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07/02/2008

New EPA Method 314.2: Two-Dimensional Ion Chromatography for Trace Perchlorate in Drinking Water



The US EPA Office of Ground Water and Drinking Water has drafted a new method for the determination of perchlorate using two-dimensional (2-D) ion chromatography and matrix elimination. Jointly developed with Dionex Corporation, this method expands on existing EPA methods 314.0 and 314.1, and is highly stable and robust for the separation of samples with high ionic strength matrices. This method also provides confirmatory analysis through the use of two column chemistries in one injection.

There are notable advantages of the 2-D matrix diversion approach. First, initial sample loading on a 4 mm column supports a large sample injection volume due to the high capacity of the analytical column. Second, the two-dimensional separation provides higher selectivity for analytes of interest relative to the matrix ions. Third, the 2 mm column provides signal enhancement of the perchlorate.

In this 2-D approach, perchlorate is partially resolved on a 4 mm column in the first dimension, collected onto a concentrator column, then resolved with high sensitivity on a 2 mm column in the second dimension. The suppressed effluent from the hydroxide eluent is water, which provides the ideal environment for ion-exchange retention and concentration before transfer to the second dimension. Because the second dimension column has a smaller cross-sectional area relative to the first dimension, detection sensitivity is enhanced. In addition, 2-D chromatography makes it possible to combine two different column chemistries, one per dimension, enabling selectivity not possible using a single-dimension separation.

Source: Dionex Corp.




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