Matrix effects in inductively coupled plasma atomic emission spectrometry using an ultrasonic nebulizer

Abstract

Matrix interferences due to the presence of nitric acid plus calcium, potassium and complex matrices containing potassium, sodium, calcium and phosphorus in inductively coupled plasma atomic emission spectrometry (ICP-AES) were studied using ultrasonic nebulisation (USN). Matrix element concentrations were in the 0–1.0 mg ml^–1 range. In order to distinguish between transport and plasma effects the analyte transport rates, excitation temperatures (T_exc), electron number densities (n_e) and Mg ionic to atomic line intensity ratios were measured in the presence and absence of matrix elements. Generally, suppression of the analyte emission in the presence of nitric acid and interfering elements was observed. At the highest matrix concentration (1.0 mg ml^–1) the average reductions in the emission intensity for calcium, composite and potassium matrices were 32, 23 and 15%, respectively. It has been shown that the presence of nitric acid and matrix elements reduces the analyte transport and the presence of matrix elements resulted in either an increase or a decrease in T_exc and n_e . The presence of potassium enhanced T_exc and n_e , whereas composite matrices and calcium produced the opposite effect. At higher matrix element concentrations the magnitude of the relative changes in the analyte emission intensity was correlated with the sum of the excitation and ionisation energies.