New Highly Selective Picrate Sensors Based on Charge-Transfer Complexes

Two novel highly selective potentiometric membrane sensors responsive to picrate ion were developed. They are based on the use of N,N′-dibenzoyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (DD18C6)-picrate and Kryptofix 222-picrate charge-transfer complexes as novel electroactive materials in poly(vinyl chloride) matrix membranes plasticized with o-nitrophenyloctylether or dioctylphthalate. The sensors show a Nernstian response with anionic slopes of -59.0 ± 0.1 and -58.0 ± 0.2 mV decade-1 over concentration ranges of 6.0 × 10-5 - 1.0 × 10-2 and 7.0 × 10-5 - 1.0 × 10-2 mol l-1 picrate ion and pH ranges of 5 - 11.5 and 5.5 - 11.5 for DD18C6 and Kryptofix 222 based picrate sensors, respectively. Both sensors show highly selectivity towards picrate ion over many hydrophilic and lipophilic anions, and exhibit a non-Hofmeister selectivity sequence, which is an improvement over methods reported so far. The sensors are used for the titrimetric determination of alkaloids using picrate as a titrant.