Overcoming reporting limit challenges
Overcoming reporting limit challenges
Environmental NEWS - Spring 2010
Overcoming reporting limit challenges
GC/MS semi volatiles principal chemist Tim Trees and
manager Rick Karam discuss NDMA data on water samples.
A common problem in the regulated community is difficulty verifying successful remediation by testing to very low analytical detection limits. Existing test methods are not always capable of determining the concentrations required by regulators. While the Specialty Services Team at Lancaster Labs was established specifically to develop new methods for a client’s unique analytical challenges, there are other analytical teams at Lancaster Labs that are also innovating to meet client needs by modifying existing published methods to achieve ultra-trace detection limits. To ensure the quality of the data produced, the method modification process at Lancaster Labs includes validation of the method detection limit along with accuracy and precision checks. Here are some examples of what can be achieved with successful method modification projects.
The required limits can be as low as the part per trillion (ppt) range, as was the case for one Lancaster Labs client that was asked to report N-nitrosodimethylamine (NDMA) to a concentration of 1 ppt. This compound is typically analyzed using EPA method 1625 or SW-846 method 8270C, which calls for liquid/liquid extraction of the water sample, extract concentration and analysis by GC/MS. The published method lists the detection limit at 5 parts per billion (ppb) or several orders of magnitude above what the client needed. Chemists at Lancaster Labs were able to use a novel modification of method 1625, along with the extremely sensitive Thermo DSQII GC/MS instruments to meet the 1 ppt requirement.
Selective ion monitoring (SIM) is another technique available to improve sensitivity for GC/MS methods. Chemists in the GC/MS Volatiles Department have used SIM to modify EPA method 524 to achieve low detection limits for selected compounds, including one client request to analyze 1,2,3- trichloropropane down to 1 ppt.