Page:NIOSH Manual of Analytical Methods - 9201.pdf/3

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CHLORINATED AND ORGANONITROGEN HERBICIDES (PATCH): METHOD 9201, Issue 1, dated 15 January 1998 - Page 3 of 11

CALIBRATION AND QUALITY CONTROL: 5. Calibrate daily with at least six working standards covering the analytical range of the method for individual analytes. a. Add known amounts of calibration solution to the diazomethane derivatizing reagent in a volumetric flask. Let stand for 1 hour. Include a calibration blank of unspiked diazomethane derivatizing reagent solution. b. Add 10 mg silicic acid to each flask and let stand for another hour. c. Filter through a 0.45 PTFE syringe filter into a GC vial. d. Analyze together with field samples, field blanks, and laboratory control samples (steps 8 and 9). e. Prepare calibration graph (peak height or area vs. µg/mL analyte). 6. Determine desorption efficiency (DE) at least once for each lot of PUF samplers used for sampling in the calibration range (step 5). a. Prepare three samples at each of six levels plus three media blanks. b. Place PUF patch in a 120-mL glass jar. Apply a known amount of calibration stock to patch. Replace lid on jar and allow to stand over night. c. Desorb the samples (steps 2 through 4) and analyze together with standards and blanks (steps 8 and 9). d. Prepare a graph of DE vs. µg analyte recovered. 7. Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration and DE graphs are in control.

MEASUREMENT: 8. Set gas chromatograph according to manufacturer’s recommendations and to conditions listed in Table 2. Inject sample aliquot manually using solvent flush technique or with autosampler. See Table 4 for retention times of selected analytes. NOTE: If peak height is greater than the range of the working standards, dilute the sample with isopropanol and reanalyze. Apply the appropriate dilution factor in calculations. 9. Measure peak height of analyte.

CALCULATIONS: 10. 11.

Determine the concentration, µg/mL, (corrected for DE) of the respective herbicide found on the patch sample (Cp) and in the media blank (Bb) from the calibration graph. Calculate the mass of herbicide, M (µg), on patch in the desorption volume, V (mL):

M

(Cp Vp

Bb Vb), µg

CONFIRMATION: Whenever the identity of an analyte is uncertain, confirmation may be achieved by analysis on a column of different polarity. If primary analysis was performed using a nonpolar or weakly polar column e.g., ( DB-1 or DB-5), confirmation should be accomplished by reanalyzing on a polar columne.g., ( DB-17 or DB-1701). See Table 4 for approximate retention times for each column type. For positive identification of high-level analytes (1 to 10 µg/mL or greater), GC/MS may be used. Table 5 gives notes on the analytical characteristics of the chlorinated and organonitrogen herbicides. EVALUATION OF METHOD: This method was evaluated over the ranges specified in Table 3. For the method evaluation, the GC analyses were done using the DB-17 column. See Table 2 and Table 4 for chromatographic conditions. The upper limits of the analytical range were set at approximately the upper ranges studied. Also presented in Table 3 are the LOD, r1 (pooled relative standard deviation), and samplestorage stability for these eight NIOSH Manual of Analytical Methods (NMAM), Fourth Edition

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