Page:NIOSH Manual of Analytical Methods - 5603.pdf/4

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ALACHLOR in AIR: METHOD 5603, Issue 1, dated 15 January 1998 - Page 4 of 5 a. Average the optical density (OD) for the negative control. b. Average the OD for each of the standards in the curve. c. Determine the percent binding (%Bo) of the standards by: %Bo = standardaverage/ negative controlaverage x 100 d. Determine the %Bo of the samples by: %Bo = sampleaverage/ negative controlaverage x 100 e. Prepare a calibration graph, %Bo vs. log concentration (ng/L) of alachlor. 13. Follow the EnviroGard alachlor assay guidelines to ensure accurate results [4]. a. The coefficient of variation for optical density (OD) of each standard in the curve15%. b. The percent binding (%Bo) for each standard in the curve should also fall within the following ranges. 100 µg/mL 64-86% 500 µg/mL 33-55% 2500 µg/mL 11-21% NOTE: See the certification sheets of particular lots of kits provided with the assay.

MEASUREMENT: 14. Set wavelength on microtiter plate reader to 450 nm, and reference wavelength to 600 or 650 nm. 15. Zero the microtiter plate reader against air, or 200 µL of water in a blank well. Within 30 minutes of adding the stop solution, read the plates at 450 nm.

CALCULATIONS: 16. Record the actual solution volumes to which the samples, sV(L), and blanks, Vb (L), were diluted. 17. From the calibration graph, determine the concentration of the sample solutions of the samples, Cs (ng/L), and media blanks, Cb (ng/L). NOTE: Blanks generally fall below the range of the calibration graph and are not included in the calculations. Variable readings for the blanks indicate a problem with the assay. 18. Using the solution volume of the samples, Vs (L), calculate the concentration, C (mg/m3), of alachlor in the volume of air sampled, Vair (L):

C

NOTE: µg/L

Cs V s Vair

10

3

, mg/m 3

mg/m3

EVALUATION OF METHOD: This method was evaluated with fortified SDB-xc extraction disks that had clean humidified air passed through them. The volume of air to be sampled was based on air levels found in a NIOSH field survey of herbicide applicators [5], and a 1:100 dilution factor in the assay.If sampling is done for longer periods of time, further dilution of the samples may be necessary. The method was evaluated over the range of 0.24 µg to 120 µg per sample. The sample precision was not statistically poolable over the entire range of the levels studied. However, they were poolable atthe 12-, 24-, and 48-µg range. The overall precision (rT) for these samples was 0.0783, with an accuracy estimate of ±17.4%. The precision, bias, and accuracy at each level studied also were determined (See Table 1). The average recovery of all levels was 100%. Samples are stable for at least 7 days at ambient temperature and 30 days refrigerated. Breakthrough was not evident at a capacity of 144 µg. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition

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