Preparation of the Sample:

The selection of proper reagents and techniques of decomposition and dissolution of the sample is a critical step for the success of AAS determination. This is frequent complete through acid digestion that produces a clear solution without loss of any of the elements to be determined. It is thus, necessary that all the reagents and solvents used within wet decomposition should be of highest purity as any impurity might raise the blank value. Common acids used for dissolution are HCl, HNO₃, aqua regia (HCl : HNO3  :: 3:1) or perchloric acid (HClO₄) that dissolve most of the inorganic materials. For the decomposition of silicate materials, thus, HF must be used. A combination of nitric acid and perchloric acid is especially meaningful for the fully destruction of fats and proteins within biological samples.

In a classical dissolution step, a suspension of the sample within acid is heated through flame or a hot plate until fully dissolution i.e., while whole solid has disappeared and a transparent solution is obtained. A decomposition temperature is the boiling point of acid. Therefore, such a wet decomposition in open vessels might give rise to systematic errors because of volatilisation losses and contamination caused through the reagents and container material, and loss of elements caused through adsorption on the vessel surface. More so, sometimes the dissolution might not be fully and it may also cause errors. In order to prevent such errors, wet decomposition methods within closed systems have been developed.