Horizon Technology, Inc.
Alicia Cannon and Brian LaBrecque, Horizon Technology, Inc.
Diquat and paraquat are fairly toxic herbicides used to control weeds and in the management of illegal marijuana fields. Concerns that they may contaminate drinking water supplies prompted development of US EPA Method 549.2, incorporating solid phase extraction (SPE), analyte extraction, and liquid chromatography analytical determination. Diquat is regulated in drinking water supplies at a level of 0.02 mg/L.
Within EPA Method 549.2, the suggested rate to load a sample onto a solid phase cartridge is 3 to 6 mL/min (Section 11.2.5). However, as advances in chemistry of the sorbent continue to be made, it may be possible to increase this speed. This note will outline the process used to extract diquat and paraquat from water samples, using a faster loading rate than what is specified in method 549.2. It will also illustrate that, although method 549.2 recommends that all glassware be silanized, excellent recoveries can be achieved without silanization of glassware, even if small portions of the glassware come in contact with the sample; such as contact with the glass syringe barrel on the SmartPrep® Cartridge Extractor. It will specifically focus on the extraction of the samples needed for an initial demonstration of capability (IDC) according to the procedures outlined in EPA Method 549.2.
The instrumentation used in this method is:
The results of the extractions performed in replicate runs of laboratory fortified blanks (LFB) for this study are given in Table I. The data was generated using a loading rate of 25 mL/min (compared to the specified rate of 3 mL/min). The average run time for each extraction was observed to be approximately 36 min. When this is compared to the EPA Method 549.2 specified load rate of 3 mL/min, the time saved was in the order of 75%. Both diquat and paraquat were recovered at concentrations higher than 90% and the relative standard deviation (RSDs) were less than 10%, demonstrating the increased flow rate still gives first-rate results.
Table I: Method 549.2 IDC results
The resulting data from the analysis performed shows that, even though the sample loading rate was increased by more than a factor of eight, the recoveries were still well within method criteria. The SmartPrep Automated Extractor is an excellent choice for those wishing to use method 549.2 in a production environment.
(1) J.W. Munch and W.J. Bashe, "Method 549.2- Determination of Diquat and Paraquat in Drinking Water by Liquid-Solid Extraction and High Performance Liquid Chromatography with Ultraviolet Detection," NERL, ORD U.S. Environmental Protection Agency, Cincinnati, Ohio, 45268, 1997.
(2) A. Cannon and B. LaBrecque, "Increasing the Efficiency of EPA Method 549.2 Using the SmartPrep Automated Cartridge Extractor," Application Note 084, Horizon Technology, 2012.
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