The development of the U.S. Environmental Protection Agency (EPA) Method 317.0 is initiated to provide a sufficiently sensitive and fundamental technique for the compliance monitoring of trace levels of bromate in drinking water. After a comparative evaluation of Method 317.0 and elimination of a chlorite interference, this method is tested by a collaborative study in order to determine the precision and bias of the method and evaluate its potential role as a future compliance-monitoring method for inorganic disinfection by-products (DBPs) and trace bromate. This technique provides a practical method for future compliance monitoring for all of the inorganic oxyhalide DBPs including trace concentrations of bromate.
The United States Environmental Protection Agency's Office of Ground Water and Drinking Water has developed a single-laboratory quantitation procedure: the lowest concentration minimum reporting level (LCMRL). The LCMRL is the lowest true concentration for which future recovery is predicted to fall, with high confidence (99%), between 50% and 150%. The procedure takes into account precision and accuracy. Multiple concentration replicates are processed through the entire analytical method and the data are plotted as measured sample concentration (y-axis) versus true concentration (x-axis). If the data support an assumption of constant variance over the concentration range, an ordinary least-squares regression line is drawn; otherwise, a variance-weighted least-squares regression is used. Prediction interval lines of 99% confidence are drawn about the regression. At the points where the prediction interval lines intersect with data quality objective lines of 50% and 150% recovery, lines are dropped to the x-axis. The higher of the two values is the LCMRL. The LCMRL procedure is flexible because the data quality objectives (50-150%) and the prediction interval confidence (99%) can be varied to suit program needs. The LCMRL determination is performed during method development only. A simpler procedure for verification of data quality objectives at a given minimum reporting level (MRL) is also presented. The verification procedure requires a single set of seven samples taken through the entire method procedure. If the calculated prediction interval is contained within data quality recovery limits (50-150%), the laboratory performance at the MRL is verified.
Determination of chlorinated phenoxyacid herbicides by gas chromatography is complicated by the fact that these compounds exhibit low volatilities due to the hydrogen bonding of their carboxylic acid and phenol functionalities. Furthermore, these functional groups can cause the parent molecule to adsorb on the stationary phase of the column, thus producing asymmetric peaks. Masking of these polar groups can significantly increase the volatility and reduce the adsorption effects of these compounds, yielding products that can undergo analysis by gas chromatography. A variety of reactions have been employed in the preparation of less polar derivatives. Two categories are examined in this work: silylation and alkylation. Within the category of alkylation, derivatization techniques examined include acid-catalyzed esterification, extractive alkylation, and base-promoted esterification. Of all the investigated techniques, base-promoted esterification is determined to be the most effective. This paper reports the application of this procedure in the development of a sensitive method for the determination of a variety of phenoxyacid herbicides at concentrations below the microgram-per-liter level in water.
