Tuesday, July 26, 2011

Confirmation Clearance Method for Difficult Vapor Screening Items

By: John Schwarz

The Environmental Monitoring Laboratory-Analytical Chemistry Team (EML-ACT) analyzes nearly 2,000 air samples monthly in support of ECBC surety laboratories, toxic chambers and MRICD laboratories just at Edgewood alone. These air samples support personnel monitoring specific operations, chemical agent room backgrounds, first entry monitoring, fume hood monitoring during standard operating procedures and many sampled items that are just waste material in preparation for disposal.

Also commonly referred to as headspace monitoring, vapor screening of waste material can be very difficult and troublesome. Many of these items require screening for multiple agents due to the way the waste was generated or because little information is known about the waste item. Often, these types of samples have been very difficult to clear for G-type agents due to interferences, or chromatographic "footprints", even when using gas chromatography mass spectrometry (GCMS). This resulted in repeated sampling and operations such as "air washing" of waste items. However, these actions are typically met with little success. Last summer, the EML-ACT special project chemist worked with a summer intern to develop an alternative analysis method for these types of samples to determine typical interferences that affect the  ability to clear the troublesome waste analyses. An example of common interference for the analysis of G-type agents was identified as diesel and gasoline. Over the summer, a new analysis method was developed that employed a Flame  Photometric Detector and a Nitrogen Phosphorus Detector coupled with the existing GCMS instrument. This new analysis splits a single sample into three streams for analysis by the specific detectors to determine the presence of Phosphorus and Nitrogen containing compounds while also using the Mass Spectrometer (MS) Detector for a full composition determination. This type of analysis provides the analyst with significantly more information about the sample and increases the confidence in identifying contaminates or chemical agents in a single analysis. Samples that had previously failed due to interferences using only the MS detector can now be cleared using one of the other detectors in this new triple detector analysis.

Today, this method has become a part of routine EML-ACT analysis resulting in faster turnaround of customer results and more efficient use of staff labor.

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