ALS Czech Republic, s.r.o. continues to expand the range of indoor and outdoor air and soil air monitoring methods. In addition to the standard volatile organic compounds (VOCs) analyzes using the Radiello samplers and SKC tubes samplers, we are now introducing the determination of volatile organic compounds, using the Waterloo Membrane Sampler™ passive samplers (WMS).

WMS advantages and benefits

The Waterloo Membrane Sampler™ (WMS) is a permeation-type passive sampler. This sampler can be used for similar purposes as Radiello, for indoor and outdoor air sampling. In addition, however, it also allows sampling of soil gas, even in case of high ambient humidity inside the boreholes, which is often an obstacle to soil gas sampling by other sampling systems. There are three types of WMS samplers dedicated to different purposes of sampling under different conditions (humidity, expected concentration of substances, etc.). The WMS samplers enable the quantitative determination of target compounds reaching accuracy and precision similar to, for example, active sampling using SUMMA canisters according to EPA TO-15. This is enabled thanks to WMS distinct advantage, which is the known value of diffusion coefficients for many common VOCs and the possibility of calculating those coefficients for virtually any VOC (based on the retention index in gas chromatography).

Advantages of Waterloo Membrane Sampler™

• Simple to use, small size
• Low limits of determination due to the accumulation of substances in the sorbent
• Information on the occurrence of contamination over a longer period of time
• Wide range of substances
• Universal use for air and soil gas
• Possibility of monitoring larger areas without the need for frequent active sampling

The great advantage of these passive samplers is that, unlike active samplers (eg SKC tubes with sorbents), which provide information about the state of the sampled environment only at the time of sampling, passive samplers allow long-term monitoring of the environment and obtained concentrations indicate average contamination during the entire sampling time (usually days or weeks). 

WMS system offers easy sampling, simple handling and transportation, as well as the achievability of low concentration limits, thanks to the accumulation of substances in the sampled medium over the entire sampling period. Due to its small dimensions, the sampler can be used for sampling of soil gas from boreholes with a diameter as little as of 1 cm.

There is an increasing number of projects, where the use of these passive samplers is preferred for the detection of hot spots with high contamination, mainly when monitoring of larger areas is required. Advantage is that mapping of cumulative concentrations of target compounds over longer period of time is giving more relevant information compared to “one time” active sampling. Employing passive samplers may save substantial cost, which would be needed for repetitive active sampling. WMS is thus suitable of anthropogenic pollution monitoring via for soil gas testing.

Sampling and analysis principals

The sampler consists of inert glass container (vial) filled with sorbent, closed with a polydimethylsiloxane (PDMS) membrane. Upon contact of the sampler with air, volatile organic compounds pass through the membrane and are subsequently trapped on the sorbent.

Configurations of WMS:

WMS-SE™ („solvent-extraction“) – excellent choice for monitoring VOC vapor concentrations in indoor air, outdoor air, and vent pipes. Strong sorbent employed in this configuration allows for extended period of time collection of samples and quantification of analytes present at different concentrations within the calibration range.  

WMS-LU™ („low-uptake rate“) – specially designed for VOC monitoring in soil gas and allow for quantitative analyses in drier subsurface conditions. The lower uptake rates mitigate the effect of sampler starvation that may occur when collecting soil gas samples with low VOC concentrations.

WMS-TM™ - („thick-membrane“) – unique sampler designed for quantitatively monitoring of VOC in soil gas in either low permeability or very wet soils.  This sampler has the lowest uptake rates of the configurations available.

Determination of VOCs from WMS samplers in ALS Czech Republic

Determination of target substances concentrations is performed on state-of-the-art instruments by a fast, sensitive and reliable method of gas chromatography with mass detection (GC-MS).

Currently ALS laboratory offers the accredited determination of 34 volatile substances, including chlorinated organic compounds, aromatic substances, BTEX, aldehydes, ketones and selected petroleum hydrocarbons. The method is suitable for quantification of substances starting at the concentration level of 0.2-0.4 µg / sampler, which, at the expected sampling time of 7 days, means reaching the limit of determination in the range of 0.004 to 0.3 mg / m3 depending on the type of sampler and compound of interest.

ALS can also provide samplers to its partners by prior arrangement.

References:

 http://www.waterloomembranesampler.com/