Abstract

A laboratory for analysis of low-ionic-strength water has been developed at the New York District office of the U.S. Geological Survey (USGS) in Troy, N.Y., to analyze samples collected by USGS projects in the Northeast. The laboratory's quality-assurance program is based on both internal and interlaboratory quality-assurance samples and quality-control procedures developed to ensure proper sample collection, processing, and analysis. The quality-assurance/quality-control data are stored in the laboratory's SAS¹ data-management system, which provides efficient review, compilation, and plotting of quality-assurance/quality-control data. This report presents and discusses data analyzed from May 1991 through June 1993.

Quality-control results for 18 analytical procedures were evaluated for bias and precision. Control charts show that four of the procedures have biases but were within control limits; they are: total aluminum (high in March and May 1993); calcium (low in 1991); chloride (low from January through June 1993); and nitrate (colorimetric method—low from June 1992 through June 1993). No quality-control sample has been developed for the organic monomeric aluminum procedure. Results from the filter-blank and analytical blank analyses indicate that, in 4 of the 14 procedures in which blanks were run, measurements approached or exceeded control limits. Organic and total monomeric aluminum concentrations showed upward trends in analytical-blanks in June 1992, but most of these values were within control limits. Total aluminum, calcium, and chloride concentrations periodically exceeded control limits. Blanks were not analyzed for pH, acid-neutralizing capacity, dissolved inorganic carbon, or nitrate (colorimetric method).

Sampling and analysis precision are evaluated in terms of the coefficient of variation obtained for duplicate and triplicate samples in 14 of the 18 procedures. Data-quality objectives were met for at least 95 percent of duplicate and triplicate samples. Data quality objectives were not met in 32 percent of the total aluminum samples; 20 percent of the total monomeric aluminum samples; and 23 percent of the dissolved organic carbon samples. Duplicate and triplicate samples were not analyzed for ammonium, fluoride, dissolved inorganic carbon, or nitrate (colorimetric method).

Results of interlaboratory quality-assurance programs are presented. Laboratory ratings for the U.S. Geological Survey's Standard Reference Sample Program show satisfactory results overall. Environment Canada's LRTAP interlaboratory study results are plotted on control charts. Data quality objectives were met in 7 of the 12 procedures, for more than 80 percent of the LRTAP samples. Data quality objectives were not met for 25 percent of the ammonium and calcium samples; 35 percent of the dissolved organic carbon and silicon samples; and 45 percent of the sodium samples.

Posted April 2010