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Coated-wire (CW) and tubular (Tu) type membrane sensors for creatinine are developed. These consist of creatinine tungstophosphate(CTP), creatinine molybdophosphate (CMP) and creatinine picrolonate (CPC) ion-pair complexes as electroactive materials dispersed in plasticized poly(vinyl chloride) matrix membranes. Electrochemical evaluation of these sensors under static (batch) mode of operation reveals near-Nernstian response with slopes of 62.9, 58.1, and 55.2 mV decade À1 over the concentration range 1 Â 10 À2 -5.0 Â 10 À6, 1 Â 10 À2 -7.5 Â 10 À5, and 1 Â 10. The lower detection limits are 0.39, 3.49, and 2.20 mg mL À1 creatinine with CTP, CMP and CPC membrane based sensors plasticized with o-NPOE, respectively. Tubular and coated wire CTP membrane sensors are incorporated in flow-through cells and used as detectors for flow injection analysis (FIA) of creatinine. The intrinsic characteristics of the detectors under hydrodynamic mode of operation in a low dispersion manifold are determined and compared with data obtained under static mode of operation. With 10 À2 mol L À1 phosphate buffer of pH 4.5 as a carrier solution, the tubular and coated wire CTP detectors exhibit rapid response of 58.9 and 50.7 mV decade À1 over the concentration range 1 Â 10 À2 -1 Â 10 À5 mol L À1 and detection limits of 0.39 mg mL À1 and 0.85 mg mL À1, respectively. Validation of the assay methods with the proposed sensors by measuring the lower detection limit, range, accuracy, precision, repeatability and between-day-variability reveals good performance characteristics confirming applicability for continuous determination of creatinine. The sensors are used for determining creatinine in human blood serum at an input rate of 40 samples per hour. No interferences are caused by creatine, most common anions, cations and organic species normally present in biological fluids. The results favorably compare with data obtained using the standard spectrophotometric method.

Reagents and chemicalsAll reagents used were of analytical grade; deionized water Two novel potentiometric sensors that are highly selective to Hg 2+ ions are described. These are based on the use of 5,5′-dithio-bis(2-nitrobenzoic acid) (DTNB) and tricyclazole (TCZ) as neutral carriers in plasticized poly(vinyl chloride) membranes. Fast Nernstian responses are obtained for Hg 2+ ions over the concentration ranges 7.0 × 10 -6 -1.0 × 10 -2 and 7.7 × 10 -6 -1.0 × 10 -2 mol l -1 at pH 1.8 -3.3 with lower detection limits of 5.0 × 10 -6 and 5.6 × 10 -6 mol l -1 (∼1 μg ml -1 ) and calibration slopes of 30.0 and 29.7 mV decade -1 with DTNB-and TCZ-based membrane sensors, respectively. Validation of the assay method reveals good performance characteristics, including long life span, good selectivity for Hg 2+ ions over a wide variety of other metal ions, long term response stability, and high reproducibility. Applications for direct determination of mercury in hazardous wastes including dental amalgam, mercury bulbs, and fluorescent lamps give results with good correlation with data obtained using cold vapor atomic absorption spectrometry.

The construction and general performance characteristics of three novel potentiometric PVC membrane sensors responsive to dicyanoargentate anion are described. The sensors are based on the use of magnesium(II)-and iron(II)-phthalocyanines as neutral ionophores and iron(II)-bathophenanthroline dicyanoargentate ion-pair complex as an ion exchanger in plasticized PVC matrices. These sensors exhibit fast, stable and near-Nernstian response (54 ± 59 mV/ decade) for the singly charged dicyanoargentate anion over the concentration range 1 Â 10 À2 ± 5.8 Â 10 À6 M. Potentiometric responses of sensors based on metal phthalocyanines and iron(II)-bathophenanthroline are stable over the pH ranges 5 ± 7 and 5 ± 12, respectively. The selectivity of the sensors are fairly good over most common anions. Use of the sensors for potentiometric determination of microgram quantities of cyanide ion after conversion into dicyanoargentate anions shows an average recovery of 99.5% and a mean standard deviation of AE 0.5%. Determination of cyanide ions in some exhausted electroplating bath samples gives results that compare favourably well with data obtained using the solid-state cyanide electrode.

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