In 1983 the United States Environmental Protection agency released drinking water method 524.2, Measurement of Purgeable Organic Compounds in Water by Capillary Column Gas Chromatography/Mass Spectrometry. Since the purge and trap method’s first release, there have been many revisions in order to update the method with the latest one being introduced in 1995. USEPA Method 524.2 is a prescriptive method for VOCs, meaning modifications to the method parameters are not allowed. “This is a general-purpose method for the identification and simultaneous measurement of purgeable volatile organic compounds in surface water, ground water, and drinking water in any stage of treatment.”1
Method 524.2 encompasses 84 volatile organic compounds (VOCs) including trihalomethanes which are common byproducts of disinfection. Sample size can be as high as 25mL to as low as 5mL as long as the analytical system can reach the required detection limits. Samples need to be purged at 40mL/min with Helium for 11 minutes and desorbed for about 4 minutes. Since USEPA Method 524.2 is a prescriptive method, these purge and trap parameters may not be altered. There are some who experience excess moisture due to the longer desorb time in this method. Moisture can negatively affect resulting chromatography. If your compliance officer is mandating a 4 minute desorb, ask about EST’s patented Desorb Flow Control (DFC) available on the Evolution. DFC can dramatically alleviate issues with long desorb parameters.
Over the years, there have been many improvements to purge and trap and Gas Chromatography/Mass Spectrometry (GC/MS) systems. They have better sensitivity and are much more efficient in analyte separation and analysis. For this reason, USEPA Method 524.2 was updated with USEPA Method 524.3 and 523.4 with the Method 523.4 allowing for laboratories to use Nitrogen as a purge gas. There are several updates to the drinking water method and right now laboratories can choose which method that they would like to use.
Among the changes to the method are the required compounds. There is now three internal standards instead of one and three surrogates in place of the two in Method 524.2. Furthermore, there is an updated list of analytes. The new methods require 76 analytes with some of the previous compounds removed and a few compounds added. Sample preservation is now less hazardous as Methods 524.3 and 523.4 use maleic and ascorbic acid for preservation in lieu of hydrochloric acid.
One of the most significant changes are the purge and trap operating parameters. The new drinking water methods allow for laboratories to optimize purge and trap parameters and significantly reduce run times. See Table 1 below.
Purge Flow Rate
Purge Volume + Dry Purge Volume
Table 1: USEPA Method 524.3 and 524.4 Method Modification Table
Autosamplers, such as the Centurion Water (W), must be capable of maintaining sample temperatures at 10°C or below. All other instrument parameters can be altered with no restrictions. Furthermore, the new method allows for Scan and Single Ion Monitoring (SIM) for better detection.
Quality Control has two noteworthy changes. First, the method requires a Minimum Reporting Limit (MRL), not a Minimum Detection Limit (MDL). The MRL is validated by the confirmation of the upper and lower Prediction Interval of Results requirement. The calibration curve requires seven calibration standards. Linearity if verified using linear or quadratic regression and weighting may be used. Calibration curves may not be forced through zero.
The Evolution purge and trap concentrator has the advantage of having an 8-port valve in order to better control the water contamination and a heated sparge vessel for lowering sample carryover. The Centurion W XYZ autosampler, has the capability of keeping drinking water samples at the required temperature and can hold up to 100 sample. The Evolution and Centurion W can provide both efficiency and reliability for drinking water purge and trap sampling.
If you are just getting started with Purge and Trap drinking water analysis, contact us to reach one of our application specialists who would be glad to offer some tips and tricks. Feel free to look at some of our application notes which will help you on your way.
In June 2009, the United States Environmental Protection Agency (USEPA) promulgated a new drinking water method, 524.3. Due to advances in analytical instrumentation, Method 524.3 allows laboratories to modify purge and trap and GCMS conditions. Currently the USEPA is investigating the option of using Nitrogen as the purge gas in a new drinking water method, 524.4.
During volatile analysis, samples are purged with an inert gas in order for the Volatile Organic Compounds (VOCs) to be swept out of the sample matrix and onto an analytical trap. For years, the established purge flow rate and time has been 40ml/min for 11 minutes. USEPA Method 524.3 changed this.
In order to measure low level purgeable volatile organic compounds in water, the United States Environmental Protection Agency (USEPA) developed the 524.2 method. This method requires a 5mL or 25mL purge volume and can be further complicated by the mandatory lower detection limits and an extended four minute desorb time.
Desorb flow control was developed in order to help manage the moisture associated with the four minute desorb time required for USEPA method 524.2. An added benefit to this process is the reduction in helium consumption when using this technique.
The compounds 2-Methylisoborneol (2-MIB) and Geosmin are the primary source of the foul odor found in drinking water. Algal contamination is the principal cause of the formation of these compounds. Geosmin and 2-MIB have such a low odor threshold, that even the slightest amount can produce an unpleasant odor and taste in drinking water.
Algal contamination in drinking water is becoming a common problem. The primary compounds that result from this contamination are 2-Methylisoborneol (2-MIB) and Geosmin. These compounds cause a musty odor in water and since the odor of these compounds have a very low threshold for detection, small amounts of contamination can cause drinking water to taste and smell unpleasant.
The third Unregulated Contaminant Monitoring Rule (UCMR 3) was finalized in April of 2012. UCMR 3 requires public water systems to monitor for a specific list of 30 contaminants under three separate lists: list one, assessment monitoring, list two, screening survey, and list three, pre-screen testing. This application note will address the volatile organic compounds found in list one, assessment monitoring contaminants. USEPA Method 524.3 and 524.4 will be the methods evaluated for sampling and analysis.