Diuron recovery

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. 9.10 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 recoveries obtained for urons from samples of soil are shown in Table 9.16. Samples of soil were fortified by adding known volumes of solutions containing (a) Monuron, Metobromuron, Diuron and Chlorbromuron or (b) Monolinuron, Chlorotoluron, Tinuron and Chloroxuron. 

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... 

For aged samples, it is often necessary to repeat the extraction steps more than once for complete recovery. The analogous classical extraction comparison would be the introduction of a second liquid phase in a separatory funnel extraction. However, because of our automated system, the introduction of a second or third extraction step is conducted easily. The modifier/entrainer can be independently introduced to the matrix without interrupting the extraction procedure. In the time estimates given for the diuron spiked Tama soil extractions, two extractions per vessel were conducted. This resulted in 3 hours for the extraction of six samples in the six vessel extractor as well as 3 horns for twelve samples in the twelve vessel extractor since the extractions are conducted in pairs. 

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. 

Farrington et al. [346] developed a high-performance liquid chromatographic method to perform positive monitoring down to 200 xg/kg of chlor-bromuron, chlorotoluron, diuron, linuron, monolinuron, chloroxuron, mono-uron and metobromuron in methanolic extracts of soils. Recoveries were in the range 97.5 to 102%. 

A method for analysis of polar pesticides in wine by the use of automated in-tube SPME coupled with LC/ESI-MS was proposed (Wu et al., 2002). In-tube SPME is a microextraction and preconcentration technique that can be coupled on-line with high-performance liquid chromatography (HPLC), suitable for the analysis of less volatile and/ or thermally labile compounds. This technique uses a coated open tubular capillary as an SPME device and automated extraction. Using a polypyrrole coating, six phenylurea pesticides (diuron, fluometuron, linuron, monuron, neburon, siduron) and six carbamates (barban, car-baryl, chlorpropham, methiocarb, promecarb, propham) were analyzed in wine. Structures of compounds are reported in Fig. 9.4. Due to the high extraction efficiency of the fiber toward polar compounds, benzene compounds, and anionic species, LODs ranging between 0.01 and 1.2pg/L were achieved, even if the sample ethanol content affects the recoveries of analytes. 

Apart from the fact that in the presence of the natural organic matter in water MN-200 loses only 10% of its capacity for the above triazine pesticides, the regeneration of MN-200 (exhausted with simazine, chlor-otoluron, isoproturon, atrazine, and diuron) proceeds easily by simple washing of the polymer with 3—5 bed volumes of acetone, methanol, ethanol, or 1-propanol [71]. Complete removal of atrazine, benazohn, bentazone, imazapyr, and triclopyr requires about 8 BV of aqueous ethanol adjusted to pH 12 at 50°C. Regeneration of carbon F-400 presents great problems 200 BV of the above most efficient reagents comprehensively removes only benazolin and triclopyr, while the recovery of other herbicides remains below 50% [70]. 

Volmer et al. studied phenylureas and sulfonylureas by TSP-LC-MS after sample concentration by Cjg SPE [175]. 15 phenylurea- and 1 thiourea pesticides besides 112 polar pesticides from other pesticide classes were examined by TSP ionisation, detection limits and TSP mass spectra of these polar compounds were presented [245], Besides other polar pesticides, the phenylurea pesticides isoproturon and diuron were on-line concentrated on a precolumn from several surface and drinking water samples and then determined by TSP-LC-MS [247]. A multi-residue TSP-LC-MS method was published by Moore et al. for the determination of the urea pesticides chlortoluron, diuron, isoproturon, and Unuron in water samples after Cig-SPE [248]. Ci8 Empore disks were applied to concentrate phenylureas from river water and spiked seawater samples prior to TSP-LC-MS. Detection limits of 2-20 (ig L and recoveries between 80 and 125% were observed [239]. TSP-LC-MS (SIM) in the positive mode allowed determination of the urea pesticides chlor-bromuron, diuron, linuron, metobromuron, monuron, neburon in apples, beans, lettuce, peppers, potatoes and tomatoes with detection limits of 0.025-1 ppm [255]. 20 other polar pesticides, linuron, which was under suspicion of being a dietary oncogenic risk (US Natl. Res. Council) was determined by TSP-LC-MS a single rapid procedure in vegetables with detection limits of 0.05-0.10 ppm [270]. TSP-LC-MS and ESI were used in a multi-residue method for determination of the sul-... 

The urea pesticides diuron, fluormeturon, neburon and Hnuron cited as potential groundwater contaminants from US EPA in the National Pesticide Survey were quantitatively determined by APCI-LC-MS(-t) [354]. APCI-LC-MS was also used to test for 46 pesticide compounds in shallow groundwater samples from two sandy and two clay catchment areas. Of the neutral polars observed, isopro-turon belonged to the most frequently found compound [351]. Sphid et al. described an APCI-LC-MS method for the determination of isoproturon and different types of pesticides and their degradation products in ground water samples. Detection Umits, recovery, precision and Hnearity data were reported [350]. 

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