Division 2.4.7 Specific requirements for inductively coupled plasma atomic emission spectrometry (ICP-AES)

Inductively coupled plasma atomic emission spectrometry (10) is a multi-element method, which allows a simultaneous measurement of various elements. To use the ICP-AES, the samples first have to be digested to decompose organic matrices. Sealed systems with microwave digestion or high pressure ashing shall be used. For a meaningful ICP-AES analysis, the instrument calibration and element or wavelength selection play an essential role. For instrument calibration, in case of linear calibration curves, it is usually necessary to measure calibration solutions of only four concentrations, because ICP-AES calibration curves are generally linear over four to six orders of magnitude of concentration. Calibration of the ICP-AES system should normally be performed with a multi-element standard, which shall be prepared in a solution that contains the same acid concentration as the measurement solution. For the linear curve, the element concentrations shall be checked.

The selection of wavelengths for measurement of the emission from the analytes is appropriate for the concentrations of the elements to be determined. When the analyte concentration falls outside of the working range of an emission line, a different emission line shall be used. At first, the most sensitive emission line (not interfered) shall be chosen, then a less sensitive line. When working at or near the detection limit, the most sensitive line for the respective analyte is usually the best choice. Spectral and background interferences are causing the major difficulties in ICP-AES. Possible interferences are e.g. simple background shift, sloping background shift, direct spectral overlap and complex background shift. Each of these interferences has its own causes and remedies. Depending on the matrices, interference corrections and optimisation of operating parameters shall be applied. Some interferences can be avoided by dilution or by adaptation of the matrices. With each batch of test samples analysed, reference and fortified material containing known amounts of the analyte(s) as well as blank material shall be treated in the same way as the test samples. For testing for a drift, the standard shall be checked e.g. after 10 samples. All reagents and the plasma gas shall be of the highest available purity.