Gas chromatographic and spectral properties of pentafluorobenzyl derivatives of 2,4-dichlorophenoxyacetic acid and phenolic pesticides and metabolites

β-Cyclodextrin-bonded silica particles as the solid-phase extraction medium for the determination of phenol compounds in water samples followed by gas chromatography with flame ionization and mass spectrometry detection

A new absorbent for solid-phase extraction (SPE) was prepared by a beta-cyclodextrin bonded silica stationary phase (CDS) has been applied to determine the concentrations of phenol compounds in water samples. SPE of selected phenolic compounds from aqueous samples were performed using 250 mg CDS. The determination was subsequently carried out by gas chromatography-flame ionization detection (GC-FID) and gas chromatography-mass spectrometry (GC-MS). Compared with available SPE, the CDS showed high sensitivity and fast velocity of mass transfer for phenolic compound because of its porous structure of beta-cyclodextrin. The relative standard deviation (RSD) for river water sample spiked with phenolic compounds at sub-ppb level was lower than 10% and limit of detection (LOD) for these compounds were between 10 and 100 ng l(-1).

Trimethylbenzoic acids as metabolite signatures in the biogeochemical evolution of an aquifer contaminated with jet fuel hydrocarbons

Evolution of trimethylbenzoic acids in the KC-135 aquifer at the former Wurtsmith Air Force Base (WAFB), Oscoda, MI was examined to determine the functionality of trimethylbenzoic acids as key metabolite signatures in the biogeochemical evolution of an aquifer contaminated with JP-4 fuel hydrocarbons. Changes in the composition of trimethylbenzoic acids and the distribution and concentration profiles exhibited by 2,4,6- and 2,3,5-trimethylbenzoic acids temporally and between multilevel wells reflect processes indicative of an actively evolving contaminant plume. The concentration levels of trimethylbenzoic acids were 3-10 orders higher than their tetramethylbenzene precursors, a condition attributed to slow metabolite turnover under sulfidogenic conditions. The observed degradation of tetramethylbenzenes into trimethylbenzoic acids obviates the use of these alkylbenzenes as non-labile tracers for other degradable aromatic hydrocarbons, but provides rare field evidence on the range of high molecular weight alkylbenzenes and isomeric assemblages amenable to anaerobic degradation in situ. The coupling of actual tetramethylbenzene loss with trimethylbenzoic acid production and the general decline in the concentrations of these compounds demonstrate the role of microbially mediated processes in the natural attenuation of hydrocarbons and may be a key indicator in the overall rate of hydrocarbon degradation and the biogeochemical evolution of the KC-135 aquifer.

Pyrrole-based conductive polymer as the solid-phase extraction medium for the preconcentration of environmental pollutants in water samples followed by gas chromatography with flame ionization and mass spectrometry detection

A pyrrole-based polymer was synthesized and applied as a new sorbent for solid-phase extraction (SPE) of some environmental pollutants from water samples. Polypyrrole (PPy) was synthesized by chemical oxidation of the monomer in nonaqueous solution. SPE of selected phenols, pesticides, and polyaromatic hydrocarbons (PAHs) from aqueous samples were performed using 200 mg PPy. The determination was subsequently carried out by gas chromatography-flame ionization detection (GC-FID) and gas chromatography-mass spectrometry (GC-MS). The polymer showed much higher recoveries for aromatic compounds than aliphatics. Preconcentration of sample volumes up 11 led to acceptable recoveries for aromatic and other tested polar compounds. The R.S.D. for a river water sample spiked with phenols, pesticides and PAHs at sub-ppb level was lower than 10% (n = 3) and limits of detection for these compounds were between 15 and 120 ng l(-1).

Combined isobutoxycarbonylation andtert-butyldimethylsilylation for the GC/MS-SIM detection of alkylphenols, chlorophenols and bisphenol a in mackerel samples

The alkylphenols, chlorophenols, and bisphenol A were determined by gas chromatography/mass spectrometry-selected ion monitoring (GC/MS-SIM) followed by two work-up methods for comparison: isobutoxycarbonyl (isoBOC) derivatization and tert-butyldimethylsilyl (TBDMS) derivatization. Eleven endocrine disrupting chemicals (EDCs) of phenols in biological samples were extracted with acetonitrile and then the acetonitrile layer underwent freezing filtration 60 degrees C for 2 hours. Solid-phase extraction (SPE) was used with XAD-4 and subsequent conversion to isoBOC or TBDMS derivatives for sensitivity analysis with the GC/MS-SIM mode. For isoBOC derivatization and TBDMS derivatization the recoveries were 92.3 approximately 150.6% and 93.8-108.3%, the method detection limits (MDLs) of bisphenol A for SIM were 0.062 microg/kg and 0.010 microg/kg, and the SIM responses were linear with the correlation coefficient varying by 0.9755-0.9981 and 0.9908-0.9996, respectively. When these methods were applied to mackerel samples, the concentrations of the 11 phenol EDCs were below the MDL.

Intercalibration of chromatographic methods for auxino phytodrugs in Solanaceae

Three chromatographic methods are considered for the determination in Solanaceae of auxino-similar phytodrugs, so called because their structure resembles an auxine plant hormone. The phytodrugs studied were: 2,4-dichlorophenoxyacetic acid, 2,4-dichlorophenoxypropionic acid, 2,4-dichlorophenoxybutyric acid, 2-methyl-4-chlorophenoxyacetic acid, 2,4,5-trichlorophenoxyacetic acid, naphthylacetic acid and 2-naphthyloxyacetic acid. Three chromatographic methods, respectively based on ion-interaction HPLC, GC-MS with intra-injector derivatisation and CC-MS with pre-injection derivatisation, were developed, optimised and validated. A comparative discussion of the advantages/disadvantages of the methods suggests a strategy for their preferential use, that is essentially a function of the matrix complexity.

New polymeric sorbent for the solid-phase extraction of chlorophenols from water samples followed by gas chromatography-electron-capture detection

A polymeric material, polyaniline, was employed as a new sorbent for solid-phase extraction (SPE) of some environmental pollutants from water samples. Chlorophenols were extracted from aqueous samples by SPE using 120 mg polyaniline and determined by gas chromatography with electron-capture detection. The acetate esters of these phenols were formed by the direct addition of acetic anhydride to the organic extractant in the presence of K2CO3. Different conditions were applied to obtain higher retaining capacity and breakthrough volumes. The results compared with those obtained by other groups. The RSD for a river water sample spiked at sub-ppb level was lower than 10% (n = 3) and detection limits were between 3 and 110 ng(-1).

Gas chromatographic profiling and screening for phenols as isobutoxycarbonyl derivatives in aqueous samples

An efficient method is described for the simultaneous determination of phenol and 49 substituted phenols present in aqueous samples. The method is based on the extractive two-phase isobutoxycarbonyl (isoBOC) derivatization with subsequent solid-phase extraction (SPE) for the direct analysis by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). Phenolic hydroxyl groups in acidic aqueous solutions were allowed to react with isobutyl chloroformate present in the dichloromethane phase containing triethylamine. The resulting isoBOC derivatives were then recovered by SPE using Chromosorb P in normal-phase partition mode, followed by direct GC and GC-MS analysis. Using this combined procedure, linear detector responses were obtained in the concentration range of 0.5-8 microg ml(-1), with correlation coefficients varying from 0.925 to 0.999 for most of the phenols studied except for 2,4-dinitorphenol (0.789). The temperature-programmed retention index (I) sets as measured on DB-5 and DB-17 dual-capillary columns of different polarity were characteristic of each isoBOC phenol derivative and thus, useful in the screening for isomeric phenols by I matching only. The mass spectral patterns, exhibiting characteristic [M-100]+, [M-200]+ and [M-300]+ ions for the mono-, di- and trihydroxybezenes, respectively with common ions at m/z 57, facilitated their rapid structural confirmation. The present method allowed rapid screening for phenols when applied to water samples spiked with phenols.

Chromatographic methods in the determination of herbicide residues in crops, food and environmental samples

The state of the art of chromatographic methods used in the determination of herbicide residues in crops, food and environmental samples is reviewed. The main structural groups of herbicides, i.e., triazines, phenyl- and sulphonylureas, carbamates, uracils and phenoxyalkanoic and arylphenoxypropanoic acids, and important degradation products (dealkylated triazines, substituted anilines, chlorophenols) are considered. Advantages and drawbacks of gas (GC), liquid (LC) and thin-layer chromatography in this type of analysis are discussed. The characteristics of a modern chromatographic method for the determination of herbicide residues are summarized and trends in the development and combination of current GC and LC methods discussed.

Determination of phenoxyacid herbicides in drinking water at the ppt-level by liquid chromatography and on-line selective preconcentration

On-line precolumn sample handling using an anion-exchanger is applied to preconcentrate phenoxyacid herbicides in aqueous samples prior to their LC separation. Since direct percolation of large sample volumes through the ion-exchanger has to be avoided owing to the high content of inorganic anions in natural waters, a two-step preconcentration is carried out: phenoxyacids are concentrated in their neutral (acidic) form by percolation of natural samples at pH 1 first through a precolumn packed with the copolymer-based PRP-1 sorbent. Then, the PRP-1 precolumn is coupled on-line with a second one packed with the anion-exchanger and 3 ml of deionised water with 35% of acetonitrile allows the phenoxyacids to be desorbed from the PRP-1 sorbent and reconcentrated on the anion-exchanger in their ionic form. The content of the anion-exchanger is analysed on-line by coupling with a C18 analytical column and elution is made with a water-acetonitrile gradient. Detection limits in drinking water from a 500-ml sample are between 15 and 35 ng/l (ppt) and identity of phenoxyacids is reinforced by the fact that analytes are preconcentrated by the anion-exchanger. This methodology can be fully automated.