Analysis of Volatile Organic Compounds Using US EPA Method 524.4 by CDS 7000 Series Automated Purge and Trap Concentrator

Abstract

In EPA Method 524.4, nitrogen is adopted to replace helium in purging volatile organic compounds from water samples. This application note demonstrates the ability of the CDS Analytical’s 7000 series purge and trap concentrator configured with a 7450 autosampler to meet and exceed the requirements of US EPA method 524.4.

Helium, which is the coolest cryogen with boiling temperature merely at 4.2K, is commercially extracted from natural gas wells. In the past two decades, the energy sector in North America has gradually moved away from using conventional natural gas to shale oil extraction. This technology shift historically has created three major crises in helium supply, including the Helium Shortage 3.0¹ in recent years, two other shortage crises in 2005-2007 and 2012-2013 respectively². To tackle with the periodical shortages and sharply arising cost of helium, US EPA has promptly altered the EPA Method 524.3, which is a VOCs testing method in drinking water, to allow using nitrogen to replace helium. This change eventually led to the birth of EPA Method 524.4 in 2013³.

CDS Analytical invented the first micro-processor controlled Purge and Trap concentrator in 1979 and won the Industrial Research and Development 100 award in 1981. The 7450 autosampler was constructed on the 2nd generation XYZ autosampler with enhanced precision. This automation platform is specially designed for the 7000 series Purge and Trap concentrator to improve the productivity. The unique 10-port micro-loop fill valve in the autosampler enables a less than 1% volume variation in adding 2 µL of Internal Standard. This translates to a superior <3% RSDs compared to other autosamplers that are using the micro syringe injection technique. The 8-port high temperature valve in the 7000 series concentrator has the capability to provide on-line moisture management, which removes the wet trap in the desorption step to increase the efficiency. Due to the various engineering features, the results coming from this combined system exceeds the requirements of EPA Method 524.4 in Calibration, Minimum Reporting Levels (MRLs) Confirmation, Accuracy and Precision Calibration in both low and mid sample concentrations.

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