Colorimetric bismuth determination in pharmaceuticals using a xylenol orange sol–gel sensor coupled to a multicommutated flow system

Abstract

A new sol–gel Bi(III) sensor was developed by incorporating xylenol orange (XO) into sol–gel thin films (<1 μm thick) coated on glass slides. Several sols were produced in order to evaluate the effect of different processing parameters on the final characteristics of the sensor. Sensor films based on tetramethoxysilane (TMOS) as precursor, nitric acid catalysis, water:alkoxide ratio of 2 and XO concentration of 1.5 g l −1 were found to be the most suitable to be used as Bi(III) sensors. They presented good sensitivity, reversibility and stability, low leaching and fast response time in the proposed working conditions. These sensors were coupled to a multicommutated flow system for the determination of Bi(III) in pharmaceutical products. The absorbance of the Bi(III)-immobilized XO complex formed was monitored at 515 nm. The regeneration of the sensor was accomplished by flowing a Cl − ion solution through the flow cell containing the sensor membranes. The procedure enables a relative standard deviation of results better than 0.8%, an analytical concentration range between 125.0 and 875.0 μg l −1, a detection limit of 7.0 μg l −1 and a sampling frequency of 45 samples per hour. The results obtained on real samples analysis were compared with those obtained by EDTA titrimetric method (British Pharmacopoeia), with relative deviation errors inferior to 5%.