Detection of trace materials with Fourier transform infrared spectroscopy using a multi-channel detector

FTIR spectroscopy is one of the most powerful methods for material characterization. However, the sensitivity of this analytical tool is often very limited especially for materials with weak infrared absorption or when spectral bands of the targeted trace material overlap with the spectral bands of major components. Fortunately, for heterogeneous samples, there is an opportunity to improve the sensitivity of detection by using an imaging approach. This paper explores the opportunity of enhancing the sensitivity of FTIR spectroscopy to detect trace amounts of materials using the FTIR imaging approach based on a focal plane array (FPA) detector. Model sample tablets of ibuprofen in hydroxypropyl methylcellulose (HPMC) have been used to exemplify the detection limits of FTIR spectroscopy using: (a) a conventional mercury cadmium telluride (MCT) detector and (b) a FPA detector. The sensitivity level was compared and it has been found that for this particular set of samples, the lowest concentration of ibuprofen in HPMC that can be detected using attenuated total reflection (ATR) measuring mode with the single element MCT detector was 0.35 wt% while using the FPA detector, the presence of drug has been detected in a sample that contains as little as 0.075 wt% of drug. The application of using this enhanced sensitivity offered by the multi-channel detector to probe trace amounts of drug particles left on the surface of a finger after handling a small amount of the drug has also been demonstrated. These results have broad implications for forensic, biomedical and pharmaceutical research.