Page:NIOSH Manual of Analytical Methods - 9205.pdf/3

CAP TAN and T HIOP HAN ATE -MET HYL: M ETH OD 9205, Issue 1, dated 1 5 Ma rch 2003 - Page 3 of 4 CALIBRATION AND QUALITY CONTRO L: 8. Determine retention times for analytes using the column and chrom atographic conditions as outlined on pages 920 5-1 a nd 9 205 -2. The approximate retention time of thiophanate-methyl is 14 minutes and cap tan is 2 1 m inutes . (See Figure 1.) 9. Ca librate daily with at least six working standards containing each of the two analytes and covering the analytical range (Table 1) for thiophanate-methyl and captan. 10. Prepare QC sam ples by placing a new patch in a 50 mL tube and spiking with known amounts of the two analytes. Allow the samples to set open until the solvent has evaporated. Cap the tube and prepare for analysis in the same manner as the field samples in steps 5-7.

MEASUREMENT: 11. Set LC according to manufacturer’s recomm endations. Set the wavelength for detection at 200 nm and flow rate at 0.200 mL/m in. 12. Injec t 5 µL aliquot of the sam ple ex tract w ith autosam pler. NOTE: If peak area of a sample is greater than the area of the highest standard, dilute with extracting solvent and reanalyze. 13. Measure peak area of the analyte.

CALCULATIONS: 14. Perform a separate regre ssion analysis of the peak area s vs. quantity of standard for each of the two analytes. De term ine the concentration ,µg /m L, (correcte d fo r DE) of the analyte in each sam ple patch (C P) and in the m edia blank (B b) from the calibration graph. 15. Ca lculate the mass of each analyte, M (:g), on a sample patch by adjusting for the volume , V (mL) of extra ction s olven t.

EVALUATION OF METHOD: This method was evaluated with a recovery study at room temperature over the range of 306.0 - 6120 µg /sa m ple for thiophanate -m eth yl and 300.4 - 6220 µg/sample for captan using spiked laboratory samples with respective average recoveries in the range of 89.1-95.5% and 89.6-96.0%. [1] The storage study at 4°C was completed at 6000 µg/sample for thiophanate-methyl, and 1500 µg /sam ple for captan with respective recovery averages of 8 6.2 -92.2 %, and 87.6 -95.7 % over the 28 days of the study. Carbendazim , which is a decomposition product of thiophanate-methyl, may also be found in the chromatogram along with the other two a nalytes. An attempt was m ade to quantitatively analyze carbendazim as a part of this method. However, reproducibility problems for carbendazim in the presence of thiophanatem eth yl has necessita ted that the analysis be only qualitative for carbendazim. The reproducibility problem was more pronounced when the ratio of thiophanate-methyl to carbendazim was grea ter than ab out eight to one. Additionally, this problem is compounded when other materials, such as benomyl, which also decomposes to produc e ca rben dazim , are present in the sa m ple. Be cau se this m etho d is un able to distinguish the decomposition source of the carbendazim, it can only pro vide qualitative data for carbendazim . Under the method conditions, its approximate retention time is 9 minutes. Fie ld sam ples have been analyze d by this m ethod. Be cause the fie ld sam ples contain ed other org anic compounds and/or interferences, it was necessary to mak e adjustments to the analysis parameters. For example, it was nec ess ary to insert a longer column rinse at the end of the solvent gradient to elute higher molecular weight compounds and/or other material from the column. It was also necessary to change the end of the gradient solvent run to have a greater organic phase ratio to help rinse the column of these materials. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition