Clayton B'Hymer

Speciation of arsenic in fish tissue using microwave-assisted extraction followed by HPLC-ICP-MS

The use of microwave-assisted extraction for the extraction of arsenic species from fish tissue is described. Quantitative extraction of arsenic from spiny dogfish muscle (CRM, DORM-2) was achieved using methanol-water (80+20, v/v) with microwave heating at 65 °C in a closed-vessel microwave system. Extractions were performed with a variety of solvents including water, two different methanol-water mixtures, and a 5% tetramethylammonium hydroxide solution. Extracted arsenic species were separated using both ion-exchange and ion-pair chromatography with ICP-MS detection. The DORM-2 along with three different varieties of fish purchased from a local market were analyzed for arsenic. In all samples, the majority of arsenic present was in the form of arsenobetaine, a non-toxic arsenic species.

Residual Solvent Testing: A Review of Gas-Chromatographic and Alternative Techniques

The purpose of this brief review is to describe and discuss some of the current analytic procedures including gas-chromatographic and alternative techniques for residual solvent testing. Residual solvents, or organic volatile impurities, are a potential toxic risk for pharmaceutic products and have been a concern of manufacturers for many years. Residual solvents have had official limits in the United States as set in USP XXV and by the FDA in 1997 and have been monitored by most pharmaceutical manufacturers extensively for more than two decades in both bulk and finished products. The chief method of analysis for residual solvents is gas chromatography, which is generally considered the preferred methodology. Sample introduction techniques include both static and dynamic headspace analysis, solid-phase microextraction, and direct injection of solution containing bulk drug substance or drug product into the gas chromatograph. Also, some alternative methodologies for residual solvent testing are discussed in this review. In conclusion, gas chromatograph-based procedures will continue to dominate residual solvent testing because of its specificity for identification of the solvent, but the use of alternative sample introduction techniques into a gas chromatograph will continue to expand in the near future.

An evaluation of extraction techniques for arsenic species from freeze-dried apple samples.

The extraction of arsenic from freeze-dried apples and subsequent determination of individual arsenic species by HPLC-ICP-MS is described. Solvent extraction with sonication using various aqueous and aqueous/solvent mixtures was initially evaluated by measuring total arsenic extracted by ICP-MS. A two step procedure using overnight treatment with alpha-amylase enzyme followed by sonication for 6 h with 40:60 acetonitrile-water was found to provide good extraction efficiency. The concentration of arsenic extracted was compared with the concentration of total arsenic in the samples determined using ICP-MS after microwave digestion in order to calculate extraction efficiency. Individual arsenic species in the extracts were measured using HPLC-ICP-MS. The three most abundant arsenic species found were arsenite, arsenate and dimethylarsinic acid. Total arsenic concentrations in the freeze-dried apple samples ranged from 8.2 to 80.9 micrograms kg-1 As, dry mass. By HPLC-ICP-MS, the relative amount of inorganic arsenic in the samples ranged from 73 to 90% of the sum of the arsenic species detected in each sample.

Evaluation of yeast-based selenium food supplements using high-performance liquid chromatography and inductively coupled plasma mass spectrometry

Six different brands of yeast-based selenium food supplements were obtained from local stores. These samples were analyzed for total selenium content and content uniformity by microwave nitric acid digestion. These supplements were also treated with milder extraction and hydrolysis conditions to analyze for the expected selenomethionine, a natural product of yeast when inoculated with selenium. A C8 high-performance liquid chromatographic (HPLC) column was used for the chromatographic determination of selenomethionine using a mobile phase of 89+10+1 (v/v/v) water–methanol–trifluoroacetic acid. Inductively coupled plasma mass spectrometry (ICP-MS) was used for the total selenium content and tablet content uniformity determination, and ICP-MS was used as the detector coupled with HPLC for the selenomethionine determination. A number of extraction and hydrolysis sample treatment procedures were tried. The two most effective appeared to be microwave heating with hydrochloric acid and with a simple overnight treatment with the enzyme Proteinase K. The six different brands of selenium supplements were found to have near label values based on total selenium, and they had reasonable tablet to tablet content uniformity values, but each brand had dramatically different profiles for the actual chemical form of selenium within the supplement. Only two brands had high levels of selenomethionine; one brand appeared to contain all inorganic selenium, and one brand appeared to contain greater than half inorganic selenium despite label claims of content being only selenomethionine.

Evaluation of a Microconcentric Nebulizer and its Suction Effect in a Capillary Electrophoresis Interface with Inductively Coupled Plasma Mass Spectrometry

An experimental consideration and common difficulty when interfacing capillary electrophoresis (CE) with plasma mass spectrometry via a pneumatic nebulizer is the suction effect caused by the natural aspiration of the nebulizer. This is a significant effect in terms of the CE experiment, since it can seriously degrade the separation of analytes. In this study, a pneumatic microconcentric nebulizer was studied as a CE interface with inductively coupled plasma mass spectrometry (ICP-MS). A self-aspirating sheath flow interface technique was used to reduce the suction effect of the nebulizer by using a separation of metallothionein I and ferritin. However, the sheath flow or make-up buffer technique has not been studied sufficiently with respect to all the effects on the CE analysis. In this evaluation, a sol-gel frit was placed in the sample introduction end in this CE system, and the contribution of the suction effect to both sample response from sample loading and elution times was observed. It was found that the studied microconcentric nebulizer could be used effectively with the self-aspirating sheath flow technique; however, the contribution of the suction effect to sample loading to the CE system is very high. The peak area response difference of an open capillary vs. a sol-gel fritted capillary was approximately one order of magnitude greater. Also, the fritted capillary experiments showed that the contribution to migration time from aspiration of the nebulizer through the CE capillary is very significant.

Chapter 7 Nebulizer sample introduction for elemental speciation

Publisher Summary The function of the nebulizer in inductively coupled plasma–mass spectrometry (ICP–MS) is to convert a liquid sample into an aerosol for introduction into the plasma. Production of an aerosol, which is defined as a finely dispersed liquid mist or spray suspended in a gas, is the easiest method to introduce a liquid sample into either an ICP or a flame. An aerosol facilitates a uniform sample introduction for both a reproducible signal output and the stable operation of the plasma. The pneumatic nebulizer is the most commonly used type of nebulizer. Three main types of liquid breakup are recognized: dropwise, stringwise, and filmwise. The breakup pattern of a liquid is a function of the gas stream velocity. Increasing velocity can change the breakup pattern in the order of dropwise, to stringwise, to filmwise. High performance liquid chromatography (HPLC) is the most commonly used technique for trace element speciation, especially in conjunction with ICP-MS detection for which it is well suited for eluent introduction. Capillary electrophoresis (CE) is also used for speciation, having the added capability of separating components based on electrophoretic mobilities.