Diuron extraction from soil

Fig. 9.10 Gas-chromatographic responses of extracts from soils (10g) containing Diuron after hydrolysis and bromination (a) 0.04ng standard (Rt=7min) (b) application of 2pl from 10ml of an extract of soil containing 0.04mg kg-1 and (c) recovery of Diuron added to soil at 0.8mg kg-1, 6pl being applied from a 50-fold dilution of (b). Pye 104 gas chromatography.

The extraction of two typical agricultural products from environmental matrices were chosen as examples for the operation of this system. Diuron, a phenylmethylurea, was freshly spiked onto Tama soil. This soil was characterized and shown to have 3.1% organic material and 14 % clay fraction. In addition, a phenyl metabolite of NUSTAR, a systemic fungicide, on wheat previously unextractable by SFE was extracted. The wheat sample was not classified for its chemical composition. Both samples were treated with radiolabeled compounds (E. I. du Pont de Nemours and Company, Du Pont Agricultural Products, Wilmington, DE) and extraction results are from liquid scintillation counting of the sample extract. Chromatographic evaluation of the Diuron from soil extracts has previously been published (2). 

Diuron from soil Diuron spiked Tama soil was the extraction example used in the six vessel multi-vessel extractor. As is illustrated in Table III, the average recovery for these samples was 97.3% and the relative standard deviation was 6.6%. When these results are compared to those obtained with the classical extraction techniques, equivalent recoveries were achieved. However, the precision associated with the classical extraction was typically 20%. Acceptable recovery ranges in classical residue analysis are from 70 to 125%. Comparing these precisions with those obtained with a one vessel SFE device, the... 

The density stepping method was then run on a spiked soil sample. Five grams of soil were spiked with the same solution of herbicide standards used to spike the celite sample and the solvent was allowed to evaporate. The spiked sample was then placed into an extraction thimble and extracted. The results were different than those obtained from the spiked celite. Even at a high density of C02 the herbicides were not extracted. Previous experience showed that using water as a modifier aided in the extraction of diuron from soils (6)(7). Therefore 1 ml. of water was added to the spiked soil and the sample rerun at a density of 0.9 g/ml of C02. The results showed a significant increase in recovery of the herbicides with the addition of water. This demonstrates that the addition of a modifier added to the extraction cell can have a significant effect upon the extraction recoveries (8)(9). The results are summarized in Table VIII. 

Neutral and basic herbicides were extracted from water made alkaline with sodium hydroxide or from soil, with chloroform extracts of soil were cleaned up on a basic alumina containing 15% of water. Acidic herbicides were extracted with ethyl ether from water acidified with hydrochloric acid or from an aqueous extract of soil prepared by treatment with 10% aqueous potassium chloride that was 0.05m in sodium hydroxide and filtration into 4m hydrochloric acid. The concentrated chloroform solution of neutral and basic herbicides was applied to a pre-coated silica gel plate containing a fluorescent indicator and a chromatogram was developed two-dimensionally with hexane-acetone (10 3) followed after drying by chloroform-nitromethane (1 1). The spots were detected in ultraviolet radiation. Atrazine, Barban, Diuron, Linuron, Monouron, Simazine and Trifluralin were successfully separated and were located as purple spots on a green fluorescent backgroimd. The ether extracts were dried over sodium sulphate. 

The separation of Diuron using the Pye 104 chromatographic is shown in Fig. 9.10 and, although greater sensitivity was obtained compared with the much older Perkin-Elmer instrument, both gave satisfactory results with adequate sensitivity. The response due to 0.04ng of Diuron is shown in (a), together with that from a soil extract (b) and a recovery on the same soil (c). 

Fig. 9.11 Typical chromatograms obtained from 5pl injections of soil extracts (a) unfortified and (b) fortified with uron herbicides at 2mg kg-1.1, Monuron 2monoLinuron 3 Metobromuron 4 Chlorotoluron 5 Diuron 6 Linuron 7 Chlorbromuron and 8 Chloroxuron.

The total extraction time for these samples was 12 minutes per extraction. However, the procedure was conducted twice for aged samples to ensure complete extraction of the desired materials. Therefore, the overall analysis time was 24 minutes per sample. This time estimate can be misleading. The design of our system is such that the extractions are conducted in a combination of serial and parallel fashion, reducing overall analysis time. Illustrated in Table I is the extraction program for Diuron from Tama soil. Prior to the start of this method program, modifier has been introduced to each extraction vessel in a stepwise fashion. This procedure is carried out to insure that there is no pressure build-up where modifier introduction... 

Extraction Program for Diuron from Tama Soil (12 Columns)... 

Cumulative Results for the Extraction of Freshly Spiked Diuron From Tama Soil Using the Multi-vessel Extractor... 

A limitation to the use of modifiers in SFC has been the detector compatibility of the specific modifier. For example, most modifiers (i.e. methanol) provide a flame ionization detector response preventing use at a large concentration. In SFE, however, this limitation does not exist since modifiers can be used in a mixed mode with CCb and the sample. Figure 1 (taken from reference 25) shows an example of the use or modifiers in SFE. Here the comparison of extraction efficiencies obtained using CO and CO2 modified with methanol is shown. The matrices extracted in these SFE experiments were an XAD-2 sorbent resin and soils. The target analytes were dibenzo[a,i]-carbazole, diuron, 2,3,7,8-tetrachorodibenzo-p-dioxin (TCDD) and linear alkylbenzenesulfonate (LAS) detergent. For each of these respective analytes the extraction efficiency increased dramatically with the use of C02/methanol modifier compared to pure CO2 only as the extracting fluid. This was even the case for the ionic compounds namely, the linear alkylbenzenesulfonates (LAS), which were quantitatively recovered. 

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