Use of enzymatic hydrolysis for the multi-element determination in mussel soft tissue by inductively coupled plasma-atomic emission spectrometry

A systematic evaluation of different variables affecting the enzymatic hydrolysis of mussel soft tissue by five enzymes, three proteases (pepsin, pancreatin and trypsin), lipase and amylase, has been carried out for the determination of trace elements (As, Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) by inductively coupled plasma-atomic emission spectrometry (ICP-AES). Enzymatic hydrolysis methods offers advantages such as a less species alteration, safer laboratory conditions and a less contaminant wastes. The enzymatic hydrolysis was performed in an incubation camera Boxcult with orbital and horizontal shaker. Variables affecting the enzymatic hydrolysis process were simultaneously studied by applying a Plackett-Burman design (PBD). For a confidence interval of 95%, the significant factors for all enzymes and for most of the elements were the pH, the incubation temperature and the ionic strength. These significant factors were optimized later by using a central composite design (CCD), which gave optimum conditions at pH of 1, incubation temperature of 37 °C and ionic strength fixed by sodium chloride at 0.2 M when using pepsin. For pancreatin, trypsin, lipase and amylase there were found two different optimum condition sets. The first one involves the use of a 0.5 M phosphate buffer (ionic strength), at a pH of 6 and at an incubation temperature of 37 °C, which allows the quantitative extraction of Al, Cr, Mn, Pb and Zn. The second conditions set employees a 0.1 M phosphate buffer (ionic strength), a pH of 9 and an incubation temperature at 37 °C, and it results adequate to extract As, Cd, Cu, Fe and Ni. Analytical performances, repeatability of the over-all procedure and accuracy, by analyzing DORM-1, DORM-2 and TORT-1 certified reference materials, were finally assessed for each enzyme. Good agreement with certified values has been assessed for most of the elements (As, Cd, Cr, Cu, Mn, Ni, Pb and Zn) when using trypsin, pepsin and/or pancreatin, except for Cd and Pb in DORM-1 and DORM-2 because of the certified contents in such certified reference materials are lower than the limit of detection (0.10 and 0.16 μg g⁻¹ for Cd and Pb, respectively, for the use of trypsin).