Method of Analysis at the U.S. Geological Survey California Water Science Center, Sacramento Laboratory – Determination of Haloacetic Acid Formation Potential, Method Validation, and Quality-Control Practices
By Barbara C. Zazzi1, Kathryn L. Crepeau2, Miranda S. Fram2, and Brian A. Bergamaschi2
Scientific Investigations Report 2005-5115, published 2005.
 
Haloacetic acids (HAA) are halogenated organic compounds commonly found in treated drinking water. HAA, like trihalomethanes (THM), are undesirable disinfection by-products (DBP) that form during the disinfection stage of the drinking-water treatment process. Natural organic carbon in the source water reacts with disinfectants [usually chlorine (Cl2)] added during treatment to form HAA and other DBP. HAA are of concern because some of the compounds have been identified as potential carcinogens and toxic to digestive and urinary organs (Herren-Freund and others, 1987; Deangelo and others, 1991; Lin and others, 1993). This method is designed to quantify nine haloacetic acids: bromochloroacetic acid, bromodichloroacetic acid, dibromochloroacetic acid, dibromoacetic acid, dichloroacetic acid, monobromoacetic acid, monochloroacetic acid, tribromoacetic acid, and trichloroacetic acid (table 1). Federal regulations currently mandate a maximum contaminant level (MCL) of 60 μg/L (micrograms per liter) for the sum of five haloacetic acids: monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid (U.S. Environmental Protection Agency, 1998).
Table 1 (View this table on a separate page.)Formulas and calibration ranges for the nine haloacetic acids and internal standard compounds analyzed by the U.S. Geological Survey method.
[Measurements shown in micrograms per liter]
Analyte FormulaCalibration range
Bromochloroacetic acidCHBrClCO2H0.2–100
Bromodichloroacetic acid CBrCl2CO2H0.2–100
Dibromochloroacetic acidCBr2ClCO2H0.5–250
Dibromoacetic acidCHBr2CO2H0.1–50
Dichloroacetic acidCHCl2CO2H0.3–150
Monobromoacetic acidCH2BrCO2H0.2–100
Monochloroacetic acidCH2ClCO2H0.3–150
Tribromoacetic acidCBr3CO2H1–500
Trichloroacetic acidCCl3CO2H0.1–50
2-bromo-1-chloropropaneCH2ClCHBrCH3internal standard
2-bromopropionic acid (surrogate)CH3CHBrCO2H0.5–250
The amount of HAA formed from a given amount of dissolved organic carbon (DOC) depends on the chemical structure of the DOC, contact time between the Cl2 and DOC, concentration of bromide (Br-) in the water, amount of Cl2 added, concentration of residual Cl2, pH, and temperature of the water (Reckhow and others, 1990). The HAA formation potential (HAAFP) is defined as the amount of HAA formed under specific conditions of pH, contact time, residual Cl2 concentration, and temperature, and is reported in units of micrograms per liter. The specific HAAFP (SHAAFP) is the HAAFP normalized to the DOC concentrations and is reported in units of millimoles of HAA per mole of carbon in the DOC. SHAAFP is a measure of the reactivity of the DOC to form HAA.
There are at least two standard methods for measuring HAA: U.S. Environmental Protection Agency (USEPA) Method 552.2 (U.S. Environmental Protection Agency, 1995) and Standard Method 6251 (American Public Health Association and others, 1995). Both methods are similar in that the HAA are extracted, methylated, and analyzed using a gas chromatograph (GC) equipped with an electron capture detector (GC-ECD). However, the Standard Method 6251 uses diazomethane as a derivatizing agent to form the methyl esters that can be analyzed by GC-ECD, while the USEPA method uses acidic methanol with slight heating to form these same methyl esters. The U.S. Geological Survey (USGS) California Water Science Center Sacramento Laboratory uses a modified version of the USEPA method.
This report presents detailed descriptions of the analytical procedures and quality-assurance/quality-control protocols used for determination of HAAFP by the USGS California Water Science Center, Sacramento, laboratory. The method accuracy, precision, and detection limits were determined.
The authors gratefully acknowledge Ellen Avery, Dana Erickson, Ben Harper, and Kelly Paxton for assistance with these experiments in the laboratory.