Oxygen removal strategies for the electroanalysis of explosives: A comparative study

The increasing use of explosive weapons in conflicts and terrorist activities highlights the need for reliable on-site detection methods of explosives. As rapid and informed decision-making is essential on the crime scene, methods that are both efficient and accurate are highly desirable. Many explosive compounds contain nitro groups, which are prone to reduction, making electrochemical analysis a promising approach for their detection. However, reductive electrochemical measurements often face interference from the reduction of dissolved oxygen, which can overlap with key signals. Therefore, removing dissolved oxygen is essential to ensure accurate results. This study compares three oxygen removal strategies for small-volume samples (<1 mL) across a pH range between 2 and 12, identifying the effective pH range for each method. The methods assessed include: (1) traditional purging with nitrogen gas, (2) enzymatic oxygen removal using glucose oxidase, and (3) sodium sulfite as an oxygen scavenger. Analyses were performed on in-house screen-printed electrodes using square wave voltammetry. The oxygen removal techniques were further evaluated in a case study focused on detecting explosive compounds 1,3,5-trinitro-1,3,5-triazinane (RDX), nitroglycerin (NG), and 2,3-dimethyl-2,3-dinitrobutane (DMNB). This study presents efficient alternatives to purging for oxygen removal at pH levels above 3 and offers more suitable solutions for on-site analyses.