Imobilização enzimática e eletrodos modificados para determinação amperométrica em fluxo de glicose, ácido ascórbico e ácido úrico

Abstract

The work aimed to develop of analytical procedures based on flow-injection analysis (FIA) system enzymatic reactions and in the specific of different enzymes, in determination of (glucose, ascorbic acid and uric acid) in different samples using amperometric detection with modified electrodes. In the first research of the work consisted of determining the levels of glucose in samples of honey, coconut water and forage. The glucose was determined using a FIA and tubular reactor with glucose oxidase (Gox) enzyme immobilized on Amberlite IRA-743 resin. A gold electrode modified with platinum or with palladium / platinum, an Ag/AgCl(sat) electrode and a stainless steel tube were employed as working, reference and auxiliary electrodes, respectively. The indirect method was based on the detection potential of + 0.60 V of the hydrogen peroxide (H2O2) generated in the oxidation of glucose by the enzyme. The method showed wide linear dynamic range (52-200 μmol L-1), quantification and detection limits of 25.9 μmol L-1 and 8.54 μmol L-1, respectively. The concentrations found in the analyzed samples were in the range of 27.7-32.8% (m/m), 19.1-35.7 g L-1 and 101-191 mg g-1 of glucose for honey, coconut water and forage, respectively. In another study was development a method, to determine the levels of ascorbic acid (AA) in samples of honey and juice using a tubular reactor with the enzyme ascorbate oxidase immobilized on Amberlite IRA-743 resin, instrumentation used was similar to the above, but replacing the working electrode modified by gold palladium (potential of +0.6 V).. The method showed wide linear dynamic range (10-250 μmol L-1), quantification and detection limits of 0.047 μmol L-1 and 0.014 μmol L-1, respectively. The concentrations found in the analyzed samples were in the range of 1.5-6.2 mg (100 g)-1 and 0.06-0.15 g L-1 of ascorbic acid for honey and juice, respectively. We also studied the possible of work with the enzyme ascorbate oxidase obtained of the cucumber, being the results were comparable with the obtained for the commercial enzyme. The latest study evaluated the levels of uric acid (UA) in samples of urine using the enzyme uricase and gold electrode modified by palladium and cellulose acetate. The direct method was based on the detection of H2O2 in potential of +0.60 V, generated in the oxidation of uric acid by the enzyme uricase. The method showed wide linear dynamic range (5-50 μmol L-1), quantification and detection limits of 3.32 μmol L-1 and 1.05 μmol L-1, respectively. The concentrations found in the analyzed samples were in the range of 287- 477 mg L-1. In all studies the results were compared with those obtained by standard methods, showing a good degree of correlation.