INVESTIGATION OF THE DISCRIMINATION BETWEEN ALUMINUM HELD WITHIN VEGETATION AND THAT CONTRIBUTED BY SOIL CONTAMINATION USING ICP-AES AND EPMA

The difficulties in the accurate determination of aluminium in plant m aterials have been known for a long time. A major problem is caused by aluminium contamination from soil/dust particles adhering to the vege tation. In this methodological approach, a combination of two analytic al techniques [electron probe micro analysis (EPMA) and inductively co upled plasma-atomic emission spectrometry (ICP-AES)] was employed to i nvestigate the aluminium held within vegetation and that contributed b y soil/dust contamination. Aluminium concentrations in NIST (formally NBS) Certified Reference Material tomato leaves (SRM 1573) and citrus leaves (SRM 1572) and NIES Certified Reference Material tea leaves (NI ES No.7) were determined by ICP-AES after acid digestion. The normal ' 'total'' acid attack (nitric and perchloric acids) gave a very low rec overy of aluminium in tomato leaves (41.9%) compared with the provisio nal value quoted by NIST. The aluminium concentrations measured for th e citrus leaves and tea leaves were much closer to the certified value s. The contribution of aluminium from Al-rich soil/dust particles in t hese reference materials was estimated semiquantitatively by computer- controlled EPMA. The aluminium held in these particles corresponded in approximate concentration to the shortfall between the acid soluble c omponent determined in this study and the certified value. Analysis by EPMA can provide, therefore, a method of estimating aluminium contrib uted by soil contamination to plant materials. The limitation of the S tandard Reference Materials for the validation of methods for the dete rmination of aluminium in vegetation are demonstrated. (C) 1996 Academ ic Press, Inc.