A Simple, Low-Cost, and Useful Preconcentration Method for Quantification of Soluble, Insoluble, and Total Oxalate in Selected Vegetables Through Spectrophotometry

The amount of dietary oxalate from food may be an important risk factor in the development of idiopathic calcium oxalate nephrolithiasis. The main aim of this research was to develop an accurate and reliable method by cloud point extraction (CPE) combined with spectrophotometry to measure the oxalate contents of selected vegetables. The method is based on ion association of stable anionic complex, which is produced by the reaction of oxalate with Mo(VI), with Toluidine blue (TBH2+), and then by extraction into micelles of octylphenol ethoxylate (Triton X-45) in the presence of NH4F as a salting-out agent at pH 6.0. Using the optimized conditions, the calibration graph was highly linear in the range of 1.2-240 mu g L-1. The detection limit of the method (LOD (3 sigma (blank)/m) was 0.36 mu g L-1, and the relative standard deviation (RSD %) as a measure of precision was in the range of 1.1-5.3 % (n = 5 for 5, 25, and 50 mu g L-1). The method was successfully applied to the speciative determination of soluble and total oxalate in vegetables after ultrasonic-assisted extraction and dilution at suitable ratios. The amount of insoluble oxalate was calculated from the analytical difference between total oxalate and soluble oxalate contents of samples with and without acidic extraction under ultrasonic power (300 W, 50 Hz) for 15 min at 60 A degrees C. The accuracy of the method was intrinsically controlled and verified by comparing the results obtained with those of an independent kinetic method as well as recoveries of spiked samples.