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The inductively coupled plasma (ICP) technique is a useful approach for multielement analysis of a wide variety of materials. Published reports have described the successful application of the ICP technique for the analysis of trace, minor, and major elements in metal alloys. When assessing the quality of analytical results using the ICP or any other technique, one must consider the contribution of various parts of the measurement process to the total error. In addition to random error, a careful evaluation of all possible sources of systematic errors must be undertaken, so that the appropriate corrections can be applied to the analytical results. Emission spectroscopists are well aware of the problems caused by spectral interferences in ferrous matrices. The inherent linearity of the ICP technique offers a correction scheme for dealing with spectral interferences, but the method of measuring correction factors and accounting for their variability warrants close examination.
Most descriptions of ICP applications report relative freedom from matrix effects. Although the magnitude of systematic errors may be less than for other spectrometric techniques, such errors can cause analytical bias, which can appreciably affect the final results. For example, it has been shown that differences in acid concentration between pure element standards and the sample can cause systematic error. This type of problem can occur when complex alloys are dissolved for ICP analysis. Examples of these kinds of errors and approaches to correcting for them are presented.
inductively coupled plasma, spectral interference, matrix effects, precision, accuracy, analysis of variance
Research chemist, Center for Analytical Chemistry, National Bureau of Standards, Gaithersburg, MD