BENZOTHIAZOLE IN ASPHALT FUME: METHOD 2550, Issue 1, dated 15 January 1998 - Page 3 of 5 a. Remove the filters from cassettes with forceps and transfer to 5-mL, or larger, vials. b. Add 4 mL of hexane. c. Allow the samples to stand a minimum of 30 minutes with occasional agitation. 7. Extract solid sorbent. a. Transfer front glass wool plug and front sorbent section to a 5-mL, or larger, sample vial. b. Transfer the back sorbent section and remaining glass wool plugs to a separate 5-mL, or larger, sample vial. c. Add 4 mL of hexane to each vial, cap, and agitate. d. Let stand for a minimum of 30 minutes with occasional agitation.
CALIBRATION AND QUALITY CONTROL: 8. Calibrate daily with at least six standards to cover the concentration range of the samples. a. Add known amounts of the standard stock solution to 10-mL volumetric flasks and bring to volume with hexane. b. Analyze with samples and blanks (steps 11 & 12). c. Prepare calibration graph (peak area vs. µg benzothiazole). 9. Determine desorption efficiency (DE) in the calibration range (step 8). Prepare three tubes at each of five levels plus three media blanks. NOTE: The sorbent bed of ORBO-42L tubes used for sampling is not always uniform in depth; therefore, ORBO-43 sampling tubes are recommended for determining DE (see EVALUATION OF METHOD). a. Inject a known amount (1 to 20 µL) of calibration stock solution, or a serial dilution thereof, directly onto the front sorbent section with a microliter syringe. b. Cap the tube and allow to stand overnight. c. Desorb (step 7) and analyze together with calibration standards (steps 11 & 12). d. Prepare a graph of DE vs. µg benzothiazole recovered. 10. Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration graph and DE graph are in control.
MEASUREMENT: 11. Set gas chromatograph according to manufacturer’s recommendations and to conditions given on page 2550-1. Inject sample manually using solvent flush technique or with autosampler. NOTE: If peak height is above the linear range of the calibration standards, dilute the sample with hexane, reanalyze, and apply the appropriate dilution factor in calculations. 12. Measure peak area of benzothiazole peak and determine µg per sample from calibration graph.
CALCULATIONS: 13. Determine the mass, µg (corrected for DE), of benzothiazole found in the sample tube front (W f), and back (Wb) sorbent sections, and in the average media blank front (B ) and back (B ) sorbent sections. f b NOTE: If Wb > Wf/10, report breakthrough and possible sample loss. 14. Calculate concentration, C, of benzothiazole in the air volume sampled, V(L): NOTE: µg/L mg/m3
C
NOTE:
µg/mL
(Wf
Wb
Bf V
Bb)
, mg/m 3
mg/m3
EVALUATION OF METHOD
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition
