Page:NIOSH Manual of Analytical Methods - 1453.pdf/3

 VINYL ACETATE: METHOD 1453, Issue 3, dated 15 March 2013 - Page 3 of 4

CALIBRATION AND QUALITY CONTROL: 8.	Calibrate daily with at least six working standards. a.	 Add 400 µL vinyl acetate to methanol in a 5-mL volumetric flask and dilute to the mark. This is the stock calibration solution. Use serial dilutions as needed to obtain the desired concentration range. b.	 Analyze with samples and blanks (steps 11 and 12). c.	 Prepare calibration graph (area vs. µg/mL). 9.	Determine desorption efficiency (DE) at least once for each lot of sorbent used for sampling in the range of interest (step 8). 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 (2 to 20 µL) of a standard mixture of vinyl acetate directly onto front sorbent section with a microliter syringe. NOTE:	Inject no more than 20 µL onto the sorbent. Dilute stock solution as appropriate. c.	 Cap the tube. Allow to stand overnight. d.	 Desorb (steps 5 through 7) and analyze with working standards (steps 11 and 12). e.	 Prepare a graph of DE vs. µg vinyl acetate recovered. 10.	Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration graph and recovery graph are in control. MEASUREMENT: 11.	Set gas chromatograph according to manufacturer’s recommendations and to conditions given on page 1453-1. 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 desorption solvent, reanalyze, and apply the appropriate dilution factor in calculations. 12.	Measure the peak area of the vinyl acetate signal. CALCULATIONS: 13.	Determine the mass, µg (corrected for DE) of vinyl acetate found in the sample front (Wf ) and back (Wb) sorbent sections, and in the average media blank front (Bf ) and back (Bb) sorbent sections. NOTE:	 If Wb > Wf /10, report breakthrough and possible sample loss. 14.	Calculate concentration, C, of vinyl acetate in the air volume sampled, V (L):

C=

(Wf + Wb) - (Bf +Bb) V

, mg/m3

NOTE: ug/L = mg/m3 EVALUATION OF METHOD: This method was validated originally by the Organic Methods Development Branch, OSHA Technical Center, Salt Lake City, UT, over the range 187 to 710 µg per sample using a carbon molecular sieve sorbent which is no longer available commercially. Breakthrough studies at 70% RH using this original sorbent, sampling an atmosphere of 150 mg/m3 at 0.19 L/min, indicated a tube capacity of approximately 9 mg of vinyl acetate. [5] This media is replaced with Carboxen 564 carbon molecular sieve sorbent (described in the equipment section, p. 1453-2) or its equivalent. The average desorption efficiency was 98.5%. Recoveries from NIOSH Manual of Analytical Methods (NMAM), Fifth Edition