Matrix-matched two-point calibration based on the standard dilution analysis method

Abstract

A two-point calibration, based on the standard dilution analysis (SDA) method, is used to achieve accurate results while analyzing complex-matrix samples by different atomic spectrometry methods. Only two calibration solutions are required per sample. Solution 1 (S1) is 50% sample and 50% of a standard containing the analytes and an internal standard (IS), and Solution 2 (S2) is 50% sample and 50% blank. The concentration of analyte in the sample is calculated from (i) the slope and intercept of an analyte vs. IS plot, (ii) the concentration of analyte in the standard added to S1, and (iii) the signal intensity of the IS present in S1. Unlike recently published work on SDA, the method presented here requires no mixing of S1 and S2, no second IS species, and no instrumental modifications or extra equipment. In this proof-of-concept study, the new approach has been used to determine Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn in different matrices: 1% v/v HNO3, 20% v/v HNO3, 0.1% m/v Na, and 0.1% m/v Ca. The analytes were accurately determined by microwave-induced plasma optical emission spectrometry (MIP OES), inductively coupled plasma OES (ICP OES), and ICP mass spectrometry (ICP-MS) using the new method. The results were compared to those from external standard calibration (EC), internal standardization (IS), and standard additions (SA). Similar and often superior recoveries compared with EC, IS and SA were achieved with the matrix-matched two-point calibration method.