Effect of organic matter content in the trace analysis of triazines in various types of soils with GC-NPD

Abstract

SummaryRecent work demonstrated that the combination of microwave assisted solvent extraction (MASE) and capillary gas chromatography with selective nitrogen detection (GC-NPD) is a viable approach for the efficient determination of triazine herbicides in soils. However, for soils with a high organic matter content or the injection of more concentrated extracts to obtain lower LOD's the performance of gas chromatographic analysis of uncleaned extracts is hampered. This results in both a decrease of the chromatographic response of analytes and a decrease in the life time of the column due to coextracted matrix substances. The effect of various types of soils on the chromatographic analysis of triazine herbicides was studied. It appeared that for the investigated samples with an organic matter content below 5 % processing of uncleaned extracts is possible. Samples with a higher organic matter content required a cleanup step. A rapid procedure on 100 mg silica cartridges has been developed using solvents compatible with the MASE extracts and the instrumental analysis. Beside the testing with different standard soils, about 120 samples of an ongoing monitoring program involving three different types of soil (organic matter content: 3-37 %) were analysed. The selected compounds atrazine, desethylatrazine, desisopropyl-atrazine and simazine could be assayed in the various soil types to a level of at least 2 lag kg -1. For soil samples with a high organic matter content (> 5 %), the rapid cleanup procedure allowed the trace analysis of the triazines and considerably increased the life time of the capillary column. Recoveries at levels from 2 to 50 tag kg -I ranged from 70 to 100 % with RSDs ranging from 5.1 to 9.5 %. Confirmation of positive sampies was carried out by gas chromatography mass spectrometry.

Comparison of gas and high performance liquid chromatography with selective detection for determination of triazine herbicides and their degradation products extracted ultrasonically from soil

“…The chromatogram of the extract of the non-spiked Soil 1 is included for comparison. Nitrogen-selective detection resulted in relatively clear and interference-free chromatograms, confirming the possibility of a direct analysis of uncleaned extracts of soils containing less than 5% of organic matter [11]. However, the fact that the less volatile sample matrix components tend to deposit in the injector glass liner or onto the front end of the column should not be neglected.…”

“…In their study of the effects of soil organic matter content on trace analysis of triazines by gas chromatography with nitrogen-selective detection, Molins and co-workers [11] demonstrated that the direct processing of uncleaned microwave assisted solvent extracts was possible if the organic matter content was below 5%. For our study, we selected agricultural soils/sediments with 1.59 -4.11% of organic matter (Table 1) and ultrasonic extraction with acetone:n-hexane 2 : 1 mixture which was reported to be efficient for the extraction of triazine herbicides from soil [4,13].…”

“…While the precipitation of humic substances from soil extracts with sodium chloride (humic substances hamper HPLC-DAD analysis) affords smoother chromatograms, compound recoveries and detection limits are not significantly improved, which is due to the large spread of data [17]. The interfering matrix substances, extracted by microwave-assisted solvent extraction from soils with an organic matter content exceeding 5%, decrease the response of the nitrogen-selective gas chromatographic detector to triazine analytes [11]. The analysis is significantly improved after the cleanup of the soil extracts on silica cartridges.…”

“…Typically, methods developed for the determination of triazine compounds in soil involve an extraction procedure and a clean-up step in order to eliminate the co-extracted interfering soil components and to preconcentrate the analytes for gas chromatographic (GC) [4 -16], high-performance liquid chromatographic (HPLC) [17 -22], and in some cases for thinlayer chromatographic determination [21,23]. The extrac-tion techniques include classical solvent extraction [4, 6 -9], Soxhlet extraction [17,18], sonicated extraction [10, 12 -14, 19, 23], microwave-assisted solvent extraction [11,14,15], pressurised liquid extraction (accelerated solvent extraction) [16], and supercritical fluid extraction (SFE) [20,21]. The last technique uses carbon dioxide modified with a mixture of methanol and water to extract triazines and their polar metabolites from the soil.…”

“…The last technique uses carbon dioxide modified with a mixture of methanol and water to extract triazines and their polar metabolites from the soil. The most common extracting solvents used in other extraction techniques are the mixtures of methanol and water [6 -9, 17], methanol and dichloromethane [11], n-hexane and dichloromethane [10], acetone and n-hexane [4,13], acetone and water [19], as well as non-mixed solvents such as methanol [7,14,18], acetonitrile [7], dichloromethane [12,16], acetone [23], and more recently hot water [14,22] or water containing 1% of methanol [15]. For the selective preconcentration of analytes extracted from soil the C 18 solid-phase extraction can be used [1, 5 -8, 16, 18], followed, if necessary, by cleaning of the eluate on an anion exchanger [6,18] or silica column [16].…”