Fiber optic sensor for NOX

Titanium and Ruthenium Phthalocyanines for NO(2) Sensors: A Mini-Review

This review presents studies devoted to the description and comprehension of phenomena connected with the sensing behaviour towards NO₂ of films of two phthalocyanines, titanium bis-phthalocyanine and ruthenium phthalocyanine. Spectroscopic, conductometric, and morphological features recorded during exposure to the gas are explained and the mechanisms of gas-molecule interaction are also elucidated. The review also shows how X-ray reflectivity can be a useful tool for monitoring morphological parameters such as thickness and roughness that are demonstrated to be sensitive variables for monitoring the exposure of thin films of sensor materials to NO₂ gas.

Evaluation of Copper(II) Eriochrome Cyanine R (ECR) Complex Immobilized in Anion Exchange Membrane as a Potential Nitric Oxide Optical Sensor

The immobilization of the copper(ii) complex of Eriochrome cyanine R (Cu(ECR)2) in anion exchange membranes was investigated in the development of an optical sensor for nitric oxide (NO) gas. The change in the absorbance spectrum of Cu(ECR)2 membranes was monitored at 445 nm on exposure to NO gas and a steady-state response was obtained following a 400 s exposure time. This response was highly linear (r2 = 0.996) up to 6 ppm NO and the detection limit was calculated to be 0.848 ppm (~28.28 μM in solution). This response was 4.7 times more sensitive to changing NO gas concentrations (0–6 ppm) compared with that of Cu(ECR)2 immobilized in silicone rubber films. This response was fully reversible by resubmersion of the membranes in copper(ii) solution following NO exposure and this reversibility was extremely reproducible (0.81%, relative standard deviation, n = 3). These anion exchange membranes were more selective to NO gas rather than O2 (80:1), NO2 (3:1), and CO (7:1) and these gases were shown not to interfere with the reaction of Cu-ECR membranes with NO itself.

A nitrite microsensor for profiling environmental biofilms

A highly selective liquid membrane nitrite microsensor based on the hydrophobic ion-carrier aquocyanocobalt(III)-hepta(2-phenylethyl)-cobrynate is described. The sensor has a tip diameter of 10 to 15 (mu)m. The response is log-linear in freshwater down to 1 (mu)M NO(inf2)(sup-) and in seawater to 10 (mu)M NO(inf2)(sup-). A method is described for preparation of relatively large polyvinyl chloride (PVC)-gelled liquid membrane microsensors with a tip diameter of 5 to 15 (mu)m, having a hydrophilic coating on the tip. The coating and increased tip diameter resulted in more sturdy sensors, with a lower detection limit and a more stable signal than uncoated nitrite sensors with a tip diameter of 1 to 3 (mu)m. The coating protects the sensor membrane from detrimental direct contact with biomass and can be used for all PVC-gelled liquid membrane sensors meant for profiling microbial mats, biofilms, and sediments. Thanks to these improvements, liquid membrane sensors can now be used in complex environmental samples and in situ, e.g., in operating bioreactors. Examples of measurements in denitrifying, nitrifying, and nitrifying/denitrifying biofilms from wastewater treatment plants are shown. In all of these biofilms high nitrite concentrations were found in narrow zones of less than 1 mm.