Improved Determination of Nitrotoluenes Using Liquid Chromatography with Photolytically Assisted Thermal Energy Analysis (LC-PAT)

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Abstract
A post-column, on-line, photolysis unit is incorporated in a normal phase, high-performance liquid chromatography (LC) system to improve the thermal energy analyzer (TEA) detectability of mono-, di- and tri-nitrotoluenes. The construction of this photolytically assisted TEA (PAT) detection approach includes the use of an ultraviolet lamp and a knitted open tubular (KOT) reaction chamber of Teflon®. The mechanism for improved detection using PAT is explored, using batch irradiations followed by LC-TEA and gas chromatography/mass spectrometry, and is postulated to involve photochemically induced isomerization leading to homolytic cleavage of the C-NO2 bond, followed by hydrogen abstraction. After optimization of photolytic residence time and cooling bath temperature, PAT allows for an improvement in the TEA detectability of trinitrotoluene and dinitrotoluene by factors of 30 and 16, respectively. Mononitrotoluene, which is not responsive under conventional TEA conditions, may be detected with good sensitivity using LC-PAT. The use of LC-PAT does not interfere with the determination of other nitro-based high explosives which exhibit adequate responses under conventional LC-TEA conditions.

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