NITROETHANE: METHOD 2526, Issue 2, dated 15 August 1994 - Page 3 of 4 b. c. 9.
10.
Analyze with samples and blanks (steps 11 and 12). Prepare calibration graph (ratio of peak area of nitroethane to peak area of internal standard vs. µg nitroethane). Determine desorption efficiency (DE) at least once for each lot of sorbent used for sampling in the range of interest. Prepare three tubes at each of five levels plus three media blanks. a. Inject a known amount (2 to 20 µL) of calibration stock solution, or a serial dilution thereof, directly onto front sorbent section (600 mg sorbent) with a microliter syringe. b. Cap the tube. Allow to stand overnight. c. Desorb (steps 5 through 7) and analyze with working standards (steps 11 and 12). d. Prepare a graph of DE vs. µg nitroethane recovered. Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration graph and DE graph are in control.
MEASUREMENT: 11.
12.
Set gas chromatograph according to manufacturer's recommendations and to conditions given on page 2526-1. Inject sample aliquot manually using solvent flush technique or with autosampler. NOTE: If peak area is above the linear range of the working standards, dilute an aliquot of the desorbed liquid with eluent, reanalyze and apply the appropriate dilution factor in calculations. Measure peak area. Divide the peak area of nitroethane by the peak area of internal standard on the same chromatogram.
CALCULATIONS: 13.
14.
Determine the mass, µg (corrected for DE) of nitroethane found in the sample front (W f) and back (W b) sorbent sections, and in the average media blank front (B f) and back (B b) sorbent sections. NOTE: If W b > W f/10, report breakthrough and possible sample loss. Calculate concentration, C, of nitroethane in the air volume sampled, V (L):
EVALUATION OF METHOD: Method S219 was issued on January 20, 1978 [2]. Synthetic atmospheres of the analyte in humidified air were generated dynamically at 22 °C and 777 torr over the range 143 to 614 mg/m 3 by calibrated syringe pump delivery of the neat analyte into a humidified dilution airstream [1,4]. The concentrations were monitored by total hydrocarbon analyzer. A 600-mg bed of sorbent retained 2.8 mg analyte before 5% breakthrough occurred at 5 L when a challenge atmosphere of 585 mg/m 3 analyte in humid air was sampled at 0.05 L/min. There were no statistically significant differences in the recoveries of 3-L samples collected from synthetic atmospheres containing 314 mg/m 3 nitroethane in humid air and stored for one or seven days at ambient temperatures prior to analysis. It was found necessary to separate the front and back sorbent sections immediately after sampling due to analyte migration during storage. Desorption efficiency averaged 0.88 in the range 0.47 to 1.9 mg per sample. A previous study found nitroethane to be unstable on activated charcoal [5]. REFERENCES: [1] [2]
Backup Data Report for Nitroethane, NIOSH Contract #210-76-0123 (unpublished). NIOSH Manual of Analytical Methods, 2nd ed., Vol. 6, S219, U.S. Department of Health and Human Services, Publ. (NIOSH) 80-125 (1980). NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
