Nitrobenzene-selective sensor

Fig. 18.10. [Nickel-(protoporphyrin IX)dimethyester], which was electropolymerised on glassy carbon with nitrobenzene as template to prepare a nitrobenzene-selective sensor [135].

Porphyrins are often employed in sensors on account of their ability to act as cation hosts and, with a suitable metal ion coordinated, as redox catalysts. Electropolymerised poly(metalloporphyrin)s have been used as potentiometric anion-selective electrodes [131] and as amperometric electrocatalytic sensors for many species including phenols [132], nitrous oxide [133] and oxygen [134]. Panasyuk et al. [135] have electropolymerised [nickel-(protoporphyrin IX)dimethylester] (Fig. 18.10) on glassy carbon in the presence of nitrobenzene in an attempt to prepare a nitrobenzene-selective amperometric sensor. Following extraction of the nitrobenzene the electrode was exposed to different species and cyclic voltammetric measurements made. A response was observed at the reduction potential of nitrobenzene (the polyporphyrin film acts only to accumulate the analyte and not in a catalytic fashion). Selectivity for nitrobenzene compared with w-nitroaniline and o-nitroto-luene was enhanced compared with an untreated electrode, while a glassy carbon-... 

The sensor mentioned under (iii) uses an ammonium ion selective electrode carrying a PVC nitrobenzene-dibenzo-18-crown-6 gel. The enzyme was immobilized by crosslinking with glutaraldehyde on a Teflon membrane. After addition of urea to the measuring solution the ammonia produced in the enzymatic reaction reaches the internal solution layer (pH 9.7) of the sensor, where it is partially converted to ammonium ion which is transferred into the nitrobenzene phase. As a result, at 370 mV a current flow was observed which was related to urea concentration. The peak current was proportional to the concentration of urea between 1 pmol/1 and 2 mmol/1. The response time of the sensor was about 1 min. 

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