Air Sampling Media
- fill a vessel of some sort with air,
- collect the contaminants on an active surface,
- dissolve the contaminants in a solution.
Air Toxics Ltd. can provide all of your sampling needs.
"Whole Air Samples"
For more detailed information on Air Sampling and Analysis, please request a copy of our Sampling Guide, Volume I.
A "whole air" sample is collected when the air is drawn into some sort of vessel (e.g. Tedlar bag, glass bulb, stainless steel "bomb" or a canister). The most two common methods for collecting a "whole air" sample are stainless steel "Summa" canisters and Tedlar bags.
This method of collection is simple - data quality issues revolve around recovering the contaminants from the vessel. Recovery is a function of several parameters including, the chemical nature of the contaminants and the surface of the vessel, the vapor pressure of the contaminant, the influence of various matrix effects, and the ability to start with a vessel free of contamination.
Methods written around a whole sample include TO-3 (VOCs), TO-12 (NMOC), TO-14A (VOCs), TO-15 (VOCs), ASTM D-5504 (reduced sulfur compounds) and a variety of atmospheric gas methods.
Sorbent Collection
For more detailed information on Sorbent-Based Sampling, please request a copy of our Sampling Guide, Volume II.
If the sample is pulled through a sorbent, the contaminants are removed from the air either by adsorption on the surface or by reacting with a coating on the sorbent to form a derivative. Sorbents come in many forms with a wide variety of surface characteristics. As a general rule, they fall into two forms: polymeric and carbonaceous. Typical polymeric sorbents are Tenax and XAD-2. Carbonaceous sorbents can be naturally occurring, such as charcoal or synthetic, such as Carbopack, CarboSieve Carbotrap, or Spherocarb. Sorbent strength is a function of the surface area. The greater the surface area, the greater the adsorbing power of the sorbent.
Once the contaminants have been collected on the surface of the sorbent they are removed, prior to analysis, using either heat or chemical extraction. If the sorbent is heated while being purged with an inert gas the contaminants are "thermally desorbed from the surface". Alternatively, the sorbent can be extracted using a suitable solvent. Thermal desorption yields a gas phase sample which is analyzed directly. Chemical extraction yields a solution, which is then analyzed.
Sorbent based methods include: TO-4 (pesticides), TO-10 (pesticides), TO-11 (aldehydes), TO-13 (SVOCs), TO-17 (VOC & SVOCs), 8260 (VOCs), and 8270 (SVOCs).
When air is bubbled through a solution, many contaminants will stay in solution. This is very efficient and offers a selective means for removing contaminants from air. The composition of the solution can be varied. For example, bubbling air through a 0.1 N HCl solution will drive organic compounds, which are slightly basic into solution. By bubbling air through an acidic solution of dinitrophenylhydrazine (DNPH), the carbonyl compounds will be derivatized to hydrazones which remain in solution. The range of potential solutions is quite large. They can be organic or inorganic. The essential criteria are (1) they have a relatively low vapor pressure so that they don't evaporate while air is being bubbled through the solution and (2) the solution is free of contamination and both thermally and chemically stable.
Solution based methods include many NIOSH methods as well as TO-5 (aldehydes), CARB 430 (aldehydes), Method 0011(BIF0011)(aldehydes).