Active sampling
Active sampling (pumped sampling) onto sorbent tubes is one of the most versatile TD sampling methods, used to target both known and unknown sample environments. This approach involves use of a pump to actively draw an air sample through the sorbent tube to trap the target analytes.
Active sampling is key to US EPA Method TO‑17, which involves pumping the sample atmosphere onto the sorbent tubes, which are then capped and transported to the laboratory, for analysis by thermal desorption. It is also the recommended sampling approach in other standard methods, including ISO 16017-1, ASTM 6196, Chinese EPA HJ 644 & HJ 734, EN 14662-1, CEN/TS 13649, NIOSH 2549, UK Environment Agency LFTGN 04, and UK HSL MDHS 72.
Overview
Pumps for active sampling include ‘grab-samplers’ and battery-powered pumps. By allowing precise volumes from between 20 mL to several hundred litres to be sampled onto tubes, it ensures compatibility with a wide concentration range (sub-ppt to high ppm). Active sampling is compatible with use of multi-bed sorbent tubes for sampling analytes over a wide volatility range and can be used for collecting VVOCs (e.g. propene and chloromethane) through to SVOCs (e.g. dodecyl phthalate and six-ring PAHs).
Benefits of active sampling over passive sampling
- High sensitivity – Allows larger volumes to be collected for optimum concentration of trace-level samples
- Wide analyte range – Enables use of up to four sorbent beds for trapping the widest volatility range
- Saves time – Faster than passive sampling, with typical times from minutes to hours
