Search

The application of laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) to the isotope ratio analysis of UOx particles has the potential to improve the isotopic determination of these particles when compared to currently utilised ICP-MS techniques. To investigate this a high-speed, integrated ablation cell and dual concentric injector design was tested in the expectation that the resulting increase in signal to noise ratio and sample ion yield would improve the determination of 234U/238U, 235U/238U and 236U/238U for such materials. However, when compared to a slower washout, more established low-volume cell design, the highly transient signals of the new design proved challenging for the mixed detector array of the multi-collector mass spectrometer, introducing a new bias. We describe a major component of this bias, referred to as 'blind time', and model its impact on UOx particle analysis. After accounting for blind time, average precisions for the uranium isotopic composition of sub-micron sized UOx particles using LA-MC-ICP-MS were 3% 1RSD for 235U/238U and 8% 1RSD for 234U/238U. When ablating a glass rather than a UOx particle, uncertainties of 1.3% 1RSD for 235U/238U were achieved for 150 nm equivalent particle sizes using LA-MC-ICP-MS. [ABSTRACT FROM AUTHOR]

Platinum–DNA adducts, and in particular Pt–GG, have been identified as the major cytotoxic species during chemotherapy treatment with platinum containing drugs. This paper reports for the first time a strategy based on the use of double species-specific isotope dilution analysis (IDA) for the quantification of carboplatin–GG adducts formed by exposing human lung carcinoma cells to carboplatin. The main challenge posed by the use of carboplatin in this pre-clinical application, in comparison with most previously reported studies using cisplatin, includes the relatively low reactivity of this drug, thus demanding for improved limits of detection to be achieved in order to perform accurate quantification of the adducts at low ng Pt per mg DNA levels with relatively small uncertainty in micro-volumes of the biological sample. This was alleviated by developing micro-flow HPLC reversed phased methodology coupled to sector field ICP-MS (R = 300), showing a limit of detection of 0.2 ng Pt per mg DNA. To perform IDA, carboplatin–GG calibrants and spikes (194Pt-enriched GG adducts) were synthesized in house and characterised for Pt mass fraction, Pt distribution and structural composition. In order to assess the accuracy of the developed procedure, in the absence of certified reference materials, a reference sample prepared by incubation of calf thymus DNA with carboplatin and characterised in house (e.g. for its total P and Pt contents and Pt–GG concentration) was analysed in parallel. The use of this sample as a quality control of the cleavage of DNA and recovery of Pt adducts from real samples makes the described strategy particularly novel. Moreover, spike recovery experiments on the cell samples with the reference carboplatin–DNA sample were undertaken. The validated methodology was applied to cultured human lung carcinoma cells exposed to carboplatin; Pt–GG adducts were found to be at a level of 5.54 ng Pt per mg DNA with a relatively expanded combined uncertainty (k = 2) of approximately 20%. The major contributing factors to the overall measurement uncertainty were the mass fraction of Pt in the natural carboplatin–GG standard, the measured isotope ratio precision of sample and calibration blends and the blend to blend variation. The SI traceable methodology presented here will be invaluable for the provision of reference values to clinical measurements and cancer clinical trials. [ABSTRACT FROM AUTHOR]

Objective: We examined the comprehensiveness of Texas college campus tobacco policies. Methods: Tobacco policies from 189 colleges were evaluated on comprehensiveness of prohibited tobacco/nicotine products and their marketing. Chi-square analyses were used to compare 2-year versus 4-year, 4-year public versus 4-year private, and rural versus urban campuses on comprehensiveness and inclusion of electronic nicotine delivery systems (ENDS). Results: Two-year campuses were more likely than 4-year campuses to have a comprehensive policy. No differences were found between 4-year public and private campuses or rural and urban settings on comprehensiveness. No differences were found for any campuses tobacco policy on inclusion of ENDS. Conclusions: College campuses should evaluate tobacco policy comprehensiveness given that comprehensive tobacco policies may result in fewer first-time tobacco users. [ABSTRACT FROM AUTHOR]

In recent years, the field of ICP-MS has seen an increasing trend towards sampling systems and methods that produce short transient signals, rather than a continuous signal response. Fast data acquisition, readout and storage are crucial to take advantage of the wealth of information available from these approaches. However, many of the current generation mass spectrometers, in particular sector-field instruments, were not designed to cope with such short duration signals. This article reports the use of a commercially available multi-channel scaler board, which facilitates capture of TTL pulses from an ICP-MS detector at a user defined time resolution down to 100 ns. The board was used to profile 400–600 μs wide signals with 10 μs resolution, derived from the nebulisation of a 50 nm gold nanoparticle suspension. Furthermore, the benefit of a 100% duty cycle was demonstrated for ∼10 ms wide signals, following ablation of individual macrophage cells with a fast response LA-ICP-MS interface. [ABSTRACT FROM AUTHOR]

This review covers developments in the design of Laser Ablation (LA) cells, the associated transport tubing assembly, and their coupling to Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) instrumentation. Recent ablation cell designs have reduced the pulse response duration for a single laser shot to ＜10 ms, using the criterion of the full peak width at 1% of the height of the maximum signal intensity. The evolution towards these low dispersion systems has been profoundly influenced by our understanding of processes driving the initial dispersion, of the design aspects of the cell and tubing that influence transport-induced dispersion and transport efficiency, and of limitations imposed by the temporal resolution of ICP-MS instruments, all of which are discussed. Rapid response LA-ICP-MS systems greatly benefit throughput and sensitivity, which are key parameters in 2D and 3D imaging at high lateral resolution. The analysis and imaging of biological material has come to the forefront as a key application of LA-ICP-MS. The impact of the technical developments in LA-ICP-MS systems on emerging applications, including multiplexed metal-tagged antibody detection (for immunohistochemistry), nanoparticle and compound hypo- and hyperaccumulation, and (intra-) cellular/histological studies, is also discussed. [ABSTRACT FROM AUTHOR]

A novel strategy is reported for the quantitative analysis of the Fe spatial distribution in biological tissue using laser ablation with ICP-MS and on-line double isotope dilution analysis (LA-ICP-IDMS). The proposed on-line IDMS method involves post-ablation introduction of an isotopically enriched 57Fe spike solution using a total consumption nebuliser. To investigate the potential applicability of the developed method to biological tissue with varying Fe concentrations (akin to those observed in bio-imaging), the effect of sample-to-calibration standard blend ratio on the accuracy of the Fe data was investigated over a range of 1 : 0.2 to 1 : 10. To achieve this, homogenised sheep brain tissue doped with Fe (251 μg g−1) was used as the model sample. Recoveries of 80–109% of the expected Fe concentration in the model tissue sample (as determined by ID-ICP-MS of the tissue digest) were obtained over a sample-to-standard ratio range of 1 : 1 to 1 : 5. A systematic estimation of measurement uncertainty for LA-ICP-IDMS was undertaken and for the first time the mass flow rate of the material was determined via single-IDMS. An overall combined expanded uncertainty (k = 2) of 15–27% was achieved for ratio matching of 1 : 1 to 1 : 5. The factors with greatest contribution to the overall uncertainty were the mass of spike, the measured ratio of the standard blend and the mass of calibrant. External calibration with internal standardisation was performed on the same model sample for the purpose of comparison. The measurement uncertainty associated with this calibration approach was for the first time estimated for LA bio-imaging by taking into account the contributions from the signal intensity variance, the errors from least squares regression and concentration of the standards. For external calibration the overall relative expanded uncertainty was approximately 50% (k = 2), with the uncertainty in the linear least squares regression (R2 of 0.9833) and the signal variation being the main contributing factors. The results for Fe in the model sample agreed well with those determined via LA-ICP-IDMS. For the first time, the potential of a LA-ICP-MS isotope dilution calibration strategy to validate higher throughput calibration methodologies (e.g. matrix-matched external calibration with internal standardisation), as would be required for routine medical applications, has been demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: The on-line coupling of gel electrophoresis with inductively coupled plasma-mass spectrometry (GE-ICP-MS) is a powerful tool for simultaneous separation, detection and quantification of bio-molecules, and has been applied to the determination of phosphorus in DNA, phosphoproteins, and phosphopeptides, gold in nano-particles, iron in metalloproteins, and iodine in aerosols, and cisplatin-oligonucleotide interactions. However, since the first report in 2005, relatively few papers have been published, perhaps reflecting the lack of familiarity with the benefits of this promising methodology. So, here for the first time, we critically review the applications of GE-ICP-MS, and explore the advantages and the limitations of the technique for various applications. Such scrutiny may be useful in not only the development of the technique but also highlighting its potential in proteomics, genomics and metallomics. [Copyright &y& Elsevier]

This paper compares different buffer systems for the electrophoretic separation of the five most abundant serum proteins on native-PAGE gel and cellulose membranes. A modified Tris-tricine system was shown to be superior for the separation of these serum proteins in a 7% m/v native-PAGE gel as compared with the traditionally used Tris-glycine and Tris-tricine methods. This modified Tris-tricine buffer system was also employed for the separation of serum proteins using a cellulose acetate membrane and very effective separation was observed as compared with the traditionally used Tris-barbital and Tris-glycine buffer systems. [ABSTRACT FROM AUTHOR]

This technical note describes the development of Laser Ablation of a Sample In Liquid (LASIL), a technique where the ablation occurs at a solid sample surface submerged in a liquid. LASIL can be performed in a 25 µl isolated, freestanding droplet that acts as a micro-laser cavity, to produce a suspended particulate that can be analysed either directly, or following in-droplet chemistry, by calibration against aqueous standards. The technique is robust and easy to implement being carried out in air, offline to the detection apparatus. The analytical characteristics of LASIL are its ease of quantification, containment of particles, the ease of generating suspended solids in solution from insoluble materials and the control over dissolution and dilution to generate measurable concentrations. NIST 611 (trace elements in glass) was employed as a test sample as it is a commonly used reference material in conventional Laser Ablation (LA) studies. Droplet LASIL allowed the quantification of trace elements in NIST 611 and also investigation of the particle sizes and shapes generated by the ablation process. Particle sizes were found to vary with laser fluence, with higher fluences producing a wider particle size distribution with greater variation in shape. The types of particles found were: jagged particles of 1–2 µm in diameter most probably created by micro-jet impingement, spherical nanometre sized particles from vapour condensation and melt ejection, and thin, string-like particles from particle agglomeration or liquid jet fragmentation. At lower fluences the particle morphology tended towards spherical shapes and formed agglomerates. At this small particle size (below 250 nm), Brownian motion ensures a very slow settling rate in the liquid medium yielding solutions that are stable for analysis over several days. Alternatively, as demonstrated here, post-ablation chemistry can be carried out in the droplet, e.g.acid dissolution, or clean up using micro-extraction techniques. The liquid droplet was analysed by inductively coupled plasma-mass spectrometry (ICP-MS) with calibration against aqueous standards. The ablation yield from the sample was normalised using the found versusknown concentration of uranium in the sample and ratioing measured elemental concentrations to this factor. LASIL on a sample immersed in liquid facilitated the study of the effect of the solution composition on the LASIL process. [ABSTRACT FROM AUTHOR]

A novel, open, non-contact cell for laser ablation, capable of sampling: large planar samples, embedded planar samples, or samples of less than 2 mm mounted on a planar platform, without an outer containment enclosure, is described. This cell, when tested on NIST-613 CRM, exhibited rapid wash-out (<3.6 s for 99% signal reduction), low limits of detection and good signal precision in LA-ICP-MS. The cell uses a dual, annular, micro-jet gas flow array to exclude atmospheric gases and to entrain the ablated sample aerosol. The micro-jet array employed enabled a sampling height, between the sample surface and the lowest plane of the cell, of up to 200 µm. The micro-jet array has the facility to be electrically biased if the application demands it, e.g.extracting a charged plume in Matrix-Assisted Laser Desorption/Ionisation (MALDI) or Desorption Electrospray Ionisation (DESI) experiments. This particular implementation of the cell featured dual sample output channels, which could enable connection of the cell to more than one analyser. A micro jet-pump was coupled to the cell to extract the ablated aerosol from the low-volume inner ablation chamber, provide mixing of the aerosol with the injector flow of the ICP and to isolate the cell from downstream conditions in the injector flow. Potential applications of this cell include: analysis of silicon wafers, gel-plates/membranes, tissue samples, multiple sample analysis in high throughput facilities; and toxic fume removal and analysis in laser scribing, cutting and etching. [ABSTRACT FROM AUTHOR]

Abstract: The complexes of Ag+ with the peptides MetGly, ProGly, GlyPro, GlyHis and GlyProAla were investigated using hybrid density functional theory at the B3LYP/DZVP level. The silver ion binding free energies at 298K to each of these peptides was calculated to be 60.8, 52.0, 54.3, 71.2 and 63.3kcalmol−1, respectively. Structural information and relative free energies are presented for several isomers for each of the five complexes. Each of the global minima found for the five complexes is a charge-solvated ion. An important finding is that the Ag+–ProGly is the only complex where a salt bridge structure is energetically favored occurring at 4.0kcalmol−1 higher in free energy than the global minimum. The Ag+ ion in this salt bridge structure is attached to the carboxylate anion of zwitterionic ProGly in which the terminal amino nitrogen is protonated. For all the other complexes studied, the salt bridge structure occurs at much higher energies. All the dipeptide complexes with Ag+, but one, exhibit a di- or tri-coordinate metal where the sites of attachment are amino and carbonyl groups. However, the highest coordination numbers are not always the global minima due to steric costs. The global minimum of the Ag+–GlyProAla complex is the only structure found in this study where the metal is tetra-coordinated, binding to the terminal amino nitrogen and all three carbonyl oxygen atoms. Silver binding to sulphur and imidazole nitrogen atoms of MetGly and GlyHis, respectively, are present in the three most energetically favored species in each of these cases. [Copyright &y& Elsevier]

An introduction is presented in which the editor discusses the changes in the journal's editorial board as well as the contributions of several of its writers to the science including Barry Sharp and Les Ebdon.