Advances in the chemical analysis of nitrite in environmental and biological samples.

Nitrite, a potential environmental pollutant, poses a significant threat to human health. Thus, accurate and sensitive detection methods are essential for effective continuous monitoring and surveillance. In this regard, a wide range of instrumental methods for the precise determination of nitrite in different types of complex samples is collected and discussed. Besides the classical methods, chromatographic and spectroscopic techniques are included. Although these methods exhibit high sensitivity and selectivity, they involve high cost and complicated operating protocols, and warrant high caution in sample preparations. Other reported techniques, such as electrochemical and bio-electrochemical methods, could offer onsite detection and disposability, and involve handheld devices. Such features are required for simple optimization, field applicability for analysis of a large number of samples, fast response, simple device calibration, and validation. Thus, nanostructure-based electrochemical approaches are widely developed and applied in the analysis of target analytes in complex biological and environmental matrices using a few microlitres of the samples, without any prior sample preparation. Therefore, to consider the global market's needs, challenges, and perspectives on each reported method for nitrite, a comprehensive discussion has been included in this review.