Method of Analysis by the U.S. Geological Survey California District Sacramento Laboratory—Determination of Trihalomethane Formation Potential, Method Validation, and Quality-Control Practices

By Kathryn L. Crepeau, Miranda S. Fram, and Noël Bush



Scientific Investigations Report 2004-5003

Sacramento, California 2004

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An analytical method for the determination of the trihalomethane formation potential of water samples has been developed. The trihalomethane formation potential is measured by dosing samples with chlorine under specified conditions of pH, temperature, incubation time, darkness, and residual-free chlorine, and then analyzing the resulting trihalomethanes by purge and trap/gas chromatography equipped with an electron capture detector. Detailed explanations of the method and quality-control practices are provided. Method validation experiments showed that the trihalomethane formation potential varies as a function of time between sample collection and analysis, residual-free chlorine concentration, method of sample dilution, and the concentration of bromide in the sample.





Purpose and Scope


Method of Analysis of Trihalomethane Formation Potential

Scope and Application

Summary of Method

Equipment and Materials

Sample Collection and Filtration

Dosing and Quenching Procedure

Dose Calculation



Quenching and Acceptance Criteria


Primary Standard Solution

Calibration Standard Solutions

Surrogate Solution

Instrument Performance

Instrument Conditions


Sample Analysis

Data Processing and Storage Procedures

EZChrom Software

Laboratory Information Management System

Method Validation

Method Precision

Effect of Sample Aging on Trihalomethane Formation Potential

Effect of Residual Chlorine Concentration on Trihalomethane Formation Potential

Effect of Dilution Method on Trihalomethane Formation Potential

Effect of Bromide Concentration on Trihalomethane Formation Potential

Quality-Control Practices

Analytical Sequence


Calibration Verification Standards

Surrogate Standard

Retention Time and Peak Shape for Analytes

Duplication Samples

Instrument Maintenance


References Cited


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