Enzymatic proteolysis and in situ digestion as strategies to determine Cs and Sr in fish by tungsten coil atomic emission spectrometry

Abstract

Papain is employed to pre-digest and homogenize fish slurries which are directly placed on a tungsten coil atomizer and digested in situ with an oxidizing mixture of HNO₃ and H₂O₂. Both Cs and Sr are determined in different fish samples by tungsten coil atomic emission spectrometry (WCAES) with limits of detection of 0.07 and 0.15 μg l⁻¹, respectively. Sample aliquots of 50 μl are dried, digested/pyrolyzed and atomized using a 400 W miniature solid-state constant current power supply and a Visual Basic temperature control program. The portable WCAES instrumental setup is composed of a small metallic atomization cell, a 2.54 cm diameter fused silica lens and a hand-held charge coupled device-based spectrometer. Tungsten filaments extracted from 24 V, 250 W commercially available light bulbs are used as atomizers. The method accuracy is demonstrated by comparing WCAES results with values obtained by ICP OES. No statistically significant differences are observed between the results from each different method at a 95% confidence level. Recovery tests are also carried out for Cs and values between 100 and 110% are obtained. The method precision is calculated to be 6.8 and 7.3% for 2.5 μg l⁻¹ of Cs and 100 μg l⁻¹ of Sr (n = 10), respectively. The method described is simple, fast and efficient, offering an interesting alternative for applications in food safety control and determinations in the field.