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Early Detection of Structural Mold with SilcoCan Air Sampling Canisters

By Silvia Martinez, Innovations Chemist

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.

Passivated SilcoCan canisters are ideal for sampling low concentrations of MVOCs. The inertness of these canisters provides an exceptional storage environment, particularly for polar and high boiling point compounds.

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.

Sample Set-up

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.

MVOCbp (°C)
1-octanol194
isoborneol212
α-terpineol214
geosmin270

Figure 1  Sample set-up for low level MVOC analysis. Excellent response was seen, even for polar and high boiling point compounds.

Sample set-up for low level MVOC analysis. Excellent response was seen, even for polar and high boiling point compounds.

Figure 2  Detect low levels of structural mold using SilcoCan canisters for air sampling (1ng on-column).

PeakstR (min)
1.2-Butanone9.047
2.2-Methylfuran9.640
3.3-Methylfuran9.962
4.2-Methyl-1-propanol10.405
5.2-Methyl-2-butanol10.791
6.1-Butanol11.506
7.3-Methyl-2-butanol12.092
8.2-Pentanol12.592
9.2-Methyl-1-butanol13.779
10.Dimethyl disulfide13.979
11.3-Hexanone14.994
PeakstR (min)
12.2-Hexanone15.080
13.2-Heptanone17.767
14.1-Octen-3-ol20.019
15.3-Octanone20.133
16.3-Octanol20.433
17.2-Pentylfuran20.476
18.2-Ethyl-1-hexanol21.163
19.1-Octanol22.013
20.2-Isopropyl-3-methoxypyrazine22.628
21.Isoborneol24.379
22.α-Terpineol24.844
23.Geosmin28.347
Microbial VOCs on Rxi-1ms
GC_AR01030
ColumnRxi-1ms, 60 m, 0.25 mm ID, 1.00 µm (cat.# 13356)
Samplemicrobial volatile organic compounds
Conc.: 2 ppbv, 60% RH
Injection
Inj. Vol.:1.0 µL split (split ratio 1:1)
Liner:1mm Split (cat.# 20972)
Inj. Temp.:200 °C
Oven
Oven Temp.:10 °C (hold 1 min) to 235 °C at 8 °C/min
Carrier GasHe, constant flow
Flow Rate:1.5 mL/min
DetectorAgilent 5973 GC/MS
Transfer Line Temp.:260 °C
Solvent Delay Time:5 min
Ionization Mode:EI
Scan Range:35-350 amu
PreconcentratorNutech 8900DS Preconcentrator
  Trap 1 Settings
Cooling temp:-160 °C
Desorb temp:20 °C
  Trap 2 Settings
Cooling temp:20 °C
Desorb temp:200 °C
  Cryofocuser
Cooling temp:200 °C
Desorb temp:200 °C
  Standard
Size:200 mL
InstrumentAgilent/HP6890 GC
NotesSample = 200 mL from canister

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