Method 502.2

Volatile Organic Compounds in Water by Purge and Trap Capillary Column Gas Chromatogrophy with Photoionization and Electrolytic Conductivity Detectors in Series

This is a general purpose method for the identification and simultaneous measurement of purgeable volatile organic compounds in finished drinking water, raw source water, or drinking water in any treatment stage . The method is applicable to a wide range of organic compounds, including the four trihalomethane disinfection by-products, that have sufficiently high volatility and low water solubility to be efficiently removed from water samples with purge and trap procedures. This method is applicable to the determination of total trihalomethanes and other volatile organic compounds (VOCs). Method detection limits (MDLs) are compound and instrument dependent and vary from approximately 0.01-3.0 µg/L. The applicable concentration range of this method is also compound and instrument dependent and is approximately 0.02-200 µg/L. Analytes that are inefficiently purged from water will not be detected when present at low concentrations, but they can be measured with acceptable accuracy and precision when present in sufficient amounts. Highly volatile organic compounds with low water solubility are extracted (purged) from the sample matrix by bubbling an inert gas through a 5 mL aqueous sample. Purged sample components are trapped in a tube containing suitable sorbent materials. When purging is complete, the sorbent tube is heated and backflushed with helium to thermally desorb trapped sample components onto a capillary gas chromatography (GC) column. The column is temperature programmed to separate the method analytes which are then detected with a photoionization detector (PID) and an electrolytic conductivity detector (ELCD) placed in series. Analytes are quantitated by procedural standard calibration. Identifications are made by comparison of the retention times of unknown peaks to the retention times of standards analyzed under the same conditions used for samples. Additional confirmatory information can be gained by comparing the relative response from the two detectors. For absolute confirmation, a gas chromatography/ mass spectrometry (GC/MS) determination according to USEPA Method 524.2 is recommended. This method requires the use of a PID to measure target analytes that cannot be measured with an electrolytic conductivity detector. If only halogenated analytes, such as the trihalomethanes are to be measured, a PID is not needed.