engleski

Urinary Oxalate Determination by Flow Injection Analysis Using Bienzymatic Biosensor in Biamperometric Measurement Mode

Calcium oxalate is the main component of urinary tract stones. Basically, oxalate is a product of protein metabolism and becomes toxic at high concentration due to production of insoluble complex salts with divalent cations (mainly calcium). Determination of oxalates in urine is important for diagnosis of many diseases and mostly indicates the presence of kidney stones. A biosensor for determination of oxalate concentration in urine has been developed by immobilisation of oxalate oxidase and peroxidase on the surface of an interdigitated gold electrode. Enzyme immobilisation was performed using BSA and glutaraldehyde. Oxalate oxidase enzyme immobilised on the surface of an interdigitated electrode converts oxalate to carbon dioxide and hydrogen peroxide according to equation 1. (1) Coimmobilised peroxidase catalyses the reaction between hexacyanoferrate(II) and hydrogen peroxide as indicated by equation 2. Hexacyanoferate(II) was a component of the buffer carrier solution. (2) The produced hexacyanoferate(III) is then reduced at the interdigitated electrode as denoted by equation 3. (3) Biamperometric current is proportional to hexacyanoferrate(III) concentration and thus also to oxalate concentration. Biamperometric measurements were made in flow conditions both in aqueous oxalate solutions (tested concentration range between 25 mM to 10 mM) and in urine samples (tested measuring range between 1 to 100 mM). Optimal working conditions were examined for flow- injection analysis, and good correlation was achieved between added oxalate quantity and the one measured by biosensor in urine matrix ( ). The influence of some interferences (ascorbic acid, uric acid, paracetamol, acetylsalicylic acid) was also studied.

biamperometric; bienzymatic; urine; oxalate; interdigitated electrode

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