Page:NIOSH Manual of Analytical Methods - 9202.pdf/3

 CAP TAN and T HIOP HAN ATE -MET HYL: M ETH OD 9202, Issue 1, dated 1 5 Ma rch 2003 - Page 3 of 4 SAMPLE PREPARATION: 7. Prepare analyst spike sam ples, solutions of isopropanol spiked with varying concentrations of the analytes of interest used for quality assurance, when field samples are received and store them together. Analyze with the field samples, blanks, and the liquid standards. Include unused 150 mL isopropanol wash of a polyethylene sampling bag as a media blank. 8. Rem ove a 1 m L aliquot from the sam ple container and filter with a 4m m 0.45 µm syringe filter.

CALIBRATION AND QUALITY CONTRO L: 9. Determine retention times for analytes using the column and chromatographic conditions as shown on pages 9202-1 & 9202-2. The approximate retention time of thiophanate-methyl is 11 minutes and cap tan is 1 9 m inutes. (See Figure 1.) 10. Calibrate daily with at least six working standards containing each of the two analytes and covering the analytical range for thiophanate-methyl and captan.

MEASUREMENT: 11. Set LC conditions according to manufacturer’s recomm endations. Set the wavelength for detection at 200 nm and the flow rate at 0.200 mL/m in. 12. Injec t a 5 µL sa m ple aliqu ot with a utos am pler. NOTE: If the peak area of a s am ple is greate r than the area of the highest standa rd, dilute with isopropanol and reanalyze. 13. Measure peak area of the analyte.

CALCULATIONS: 14. Perform a separate regression analysis of peak area vs. concentration of standard for each of the analytes. Determine the concentration, C (:g/mL), of the analyte in each sample from the calibration graph. 15. Ca lculate the m ass of ea ch analyte, M (:g), in the submitted sample volume, V(mL). Use a volume of 150 mL for the volume of the sample.

EVALUATION OF METHOD: This method was evaluated with a recovery study at room tem perature over the range of 8949-60270 µg /sa m ple for thiophanate -m eth yl and 13140-44070 µg/sa m ple for captan using spiked laboratory samples with respective average recoveries in the range of 91.1-100% and 93.7-95.3%. [1] A reco very study at 4°C was also performed o ver the range of 8940-60420 µg/sample for thiophanate-methyl and 13130-43930 µg /sa m ple for captan using sp iked laboratory sam ples with respective average recoveries in the range of 101111% and 102-105%. The storage study at room temperature was completed at 33990 µg/sample for thio phanate -m eth yl and 2620 0 µg/sam ple for captan with respective recovery averages of 102-107% and 102-127% over the 28 days of the study. The storage study at 4°C was completed at 34130 µg/sample for thio phanate -m eth yl, and 25520 µg/sample for captan with respective recovery averages of 110-121% and 102-112% over the 27 days of the stud y. Originally, carbendazim was included in the investigation since it is a breakdown product of thiophanatem eth yl. Atte m pts to quantita tively m easure carbendazim suffe red from rep roducibility problems prom pting carbendazim ’s rem oval from this m etho d as an analyte that can be quantified. This method may be used to qualitatively determ ine carbendazim. Under m eth od conditions, its approxim ate retention tim e is 6 minutes.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition