Abstract
An amperometric flow biosensor for oxalate determination in urine samples after enzymatic reaction with oxalate oxidase immobilized on a modified magnetic solid is described. The solid was magnetically retained on the electrode surface of an electrode modified with Fe (III)-tris-(2-thiopyridone) borate placed into a sequential injection system preceding the amperometric detector. The variables involved in the system such as flow rate, aspired volumes (modified magnetic suspension and sample) and reaction coil length were evaluated using a Taguchi parameter design. Under optimal conditions, the calibration curve of oxalate was linear between 3.0–50.0 mg·L−1, with a limit of detection of 1.0 mg·L−1. The repeatability for a 30.0 mg·L−1 oxalate solution was 0.7%. The method was validated by comparing the obtained results to those provided by the spectrophotometric method; no significant differences were observed.
Highlights
Measurement of oxalate in urine is of clinical interest, as an increase in oxalate excretion through urine indicates hyperoxaluria, renal failure, kidney lesions and pancreatic insufficiency [1].Different analytical techniques have been applied for quantification of oxalate in urine such as enzymatic spectrophotometric, liquid and gas chromatography, capillary electrophoresis and ion chromatography [2,3,4,5,6,7]
Biosensors using direct determination of enzymatically produced hydrogen peroxide have been avoided in clinical samples because they require high potentials during detection (>1.0 V) causing interference produced by ascorbic acid, uric acid and other components of the sample
We propose a sequential injection biosensor with amperometric detection for oxalate determination in urine based on an electrode modified with Fe (III)-tris(2-thiopyridone)borate complex as mediator coupled with injection of magnetic solid modified with oxalate oxidase (OxOx), as recognition element, transiently retained on the electrode surface subjected to an external magnetic field
Summary
Measurement of oxalate in urine is of clinical interest, as an increase in oxalate excretion through urine indicates hyperoxaluria, renal failure, kidney lesions and pancreatic insufficiency [1]. Biosensors using direct determination of enzymatically produced hydrogen peroxide have been avoided in clinical samples because they require high potentials during detection (>1.0 V) causing interference produced by ascorbic acid, uric acid and other components of the sample This disadvantage has been overcome by using electron-mediated enzyme electrodes. OxOx), using an internal chamber with enzyme in solution, has been applied to solve the regeneration problem, but the enzyme consumption is higher than using it immobilized [13,14] This concept might be exploited mainly using sequential injection analysis (SIA) [15]. We propose a sequential injection biosensor with amperometric detection for oxalate determination in urine based on an electrode modified with Fe (III)-tris(2-thiopyridone)borate complex as mediator coupled with injection of magnetic solid modified with OxOx, as recognition element, transiently retained on the electrode surface subjected to an external magnetic field. System was tested in human urine samples and showed to be adequate concerning robustness, sampling rate and quality of analytical results
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