CHLORINATED AND ORGANONITROGEN HERBICIDES (AIR SAMPLING): METHOD 5602, Issue 1, dated 15 January 1998 - Page 3 of 14
8. Filter an aliquot through a 0.45-µm PTFE filter into a 2-mL GC vial or limited volume GC vial. CALIBRATION AND QUALITY CONTROL: 9. Calibrate daily with at least six working standards covering the analytical range of the method for individual analytes. Three standards (in duplicate) should cover the range from LOD to LOQ. a. Add known amounts of calibration stock solution to the diazomethane derivatizing reagent in a volumetric flask and let stand for 1 hour. Include a calibration blank of unspiked diazomethane derivatizing reagent solution. b. Add 10 mg silicic acid to each standard vial, and let stand for an additional hour. c. Filter through a 0.45-µm syringe filter into a GC vial. d. Analyze together with field samples and blanks (steps 12 and 13). e. Prepare calibration graph (peak area or height vs. µg analyte). 10. Determine desorption efficiency (DE) at least once for each lot of OVS tubes used for sampling. Independently prepared quality control herbicide solutions in extraction solvent must be prepared at concentrationswithin the analytical range. Prepare three samplers at each of six levels plus three media blanks. a. Remove and discard back sorbent sections of samplers and media blanks. b. Remove cap from large end of sampler tube. Pull up PTFE retainer ring to prevent trapping of spiking solution under ring. Apply a known amount of calibration stock solution to face of quartz fiber filter. Pull air through for one hour at 0.2 to 1 L/min. c. Desorb the samples (steps 5 through 8) and analyze together with working standards and blanks (steps 12 and 13). d. Prepare a graph of DE vs. µg analyte recovered. 11. Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration and DE graphs are in control. MEASUREMENT: 12. Set gas chromatograph according to manufacturer’s recommendations and to conditions listed in Table 2.. Inject 2-µL 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 with extraction solvent and reanalyze. Apply the appropriate dilution factor in calculations. 13. Measure peak height or area of analyte.
CALCULATIONS: 14. Determine the mass, µg (corrected for DE), of respective analyte found in the sample front (W f) and back (Wb) sorbent sections, and in the media blank front (B f) and back (Bb) sorbent sections from the calibration graph. NOTE: The filter is combined with the front section. If W b > Wf/10, report breakthrough and possible sample loss. 15. Calculate concentration, C, of analyte in the air volume sampled, V (L):
C
NOTE: µg/mL
(Wf
Wb V
Bf
Bb)
, mg/m 3
mg/m3
CONFIRMATION: Whenever the identity of an analyte is uncertain, confirmation may be achieved by analysis on a column of NIOSH Manual of Analytical Methods (NMAM), Fourth Edition
