John J. Evans

High-performance liquid chromatographic separation of the enantiomers of organophosphorus pesticides on polysaccharide chiral stationary phases.

High-performance liquid chromatographic separation of the individual enantiomers of 12 organophosphorus pesticides (OPs) was obtained on polysaccharide enantioselective HPLC columns using alkane-alcohol mobile phase. The OP pesticides were crotoxyphos, dialifor, fonofos, fenamiphos, fensulfothion, isofenphos, malathion, methamidophos, profenofos, crufomate, prothiophos and trichloronate. The enantiomers of fenamiphos, fensulfothion, profenofos and crufomate were separated on CHIRALPAK AD; the enantiomers of fenamiphos were also separated on CHIRALPAK AS; the enantiomers of methamidophos, crufomate and trichloronate were separated on CHIRALCEL OD; the enantiomers of crotoxyphos, dialifor, fonofos, malathion, prothiophos and trichloronate were separated on CHIRALCEL OJ; and the enantiomers of isofenphos were separated on CHIRALCEL OG. Baseline or partial separation of the enantiomers of six of these OP pesticides was obtained on CHIRALCEL OJ. In continued method development, the separation of the enantiomers of the 12 OPs was investigated more extensively on CHIRALCEL OJ to determine whether the mobile phase composition, flow-rate and column temperature could be optimized to yield at least partial separation of the enantiomers. Chromatographic conditions were found that gave either baseline or near baseline separations of the enantiomers of the 12 OPs on the CHIRALCEL OJ column.

Determination of perchlorate at parts-per-billion levels in plants by ion chromatography.

A method for the analysis of perchlorate in plants was developed, based on dry weight, and applied to the analysis of plant organs, foodstuffs, and plant products. The method reduced greatly the ionic interferences in water extracts of plant materials. The high background conductivity, due to the plant matrix, was reduced sufficiently to allow quantitation of perchlorate with little or no matrix interference. Ion chromatography (IC) on a microbore AS16 anion-exchange column and a conductivity detector was used for separation and detection of perchlorate from the ionic plant extract. The extract was heated to precipitate proteins, centrifuged, exposed to alumina, and filtered through a cartridge filled with divinylbenzene to yield a water clear extract for IC analysis, even from highly colored solutions. Heating the extract and treatment with alumina reduced substantially the ionic content of the extracts without loss of perchlorate.

Analysis of perfluorinated carboxylic acids in soils II: optimization of chromatography and extraction.

With the objective of detecting and quantitating low concentrations of perfluorinated carboxylic acids (PFCAs), including perfluorooctanoic acid (PFOA), in soils, we compared the analytical suitability of liquid chromatography columns containing three different stationary phases, two different liquid chromatography-tandem mass spectrometry (LC/MS/MS) systems, and eight combinations of sample-extract pretreatments, extractions and cleanups on three test soils. For the columns and systems we tested, we achieved the greatest analytical sensitivity for PFCAs using a column with a C(18) stationary phase in a Waters LC/MS/MS. In this system we achieved an instrument detection limit for PFOA of 270 ag/microL, equating to about 14 fg of PFOA on-column. While an elementary acetonitrile/water extraction of soils recovers PFCAs effectively, natural soil organic matter also dissolved in the extracts commonly imparts significant noise that appears as broad, multi-nodal, asymmetric peaks that coelute with several PFCAs. The intensity and elution profile of this noise is highly variable among soils and it challenges detection of low concentrations of PFCAs by decreasing the signal-to-noise contrast. In an effort to decrease this background noise, we investigated several methods of pretreatment, extraction and cleanup, in a variety of combinations, that used alkaline and unbuffered water, acetonitrile, tetrabutylammonium hydrogen sulfate, methyl-tert-butyl ether, dispersed activated carbon and solid-phase extraction. For the combined objectives of complete recovery and minimization of background noise, we have chosen: (1) alkaline pretreatment; (2) extraction with acetonitrile/water; (3) evaporation to dryness; (4) reconstitution with tetrabutylammonium-hydrogen-sulfate ion-pairing solution; (5) ion-pair extraction to methyl-tert-butyl ether; (6) evaporation to dryness; (7) reconstitution with 60/40 acetonitrile/water (v/v); and (8) analysis by LC/MS/MS. Using this method, we detected in all three of our test soils, endogenous concentrations of all of our PFCA analytes, C(6) through C(10)-the lowest concentrations being roughly 30 pg/g of dry soil for perfluorinated hexanoic and decanoic acids in an agricultural soil.

Analysis of fluorotelomer alcohols in soils: Optimization of extraction and chromatography

This article describes the development of an analytical method for the determination of fluorotelomer alcohols (FTOHs) in soil. The sensitive and selective determination of the telomer alcohols was performed by extraction with methyl tert-butyl ether (MTBE) and analysis of the extract using gas chromatography with detection and quantification by mass spectrometry operated in the positive chemical ionization mode. The protonated molecular ion, [M+H](+) and a fragment ion (loss of HF+H(2)O) m/z 38 less than the molecular ion were monitored to identify tentatively FTOHs in MTBE extracts of contaminated soils. The FTOHs were confirmed by treatment of the extract with a silylation reagent and observing the disappearance of the FTOH response and the appearance of peaks attributable to the [M+H](+) ions of the trimethylsilyl derivatives. Mass-labeled FTOHs were used as recovery and matrix internal standards. Recovery experiments on soils shown to be free of endogenous FTOHs at instrument detection limits (IDL) of 16 fg/microL for 6:2 FTOH, 10 fg/microL for 8:2 FTOH and 14 fg/microL for 10:2 FTOH yielded a limit of quantitation (LOQ) of 190, 100, and 160 fg/microL for 6:2 FTOH, 8:2 FTOH, and 10:2 FTOH, respectively when 3 g samples of soil were extracted with 1 mL MTBE. The levels of the 6:2 FTOH, 8:2 FTOH, and 10:2 FTOH in five soils contaminated with FTOHs by exposure to the laboratory atmosphere during air drying were determined. In these air-dried soils, concentrations of FTOHs ranged from non-detectable to 3600 fg/microL (0.6 ng/g) of the 6:2 FTOH in the extract of a commercial topsoil. This method was used to determine even and odd numbered FTOHs from 6:2 through 14:2 in soils from fields that had received applications of sewage sludge. Concentrations of FTOHs in these sludge-applied soils ranged as high as 820 ng/g of dry soil for the 10:2 FTOH.

Accumulation of perchlorate in tobacco plants: development of a plant kinetic modelElectronic supplementary information (ESI) available: Tables S1 and S2 showing perchlorate content in tobacco plants and solutions and Figs S1 and S2 showing mean nutrient solution utilization rates and average fresh weights for perchlorate-amended plants. See http://www.rsc.org/suppdata/em/b3/b300570d/

Previous studies have shown that tobacco plants are tolerant of perchlorate and will accumulate perchlorate in plant tissues. This research determined the uptake, translocation, and accumulation of perchlorate in tobacco plants. Three hydroponics growth studies were completed under greenhouse conditions. Depletion of perchlorate in the hydroponics nutrient solution and accumulation of perchlorate in plant tissues were determined at two-day intervals using ion chromatography. Perchlorate primarily accumulated in tobacco leaves, yielding a substantial storage capacity for perchlorate. Mass balance results show that perchlorate degradation was negligible in plants. Tobacco plants were shown to effectively accumulate perchlorate over a wide range of initial concentrations (10 ppb to 100 ppm) from the hydroponics solution. Results suggest that plants are potential plants for the phytoremediation of perchlorate. A mathematical model was developed to describe the distribution of perchlorate in tobacco plants under rapid growth conditions. The Plant Kinetic (PK) model defined a plant as a set of compartments, described by mass balance differential equations and plant-specific physiological parameters. Data obtained from a separate hydroponics growth study with multiple solution perchlorate concentrations were used to validate predicted root, stem, and leaf concentrations. There was good agreement between model predictions and measured concentrations in the plant. The model, once adequately validated, can be applied to other terrestrial plants and inorganic chemicals currently used for both phytoremediation and ecological risk assessment.