A thorough understanding of the analytical benefits and characteristics of the implementation of exact matching with HP-ICP-OES will enable HP-ICP-OES to be applied more effectively to a variety of NIST measurements. Such measurements include, but are not limited to, value assignment measurements for NIST Standard Reference Materials (SRMs). The accuracies and uncertainties attainable with HP-ICP-OES will be improved, benefitting NIST and many NIST customers. The findings of these studies will also enable users of HP-ICP-OES outside NIST to perform better analyses.
HP-ICP-OES was developed at NIST approximately a decade ago as a means of performing high-accuracy, low-uncertainty chemical analyses. HP-ICP-OES incorporates a robust experimental design, a unique drift correction procedure, a judiciously chosen internal standard, and gravimetric sample handling. It has become one of the main methodologies used at NIST for value assignment of SRMs that are certified for elemental content, including the SRM 3100 series single-element standard solutions. When HP-ICP-OES was first developed, it was assumed that the plasma would be sufficiently immune to matrix effects and small variations in analyte and internal standard element mass fractions to obviate any need for exact matching of standards to samples. Careful but less than exact matching was thought to be adequate. However, experience has shown that this is not necessarily the case. For many analytes, HP-ICP-OES precision and accuracy can be improved through exact matching.