Question

6. Compare the advantage and disadvantages of sorbent trap sampling with canister sampling.

Answer 1

sorbent trap sampling and canister sampling are the methods for sampling the volatile organic chemicals (VOCs) in ambient air for analysis. The representative sample of pollutant is then typically analyzed by Gas Chromatography -Mass Spectrometry. The choice of air sampling method depends on the volatility and polarity range of the VOCs of interest. Following are the advantage and disadvantages of sorbent trap sampling and canister sampling.

Canister Sampling

• Advantages

1. Canisters are easy for cleanup
2. Multiple analysis possible with canister sampling
3. canisters have good storage stability
4. No breakthrough of target compounds with canister sampling
5. No electrical power needed for filling canister
6. No thermal desorption needed for canister
7. Canisters are rugged and safe to use

• Disadvantages

1. Canisters have significant initial cost
2. canisters are bulky compared to sorbent tubes
3. Canisters can work with limited sample volume compared to sorbents
4. Canister sampling is generally not applicable to polar VOCs as they get adsorbed over canister wallls
5. Canisters are susceptible to contamination from sampler elements
6. No initial discrimination against water vapor can be achieved in canister sampling.

Sorbent trap sampling

• Advantages

1. Sorbent tubes also provide greater sample stability as polar compounds are prone to adsorption onto the canister walls
2. Sorbent tubes are easy to transport,
3. Sorbent tubes are compatible with a wider range of compounds, and are inherently compatible with a much wider range of air sample volumes. They are also compatible with analytes over a much wider polarity and volatility range.
4. The process of thermal desorption of sorbent tubes cleans the tube automatically
5. Sorbent tubes have relatively low cost to buy, transport and store.
6. Suitable for diffusive and pumped sampling
7. Sorbent trap sampling is the simplest way of collecting time weighted average (TWA) samples as required by many clean air and industrial hygiene regulation

• Disadvantages

1. The sorption and desorption efficiencies may not be 100% and that the background impurities in the sorbent tubes may limit detection in samples containing low concentrations
2. Sorbent sampling has Breakthrough issues
3. sorbent sampling faces spike recovery issues
4. Relative deviation is observed in sorbent trap sampling