Determination of trans,trans‐muconic acid in workers' urine through ultra‐performance liquid chromatography coupled to tandem mass spectrometry

A novel method for the biological monitoring of benzene‐exposed workers has been developed through ultra‐performance liquid chromatography coupled to tandem mass spectrometry. The method uses trans,trans‐muconic acid in urine as the benzene‐exposure biomarker. The method was developed using a triple quadrupole mass spectrometer with enough sensitivity to facilitate diluting and injecting the urine samples directly, rather than performing a solid‐phase extraction procedure as is common in the available protocols. Moreover, compared with a conventional high‐pressure liquid chromatography system, the separation power provided by the ultra‐performance liquid chromatography system allows a 10‐fold reduction in run time. The method was adjusted to a dynamic range of between 198.9 and 4916.7 µg/L to cover the biological exposure index of trans,trans‐muconic acid in urine. Also, the method demonstrated intra‐day and inter‐day precision at 98%, and accuracy within an acceptable range of 101 ± 8%. The method has been used to quantify various types of urine samples, such as workers' urine and inter‐laboratory proficiency tests. Depending on the sample, the quantified levels ranged from less than the limit of quantitation to 3836.7 µg/L. No levels exceeding the calibration range were detected in the urine of workers, and the reported concentrations in urine for the proficiency tests were, as expected, based on known values. Moreover, the new method using sample dilution and faster chromatographic run was more effective, facilitating fast communication of results, as needed, to decision‐makers. Copyright © 2012 John Wiley & Sons, Ltd.     

Minireview: Advances in Germanium Isotope Analysis by Multiple Collector–Inductively Coupled Plasma–Mass Spectrometry

The advent of multiple collector–inductively coupled plasma–mass spectrometry (MC-ICP-MS) has made the high-precision determination of Ge isotopes possible, which leads to the widespread application of Ge isotopes in earth, ocean, and cosmochemistry fields. This paper reviews the history of Ge isotope analysis, chemical dissolution and purification, and mass spectrometry measurements. Concentrated HNO₃ is sufficient to dissolve nearly all types of samples and HF is also involved for Si-rich samples. Low-temperature ashing prior to dissolution is an alternative way to preconcentrate Ge in organic-rich samples. For different matrices, Ge isotopes can be determined by MC-ICP-MS coupled with a traditional nebulizer system or hydride generation system after two-step separation, one step cation/anion-exchange separation, or Mg/Fe co-precipitation protocols. Ion-exchange column methods are suitable for samples with elevated matrix and Ge content such as sulfides, iron oxides, silicate rocks, and coals, whereas Mg or Fe coprecipitation methods are particularly suitable for all kinds of water. Hydride generation systems are improved over traditional nebulizer system due to the smaller sample quantity and fewer matrix-related interferences. Sample-standard bracketing, double spike, and external Ga isotope normalization are used to mass bias correction and yield consistent results. Analytical methods involving Ge-poor samples and Ge isotope analyses based on different Ge species or specific Ge compound in natural environment will be important prospects in the further study. For further applications of Ge isotopes in mineral deposits such as sulfide and iron oxide deposits, sulfides, and iron oxides reference materials should be developed in the future.     

Optimization of Pretreatment Method for Alkylmercuries Speciation in Coal by High‐Performance Liquid Chromatography Coupled with UV‐Digestion Cold Vapor Atomic Fluorescence Spectrometry

Abstract

Exhaustive extraction of analytes in their original chemical forms from samples with complex matrices is a pivotal step for speciation analysis. Herein we propose a pretreatment method for extracting and preconcentrating methylmercury and ethylmercury from coal samples by using KBr–H₂SO₄/CuSO₄–C₆H₅CH₃–Na₂S₂O₃ system. The extraction conditions, including the volume of the organic phase and the extraction time, were optimized in detail. Speciation analysis of alkylmercuries was carried out by high‐performance liquid chromatography online coupled with UV‐digestion and cold vapor atomic fluorescence spectrometry. The detection limits were 0.6 ng mL^?1 for methylmercury and 1 ng mL^?1 for ethylmercury, respectively. The recoveries of methylmercury and ethylmercury spiked in a sample were 84% and 82%, respectively. The method was applied successfully to analysis of alkylmercuries in four coal samples collected from northeast China.     

Cyclic sample pooling using two‐dimensional liquid chromatography system enhances coverage in shotgun proteomics

We report a cyclic sample pooling technique devised in two‐dimensional liquid chromatography–electrospray ionization mass spectrometry (LC‐ESI‐MS) shotgun proteomics that renders deeper proteome coverage; we combined low pH reversed‐phase (RP) LC in trifluoroacetic acid in the first dimension, followed by cyclic sample pooling of the eluate and low‐pH RP‐LC in formic acid in the second dimension. The new protocol has a significantly higher resolving power suitable for LC‐ESI‐MS/MS shotgun proteomics. Copyright © 2013 John Wiley & Sons, Ltd.     

Gauss–Seidel Estimation of Generalized Linear Mixed Models With Application to Poisson Modeling of Spatially Varying Disease Rates

Generalized linear mixed models (GLMMs) are often fit by computational procedures such as penalized quasi-likelihood (PQL). Special cases of GLMMs are generalized linear models (GLMs), which are often fit using algorithms like iterative weighted least squares (IWLS). High computational costs and memory space constraints make it difficult to apply these iterative procedures to datasets having a very large number of records.

We propose a computationally efficient strategy based on the Gauss–Seidel algorithm that iteratively fits submodels of the GLMM to collapsed versions of the data. The strategy is applied to investigate the relationship between ischemic heart disease, socioeconomic status, and age/gender category in New South Wales, Australia, based on outcome data consisting of approximately 33 million records. For Poisson and binomial regression models, the Gauss–Seidel approach is found to substantially outperform existing methods in terms of maximum analyzable sample size. Remarkably, for both models, the average time per iteration and the total time until convergence of the Gauss–Seidel procedure are less than 0.3% of the corresponding times for the IWLS algorithm. Platform-independent pseudo-code for fitting GLMS, as well as the source code used to generate and analyze the datasets in the simulation studies, are available online as supplemental materials.     

Analysis of toldimfos in porcine muscle and bovine milk using liquid chromatography–triple quadrupole mass spectrometry

An analytical method was developed for the detection of toldimfos sodium residues in porcine muscle and bovine milk using liquid chromatography–triple quadrupole tandem mass spectrometry (LC–MS/MS) analysis. The drug was extracted from muscle and milk using 10 mm ammonium formate in acetonitrile and then purified using n ‐hexane. The drug was well separated on a Luna C₁₈ column using a mixture of 10 mm ammonium formate in ultrapure water (A) and acetonitrile (B) as the mobile phase. Good linearity was achieved over the tested concentration range (0.005–0.03 mg/kg) in matrix‐matched standard calibration. The determination coefficients (R ² ) were 0.9942 and 0.9898 for muscle and milk, respectively. Fortified porcine muscle and bovine milk contained concentrations equivalent to and twice the limit of quantification (0.005 mg/kg) yielded recoveries in the range of 75.58–89.74% and relative standard deviations of ≤8.87%. Samples collected from large markets located in Seoul, Republic of Korea, tested negative for toldimfos sodium residue. In conclusion, ammonium formate in acetonitrile can effectively extract toldimfos sodium from porcine muscle and bovine milk without solid‐phase extraction, which is usually required for cleanup before analysis. This method can be applied for the routine analysis of toldimfos in foods of animal origins.     

Focused ion beam preparation of samples for X‐ray nanotomography

The preparation of hard material samples with the necessary size and shape is critical to successful material analysis. X‐ray nanotomography requires that samples are sufficiently thin for X‐rays to pass through the sample during rotation for tomography. One method for producing samples that fit the criteria for X‐ray nanotomography is focused ion beam/scanning electron microscopy (FIB/SEM) which uses a focused beam of ions to selectively mill around a region of interest and then utilizes a micromanipulator to remove the milled‐out sample from the bulk material and mount it on a sample holder. In this article the process for preparing X‐ray nanotomography samples in multiple shapes and sizes is discussed. Additionally, solid‐oxide fuel cell anode samples prepared through the FIB/SEM technique underwent volume‐independence studies for multiple properties such as volume fraction, average particle size, tortuosity and contiguity to observe the characteristics of FIB/SEM samples in X‐ray nanotomography.     

Magnetic properties of carbon nanosheets

Two-dimensional carbon nanosheets have been fabricated using inductively coupled radio frequency plasma-enhanced chemical vapour deposition. The structural properties of the nanosheets have been characterised using atomic force microscopy, scanning electron microscopy and X-ray diffractometer. The magnetisation of the samples was studied using vibrating sample magnetometer. The magnetisation of the nanosheets was found to be diamagnetic for fast synthesis processes (30 and 60 min). On the other hand, the nanosheets exhibited a weak ferromagnetic response for the slow (120 min) synthesis process. Energy dispersive spectrometry and atomic absorption spectroscopy confirmed that the magnetisation exhibited by the carbon nanosheets was an intrinsic property and that it was not due to contamination from the substrate. Raman spectroscopy studies revealed that the ferromagnetic carbon nanosheets have a higher ratio (1.20) of graphite peak (I _G) to disordered peak (I _D) than normally expected (0.75–0.90). Available data indicated that the magnetisation was due to the presence of structural disorders.     

Novel thionin-functionalised core shell magnetic nanoparticles for dispersive solid-phase extraction of Hg(II) in food and water samples

To develop an accurate and precise method for separation and pre-concentration of Hg(II), a novel thionin functionalised core shell structure magnetic material has been prepared and characterised. The extraction ability of the material was evaluated by magnetic solid-phase extraction coupled with inductively coupled plasma mass spectrometry determination of Hg(II) in food and water samples. Combining the advantages of magnetic separation with selective extraction of thionin towards Hg(II), the material exhibits enhanced enrich selectivity and efficiency for Hg(II). The experimental parameters influencing Hg(II) extraction efficiency, including pH of the aqueous solution, the dosage of the adsorbent, extraction time and sample volume, were systematically investigated. Under the optimised conditions, concentration of Hg(II) at 1.0 μg L^?1 can be successfully enriched by the material without the interference of the common co-existing ions. The enrichment factor and adsorption capacity were 250 and 75.2 mg g^?1, and precise of the method was confirmed by analysing the spiked food, water samples and standard water reference samples with the recoveries of 92.5–101.8%.     

The Role of Column Switching in Analysing Complex Samplest

Abstract

Our objective in using column switching is primarily to achieve the desired separation in the minimum analysis time. Complimentary to this aim is the need for sample and column cleanup followed by column re-equilibration. Finally, all operations should be capable of automation. Fundamental to column switching methodology is the concept of Zone cutting, where part of the chromatogram is transferred to another column. This forms the basis of sample cleanup and is a very versatile and powerful method. Multiple zone cutting is also possible to further increase the scope of cleanup or to minimise analysis time. Zone cutting is also complimentary to the techniques of trace enrichment and recycling. Examples will be given involving the use of these techniques in the analysis of complex matrices such as urine, plant extracts, wine and serum. The latter will be used to propose a novel approach to the quantitative analysis of anti-convulsants in serum using hexobarbital as internal standard.