Automated matrix-matching calibration using standard dilution analysis with two internal standards and a simple...

Simple data processing and unattended calibration are achieved in automated standard dilution analysis (aSDA) using two internal standards and an inline lab-made mixing chamber furnished from a common plastic syringe. Only two calibration solutions are required per sample, which minimizes reagent consumption and waste generation. Solution 1 contains 50% sample and 50% of a standard containing the analytes and internal standard 1 (IS₁). Solution 2 has 50% sample and 50% of a blank containing internal standard 2 (IS₂). The concentration of analyte in the sample is calculated from (i) the slope and intercept of an analyte vs. IS₁ plot, (ii) the concentration of analyte in the standard added to Solution 1, and (iii) the intercept of a second plot with IS₁vs. IS₂. The aSDA method was used to determine Cd, Co, Cr, Cu, Pb and Zn in tap and creek water, beer, cola soft drink, mouthwash, cough syrup and cachaça by ICP OES. Addition/recovery experiments involving these same samples and other challenging matrices (i.e. 40% v/v HNO₃, and 1% m/v Na, Ca or C) were performed to evaluate the method's accuracy. The results were compared with values obtained with external standard calibration (EC), internal standardization (IS) and standard additions (SA). Considering all samples and analytes evaluated, aSDA provided the best accuracy, with an average absolute error (ε‾=|analytepercentrecovery-100|) of 4% (EC, IS and SA had 13%, 9% and 7% errors, respectively). The aSDA strategy is a simple and inexpensive alternative to traditional methods. It has great potential for broad implementation with existing ICP OES instrumentation, as it requires little modification to systems already in place in routine laboratories.