Optical chemical sensors or optodes have become an important area of research since their introduction two decades ago. The development of optical nitrite sensor is of great interest because of their possible application in biotechnology, ecology, medicine and environmental studies. In this research, two optical nitrite sensors were described by direct immobilizing of two indicators dye in optical sensing films for monitoring of trace amounts of nitrite in food and environmental samples. Those sensors were fabricated by immobilization of Brilliant cresyl blue (BCB) and Thionine to cellulose acetate films that have previously been subjected to an exhaustive base hydrolysis. Those indicators undergo oxidation in the presence of bromate in acidic media. Nitrite acts as a catalyst for those oxidation reactions. Those reactions cause decreasing in the absorbance of the membrane sensors at 570 and 568 nm. The decreasing in the absorbance of the sensor in the presence of nitrite at a fixed time of 2.0 and 3.0 min for BCB and Thionine membrane, respectively were used as a membrane signal. Those sensors are irreversible. Under the optimum conditions for the sensor based on BCB, the optode has a linear dynamic range of 63.3 × 10-5 - 3.7 × 10-9 M and limit of detection of 1.7 × 10-9 M nitrite. The response time of the optode is up to 2 min depending on the concentration of nitrite. The relative standard deviation for the eight replicates determination of 3.6 × 10-8 M nitrite was reported 3.2%.
The sensor based on immobilizing of Thionine has a linear rang of 2.2 × 10-5 - 2.2 × 10-7 M and limit of detection of 1.8 × 10-7 M nitrite, under the optimum conditions. The response time of the optode is up to 3 min and the relative standard deviation for the eight replicates determination of 2.2 × 10-5 and 2.2 × 10-7 M nitrite were 6.5% and 5.5%, respectively. This sensor has a good selectivity for determination of nitrite in real sample such as waste water and sausage samples.
Optical sensor, Optode, Nitrite, Brilliant cresyl blue, Thionine.