Design a Novel Colorimetric Chemosensor for Selective Detection and Determination of Carbonate ion Based on Phosphotungstic acid Complexes of Neutral red in Water Media

Carbonate is one of the onions that is only slightly toxic, but large doses are corrosive to the gastro-intestinal tract where symptoms may include severe abdominal pain, vomiting, diarrhea, collapse and death [۱]. Colorimetric sensing which invariably bank on “naked-eye “sensing, has gained additional impetus owing to the ease in monitoring of the process without resorting to sophisticated techniques. Thus a great deal of effort has been invested in developing simple-to-make and use “naked-eye “diagnostic tools for sensing of analytes [۲, ۳]. These receptors are rather difficult to synthesize or require expensive instruments for detections. Taking this dilemma into consideration recently, we have undertaken an extensive research program to explore bromo pyrogallol red as an easily available dye demonstrated a high chromogenic receptor for cations and anions [۴, ۵]. In this work, we disclose a new approach toward this goal. We manifest a novel neutral red (NR) based colorimetric chemosensor for carbonate ions in aqueous media. The phosphotungstic acid (PTA) binding property of NR was studied by the use of UV– Vis spectrophotometry and the attended color changes allowed assessment of the complex property of NR. Initial experiments aimed at the optimization of concentration of PTA led us to treat aqueous solution of CO۳۲ˉ with NR-PTA formed in solution. Spectrophotometric monitoring of the changes revealed that the peak at ۶۴۶ nm increased instantaneously with concomitant color change, because CO۳۲ˉ is a strong p-acceptor. In order to support the above hypothesis, the process was repeated using scaled up quantities which unequivocally establish the proposed mechanism. The complex of NR-PTA also displayed ability to detect up to ۰.۱۸ μmol L-۱ for CO۳۲ˉ. This method could have potential application in a variety of cases requiring rapid and accurate analysis of CO۳۲ˉ for real samples.