When Sampling Formaldehyde, The Medium Matters
Formaldehyde in air can be sampled in several different ways, using several different sampling media. Options vary from impinger, to treated sorbent, to passive monitors. NIOSH Method 3500 is based on the original impinger method (NIOSH 125), which was issued in 1973. Unfortunately, sampling with impingers proved to be quite cumbersome.
Sampling strategies for formaldehyde changed when NIOSH Method 2541 and OSHA Method 52 were issued. These methods used sorbent tubes containing treated XAD as the collection medium, thus eliminating the impinger.
The treated XAD tubes referenced in NIOSH 2541 and OSHA 52 have some inherent problems related to the sorbent material. Low levels of formaldehyde contamination can frequently be found in field and laboratory tube blanks. This background can vary in amount and may not be consistent within the same lot of tubes. For the past several years we have routinely kept track of these background levels and correct sample results for an averaged sorbent background level, if necessary. This is why we ask that you get your sampling media from Galson. Without this correction applied to sample values, reported levels may contain a high bias.
The latest update to formaldehyde sampling is NIOSH 2016, dated January 15, 1998. This method uses dinitrophenyl hydrazine (DNPH) treated silica gel tubes. Analysis by HPLC provides detection limits that are lower than the GC methods. The DNPH tubes seem to be very consistent with little to no background levels of formaldehyde present. Better detection limits and lower background are the reasons Galson lists NIOSH 2016 as the preferred analytical method.
All treated sorbent tubes have preferred freezer storage both prior to and after sampling. This is very important! The tubes should be kept cold prior to sampling to maintain chemical stability of treated sorbent. Samples should be kept cold after collection to maintain stability of derivative formed during sampling. Galson will provide a cooler and ice pack with your media request to make this requirement easily manageable.
Four types of passive monitors are also available for collection and analysis of formaldehyde. Each is designed for specific exposure times varying from 15 minutes (STEL), 2 types for 8 hour (PEL) and one for indoor air quality (IAQ) for 5-7 days. Please be sure to expose each badge for the length of time recommended.
For questions on formaldehyde sampling or to order sampling tubes, please contact client services at 888-432-5227.