Multi-wavelength internal standardization using inductively coupled plasma optical emission spectrometry

Recent developments in trace analyte determinations can largely be described as "multi-signal" methods, in which both axes of calibration curves are measured instrumental signals instead of the traditional relationship between analyte signal and concentration. While multi-signal methods have various benefits, many are limited in sample throughput, have a limited ability to correct for matrix effects, or require each analyte species to have several significant measurable signals. Multi-wavelength internal standardization (MWIS) is a novel strategy that directly addresses the limitations of some of the recently described multi-signal techniques, using multiple emission wavelengths for both analyte species and a suite of internal standards.

Proof-of-concept for MWIS was obtained using inductively coupled plasma optical emission spectrometry (ICP-OES). Spike recovery experiments using complex matrices difficult for ICP-OES provided analyte recoveries of approximately 100 % with relative standard deviations on the order of 1 %. The proposed MWIS method was compared to (and outperformed) traditional calibration strategies, as well as the multi-signal methods it was developed to address. MWIS was validated through the analysis of certified reference materials, with recoveries for all analytes ranging from 90 to 118 %.

MWIS offers direct improvement over some of the more recently described multi-signal calibration techniques, resulting in an extraordinarily high number of calibration points even though only two solutions are prepared. Monitoring multiple internal standard signals allows the strategy to be applied to important analytes that have few suitable emission wavelengths such as As and Pb. In addition, spectral interferences are easily identified and are simple to exclude from the calculation.