Reduce Helium Consumption by Using Nitrogen Purge Gas for VOCs in Drinking Water

Hazardous waste and waste water laboratories have been saving helium and money using nitrogen as a purge gas for quite a while when performing EPA Methods 8260 and 624 respectively. Until recently, this has not been an option for EPA Method 524, the measurement of purgeable organics in drinking water. I know many drinking water labs are still running EPA method 524.2, which requires the He purge of a 25 mL sample; however, those of you out there looking to save some cash should seriously consider the newer method 524.4 (full method text can be found here).

EPA Method 524.4 consists of a 5 mL sample purge using nitrogen gas. The smaller sample volume improves response factors for some of the more polar compounds with lower purging efficiency (such as alcohols and ketones), and the method performance using nitrogen purge is nearly identical to the 5 mL sample purge using helium (EPA Method 524.3). I presented on this topic last year at PittCon in Philadelphia, and my poster shows performance data for every compound on the standard compound list at the low, mid and high level concentrations, as well as results for recently shocked (with sodium hypochlorite) private well water sample. The performance data is color coded for when method criteria were not met for a specific compound at a specific level; notice how the He and N2 data are nearly identical, failures and all.