Peter C. Uden

Characterization of nonvolatile aqueous chlorination products of humic substances.

The formation of nonvolatile chloroorganics produced during the aqueous chlorination of humic substances was followed qualitatively and quantitatively. The effects of reaction time, NaOCl to C ratio, pH, and source of humic material were studied with respect to the quantitative formation of chloroform, dichloroacetic acid, trichloroacetic acid, and chloral hydrate. Other gas-chromatographable chloroorganics formed from the chlorination of fulvic acid were produced at levels below these four compounds. Chlorine-selective fingerprint studies were also undertaken to follow the formation of 17 major chlorinated products.

Selenium speciation in enriched and natural samples by HPLC-ICP-MS and HPLC-ESI-MS with perfluorinated carboxylic acid ion-pairing agents.

Selenium-enriched plants, such as hyperaccumulative phytoremediation plants (Astragalus praleongus, 517 micrograms g-1 Se, and Brassica juncea, 138 micrograms g-1 Se in dry sample), yeast (1200, 1922 and 2100, micrograms g-1 Se in dry sample), ramp (Allium tricoccum, 48, 77, 230, 252, 405 and 524 micrograms g-1 Se in dry sample), onion (Allium cepa, 96 and 140 micrograms g-1 Se in dry sample) and garlic (Allium sativum, 68, 112, 135, 296, 1355 micrograms g-1 Se in dry sample) were analyzed by HPLC-ICP-MS for their selenium content and speciation after hot water and enzymatic extractions. Reference samples with natural selenium levels, such as onion and garlic controls, cooking garlic powder, baking yeast powder and a commercial garlic supplement were also analyzed. Selected samples were also examined by HPLC-electrospray ionization (ESI)-MS. HPLC was mostly carried out with 0.1% heptafluorobutanoic acid (HFBA) as ion-pairing agent in 1 + 99 v/v methanol-water solution, but 0.1% trifluoroacetic acid (TFA) in 1 + 99 v/v methanol-water solution was also utilized to permit chromatography for compounds that did not elute with HFBA. More than 75% of the total eluting selenium compounds, based upon element specific detection, were identified from retention time data and standard spiking experiments, and between 60 and 85% of compounds were identified by MS, with up to 25% of the total eluting molecular selenium species being unidentified as yet. Limits of quantification (LOQ, defined as the concentration giving an S/N of 10) for HPLC-ICP-MS were in the range 2-50 ng mL-1 Se in the injected extracts for the selenium-enriched samples and 2-10 ng mL-1 Se for the natural selenium level samples. LOQ values for HPLC-ESI-MS were ca. 100 times higher than those measured by HPLC-ICP-MS.

Species-selective determination of selenium compounds in biological materials: (technical report).

There is substantial evidence of the complexity of selenium speciation in living organisms and of the importance of the selective determination of the particular species of this element in order to understand its metabolism and biological significance in clinical chemistry, biology, toxicology, and nutrition. The state-of-the-art of analytical techniques available for this purpose is critically evaluated with particular emphasis on the element-selective detection and identification of the detected selenium compounds. Whereas there are a number of techniques available that are able to detect various selenium species in living organisms selectively, few techniques exist that are able to identify and to characterize the species detected.

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 selenium compounds utilizing perfluorinated carboxylic acid ion-pairing agents and inductively coupled plasma and electrospray ionization mass spectrometric detection

Increasing speciation demands in clinical chemistry, toxicology and nutrition have made the determination of the total elements in a sample inadequate; the amount of an element and the chemical forms in which it is present need to be known. Inductively coupled plasma mass spectrometry (ICP-MS) was used after high-performance liquid chromatographic (HPLC) separation, as was electrospray ionization mass spectrometry (ESI-MS). The effect of variation of the number of carbon atoms in perfluorinated carboxylic acids used as ion-pairing agents for the separation of selenium compounds was examined. Trifluoroacetic acid (0.1%), pentafluoropropanoic acid (0.1%) or heptafluorobutanoic acid (0.1%; HFBA) were alternatively used as additives to methanol-water (1:99, v/v) solutions as mobile phases. Reversed-phase HPLC-ICP-MS with 0.1% HFBA in the mobile phase allowed more than 20 selenium compounds to be separated in 70 min in an isocratic elution mode; the separation of natural selenium-enriched sample extracts was examined and explained. The pH of the 0.1% HFBA solution was modified with hydrochloric acid or ammonia and the pH of the sample extracts before injection was modified in order to overcome unwanted double peak formation in the chromatograms of sample extracts. Oxidations of standard gamma-glutamyl-Se-methylselenocysteine and Se-methylselenocysteine were carried out using 30% H2O2 solution and identifications of selenium-containing oxidation products were made using HPLC-ICP-MS and HPLC-ESI-MS. The principal organic oxidation product in both cases was methaneseleninic acid (MeSeO2H).

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 the principal selenium compounds in selenium-enriched natural sample extracts by ion-pair liquid chromatography with inductively coupled plasma- and electrospray ionization-mass spectrometric detection

Selenium-enriched garlic and yeast sample extracts and digests were analyzed using ion-pair high performance liquid chromatography (HPLC) with on-line inductively coupled plasma-mass spectrometric (ICP-MS) and electrospray ionization-mass spectrometric (ESI-MS) detection. The principal selenium compounds in these samples were identified as selenomethionine, and Se-adenosyl-selenohomocysteine in yeast, and γ-glutamyl-Se-methyl-selenocysteine and possibly γ-glutamyl-selenomethionine in garlic. The compounds identified account for 85 and 90% of the total selenium content of the yeast and the garlic samples, respectively. On-line HPLC-ESI-MS selected ion chromatograms (SIC) and mass spectra of selenium compounds extracted from selenium enriched samples are presented. Limits of quantification (LOQ, defined as S/N = 10) for HPLC-ICP-MS were in the range 10–50 ng mL–1 Se in the injected extracts. LOQ values for HPLC-ESI-MS were ca. 100 times higher than those of HPLC-ICP-MS.

Element-specific chromatographic detection by atomic absorption, plasma atomic emission and plasma mass spectrometry

Reviewed are the principles and applications of contemporary methods of element selective chromatographic detection utilizing atomic absorption, emission and mass spectrometry, these adding an information based dimension to time-based monitoring. Flame and furnace atomic absorption are considered for GC and HPLC detection, while microwave induced plasma (MIP) emission is the focus for GC and inductively coupled plasma (ICP) emission for HPLC. Other plasma emission systems are also reviewed. Both MIP and ICP coupled mass spectrometry are covered for GC and HPLC detection. Supercritical fluid chromatographic (SFC) and field flow fractionation (FFF) interfaces are also considered. Analytical performance in terms of quantitative detection limits and elemental selectivity are considered. Examples are drawn from metal and non-metal detection, considering environmental, petrochemical, geochemical, agricultural and chemical fields.

High-pressure liquid chromatography of metal diethyl-dithiocarbamates with u.v. and d.c. argon-plasma emission spectroscopic detection

Abstract The separation of copper(II), nickel(II) and cobalt (III) diethyldithiocarbamates is reported by adsorption high-pressure liquid chromatography on 8-μm diameter spherical silica. Best resolution is found with a 5:15:80; acetonitrile:diethyl ether : Skelly B (petroleum hydrocarbon) mobile phase, any on-column degradation being avoided by pretreatment of the column with pyridine. U.v. detection limits at 254 nm are established in the 5–10 ng of metal region. An interfaced d.c. argon-plasma emission spectroscopic detection system in series with the u.v. detector, is used to confirm the metal content of eluted peaks and permit specific element detection.

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.