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

U radu je predložena jednostavna metoda za indirektno spektrofotometrijsko određivanje oksalata. Kompleksiranjem iona bakra s Reactive Blue 4 (RB4) bojilom razvili smo jednostavan, jeftin i selektivan kolorimetrijski kemijski senzor za određivanje oksalata u realnim uzorcima vodenih otopina i na čvrstoj podlozi (papiru). Dodatkom oksalata nebesko plava boja otopine kompleksa Cu2+-RB4 prešla je u tamnoplavu (nekompleksirano bojilo RB4), uslijed nastajanja stabilnijeg kompleksa Cu2+-oksalat. Linearan odnos apsorbancije i koncentracije oksalata dobiven je u području od 1,76 do 49,4 μmol/L, s limitom detekcije 0,62 μmol/L. Pri takvom načinu rada nije došlo do interferencije drugih slobodnih aniona ili askorbinske kiseline prisutnih u realnim uzorcima, pa su izbjegnuti sljedeći postupci: priprema uzorka, izdvajanje analita, uporaba smjese organskih otapala, enzimska reakcija u više koraka, kemijska modifikacija analita, te uporaba složenije instrumentacije. Oksalati su uspješno određeni u različitim uzorcima, poput urina, gljiva i špinata, što dokazuje primjenjivost metode. Osim toga, ovaj kolorimetrijski senzorski sustav može se rabiti za mjerenje koncentracije oksalata u protoku, što je posebno važno kod velikog broja uzoraka.The 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 (C2O4 2–) as inputs and UV-Vis absorbance signal as the output with potential monitoring applications

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

The 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 (C2O4 2–) as inputs and UV-Vis absorbance signal as the output with potential monitoring applications