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Trace analysis of triazine compounds in water, soil, and urine by gas and high performance liquid chromatography with selective detection

Symmetric triazine compounds belong to a group of selective herbicides used in control of broadleaf and grassy weeds in a variety of crops during the last 40 years. According to the substituent in the 2-position they can be divided into three groups: chloro-, methoxy- and ethylthiotriazines. The mechanisms of their degradation include N-dealkylation, dechlorination and oxidation. The most common chlorotriazine studied in the water and soil environment and in biological samples is atrazine, a herbicide of high application rate especially in intensive corn cultivation areas. To asses the environmental impact and human exposure to triazine herbicides we have developed and introduced sensitive and selective analytical methods for their determination in environmental water and soil samples as well as in human urine. The methods are based on solvent or solid-phase extraction of parent compounds and their degradation products from environmental and biological matrices followed by capillary gas chromatography with nitrogen thermionic specific (GC-TSD), electron capture (GC-ECD) or mass selective (GC-MS) detection or by high-performance liquid chromatography with photodiode array absorption detection (HPLC-DAD). The trace enrichment of triazine compounds from water samples is performed by solid-phase extraction on octadecylsilica (C18) or stiren-divinylbenzene (SDB) sorbents and from soil samples by multiple ultrasonic extraction with acetone/n-hexane mixture. Recoveries of unchanged triazine herbicides extracted from water by C18 solid-phase extraction technique are effective with acetone elution. This is not the case for more polar compounds such as atrazine mono- and didealkylated degradation products that have low breakthrough volumes with this sorbent. The SDB sorbent allows the same percent recoveries (>90%) for chloro- and methylthiotriazines, including dealkylated atrazine degradation products, present in water at concentrations 0.1-1 μg/l. GC-TSD and HPLC-DAD detection limits of triazines accumulated by SDB extraction from 500-ml water samples and eluted with acetone are lower than 5 ng/l. The ultrasonic extraction of chloro-, methylthio- and methoxytriazines from soil gives for most of the compounds acceptable recoveries (>70%). Due to the high efficiency of GC capillary columns and interference-free GC-TSD and GC-MS (ion trap detector) chromatograms the GC analysis of soil extracts allows simultaneous determination of a greater number of different triazine compounds than HPLC-DAD analysis. Comparison of GC-TSD (detection limits 5-15 ng/g) with GC-ECD determination of chlorotriazines in soil indicated about ten times higher sensitivity of ECD for determination of didealkylated atrazine and cyanazine and about the same sensitivity for atrazine. Detection limits achieved by HPLC-DAD analysis of soil extracts were for most of the compounds comparable with GC-TSD determination. The measurement of specific metabolites in human urine enables a direct assessment of human exposure to triazine compounds and of levels of absorption in different conditions of exposure [1]. We developed three different extraction procedures for accumulation of parent triazine herbicides (atrazine, simazine, prometryn, and ametryn) and of three chlorodealkylated atrazine metabolites from human urine: extraction with diethyl ether [2] and solid-phase extraction on C18 [2] and SDB [3] sorbents. The procedures were optimised for final HPLC and/or GC analysis. Multiple extraction of NaCl-saturated urine with diethyl ether did not prove uniformly efficient for trace enrichment of chloro- and methylthiotriazine compounds. At ng/ml concentration levels the diethyl ether extraction recoveries of atrazine and simazine were almost quantitative while recoveries of other triazines ranged from 58% for deisopropylatrazine to 85% for deethylatrazine. The sensitivity of determination of extracted compounds by GC-TSD ranged from 5 ng/ml for atrazine to 30 ng/ml for didealkylated atrazine. C18 solid-phase extraction with acetone as eluting solvent resulted in about 100% recoveries of all parent herbicides with GC-TSD detection limits of 5 ng/ml for atrazine and 10 ng/ml for other herbicides. Comparably high accumulation efficiencies of less hydrophobic mono- and didealkylated atrazine metabolites were achieved from acidified urine samples (pH 2-3) only at concentrations lower than 100 ng/ml. GC-TSD and GC-ECD proved equally sensitive for analysis of urinary chlorotriazines atrazine, simazine, and monodealkylated atrazines, whereas ECD significantly excelled in sensitivity to deethyldeisopropylatrazine. The SDB sorbent can quantitatively retain the urinary chloro- and methylthiotriazine herbicides as well as dealkylated chlorotriazines. The sensitivity of HPLC-DAD determination was 10 ng/ml for the parent pesticides and 20 ng/ml for monodealkylated chlorotriazines. However, SDB solid-phase extraction resulted not only in trace enrichment of target triazine compounds but also of polar urinary components. To achieve an interference-free HPLC-DAD chromatogram it was necessary to precede the elution of triazines with acetone by washing the cartridge with solution of acetonitrile in water. The most polar didealkylated atrazine metabolite was completely lost during this despite its efficient retention on the SDB sorbent. For GC-TSD and GC-MS analysis the interfering polar matrices can be eliminated by rinsing the sorbent with pure water. The parent triazine compounds concentrated in the aqueous residue after evaporation of acetonic eluate can be efficiently reextracted into n-hexane, a non-polar solvent suitable for capillary GC. The same solvent was not efficient for reextraction of dealkylated atrazines. The equally high recoveries of parent compounds and less hydrophobic metabolites were achieved by reextraction of triazines from aqueous residue into ethyl acetate after addition of sodium sulphate. The detection sensitivity of GC-TSD and GC-MS (ion trap detector) determination ranged from 10 ng/ml for atrazine, simazine and deethylatrazine to 25 ng/ml for didealkylated atrazine. The methods developed for analysis of urinary triazines were applied for confirmation of occupational exposure during synthesis and formulation of atrazine. [1] M. Maroni, C. Colosio, A. Ferioli, A. Fait, Toxicology 143 (2000) 97-102. [2] G. Mendaš, B. Tkalčević, V. Drevenkar, Anal. Chim. Acta 424 (2000) 7-18. [3] G. Mendaš, V. Drevenkar, L. Zupančič-Kralj, J. Chromatogr. A 918 (2001) 351-359.

Triazine compounds; water; soil; urine; gas chromatography; high performance liquid chromatography; selective detection

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