Internal standard method coupled with a gravimetric standard addition method for elemental measurements by ICP-MS

An internal standard method coupled with a gravimetric standard addition method (ISM-SAM) with a single spiked sample was proposed as a strategy for elemental measurements. Equations are given for measurement of the element based on its ratios to the internal-standard in the spiked sample and to the non-spiked sample. Optimization of the relative quantity of the standard solution was carried out to improve the precision of the measurement, the results obtained showed that a high-precision measurement could be obtained when the concentration of the measurand in the spiked sample was over 2-fold of that in the non-spiked sample. Measurement of Cu in a test solution was performed in parallel to the measurement by inductively coupled plasma mass spectrometry (ICP-MS) and isotope dilution (ID-) ICP-MS, and the results indicate that the present method has similar reliability to those of ID-ICP-MS and ICP-MS. Furthermore, the ISM-SAM method was applied to the analysis of P in two certified reference materials (CRMs) issued by the National Metrology Institute of Japan (NMIJ) with different mono-isotopic elements (Be, Al, Sc, As, Y, Rh, and Cs) as the internal standard elements. All of the results agreed with the certified values of the CRMs. The results neither depended on the atomic number nor depended on the ionization rate of the internal standard element. The present method was also applied to the analysis of other elements in CRMs of tea leaf powder, seaweeds, and swordfish tissue, providing accurate results.