EPA Method 507

Determination of Nitrogen- and Phosphorus-Containing Pesticides in Water by Gas Chromatography with a Nitrogen-Phosphorus Detector – Revision 2.1.

Summary:
A 1 L sample is extracted with methylene chloride by shaking in a separatory funnel or mechanical tumbling in a bottle. The methylene chloride extract is isolated, dried, and concentrated to a volume of 5 mL during a solvent exchange to methyl tert-butyl ether (MTBE). The concentrations of pesticides in the extract are measured using capillary column gas chromatography (GC) system equipped with a nitrogen-phosphorus detector (NPD).

Scope:
This method determines certain nitrogen- and phosphorus-containing pesticides in ground water and finished drinking water.

Citation:
Methods for the Determination of Organic Compounds in Drinking Water – Supplement III (EPA/600/R-95-131)

Interferences:
(A) Glassware contamination: Thoroughly clean glassware, including baking or solvent rinse.(B) Reagent contamination: Use high purity reagents.(C) Contamination from sample carryover: Rinsing apparatus with water and purging equipment between analyses can minimize contamination.(D) Matrix interferences: Matrix interferences may caused by contaminants that are coextracted from the sample.(E) Solvents: The same solvent must be used to prepare samples and standards to make sure responses are comparable.

QC Requirements:
Initial demonstration of laboratory capability (includes analysis of standards), followed by surrogate recoveries, laboratory reagent blanks (LRBs), laboratory fortified samples, laboratory fortified blanks (LFBs), and QC performance samples. A method detection limit (MDL) must also be determined for each analyte.

Maximum Holding Time:
14 days generally (see Sampling Handling for exceptions).

Media:
WATER

Subcategory:
Organic

Concentration:
Ranges differ for each analyte depending on matrix and instrumentation.

Precision:
Precision and accuracy values were determined using data from 7 to 8 replicate analyses of a reagent water sample fortified with the analytes of interest.

Detection:
MDLs were determined using the standard deviation of 7 or 8 replicate analyses of an analyte-fortified reagent water sample multiplied by the t-value for (# of samples -1) degrees of freedom at the 99% confidence level. Detailed instructions for how MDLs are determined are found at 40 CFR part 136, Appendix B.

Revision Number:
Revision 2.1, 1995