Method 549.1

Determination of Diquat and Paraquat in Drinking Water by Liquid-Solid Extraction and High Performance Liquid Chromatography with Ultraviolet Detection

This method is for the determination of diquat (1,1'-ethylene-2,2'-bipyridilium dibromid salt) and paraquat (1,1'-dimethyl-4,4'- bipyridilium dichloride salt) in drinking water and finished drinking water.  250mL of sample is adjusted to pH 10.5.  The sample is extracted using a C8 solid sorbent cartridge or C8 disk that has been specifically prepared for the reversed-phase, ion-pair mode.  The disk is eluted with 4.5mL of an acidic aqueous solvent  and analyzed by HPLC with a photodiode array detector. 

Avoid sample contact with any glass during the sampling procedure as it may cause loss of analytes. The substitution of polyvinylchloride (PVC) for glass is recommended.





(EPA: Office of Water)


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Method Data

Hold Times, Preservatives, Preps, Collection, Analytical & Documentation
Holding Time:   7 days from sample collection to extraction and 21 days from extraction to analysis.
Preservatives:   Samples must be iced or refrigerated to 4°C from collection until extraction. Biologically active samples are preserved with sulfuric acid to pH 2. Samples with residual chlorine are preserved with 100mg/L sodium thiosulfate. Protect samples from light.
Required Preps:   250mL Amber PVC high density bottles or silanized amber glass bottles
Collection Method:   Grab sampling
Analytical Methodology:   HPLC with ultraviolet detection

Analyte List*

Analyte Formula CAS Number Detection Limit
Paraquat (Paraquat dichloride)
Diquat (Diquat dibromide)

* The analytes and detection limits listed for each method represent the typical detection limits and analytes reported for that particular method. Keep in mind that analyte lists may vary from laboratory to laboratory. Detection limits may also vary from lab to lab and are dependent upon the sample size, matrix, and any interferences that may be present in the sample.