The difficulties in the accurate determination of aluminium in plant materials have been known for a long time. A major problem is caused by aluminium contamination from soil/dust particles adhering to the vegetation. In this methodological approach, a combination of two analytical techniques [electron probe micro analysis (EPMA) and inductively coupled plasma-atomic emission spectrometry (ICP-AES)] was employed to investigate the aluminium held within vegetation and that contributed by 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 (NIES No.7) were determined by ICP-AES after acid digestion. The normal ''total'' acid attack (nitric and perchloric acids) gave a very low recovery of aluminium in tomato leaves (41.9%) compared with the provisional value quoted by NIST. The aluminium concentrations measured for the citrus leaves and tea leaves were much closer to the certified values. The contribution of aluminium from Al-rich soil/dust particles in these 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 component determined in this study and the certified value. Analysis by EPMA can provide, therefore, a method of estimating aluminium contributed by soil contamination to plant materials. The limitation of the Standard Reference Materials for the validation of methods for the determination of aluminium in vegetation are demonstrated. (C) 1996 Academic Press, Inc.
