Sample preparation:
The solution preparation for the analysis using ICP-AES depends on the nature of the sample and the concentration of elements to be determined. There are two main types of sample preparation methods used for ICP analysis. These are explained below.
i) Acid digestion method
You have learnt about the acid digestion method of sample preparation. In the acid digestion method, the acids use their oxidising or reducing properties for the dissolution of the analyte. You would recall that acid digestion generally produces a clear solution of the analyte without loss of any of the elements to be determined. Thus, one must take care of the possible loss of volatile elements. For example, in the acid digestion using HCl, there is a possibility of the loss of As, Se, Sn as their volatile chlorides. Same, in case of sulphuric acid, the formation of precipitates of Ca, Ba, Pb is additional a potential source of error.
Another aspect that needs attention of the analyst is that the quantity of acid or flux in the solution must be as low as possible so that there is minimum perturbation of the plasma. Some of the acids perturb the plasma more than the others. Accordingly, there is an order of preference of the acid to be used for sample preparation. The decreasing order of there preference is as follows.
HNO3 > HCl > HClO4 > H2SO4 > H3PO4
ii) Dry attack method
In dry attack method, the sample preparation involves an alkaline fusion as well as high temperature calcination (450 - 600 °C) followed by acid recovery of ashes. However in this method the losses due to volatilisation and insolubilisation are not negligible. More so there is a possibility of contamination of the solution due to the reagents.