Early Detection of Structural Mold with SilcoCan Air Sampling Canisters
Early detection of mold growth in buildings is critically important to protecting human health and property values. Restek SilcoCan canisters allow low levels of mold to be detected in air samples—before it can be seen—providing an opportunity for structural repair and safer living conditions.
Mold growth in homes has been linked to serious human health and property value issues; thus, early detection is of increasing importance. Mold releases microbial volatile organic compounds (MVOCs) which can be sampled in air and identified by GC/MS analysis, even prior to visual detection methods. MVOCs attributed to fungal growth include terpenes, ethers, ketones, alcohols, aldehydes, aromatic and chlorinated hydrocarbons, sulfur-based compounds, and amines. These compounds are not unlike other volatile organic compounds commonly analyzed in environmental and industrial hygiene laboratories, and the same equipment can be used to collect, positively identify, and quantify MVOCs.
Due to the polar nature of many MVOCs, and the low concentrations found in early detection, a passivated, large volume collection device is needed for sampling. SilcoCan canisters are an excellent choice for sampling and analyzing MVOCs. The canister surface, passivated with a chemically bonded fused silica layer, has been shown to provide the stability and inertness needed for collecting and storing low level volatiles (ppbv) such as those analyzed by EPA methods TO-14A and TO-15, including sulfur-containing compounds and microbial VOCs. Here we show a successful application of highly inert SilcoCan canisters and GC/MS for monitoring low level mold growth in building structures.
For our analysis, we began with standard solutions of 23 MVOCs in methanol at 100µg/mL. The compounds were separated by chemistry into four solutions to prevent degradation reactions: alcohols, ketones, 2-isopropyl-3-methoxypyrazine, and geosmin. After cleaning and evacuating a SilcoCan canister, 210µL of water were added to the canister to simulate natural humidity and aid recovery. After equilibration, 2µL of each solution were added to the canister. Finally, the canister was pressurized to 30psig with dry nitrogen to yield a final concentration of 2.2ng/200mL for each MVOC, or 1.4 to 3.8ppbv of each MVOC. (The final ppbv concentration is molecular weight-dependant.) To boost recoveries of the higher-boiling compounds, we used a Restek Air Canister Heating Jacket set to 75°C. The sample was heated to 75°C for 30 minutes prior to, and during testing. Boiling points of some of the lower volatility MVOCs are shown in Table I.
23 MVOCs Identified in Less than 30 Minutes
Sample analysis was conducted using standard air analysis equipment such as is used in environmental laboratories. In our case, we used a Nutech 8900DS autosampler and preconcentrator attached to an Agilent 6890/5973 GC/MS. Volatiles in the sample are concentrated by a cryogenic trap followed by an adsorbent trap, then cryofocused for injection into the GC/MS. Figure 1 shows a schematic of the sampling and preconcentration process. An Rxi-1ms column was used to provide separation at the ultra-low bleed levels required for spectroscopic analysis. The MVOC sample was analyzed by concentrating 200mL of the 0.011ng/mL gaseous mix using a 1:1 split for only 1ng on column of each MVOC. The resulting chromatogram, shown in Figure 2, shows excellent peak response and resolution for the 23 compounds in less than 30 minutes.
SilcoCan canisters easily provide the inertness and stability required for the collection, storage, and analysis of MVOCs, especially for polar and high-boiling compounds. Air sampling of MVOCs using SilcoCan canisters allows for early detection of fungal growth, providing an opportunity for structural treatments to eradicate damaging mold.
Table I Boiling points of low volatility MVOCs.
Figure 1 Sample set-up for low level MVOC analysis. Excellent response was seen, even for polar and high boiling point compounds.