Eric Denoyer

Speciation of selenoamino acids and organoselenium compounds in selenium-enriched yeast using high-performance liquid chromatography inductively coupled plasma mass spectrometry

As part of an ongoing study to identify selenium compounds with cancer chemopreventive activity, selenium-enriched yeast was analyzed by HPLC–ICP-MS. More than twenty selenium-containing species were found in hot water and enzymatic hydrolysis extracts of the yeast. Trifluoroacetic acid was used as an ion-pairing agent in a water–methanol mobile phase with reversed-phase chromatography on an octylsilane stationary phase. The presence of selenocystine, selenomethionine and methylselenocysteine was confirmed by comparative retention of standards. The column efficiency was 8500 theoretical plates and the mobile phase was compatible with standard ICP-MS operating conditions.

High-performance liquid chromatography of selenoamino acids and organo selenium compounds - Speciation by inductively coupled plasma mass spectrometry

As part of an ongoing study to identify selenium compounds with cancer chemopreventive activity, extracts of selenium-enriched samples were analyzed by HPLC-inductively coupled plasma (ICP)-MS. Ion-exchange, ion pair and derivatization methods for reversed-phase HPLC were considered and advantages and disadvantages for each compared. Anion exchange allows separation of selenite and selenate, but otherwise provides poor separation. Pre-column derivatization and reversed-phase chromatography provides separation of compounds with terminal amine functionalities, but many other species elute in the void volume. The ion pair method gave optimal separation and was compatible with standard ICP-MS operating conditions.

Identification of selenium species in selenium-enriched garlic, onion and broccoli using high-performance ion chromatography with inductively coupled plasma mass spectrometry detection

Six standard selenium species including selenocystine, methyl selenocysteine, selenite, selenomethionine, allyl selenocysteine and selenate have been separated by high-performance ion chromatography on a Hamilton PRPX-100 column and detected by ICP-MS. Selenium enriched vegetables were analysed. Five selenium species and several unknown peaks were detected.

Flow Injection Determination of Mercury with Preconcentration by Amalgamation on a Gold-Platinum Gauze by Inductively Coupled Plasma Mass Spectrometry

Trace concentrations of mercury in water samples were determined by a method involving a preconcentration procedure and inductively coupled plasma mass spectrometry (ICP-MS) detection. Mercury vapour, generated by tin(II) chloride as the reductant, was trapped by amalgamation on a gold–platinum gauze, released by controlled heating and detected by ICP-MS. A flow injection sample introduction system with time-based injection was used and the sensitivity was found to be proportional to the mass of mercury introduced. Quantitative recoveries of mercury from open ocean sea-water, coastal sea-water and fresh water reference materials were obtained. A detection limit of 200 pg l–1 for a 25 ml sample was obtained. The precision of the method was 1%(relative standard deviation) at 1 µg l–1.

Determination of technetium-99, thorium-230 and uranium-234 in soils by inductively coupled plasma mass spectrometry using flow injection preconcentration

A new method is described for the determination of 99Tc, 230Th, and 234U at ultra-trace levels in soils. The method used flow injection (FI) for on-line preconcentration of 99Tc, 230Th and 234U prior to detection using inductively coupled plasma mass spectrometry (ICP-MS). The FI-ICP-MS method results in greater sensitivity and freedom from interferences compared with direct aspiration into an ICP mass spectrometer. Detection limits are improved by approximately a factor of 10. The FI-ICP-MS method is also faster, less labour intensive and generates less laboratory waste than traditional radiochemical methods. The accuracy of the method was tested for 99Tc by comparison to liquid scintillation counting and for 230Th and 234U by analysis of a US Department of Energy reference soil. Detection limits in the soil for 99Tc, 230Th and 234U were 11 mBq g–1(0.02 ng g–1), 3.7 mBq g–1(0.005 ng g–1) and 0.74 mBq g–1(0.003 ng g–1), respectively. Sample preparation, analysis protocol, and method validation are described.

Simultaneous determination of Co, Mn, P and Ti in PET samples by solid sampling electrothermal vaporization ICP-MS

The coupling of a graphite furnace to an ICP mass spectrometer results in a method that combines the suitability of the graphite furnace for handling solid samples with the detection power of ICP mass spectrometry (ICP-MS). Surprisingly, the majority of previous work devoted to solid sampling electrothermal vaporization (ETV) ICP-MS has only dealt with the determination of a single element, thereby wasting the pronounced multi-element capabilities of the detection method. In this work, solid sampling ETV-ICP-MS was used for the simultaneous determination of Co, Mn, P and Ti in two PET (polyethyleneterephthalate) materials, showing the suitability of the approach used for this kind of analysis. For this determination, the problems caused by the different furnace chemistry of the elements had to be tackled. In order to enable the determination of P, a combination of Pd and ascorbic acid was used as a chemical modifier. Different calibration methods—external calibration using either an aqueous standard solution or a solid standard and single standard addition—were studied and the results obtained were compared with those obtained by (i) ICP atomic emission spectrometry after sample dissolution and (ii) X-ray fluorescence. External calibration using a solid external standard and single standard addition were proved to be equally successful, but the latter is more practicable as only an aqueous standard solution is required.

Analysis of solid samples by ICP-mass spectrometry

SummaryICP-Mass spectrometry is typically used as a technique for very rapid multielement analysis at trace and ultra-trace levels of solutions by continuous sample aspiration and nebulization. However, ICP-MS is well suited to be used as a detector for other sample introduction devices. For the analysis of solid samples laser sampling and electrothermal vaporization accessories may be used as sample introduction devices for ICP-MS. Laser sampling permits the analysis of many different types of solid materials. For solid sampling ETV-ICP-MS analysis it is of advantage to reduce the sample to a fine powder prior to analysis. For automated analysis powders may be introduced as slurries into the graphite furnace by means of a slurry sampling device. Since appropriate certified solid reference materials are not always available for calibration, or since they are not certified for all analyte elements of interest, the analyses discussed in this contribution were performed semiquantitatively. The instrument response function was established using reference materials which were similar in their composition to the samples. The results of semiquantitative bulk analyses of glass (NIST 612) and geological material (USGS GXR-3) by laser sampling ICP-MS are in good agreement with the certified values. The concentrations of the analytes determined in the glass sample were in the range of 10 μg/g to 80 μg/g. The lowest analyte concentration in the geological sample was 0.4 μg/g (Eu) and the highest was approximately 186 mg/g (Fe). The precision achieved was in the order of 5% to 15%. Laser sampling ICP-MS is not only suitable to bulk analysis but also to analyses where spatial information is required. As an example for such an application the determination of Pb in a wine bottle cork stopper is dicussed. The slurry sampling technique was used for the semiquantitative analysis of NIST coal reference samples by electrothermal vaporization ICP-MS. The accuracy achieved with this approach was within a factor of ±2 of the reference values.

Semiquantitative analysis of environmental materials by laser sampling inductively coupled plasma mass spectrometry

Laser sampling inductively coupled plasma mass spectrometry has been used for the semiquantitative analysis of several solid sample material types that are encountered in the environment. Particulate samples are mixed with a cellulose-based binding agent and pressed into pellets for direct solid sampling by the laser. Semiquantitative analysis results are typically accurate to within 20–40% using internal standardization and within a factor of 2–3 without internal standardization. Precision is typically better than 15% relative standard deviation. Detection limits were limited by the purity of the binding material used to produce the pellet and typically ranged between 0.002 and 1.0 µg g–1. Analytical figures of merit of the technique are evaluated and results are discussed in terms of the application of the technique to environmental analysis.

Analysis of samples containing large amounts of dissolved solids using microsampling flow injection inductively coupled plasma mass spectrometry

The use of microsampling flow injection inductively coupled plasma mass spectrometry for the multi-elemental analysis of samples containing large amounts of total dissolved solids is described. The flow injection parameters such as sample delivery rate and sample loop volume were optimized with respect to signal peak height and stability. Short-(5 min) and long-(>2 h) term precision of the technique were investigated and detection limits in a 3% m/v NaCl matrix were determined. The detection limits for flow injection were 2–5 times better than those for continuous flow sample aspiration of the same matrix. Standard reference rock material AGV-1 from the United States Geological Survey was analysed after lithium tetraborate fusion (>1.2% m/v salt) to demonstrate the accuracy of the proposed method. Recovery experiments were carried out using spiked (10 µg l–1) 1 and 3% m/v NaCl solutions and were found to be acceptable for such matrices ranging from 83 to 119%.

The Search for Anticarcinogenic Organoselenium Compounds from Natural Sources

ABSTRACT: Consumption of Se-enriched plants or yeast-based nutritional supplements is reported to reduce the risk of cancer. Separation and identification of natural organoselenium compounds in these plants is essential to understand the basis for their biological activity. Earlier work suggests that plants convert inorganic selenium in the soil or growth medium into organoselenium compounds, such as selenoamino acids, following a route similar to the sulfur assimilatory pathway. To separate and detect selenoamino acids in plant extracts, we employ ion pair LC with an inductively coupled plasma mass spectrometer (ICP-MS) detector and capillary GC with an atomic emission detector (AED), for underivatized and derivatized compounds, respectively. Volatile selenium compounds, such as those found in human garlic breath, have been analyzed using GC-AED. Results involving Se-enriched garlic and yeast-based nutritional supplements are presented.