Development of a New Colorimetric Chemosensor for Selective Determination of Urinary and Vegetable Oxalate Concentration Through an Indicator-Displacement Assay (IDA) in Aqueous Media

Abstract

SUMMARYThe paper proposes a method that exhibits operational simplicity for the indirect spectrophotometric determination of oxalate ion. We developed Reactive Blue 4 (RB4) as a sensor by complexation with copper ion as a simple, inexpensive yet selective colorimetric chemosensing ensemble for the recognition of oxalate over other available competitive analytes via indicator displacement assay (IDA) in both solution (aqueous medium) and solid state (paper-based experiment). The addition of oxalate to RB4-Cu2+ complex changed the colour from sky blue to dark blue due to the regeneration of RB4 by the chelation of oxalate as the competitive analyte with Cu2+. The absorbance band increase is linear with oxalate concentration from 1.76 to 49.4 µmol/L with a detection limit of 0.62 µmol/L. This measurement mode did not show any influence of interferences (available anions and ascorbic acid). This approach eliminated the need for the separation stages, enzymatic multiple-step reactions, sample preparation, organic solvent mixture, chemical modifications and equipment developed to a high degree of complexity. The oxalate determination gave results in different real samples such as urine, mushroom and spinach, which demonstrated the applicability of the existing method. Furthermore, this colorimetric system can serve as IMPLICATION molecular logic gate using Cu2+ and oxalate (C2O42–) as inputs and UV-Vis absorbance signal as the output with potential monitoring applications.

Analytical Methods for Oxalate Quantification: The Ubiquitous Organic Anion

“…Several additional colorimetric or fluorescent indicator-based methods have been reported, generally with lower sensitivity than electrochemical or mass-spectrometry-based methods [ 43 , 44 , 45 , 46 , 47 , 48 , 50 , 52 ]. All of these methods have the advantage of simple sample preparation, but invariably, they have either not been tested for interference from other organic anions, or interference has clearly been demonstrated.…”

Oxalate in Foods: Extraction Conditions, Analytical Methods, Occurrence, and Health Implications

“…For example, prior to HPLC analysis, there have been reports of the use of solid-phase extraction (SPE) [35,55,69], purification with ion exchange [35], concentration [35,69], and, specifically for soluble oxalates, acidification with HCl to stabilize ascorbic acid which can be present and cause oxaloneogenesis at pH above 5, resulting in an overestimation [1,63,64,72]. For spectrophotometric methods, evaporation and subsequent redissolution for total oxalate analysis have been mentioned [58] and, once again, adjustment of pH, which is relevant for soluble oxalates [41,76,78].…”

“…The studies analyzed for this matter include catalytic/kinetic methods. In other words, these procedures follow a spectrophotometric reaction which has some kind of oxalate intervention, either as a reagent [30,41,58,[75][76][77], catalyst [31,37,38,74,[78][79][80][81][82], or activator [54]. Some manuscripts mention other studies in which oxalate acts as an inhibitor [54,78].…”

“…This method is based on the interaction of oxalates with a material of silica-titania xerogel with eriochrome cyanine R (Si-Ti/ECR) which causes sensor material discoloration, with absorbance being used as an analytical signal [41]. According to Tavallali et al [76], the reaction of Reactive blue 4 (RB4)-Cu 2+ with oxalate can be used for oxalate determination in food samples. The addition of oxalate to the RB4-Cu 2+ complex increased the absorption band intensity at 607 nm and changed the color from sky blue to dark blue due to the regeneration of RB4 by the chelation of oxalate with Cu 2+ , since the binding constant of Cu 2+ with oxalate is larger than that of Cu 2+ with RB4.…”

A simple, sensitive, and selective colorimetric chemosensor for sequential determination of dual analytes, Ce3+, H2PO4−, and its applications in the logic gate construction and the system of keypad lock

“…The synthesis of most of the new multifunctional chemosensors is relatively complicated and time-consuming [18]. In recent years, our team has designed and introduced simple and fast chemosensors that detect and measure cations, anions, and other analytes using commercial dyes [19][20][21][22][23][24][25][26][27][28][29][30][31][32].…”