Selective anion recognition: Charged diaza crown ethers based electrochemical sensors for chromate ions

Attempts have been made to develop a poly(vinyl chloride) (PVC) based sensor for CrO42− ions using positively charged diaza crown ethers (12-crown-4 and 18-crown-6) with dibutylphthalate (DBP), dioctylphthalate (DOP) and chloro naphthalene (CN) and dioctylsebacate (DOS) as plasticizing solvent mediators. These sensors work well over a wide concentration range 5.0 × 10−6 to 1.0 × 10−1 M (detection limit up to 0.3 ppm) with Nernstian slope (29.6 mV/decade) between pH 6.5 to 10.0 with a fast response time of <10 s. The selectivity coefficient values as determined by Match Potential Method (MPM) indicate excellent selectivity for Cr(VI) ions over a large number of ions. Interference caused by common anions, viz. Cl− and SO42− has been investigated in simulated mixtures containing high concentration level of interfering ions and the sensor was found to be tolerant against these anions. These sensors exhibit adequate shelf-life (>3 months) with good reproducibility (S.D. ±0.2 mV). Quantification of Cr(VI) in electroplating waste was successfully achieved using the proposed sensor.