Multi-flow calibration applied to microwave-induced plasma optical emission spectrometry

Abstract

Multi-flow calibration (MFC) is based on a single calibration standard and multiple nebulization gas flow rates (Q). Analytical signals are recorded at different Q conditions, and intensities from calibration standards and samples are plotted on the x and y axes, respectively. The analyte concentration in the sample is calculated by multiplying the standard concentration by the calibration plot slope. In the present work, MFC is used to determine Cr, Cu, Fe and Mn in water and food samples by microwave-induced plasma optical emission spectrometry. Analyte percent recoveries for certified reference materials and addition/recovery experiments were in the 91–112% and 84–134% ranges for MFC and external standard calibration (EC), respectively. The limits of detection (LODs) for Cr, Cu, Fe and Mn were 20, 5, 7 and 2 μg L⁻¹ using MFC (0.6, 8, 20 and 1 μg L⁻¹ for EC). Precisions were in the 0.9–12.2% and 1.9–23.9% ranges for MFC and EC, respectively. MFC may minimize matrix effects as it exposes all solutions to a variety of plasma conditions. This normalizing effect may be capable of improving accuracies compared with EC for simple to moderately complex matrix samples. One of MFC's main limitations is the potential for systematic errors associated with solution preparation (a single calibration standard is used). Variation in Q may also result in higher LODs and lower sample throughputs compared with EC. On the other hand, neither negative effects due to a poor choice of Q nor additional experiments to optimize it are required with MFC.