Towards a calibration-less ICP-AES method for the determination of trace elements in aqueous solutions: Double ratio plasma diagnostics combined with an internal standard

We propose a calibration-less approach to determine the concentration of the analytes in a solution in Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). This approach is a variant of the calibration-free algorithm developed for Laser-Induced Breakdown Spectroscopy analysis. The method assumes that the plasma is in local thermodynamic equilibrium (LTE) and requires that plasma temperature and electron number density are spectroscopically measured. Since the excitation and ionization conditions of the plasma are taken into account, matrix effects don't degrade the analytical performance of this method. In the variant presented here, the relative abundance of trace elements is determined and then the known concentration of an internal standard is used to convert the results in concentration values. A set of multi-element standard solutions was prepared and analyzed with both calibration curves and calibration-less with internal standard (CLIS) approach. The performance of CLIS was close to that of calibration curves. The main difference among the two approaches is that CLIS requires much less measurement time, but, at present, more processing time.