ETHYLENE DIBROMIDE: METHOD 1008, Issue 2, dated 15 August 1994 - Page 3 of 4 9.
10.
Determine desorption efficiency (DE) at least once for each batch of charcoal used for sampling in the calibration range (step 8). Prepare three tubes at each of five levels plus three media blanks. a. Remove and discard the back sorbent section of a media blank sampler. b. Inject a known amount of calibration stock solution directly onto front sorbent section with a microliter syringe. c. Cap the tube. Allow to stand overnight. d. Desorb (steps 5 through 7) and analyze together with working standards (steps 11 and 12). e. Prepare a graph of DE vs. µg ethylene dibromide recovered. Analyze three quality control blind spikes and five 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 1008-1. Inject sample aliquot manually using solvent flush technique or with autosampler. Retention times under these conditions are: ethylene dibromide, 2.2 min; 1,2-dibromo propane, 2.9 min; and 1,1,2,2-tetrachloroethane, 4.1 min. NOTE: If peak area is above the linear range of the working standards, dilute an aliquot of the desorbed liquid, reanalyze, and apply the appropriate dilution factor in the calculations. Measure peak area. Divide the peak area of analyte by the peak area of internal standard on the same chromatogram.
CALCULATIONS: 13.
14.
Determine the mass, µg (corrected for DE) of ethylene chlorohydrin 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 ethylene dibromide in the air volume sampled, V (L):
EVALUATION OF METHOD: P&CAM 260 [1] was evaluated with coconut shell charcoal (SKC Lot 106 and MSA Lot 6) fortified with solutions of ethylene dibromide. Average recoveries ranged from 0.85 to 0.93; overall precision (s r) was 0.044 (31 samples, pooled) [3]. Samples based on 0.2- and 2-µg quantities of ethylene dibromide were stable on charcoal during storage below -20 °C for 13 and 12 days, respectively. Gasoline samples which contained ethylene dibromide were placed into U-tubes; ethylene dibromide vapor was collected with charcoal tubes (flow rate of air was 0.6 L/min). Recoveries were 0.91 and 0.93 for 0.2- and 2.4-µg quantities of ethylene dibromide, respectively. No significant breakthrough from front sections of charcoal occurred with 200-µg quantities of ethylene dibromide in the vapor phase (flow rate of air was 0.6 L/min); quantities of ethylene dibromide (if any) on the back sections of charcoal were less than 0.04 µg (<0.02%). Breakthrough was determined for SKC Lot 105 charcoal [5]. At an ethylene dibromide concentration of 446 mg/m 3 in dry air, the effluent concentration was 2% of the test concentration after 4 h of sampling (48 L air). Thus, the capacity of the charcoal was at least 21 mg ethylene dibromide under these conditions. In the analysis of a large set of field samples over a period of seven days, DE was found to vary day-to-day in the range of 0.76 to 0.87 at 0.1 µg ethylene dibromide per sample [6]. Overall precision ( SˆrT) and bias were not determined. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
