Page:NIOSH Manual of Analytical Methods - 2515.pdf/3

 DIAZOMETHANE: METHOD 2515, 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 methyl octanoate to that of the internal standard vs. µg methyl octanoate). Determine desorption efficiency (DE) at least once for each lot of coated XAD-2 resin 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 back sorbent section of a media blank sampler. b. Inject a known amount of methyl octanoate 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 with working standards (steps 11 and 12). e. Prepare a graph of DE vs. µg methyl octanoate 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 2515-1. 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 with eluent, reanalyze, and apply the appropriate dilution factor in calculations. Measure peak area. Divide the peak area of analyte by the peak area of internal standard on the same chromatogram.

CALCULATIONS: 13.

14.

15.

Determine the mass, µg (corrected for DE) of methyl octanoate 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. Convert µg methyl octanoate to µg diazomethane by multiplying the corrected µg per sample by the conversion factor 0.2657 (molecular weight ratio, 42.04/158.24), and calculate apparent concentration, C a (mg/m 3), of diazomethane in the air volume sampled, V (L):

Calculate the recovery (R) from the equation:

NOTE: This recovery was experimentally determined over the apparent concentration range 0.12 to 0.7 mg/m 3 and may not be valid outside that range [1]. 16. Calculate corrected concentration, C (mg/m 3):

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94