Paper-based device for urinary oxalate detection

Abstract

In this work, a simple method for urinary oxalate determination was developed using testing paper modified with reddish-brown Fe(III)-curcumin complex. Oxalate in sample interacted with Fe(III) ions on the surface of the testing paper to form a Fe(III)-oxalate complex in solution, resulting in a decrease of the amount of Fe(III)-curcumin complex on the paper surface. The amount of the remaining Fe(III)-curcumin complex on the testing paper was inversely proportional to the oxalate level in the sample solution. A change of the testing paper color from reddish-brown to yellow could be observed and the color intensity was determined by ImageJ program. The effect of various parameters was investigated. The suitable condition for the testing paper preparation was by using 7.5 mM of curcumin and 0.25 mM of Fe(III) in 0.01 M of hydrochloric acid. The detection of oxalate was achieved at pH 2 with the sample volume of 3 mL and 10 minutes detection time. The sample detection by the testing paper should be repeated 3 times. The proposed method provided a linear range from 0 to 100.0 µM with a limit of detection of 0.8 µM. The effect of the urine sample matrix was also examined and the standard addition method was applied to detect oxalate in urine samples. The percentage of recovery and the standard deviation of the results observed were 95-109% and 3.2-7.6%, respectively. This method could be applied to screen the oxalate level in human urine sample with acceptable accuracy and precision.