Trace aluminium determination in biological samples after microwave digestion followed by solid phase extraction with l-methionine on controlled pore glass

Abstract

Aluminium is an element found in biological samples at low concentrations and aluminum-related neuropathological diseases in human beings have been reported. For this reason the determination of Al in this type of samples requires the development of enrichment methods capable of improving the instrumental detection for this analyte. l-methionine immobilized on controlled pore glass (CPG) was tested for the retention of aluminium. This adsorbent material was packed in a conical minicolumn and connected to an on-line flow injection system. An inductively coupled plasma optical emission spectrometer associated to an ultrasonic nebulization system (USN-ICP OES) was used for aluminium detection. Al(III) was retained at pH 12.5 and removed from the column with 20% (v/v) HNO3. The precision of the preconcentration method was evaluated by passing a measured volume of aluminium standard solution (1 μg L- 1) through the minicolumn and repeating this procedure five times. The relative standard deviation (RSD) was 2.5%, calculated with the peak heights obtained. A total enhancement factor of 1600 was attained for a sample volume of 10 mL (10-fold for the ultrasonic nebulization system and 160-fold for the preconcentration methodology). The detection limit (DL), calculated as the amount of Al required to yield a net peak equal to three times the standard deviation of the blank solution, was 25 ng L- 1. The proposed system was successfully applied to the determination of aluminium in urine, hair, and saliva samples, which were pretreated using a microwave digestion methodology with the introduction of a digestion program for saliva. The average aluminium levels found in urine, hair, and saliva samples were 5.5 μg L- 1, 19 μg g- 1 and 93 μg L- 1 respectively.