EPA Method 1631

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EPA Method 1631:
Mercury in Water Using CVAFS. Official Name: Mercury in Water by Oxidation, Purge and Trap, and Cold Vapor Atomic Absorption Fluorescence Spectrometry

This method allows for the determination of mercury at a minimum level of 0.5 parts-per-trillion and supports measurements for mercury published in the National Toxics Rule and in the Final Water Quality Guidance for the Great Lakes System. Includes Guidance for Implementation and Use of Method 1631 and Revision E to the method, which contain additional and revised requirements. Mercury in a sample is oxidized using BrCl. Oxidized mercury in the sample is then reduced to volatile elemental mercury using SnCl2. Elemental mercury is purged with nitrogen and collected on a gold sand trap. After sufficient mercury has been collected, the trap is heated and desorbed mercury is purged into a cold-vapor atomic fluorescence spectrometer (CVAFS). The concentration of desorbed mercury is measured using the CVAFS system. The use of automated flow-injection systems in analyses is specifically allowed in this version of the method. This method replaces the previously approved Method 1631 Revision C.

This method determines mercury in filtered and unfiltered water.

Method 1631, Revision E: Mercury in Water by Oxidation, Purge and Trap, and Cold Vapor Atomic Fluorescence Spectrometry. EPA-821-R-02-019. U.S. Environmental Protection Agency, Office of Water, August 2002, 38 p.

(A) Contamination by carryover: Samples known or suspected to contain the lowest concentration of mercury should be analyzed first followed by samples containing higher levels.(B) Contamination by samples: Samples known or suspected to contain Hg concentrations greater than 100 ng/L should be diluted prior to bringing them into the clean room or laboratory processing trace metals samples.(C) Contamination by indirect contact: Every piece of apparatus directly or indirectly used in the collection, processing, and analysis of water samples must be thoroughly cleaned.(D) Contamination by airborne particulate matter: Samples may be contaminated by airborne dust, dirt, particles, or vapors from unfiltered air supplies; nearby corroded or rusted pipes, wires, or other fixtures; or metal-containing paint.(E) Contamination from reagents: Use high purity reagents.(F) Iodide concentrations from 30 to 100 mg/L; at iodide concentrations greater than 3 mg/L, pre-reduce with SnCl2.

QC Requirements:
Each laboratory that uses this Method is required to operate a formal quality assurance program. The minimum requirements of this program consist of an initial demonstration of laboratory capability, ongoing analysis of standards and blanks as a test of continued performance, and the analysis of matrix spikes (MS) and matrix spike duplicates (MSD) to assess precision and recovery. Laboratory performance is compared to established performance criteria to determine that the results of analyses meet the performance characteristics of the Method.

Maximum Holding Time:
90 days - See Sample Handling



0.5 - 100 ng/L, extendable upward

Precision and recovery data for reagent water, freshwater, marine water, and secondary effluent are given in Table 3 of the Method.

The method detection limit (MDL) as determined by 40 CFR 136, Appendix B.

Revision Number:
Revision E, August 2002

Test Description:
Mercury in Water/ Ox