A micro-scale mercury cathode electrolysis procedure for on-line flow injection inductively coupled plasma mass spectrometry trace elements analysis in steel samples

Abstract

An on-line matrix-analyte separation technique was developed for flow injection inductively coupled plasma mass spectrometry (FI–ICP-MS) trace analysis. A micro electrolytic cell was designed to be inserted in the FI manifold. The technique was used to separate Zr, Hf, Y, rare earth elements (REEs), Th and U from a steel-matrix (Fe, Cr, Ni, Co, Mn and Mo). A microwave-assisted HNO3–HCl–HF–H2SO4 digestion procedure, with temperature/pressure regulation, was used for sample dissolution. Obtained solutions were evaporated to SO3 fumes, and 2 ml of this diluted sulphuric solution were introduced in the electrolytic cell through the manifold circuit. After matrix removal, the electrolyte was conducted to load a 300 μl sample loop to be injected into the plasma torch. Direct multielement standard solutions in diluted sulphuric acid (without matrix matching and sample pretreatment) were applied for external calibration. The determination limits, with reference to the solid, were improved by a factor of about 10 compared with that obtained from direct measurements of 0.1% (m/v) sample solutions. The relative standard deviations for all the analytes were better than 3.5% for concentrations above 10 times the limit of quantification. The developed method was applied in the determination of certified elements in Steel Reference Materials: NIST 363 and NIST 364. Recoveries from 0.200 g test portions of high-purity iron spiked at two different concentration levels were found better than 97%.