Aluminium determination in foods by using spectrophotometric oxine and flame AAS methods

Results of aluminium determinations obtained by employment of N2O-C2H2 flame AAS method and spectrophotometric oxine (SO) method in teas, fresh leaves of celery and some other food samples were compared. The samples were digested for few hours in teflon beakers with use of a mixture of concentrated acids (H2SO4 + HNO3 + HCIO4), and then transported for final destruction into platinum dishes for ashing. The obtained stock sample solutions were used for examination by both methods. The accuracy was checked with recovery test of aluminium added to the samples before decomposition. With employment of AAS-method 83.3% to 100% (mean 94.2 +/- 8.1%) of added aluminium was recovered, and in the SO method from 86.4 to 109.3% (mean 98.6 +/- 5.2%). Great care is necessary for preparation of the blank. Food products containing higher levels of aluminium (i.e. teas and herbs) can be determined directly by the employed AAS-method using 1-2 g of samples for decomposition, while foods containing low levels of aluminium need use of larger samples for decomposition (i.e. 5-10 g or even more than 50 g in the case of strawberry or fresh leaves of celery) and the obtained ash should be dissolved to as low as possible of final volume of stock sample solution. The SO method is about 7 to 10 times more sensitive than the nitrous-oxide flame AAS method and enable to determined about 2.5 micrograms of Al per sample in form of oxine complex extracted into a 5 ml chloroformic phase. In the case of AAS-method the lowest determined level of aluminium amounted about 6 micrograms/ml of the examined sample solution. The results of both methods are strong correlated, as it is showed by the correlation coefficient (r = 0.97) at the level of significance alpha = 0.05.