Analysis of Trace Metals in Sodium by Flameless Atomic Absorption Spectrophotometry
The determination of trace metals in sodium is usually carried out by distilling off the sodium in vacuum and analysing the residue by flame Atomic Absorption Spectrophotometry (1–3). The distillation is done to avoid aspirating a highly concentrated solution which would lead to problems such as clogging of the nebuliser and severe spectral interference. Moreover distillation also serves as a concentration step. A sample weight of 50 gms has been used for the analysis of nuclear grade sodium (2). In our laboratory we have followed the method of distillation and analysis by flame AAS for the commercial sodium samples. But there are certain situations where it is desirable to avoid the distillation step as in the case of the analysis of volatile impurities such as Zn, Cd and Pb which are lost partially or wholly during the distillation process. Moreover use of small sample size is desirable especially while analysing the primary sodium. With these objectives a direct method to analyse sodium by AAS using the graphite furnace atomiser has been developed in our laboratory. With the superior sensitivities (10-12 g) attainable with very small sample volumes (20 μl) we have found that it is possible to determine various impurities such as Cu, Cr, Co, Mn and Pb directly by placing as low as 2 mg of the sample in the graphite cuvette. By employing a suitable temperature programme it has been possible to remove the bulk of the matrix before atomisation, thereby minimising the matrix interference. This paper describes the direct method developed in our laboratory for the analysis of sodium and compares it with the distillation cum flame AAS method.
KeywordsTrace Metal Sodium Nitrate Lanthanum Chloride Flame Atomic Absorption Spectrophotometry Volatile Impurity
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