A Simple, Low-Cost, and Useful Preconcentration Method for Quantification of Soluble, Insoluble, and Total Oxalate in Se
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A Simple, Low-Cost, and Useful Preconcentration Method for Quantification of Soluble, Insoluble, and Total Oxalate in Selected Vegetables Through Spectrophotometry Nail Altunay 1 & Ramazan Gürkan 1
Received: 4 May 2015 / Accepted: 14 July 2015 # Springer Science+Business Media New York 2015
Abstract 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 μg L−1. The detection limit of the method (LOD (3σblank/m) was 0.36 μg 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 μg 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 Highlights • The method is simple, low cost, sensitive, and eco-friendly. • The accuracy was validated by comparing the results to those of the independent kinetic method. • TBH2+ was successfully used in the preconcentration of oxalate in the presence of Mo(VI) at pH 6.0. • The low-cost method with good accuracy can be an alternative to other techniques in the literature. • An accurate and reliable determination of soluble, insoluble, and total oxalate in vegetables has been successfully developed in this study. * Nail Altunay [email protected] 1
Department of Chemistry, Faculty of Science, University of Cumhuriyet, TR-58140 Sivas, Turkey
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 °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. Keywords Oxalate . Toluidine blue . Mo(VI) . Cloud point extraction . Vegetable samples . Spectrophotometry
Introduction The main sources of dietary oxalate are plants and herbal products (Hönow and Hesse 2002). Oxalate is widely distributed in plant foods in a readily water-soluble form as potassium, sodium, and ammonium oxalates and as insoluble calcium oxalates (Holloway et al. 1989). Oxalate forms strong chelates with dietary calcium, thus rendering the complex unavailable for absorption and assimilation. It precipitates as insoluble salts accumulating in the renal g
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