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

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 (TBH 2+ ), and then by extraction into micelles of octylphenol ethoxylate (Triton X-45) in the presence of NH 4 F 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 (3σ blank /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 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.

A New Ultrasonic Assisted Cloud Point Extraction and Preconcentration Procedure for the Spectrophotometric Oxalate Determination in Beverages

“…As will clearly understood from results, the application of the method permits to interference-free determination of oxalate in the selected samples. Finally, when compared with analytical features of our previous study [25], it is clear that the present study shows lower detection limit, good precision and higher preconcentration factor with a reasonable sensitivity enhancement in linearity range of 425-fold. The Analytical Applications The accuracy of the method was verified in two ways: firstly through the spiked recoveries and secondly by analysis of similarly pretreated, extracted and diluted beverage samples with the reference method.…”

“…The details related to modification are given in our first study [25], in which the oxalate fractions of vegetable samples are monitored and determined with a similar analytical approach. In this context, the samples, which similarly were pretreated and extracted, were submitted to a fixed time of 3 min and an induction period of 12 min in ultrasonic bath (300 watt, 40 kHz) at 35 o C under the optimal reagent conditions, and then their oxalate levels were kinetically determined by spectrophotometry at 525 nm.…”

“…The UA-CPE was successfully coupled to spectrophotometry greatly to improve its detection limit and the selectivity. The UA-CPE was successfully applied to preconcentration of organic and inorganic species like 5-hydroxymethylfurfural (5-HMF) in different honey and acidic beverage samples [22], sulfite as food additive [23], total iodine in milk based products [24] and also oxalate with a reasonable sensitivity difference in vegetable matrices [25] by our research group.…”

Immobilization of Tris(1,10‐phenanthroline)ruthenium on Acetylene Carbon Black for Regenerable Electrochemiluminescence Sensors Free from Ionic Exchanger

“…The study shows that acetylene carbon blackbased regenerable ECL sensor holds great promise in detecting other co-reactants and biosensing. Chemically modified carbon paste electrode 1.5 × 10 À 6 -3.9 × 10 À 2 M 7.0 × 10 À 7 M > 2 months [23] Spectrophotometry with preconcentration 0.01-2.7 μM 4 × 10 À 3 μM ND [24] Carbon ionic liquid electrode modified with TiO 2 À Fe nanoparticles 5.0 × 10 À 5 -3.0 × 10 À 3 M 2.3 × 10 À 5 M > 40 days [25] Tris(2,2'-bipyridyl)ruthenium(II) immobilized in titaniaperfluorosulfonated ionomer composite films 1 μM-1 mM 1 μM 3 weeks [26] Tris(2,2'-bipyridyl)ruthenium(II) immobilized in Nafion 1 μM-100 mM 1 μM Several days [8b] Ru(bpy) 3…”

Preconcentration of sulfite from food and beverage matrices by ultrasonic assisted-cloud point extraction prior to its indirect determination by flame atomic absorption spectrometry

“…The use of the UA-CPE as an alternative to conventional solvent extraction techniques such as liquid-liquid extraction (LLE) and solid phase extraction (SPE) has the following advantages such as relatively low toxicity, high preconcentration factor, lower cost, higher safety and simplicity. 17,18 Also, the UA-CPE was efficiently coupled to FAAS, and successfully used in order to enhance its low detection limit as well as the selectivity of the technique.…”