VOC, BTEX & VPH Water Sample Preservative Changes

by Patrick Novak, Sr. Account Manager

In June 2007, the British Columbia Ministry of Environment (BC MOE) changed their volatile organic compound (VOC) method. This change, along with their new recommendations, prompted CANTEST to change the bottle preservative for the sampling of volatile organic compounds (VOCs) in water.

Non Chlorinated Water Sources

40 mL VOC vials with Teflon lined septa lids used for volatile hydrocarbons in water analysis now contain sodium bisulphate (NaHSO4) as the preservative instead of liquid hydrochloric acid (HCl), which was used in the past. Although the use of hydrochloric acid (HCl) or sulphuric acid (H2SO4) is still valid as an alternative preservative for the method, these changes are being made because the sodium bisulphate has clearly demonstrated the prevention of microbial degradation of VOCs. Sodium bisulphate will be used for the analysis of VOCs, BTEXS (benzene, toluene, ethyl benzene, xylenes and styrene), VPH (volatile petroleum hydrocarbons) and MTBE (methyl tert-butyl ether).

Chlorinated Water Sources

This preservation is valid for most sampling events, except when a water source has been recently chlorinated. If the source has been recently chlorinated and you are sampling for the above analysis, please contact your laboratory representative to obtain vials with the preservative relevant for a chlorinated water source. The recommended preservative in this situation is sodium thiosulphate which is used to turn chlorine into chloride.

The New Methodology Referenced

The BC MOE provides the new methodology, along with additional details, in the official update and Appendix A of Draft EPA Method 5035A.

Best Practices

Some good things to remember when sampling for VOCs in water to ensure the best recoveries possible are:

• VOC samples should be collected in at least duplicate to ensure for re-analysis or dilutions. 
• Do not pre-rinse vials with sample. 
• Collect sample with as little aeration as possible and ensure no bubbles are present in the vial (zero headspace).
• Ship and store samples at 4oC. 
• Get samples to the laboratory as soon as possible for analysis.

Patrick Novak is part of CANTEST’s Technical Service Team. He can be contacted at pnovak@cantest.com or 1 800 665 8566.

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