ALS Utilise the Latest Methodology for Sampling Vapours
Jun 29, 2017
Silonite® canisters offer a very effective method of sampling volatile organic compounds (VOCs) and other gases. This method is now available from ALS Hawarden and is suitable for a wide range of applications including soil gas, sub-slab, ambient and indoor air.
Silonite® canisters are supplied under vacuum from the ALS Hawarden laboratory. The sample train restricts the flow of sample uptake into the canister. The sample train ensures that vapour samples are collected at a controlled flow rate. The assembly also includes a vacuum gauge that indicates when the canister is close to atmospheric pressure. Canisters feature a silonite® coating that provides an extremely inert receiving vessel to collect vapour. Once sampling is complete, canisters are sent to the ALS Hawarden laboratory for analysis in specially designed carrier boxes.
Interest in canisters in the UK is more recent, but this approach is now becoming increasingly adopted by consultants investigating and assessing risks from sites where VOCs may be present. As part of detailed quantitative risk assessment, indoor air sampling can confirm the presence of a vapour pathway. Canisters have also been used for validation purposes by range of remediation companies.
With on-going improvements, canisters have continued to grow in popularity in the US, particularly for those involved in vapour intrusion, due to their:
- Ease of sampling,
- Extended holding times
- Ability to perform multiple analyses in the laboratory.
A GC-grade Silonite® ceramic coating enables much wider range of recovery relative to other methods and by taking the whole sample into the canister, there is no reliance on sorbents or chance of breakthrough. Repeat analysis is also possible using this method.
- VOCs target list (based on TO-15)
- TPH Aliphatic and Aromatic split
- Permanent gases
- C1-C7 analysis
Permanent gases and VOCs should not necessarily be considered separately since they often occur together. The presence of methane, carbon dioxide and oxygen are often used an indicator of natural attenuation of petroleum hydrocarbons. Canisters are very useful for very volatile compounds such as vinyl chloride and chloromethane. New internal surface coatings have made it possible to include more reactive compounds such as hydrogen sulphide as part of the list of analytes. Helium is typically used for leak detection within monitoring wells. Preference is given to helium as a tracer because its presence doesn’t interfere with TO-15 analysis and can be measured in the field using a handheld detector which allows quantitative comparison with laboratory results.
The 1.4L canister (also known as a Silocan) is much easier to use and transport than the traditional 6L version. Along with a reduction in canister size has been the development of deactivated glass (Bottle-Vac) canisters.
In terms of the laboratory analysis, the analytical method utilities a multi-staged, cold trapping system that can separate the major components from the target VOCs of interest prior to injection into a GC. Analytes are separated on an appropriate analytical column before being detected by Mass Selective Detector. Analyte responses are quantified against a 6-point calibration curve and corrected against internal standards. In the case of non-target compounds being identified with the sample, the response factor of the nearest standard is used to calculate analyte concentration.
If you require any more information on the above, you would like to Request a Quote or for any other analytical enquiry, please contact your Customer Service Co-Ordinator or Contact us on 01244 528 744.