Light hydrocarbon analysis in water samples – not just a headspace method anymore

Living in Pennsylvania during this natural gas boom stirs passionate, mixed emotions about the economic benefits verses the environmental costs of drilling for this resource. While it is tempting to provide you all my thoughts on the subject, I’ll keep my opinions to myself and simply provide our blog readers some interesting information I recently stumbled across while checking out the Pennsylvania Department of Environmental Protection  (PA-DEP) website.

When the Marcellus Shale natural gas drilling in Pennsylvania really started taking off several years ago, we (tech service) were taking quite a few calls about analyzing C1 through C4 (methane through butane) in water samples. Many of our customers had tried this analysis using their purge & trap (p&t) instruments without success, because the only available traps on the market at that time were not capable of trapping methane. As a result, the only two ways I knew how to do this analysis were to use either headspace (like shown here) or liquid injections. Several years later, Teledyne Tekmar published an application note using p&t titled Alternative Methods to RSK 175 Using Purge and Trap Concentration and Automated Headspace for the Analysis of Dissolved Gases in Drinking Water.

 

Now, for the first time, I have seen a published method using purge & trap (PA-DEP 9243, link below).

Light Hydrocarbons in Aqueous Samples via Purge and Trap

 

So, how well does this method work? I have no idea, but if someone out there has tried it, I would like to hear back from you.

(Note – I did find a typo in the method; the Restek U-Bond PLOT column they mentioned should be listed with a 20µmdf film-thickness (not 0.2µmdf). The Restek catalog number for this column is 19749. The catalog number for the ShinCarbon column is 19809.)

Chromatogram above from Teledyne Tekmar using the Restek U-Bond.

 

 

As a final note, I would like to thank co-workers Chris English for a previous post (link below) which laid the groundwork for this post, and Chris Rattray for contacting Teledyne Tekmar to confirm that the trap used in this method was their proprietary trap P/N: 15-0885-403.

Modified EPA SOP RSK-175 Using a Teledyne Tekmar Purge and Trap Concentrator

3 Responses to “Light hydrocarbon analysis in water samples – not just a headspace method anymore”

  1. Nicely done blog Alan… American Society for Testing and Materials (ASTM) has formed a new subcommittee (D18.26) on Hydraulic Fracturing to determine best practices to include assisting the oil and gas industry in the safe management and disposal of drilling fluids; as well as, supporting effective groundwater monitoring.
    http://www.astm.org/COMMIT/D1826.htm

  2. Nathan Valentine says:

    Thanks for the write up/update.

    This method has been in the works for some time and seemed like a no brainer considering how prevalent purge and trap concentrators are in environmental labs.

    As far as the method itself goes, the thing we get asked most about is sample prep, and it is actually the most challenging part. In standard VOC analysis, you don’t run anything anywhere near its saturation point in water. Making and handling these saturated standards and getting consistency takes some practice. We can’t just order a standard from Restek like we normally do (at least not yet).

  3. Alan Sensue says:

    Hi Nathan. Thank you for reading my post, and for the valuable feedback. Alan

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