The Chromatography Group at WETLAB has been very busy over the past year.  It has been an exciting time in both areas of production and method development.  They have been providing data to our clients for Total Petroleum Hydrocarbons (TPH), Total Organic Carbon and recently completed method development for Volatile Organic Compounds (VOC).  The group is currently finishing method development for VOC in soils and Halo acetic Acids (HAA5) and readying them for production in September of 2023.  With these new methods online, we look forward to the opportunity to increase our ability to offer data for environmental solutions.  Providing high level quality data starts at the collection process. In this issue of Lessons from the Lab we would like to share some best practices for Volatile Organic Compounds (VOC) analysis collection.

The methodology for VOC analysis requires the addition of chemical preservatives prior to sample collection.  WETLAB provides pre-preserved vials to collect the samples for your convenience.  Depending on the matrix and/or compounds of concern, there are specific preservatives required.  For drinking analyzed via EPA 524.2, samples are to be acidified to pH of <2 at the time of collection, but after dichlorination.  WETLAB provides zero headspace vials with 1:1 HCl.  Samples for TTHM (Bromodichloromethane, Bromoform, Chlorodibromomethane, Chloroform (Trichloromethane)) may be preserved with sodium thiosulfate.  For non-drinking water matrices analyzed by EPA 624.1 or 8260, samples are to be acidified to pH of <2 at the time of collection in vials with 1:1 HCl.  Should 2-Chloroethyl vinyl ether, Acrolein or Acrylonitrile be required, a second set of samples must be taken in unpreserved vials.

All samples should be chilled to 4°C ± 2°C when collected and maintained at that temperature until analysis.  During sample collection, the vials should be filled so that no air bubbles are trapped when the bottle is sealed, per SW-846 5021A “Volatile Organic Compounds in Various Matrices Using Equilibrium Headspace Analysis”: Due to differing solubility and diffusion properties of gases in liquid matrices at different temperatures, it is possible for the sample to generate some headspace during storage. The diameter of any bubble caused by degassing upon cooling the sample should not exceed 5 – 6 mm. When a bubble is present, also inspect the cap and septum to ensure that a proper seal was made at the time of sampling. The presence of a macro bubble in a sample vial generally indicates either improper sampling technique or a source of gas evolution within the sample. The latter case is usually accompanied by a buildup of pressure within the vial, (e.g. carbonate-containing samples preserved with acid). Studies conducted by the USEPA (EMSL-Ci, unpublished data) indicate that “pea-sized” bubbles (i.e. bubbles not exceeding 1/4 inch or 6 mm in diameter) did not adversely affect volatile data. These bubbles were generally encountered in wastewater samples, which are more susceptible to variations in gas solubility, than groundwater samples.

Another good practice for sample collection is to completely fill out a chain of custody form and sample bottles, with system name and ID, sample point ID, sample collection date and time, and sample matrix. 

If you have questions regarding sample collection procedures, please feel free to contact WETLAB Client Services at 775-355-0202. 

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