A newly synthesized macrocyclic dithioxamide receptor for phosphate sensing

Polyvinyl chloride (PVC) based membranes using macrocyclic dithioxamide receptor (I) derived from isophthaloyl dichloride and dithioxamide have been prepared and explored as HPO42−-selective sensors. Effect of various plasticizers viz., bis(2-ethylhexyl) sebacate (DOS), dibutylphosphate (DBP), tri-n-butylphosphate (TBP), O-nitrophenyl octyl ether (NPOE), tris(2-ethylhexyl)phosphate (TEHP) and a cation excluder, tridodecylmethylammonium chloride (TDDMACl) was studied in detail and improved performance was observed at several instances. Optimum performance was observed with the membrane having (I)-PVC–TDDMACl–NPOE in the ratio 2:33:1.5:63.5 (w/w). The sensor works satisfactorily in the concentration range 1.7 × 10−6 to 1.0 × 10−2 M (detection limit 0.2 ppm) with Nernstian compliance (29.6 mV/decade of activity) at pH 8.0 with a fast response time of about 8 s. The potentiometric selectivity coefficient values as determined by the matched potential method (MPM) and the fixed interference method (FIM) indicate selective response for HPO42− in presence of interfering ions. The sensor exhibits adequate shelf life (∼2 months) with good reproducibility (S.D. ± 0.4 mV). The sensor was also used successfully in the potentiometric titration of HPO42− with Ba2+.