Using reference materials to improve the quality of data generated by USEPA analytical methods.

The quality of data generated for the analysis of environmental samples is critical to State and Federal regulatory agencies to ensure that decisions based upon the amounts of contaminants in environmental samples are truly protective of public health. The quality and validation of these measurements using the approved analytical methodology could be significantly enhanced by incorporating certified reference materials as part of the quality control protocols, yet this has not been widely implemented. Data from certified reference materials can provide critical information that can impact assessments regarding data use that is unavailable by other means. Using the analysis of Cr(vi) in soil extracts as the test case, some of the issues surrounding the use of certified reference materials for environmental applications are discussed in this paper, including the relative cost, and the availability and applicability regarding element coverage and content.

Development of reference materials for the analysis of acid-extractable metals in sludge.

The development of reference materials to verify the determination of metals in sludge is described. Effluents from domestic and industrial treatment facilities were dried, size-reduced and homogenized. Multiple aliquots of each material were analyzed in two different government laboratories to determine reference values for the acid-extractable concentrations of more than 15 metals. These acid-extractable concentrations are distinct from total metal values. Different sample preparation and instrumental methods, along with internal quality assurance protocols, were used to confirm the results. The data show good agreement for most metals in the domestic material. Reference values for the leachable concentrations of several toxic metals and major constituents will become part of the Certificate of Analysis for Standard Reference Material (SRM) 2781 issued by the National Institute of Standards and Technology (NIST). Data for the candidate industrial sludge reference material are also presented and discussed.

The determination of lead in total suspended air particulates by x-ray fluorescence spectroscopy.

A method has been developed for the measurement of lead in air particulates collected on glass fiber filter paper with wavelength-dispersive x-ray fluorescence spectroscopy (WDXRF). Analyses conducted by both WDXRF and an EPA-approved procedure that employs acid sonication followed by analysis of the extract by atomic-absorption spectroscopy (AAS) shows excellent agreement between the two methods. WDXRF calibration was accomplished with standards prepared from known additions of Pb to unexposed glass fiber filter discs. Method equivalency has also been demonstrated by the analysis of several reference materials and the statistical analysis of quality control data. The WDXRF procedure has also been used to evaluate the distribution of Pb in the particulates across the surface of the filter.

Electrothermal atomic-absorption spectrometric analysis of lake waters for Mn, Fe, Pb and Cd.

Analyses have been made for trace metals in surface waters from lakes known to be sensitive to inputs of acidic deposition. Electrothermal atomic-absorption spectrometry was used for direct measurement of the low metal concentrations. The studies revealed non-spectral interferences resulting from small amounts of inorganic material in the sample matrix that prevent accurate measurements of Mn and Pb. Several types of interferences were identified by means of a computer coupled to the atomic-absorption spectrometer and procedures to overcome them were evaluated. Matrix modification with nitric acid is required for the determination of Mn. Atomization from a platform inserted within the graphite tube is necessary for interference-free Pb determination.