experimental data and/or evaluation of correlation coefficients. Two bioequivalence studies carried out for pharmaceutical formulations containing metformin gave us the opportunity to appreciate the impact of the MS response linearization method (logarithm and 1/x weighted linear regression) on method quality characteristics. The sample preparation was based on protein precipitation with acetonitrile. Chromatographic separation was achieved on a Zorbax CN column (mobile phase acetonitrile and aqueous 10 m m ammonium acetate solution, pH 3.5). Tandem MS detection was performed on a triple quadrupole spectrometer equipped with an electrospray source, operated under positive-ion mode. The method was validated and used for evaluation of the bioequivalence of formulations containing 500 and 1000 mg metformin. The 500 mg metformin study used logarithms for linearization of the detector response, while the 1000 mg metformin study was based on 1/x linear weighted regression. Data resulting from validations and studies completion were compared with evaluate the impact of the response linearization on the method quality characteristics.

The effect of column temperature on the separation of the sixteen polycyclic aromatic hydrocarbons (PAHs) of mixture SRM 1647a of the US Environmental Protection Agency has been studied on different micropacked ODS columns. Isothermal temperature optimization was successfully used for complete separation of the PAHs on a polymeric ODS stationary phase, whereas temperature programmed conditions were selected for separation on a monomeric ODS stationary phase.

The decomposition of three β-lactam antibiotics (amoxicillin, oxacillin and ampicillin) in aqueous solution was investigated using a dielectric barrier discharge (DBD) in coaxial configuration. Solutions of concentration 100 mg/L were made to flow as a film over the surface of the inner electrode of the plasma reactor, so the discharge was generated at the gas-liquid interface. The electrical discharge was operated in pulsed regime, at room temperature and atmospheric pressure, in oxygen. Amoxicillin was degraded after 10 min plasma treatment, while the other two antibiotics required about 30 min for decomposition. The evolution of the degradation process was continuously followed using liquid chromatography-mass spectrometry (LC-MS), total organic carbon (TOC) and chemical oxygen demand (COD) analyses.

The possibility of forming ion-pairs between bile acids (sodium taurocholate, sodium taurodeoxycholate and sodium taurochenodeoxycholate) and different compounds (pralidoxime, obidoxime and pyridostigmine) having a cationic character has been studied in reversed-phase liquid chromatography (RP-LC). This study can be useful in understanding the role of bile acids in the transport of ionic species through hydrophobic membrane. The present study focused on the influence of mobile phase composition on the retention parameters of chosen compounds (percentage of acetonitrile, pH of aqueous omponent or ionic strength). For constant concentration of bile acids in aqueous component of mobile phase the functional dependencies between the logarithm of the retention factor (k) and the methanol content in the mobile phase followed a binomial pattern (U-shaped), with a minimum positioned within the interval 70–85% methanol. Copyright © 2010 John Wiley & Sons, Ltd.

Analytical aspects related to the assay of pentoxifylline (PTX), lisofylline (M1) and carboxypropyl dimethylxanthine (M5) metabolites are discussed through comparison of two alternative analytical methods based on liquid chromatography separation and atmospheric pressure electrospray ionization tandem mass spectrometry detection. One method is based on a 'pure' reversed-phase liquid chromatography mechanism, while the second one uses the additional polar interactions with embedded amide spacers linking octadecyl moieties to the silicagel surface (C-18 Aqua stationary phase). In both cases, elution is isocratic. Both methods are equally selective and allows separation of unknowns (four species associated to PTX, two species associated to M1) detected through specific mass transitions of the parent compounds and owning respective structural confirmation. Plasma concentration-time patterns of these compounds follow typical metabolic profiles. It has been advanced that in-vivo formation of conjugates of PTX and M1 is possible, such compounds being cleaved back to the parent ones within the ion source. The first method was associated with a sample preparation procedure based on plasma protein precipitation by strong organic acid addition. The second method used protein precipitation by addition of a water miscible organic solvent. Both analytical methods were fully validated and used to assess bioequivalence between a prolonged release generic formulation and the reference product, under multidose and single dose approaches.

The decomposition of a model pharmaceutical compound, pentoxifylline, in aqueous solution was investigated using a dielectric barrier discharge (DBD) in coaxial configuration, operated in pulsed regime, at atmospheric pressure and room temperature. The solution was made to flow as a film over the surface of the inner electrode of the plasma reactor, so the discharge was generated at the gas-liquid interface. Oxygen was introduced with a flow rate of 600sccm. After 60min plasma treatment 92.5% removal of pentoxifylline was achieved and the corresponding decomposition yield was 16g/kWh. It was found that pentoxifylline degradation depended on the initial concentration of the compound, being faster for lower concentrations. Faster decomposition of pentoxifylline could be also achieved by increasing the pulse repetition rate, and implicitly the power introduced in the discharge, however, this had little effect on the decomposition yield. The degradation products were investigated by liquid chromatography-mass spectrometry technique (LC-MS). The evolution of the intermediates during plasma treatment showed a fast increase in the first 30min, followed by a slower decrease, so that these products are almost completely removed after 120min treatment time.

Retention of a model set of sulfonylurea compounds has been studied under RP-LC conditions, considering competitional effects brought by different alcohols (ethanol, 1-propanol, 2-propanol, 1-butanol, 1-pentanol, and 1-octanol) used as additives in the organic component of the mobile phase (methanol). The capacity factors determined for the model compounds decreased with the increase of the hydrophobic character of the organic additive in the mobile phase. The amount of the additive within the organic component of the mobile phase was kept constant (1% as volumetric ratio). Retention was studied at different mobile phase compositions (aqueous to organic component ratios). Different functional fitting models were used to correlate retention to the content of the organic component in the mobile phase. Extrapolation of retention expressed as capacity factor to a mobile phase composition free of organic component is well correlated to the hydrophobic characteristics of the organic additives. The adsorption model was used for tuning the experimental find-outs. The possibility of controlling retention through the competitive effects induced by hydrophobic additives in the mobile phase is highlighted.

Research on the chemical composition of fossil resins has evolved during the last decades as a multidisciplinary field and is strongly oriented toward the correlation with their geological and botanical origin. Various extraction procedures and chromatographic techniques have been used together for identifying the volatile compounds contained in the fossil resin matrix. Hyphenation between thermal desorption (TD), gas chromatography (GC) and mass spectrometry detection (MS) has been chosen to investigate the volatile compounds fraction from ambers with a focus on Romanite (Romanian amber) and Baltic amber species. A data analysis procedure was developed for the main purpose of fingerprinting ambers based on the MS identity of the peaks generated by the volatile fraction, together with their relative percentual area within the chromatogram. Chromatographic data analysis was based entirely on Automated Mass Spectral Deconvolution &Identification System (AMDIS) software to produce deconvoluted mass spectra which were used to build-up a mixed mass spectra and relative retention scale library. Multivariate data analysis was further applied on AMDIS results with successful discrimination between Romanite and Baltic ambers. A special trial was conducted to generate pyrolysis "like" macromolecular structure breakdown to volatile compounds by gamma irradiation with a high absorbed dose of 500 kGy. Contrary to our expectations the volatile fraction fingerprints were not modified after irradiation experiments. A complementary non-destructive new approach by ESR spectroscopy was also proposed for discriminating between Romanite and Baltic ambers.

The assay of diltiazem (DLTZ) and its active metabolites desacetyldiltiazem (DAcD) and desmethyldiltiazem (DMeD) in plasma samples was achieved by means of an HPLC/(ESI)MS(2) method. The diastereoisomer of diltiazem, namely {(2R,3S)-5-[2-(dimethylamino)ethyl]-2-(4-methoxyphenyl)-4-oxo-2,3,4,5-tetrahydro-1,5-benzothiazepin-3-yl acetate} was used as internal standard (IS). Sample preparation was based on protein precipitation by means of organic solvent addition (acetonitrile). The isocratic elution based on a reversed-phase mechanism allows good separation of the analytes within 15 min. Atmospheric pressure electrospray ionization was used. All analytes were monitored in the MS(2)-MRM mode. A fragmentation schema is proposed for the target compounds. As the method was designed for bioequivalence purposes, a full validation procedure was considered. On validation, nonlinear calibrations were observed. Consequently, concentration intervals requiring nonlinear calibrations are discussed. Low limits of quantification in the 0.6-1 ng/mL concentration range were obtained. The analytical method was successfully applied to a single dose (120 mg), open-label, randomized, two-period, two-sequence, crossover bioequivalence study of two commercially available solid oral dosage pharmaceutical formulations (tablets).

Inter- and intra-individual variability of the loratadine (LOR) metabolism in Caucasian subjects was assessed during a bioequivalence study for two pharmaceutical formulations (solid oral dosage forms) containing 10 mg of the active substance. The analytical data were obtained by applying a reliable, low-cost and sensitive ion pair liquid chromatography/fluorescence (IPLC/FLD) method for determination of both loratadine and descarboethoxyloratadine (DCL) in human plasma samples. The sample preparation procedure is based on liquid–liquid extraction of the target analytes from alkalinized plasma using diethyl-ether. The separation of the analytes and 8-chloroazatadine as internal standard (IS) was achieved through an isocratic ion pair (IP) elution on a Purospher® STAR RP-18 column. The mobile phase containing sodium dodecyl sulfate (SDS) as ion pairing agent was pumped at a flow rate of 1 mL/min. Fluorescence detection (FLD) was achieved at 280 nm (excitation) and 440 nm (emission) wavelengths. The increased sensitivity of the method is also based on a large sample injected volume (250 µL). Linear response was found over the 0.5–20 ng/mL concentration interval for both target compounds. Low limits of quantification (LLOQ) around 0.3 ng/mL were found for LOR and DCL. Method validation is presented. Copyright © 2007 John Wiley & Sons, Ltd.

Bioequivalence data for two pharmaceutical formulations (solid oral dosage forms) containing carvedilol is presented for both racemic and enantiomers of the active substance. This was achieved by on-line coupling of two liquid chromatographic separations followed by fluorescence detection. The first LC dimension was used for a fast separation of racemic carvedilol from propranolol (IS) and the endogenous matrix, by means of a reversed phase mechanism. The peak of racemic carvedilol was on-line transferred to the second enantioselective LC dimension, based on a reversed phase separation on cellulose tris(3,5-dimethyl-phenylcarbamate) stationary phase. Both stages were monitored over a single run by means of a fluorescence detector operated at an excitation wavelength of 285 nm and an emission wavelength of 355 nm. Automated shortcutting of the racemic carvedilol peak to the chiral column and simultaneous detection over the two LC dimensions have been obtained by using an experimental set-up based on two six-port rotative switching valves. Linearity was demonstrated on the interval 2-150 ng/mL for racemic carvedilol and on 1-75 ng/mL intervals for enantiomers. LLOQ fits between 0.7 and 1.4 ng/mL. Recoveries of the target compounds are 87+/-4 and 81+/-4% for the IS. Precision ranged from 0.6 to 2.5% and the mean accuracy obtained on quality control samples (measured as % bias) over the whole study falls between -0.8 and 6.3%.

A simple, high-throughput, highly selective and sensitive HPLC-FLD method for isolation and determination of furosemide and/or norfloxacin in human plasma samples following a simple organic solvent deproteinization step with acetonitrile as sample 'clean-up' procedure is reported. One of the two drug substances plays the internal standard role for the determination of the other. Separation of analyte and internal standard was achieved in less than 5.3 min (injection to injection) on a Chromolith Performance RP-18e column, using an aqueous component containing 0.015 mol/L sodium heptane-sulfonate and 0.2% triethylamine brought to pH = 2.5 with H(3)PO(4). The composition of the mobile phase was: acetonitrile-methanol-aqueous component = 70:15:15 (v/v/v) and the flow-rate was set up to 3 mL/min. The chromatographic method applied to the determination of furosemide relies on fluorescent detection parameters of 235 nm for the excitation wavelength, and 402 nm for the emission wavelength. In case of norfloxacin, the excitation wavelength is set up to 268 nm and the emission wavelength is set up to 445 nm. The overall method leads to quantitation limits of about 27 ng/mL for furosemide, and 19.5 ng/mL for norfloxacin, using an injection volume of 250 microL. The method was applied to the bioequivalence study of two furosemide-containing formulations.