Page:NIOSH Manual of Analytical Methods - 2536.pdf/3

 VALERALDEHYDE: METHOD 2536, Issue 2, dated 15 August 1994 - Page 3 of 5 SAMPLE PREPARATION: 4. 5. 6. 7. 8.

Score each sampler with a file in back of the back sorbent section. Break sampler at score line. Remove and place back glass wool plug and back sorbent section in a vial. Transfer front section with remaining glass wool plugs to a second vial. Add 2.0 mL toluene to each vial. Screw cap tightly onto each vial. Agitate in an ultrasonic bath for 60 min.

CALIBRATION AND QUALITY CONTROL: 9.

10.

11.

Identification of analytical peaks. a. Add known amounts of valeraldehyde oxazolidine stock solution to toluene in 10-mL volumetric flasks and dilute to the mark. b. Analyze (steps 12 and 13) with samples and blanks for qualitative identification of derivative peaks. Calibrate daily with a least six working standards prepared in triplicate covering the range 2 to 3900 µg valeraldehyde per sample. a. Weigh 120-mg portions of unused sorbent from media blanks into vials. b. Add aliquots (1 to 10 µL) of valeraldehyde stock solution or dilutions thereof to the sorbent. Cap vials and allow to stand overnight at room temperature. c. Desorb (steps 7 and 8) and analyze (steps 12 and 13) with samples and blanks. d. Prepare calibration graph (combined peak area vs. µg valeraldehyde). NOTE: Because the standard samples are prepared on media blanks, no additional blank correction or desorption efficiency correction is necessary. Check desorption efficiency in the range of interest and at least once over the entire range of the method with each lot of sorbent used. (APPENDIX C). Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration graph is in control.

MEASUREMENT: 12.

13.

Set gas chromatograph to manufacturer's recommendations and to conditions given on page 2536-1. Inject 1-µL sample aliquot. NOTE: If the amount of valeraldehyde oxazolidine in the aliquot exceeds the capacity of the column, dilute with toluene, reanalyze and apply the appropriate dilution factor in calculations. The upper limit for the column on (page 2536-1) is equivalent to ca. 260 µg valeraldehyde per sample. Measure total peak area of the two analyte peaks. NOTE: On the recommended column, valeraldehyde oxazolidine gives two peaks, since the diastereoisomers are resolved with retention times 5.4 and 6.3 min. Retention time for 2-(hydroxymethyl)piperidine is 2.2 min for these conditions.

CALCULATIONS: 14.

15.

Determine the mass, µg, of valeraldehyde found in the sample front (W f) and back (W b) sorbent sections. NOTE: If W b > W f/10, report breakthrough and possible sample loss. Calculate concentration, C, of valeraldehyde in the air volume sampled, V (L):

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