Page:NIOSH Manual of Analytical Methods - 2506.pdf/3

 ACETONE CYANOHYDRIN: METHOD 2506, Issue 2, dated 15 August 1994 - Page 3 of 5

10.	Determine desorption efficiency (DE) at least once for each lot of samplers used for sampling in the calibration range (step 9). Prepare three tubes at each of five levels plus three media blanks. a.	 Remove and discard back sorbent section of a media blank sampler. b.	 Inject a known amount of calibration stock solution or a serial dilution thereof directly onto front sorbent section with a microliter syringe. c.	 Cap the tube. Allow to stand overnight. d.	 Desorb (steps 6 through 8) and analyze together with working standards and blanks (steps 12 and 13). e.	 Prepare a graph of DE vs. µg acetone cyanohydrin recovered. 11.	Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration graph and DE graph are in control. MEASUREMENT: 12.	Set gas chromatograph according to manufacturer’s recommendations and to conditions given on page 2506-1. Inject sample aliquot manually using solvent flush technique, or auto sampler. = 3.2 min under these conditions. NOTE:	If peak area is above the linear range of the working standards, dilute an aliquot of the sample solution with ethyl acetate, reanalyze and apply the appropriate dilution factor in calculations. 13.	Measure peak area. CALCULATIONS: 14.	Determine the mass, µg (corrected for DE), of acetone cyanohydrin found in the sample front and back sorbent sections, and in the average media blank front  and back  sorbent sections. NOTE:	If >  /10, report breakthrough and possible sample loss. 15.	Calculate concentration,, of acetone cyanohydrin in the air volume sampled, (L): , mg/m³. EVALUATION OF METHOD [1]: Calibration curve: Over the range 2.5 to 250 ng acetone cyanohydrin injected (0.5 to 50 µg per sample), the correlation coefficients of NPD response with mass injected ranged from 0.998 to 0.999 for peak height and from 0.990 to 0.996 for peak area. Recovery of spiked samples after storage for one week at room temperature was ≥98% over the range 0.5 to 50 µg per sample. Independent verification of sample concentrations generated dynamically was not possible. The method was evaluated by evaporating 1, 10, or 50 µg of analyte from U-tubes onto the sorbent tube. Three liters of humid air (RH = 80%) were then drawn through the tube at 0.2 L/min for 15 min. Two sets of six samples at each level were generated. One set of six samples at each level was stored for one day at room temperature. The other sample sets were stored for five to seven days at 0 °C. Recovery was ≥ 89% ( = 10.6%). Experiments also showed that storage of 1 or 10 µg samples collected as above, but stored at ambient temperature for four days, gave recoveries of 62 to 80%. A maximum of 2% mass breakthrough to the backup section was obtained when 10 to 100 µg aliquots of analyte were evaporated from U-tubes into a stream of humidified air (RH = 80%) onto the sorbent at 0.2 L/min for 60 min. Recovery from the primary sorbent section for all samples was ≥ 92%.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition