Automated standard dilution analysis using a four-port switching valve for fast inductively coupled plasma optical emission spectrometry determination

Abstract

A switching valve accessory currently available in newer models of inductively coupled plasma optical emission spectrometry (ICP-OES) instruments is used to fully automate the standard dilution analysis calibration method (SDA). Al, Ba, Co, Cr, Cu, Fe, Mg, Mn, Ni, P, V and Zn are determined in several matrices, such as 0.5% m/v Ca, 0.6% m/v Na, apple cider vinegar, apple juice, cola soft drink, green tea, mouthwash, and vodka by ICP-OES. No sample preparation other than simple dilution in 1% v/v HNO₃ is required. Only two calibration solutions are used in SDA: S1, which is a mixture of 50% v/v sample and 50% v/v of a standard solution containing the analytes and an internal standard (IS₁); and S2, which contains 50% v/v sample and 50% v/v of a blank solution containing a second internal standard (IS₂). In the present study, a 0.25 mL sample loop is used with a four-port switching valve to autonomously perform S1 and S2 mixing for SDA determinations. The automated SDA method provides limits of detection in the 2–30 μg L⁻¹ range, and repeatability values corresponding to 0.4–3% RSD (n = 10) for all analytes. Accuracy was evaluated by analyzing a reference material (EPA Water Pollution Standard 1), and by addition and recovery experiments, which resulted in analyte percent recoveries in the 90.1–106% range for all analytes. SDA results were comparable to those obtained with the traditional external standard calibration (EC), internal standard (IS), and standard additions (SA), with the advantages of higher sample throughputs than SA and more accurate results than those obtained with EC and IS.