Quantification of DNT isomers by capillary liquid chromatography using at-line SERS detection or multivariate analysis of SERS spectra of DNT isomer mixtures

With the global surge of terrorism and the increased use of bombs in terrorist attacks, national defence and security departments now demand techniques for quick and reliable analysis, in particular, for detection of toxic and explosive substances. One approach is to separate different analytes and matrix material before detection. In this work microliquid chromatography was used to separate two dinitrotoluene (DNT) isomers prior to detection via online UVVis spectroscopy. For identification, retention times were compared with reference samples and quantification was done by integration of UVVis absorption. Because UV detection is not particularly selective, Raman microscopic analysis was coupled to the liquid chromatography using a flow-through microdispenser. Because DNT is difficult to detect with conventional Raman spectroscopy, the sensitivity was increased via surface-enhanced Raman scattering (SERS) using silver-quantum dots. Different analytical approaches to identify and quantify mixtures of two DNT isomers were evaluated. Good quantitative results were obtained using UV detection after microchromatographic separation (Limit of Detection: 0.11 and 0.06 for 2,4-DNT and 2,6-DNT). Coupling with SERS allowed for more confident differentiation between the highly structurally similar DNT isomers because of the additional spectral information provided by SERS. The application of a partial least squares algorithm also allowed direct SERS detection of DNT mixtures (root mean square error of prediction: 0.82 and 0.79?mg.L1 for 2,4-DNT and 2,6-DNT), circumventing the time-consuming separation step completely. Copyright (c) 2012 John Wiley & Sons, Ltd.