To assess the possible applications of the procedure, the effect of foreign ions which interfere with the determination of iron, copper, zinc and lead ions by the presented method or/and often accompany analyte ions in various real samples was examined with the optimized conditions
presented above. A fixed amount of analytes was taken with different amounts of foreign ions and the recommended procedure was followed. The recoveries of analytes were higher than 95%. Tolerable limit was defined as the highest amount of foreign ions that produced an error not exceeding 5% in the determination of investigated analyte ions by the combination of the SDS coated alumina solid phase extraction procedure and the flame atomic absorption spectrometric determination methods. The results are summarized in Table 2. As can be seen, large numbers
of ions used have no significant effect on the determination of analyte ions.