Page:NIOSH Manual of Analytical Methods - 2538.pdf/4

 ACETALDEHYDE: METHOD 2538, Issue 2, dated 15 August 1994 - Page 4 of 4 APPENDIX A: PREPARATION OF CALIBRATION STOCK SOLUTION Prepare by diluting a known amount of acetaldehyde with toluene: a. Determine the weight of a sealed 25-mL volumetric flask containing approximately 15 mL of toluene. b. Place the sealed volumetric flask and a 1-mL pipet in the same freezer used to store the acetaldehyde. c. After 30 minutes, remove the sealed volumetric flask, 1-mL pipet and the acetaldehyde. d. Immediately pipet 1.0 mL of acetaldehyde into the cold flask, reseal the flask and allow it to warm to room temperature. e. Reweigh the flask and subtract the tare weight from the weight of the reweighed flask to determine the weight of acetaldehyde added. f. Dilute the contents of the flask to the mark with toluene. g. Store the stock standards in a freezer. Prepare fresh stock standards every 10 days. APPENDIX B: PREPARATION OF XAD-2 SORBENT COATED WITH 2-HMP Weigh 125 g of crude XAD-2 adsorbent into a 1-L Erlenmeyer flask. Add about 200 mL of water to the flask and then swirl the mixture to wash the adsorbent. Discard any adsorbent that floats to the top of the water and then filter the mixture using a fritted Buchner funnel. Transfer the adsorbent back to the Erlenmeyer flask and repeat the water wash and the filtration. Air-dry the adsorbent for about 2 min. Transfer the adsorbent back to the Erlenmeyer flask and then add about 200 mL methanol to the flask. Swirl and filter the mixture as before. Transfer the washed adsorbent to a 1-L evaporative flask and remove the methanol using rotary evaporation. Cool the flask to room temperature and add 13 g of 2HMP and 200 mL of toluene to the flask. Swirl the mixture and then allow it to stand for an hour. Remove the toluene using rotary evaporation. Seal the flask and allow the coated adsorbent to stand overnight at ambient temperature. Transfer the coated adsorbent to a Soxhlet extractor. Extract the material with toluene for about 24 hours. Replace the contaminated toluene with fresh toluene and continue the extraction for an additional 24 hours. Replace the second aliquot of contaminated toluene with methanol and continue the Soxhlet extraction for 4 hours. Transfer the adsorbent to a weighed 1-L, round-bottomed, evaporative flask and remove the methanol using the rotary evaporation apparatus. Determine the weight of the adsorbent and then add an amount of 2-HMP, which is 10%, by weight, of the adsorbent. Add 200 mL toluene and swirl the mixture. Allow the flask to stand for 1 hour. Remove the toluene using rotary evaporation. If the last traces of toluene are difficult to remove, add about 100 mL of methanol to the flask, swirl the mixture and then remove the solvents using rotary evaporation. XAD-2 adsorbent treated in this manner will often contain residual formaldehyde derivative levels of about 0.1 µg/150 mg of adsorbent. The formaldehyde blank level and potential acrolein and acetaldehyde chromatographic interferences should be determined at this time. If the formaldehyde blank and/or any interference is determined to be too high, return the lot to the Soxhlet extractor, extract with toluene again and recoat with 2-HMP. This process can be repeated until an acceptable blank and/or level of chromatographic interferences is attained. The coated adsorbent is now ready to be packed into sampling tubes. The sampling tubes should be stored in the dark and separated by lot number. A sufficient amount of each lot of coated adsorbent should be retained to prepare analytical standards for use with air samples from that lot number.

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