Applications of attenuated total reflection infrared spectroscopic imaging to pharmaceutical formulations

This paper demonstrates an approach to obtain chemical images of pharmaceutical tablets using attenuated total reflection infrared (ATR-IR) spectroscopy. FT-IR images with different fields of view and spatial resolution have been obtained using a combination of different ATR accessories. FT-IR imaging with the diamond ATR accessory and micro-ATR imaging technique have been compared. With the diamond ATR imaging accessory, compaction to a tablet can be performed and the chemical image measured in situ. It has been found that the diamond ATR imaging accessory gives information on the overall distribution of different components in a tablet while the micro-ATR imaging technique provides a closer look at the tablet with 4-microm spatial resolution. Low-concentration components down to 0.5% have been detected by the micro-ATR method. Both experimental and commercial systems are studied in this paper.

Confocal Raman microscopy of supercritical fluid dyeing of polymers

Supercritical CO2 was used as a medium to introduce azo-dyes into polymers (PMMA and PET). Confocal Raman microscopy has been applied using dry metallurgical and oil objectives to measure the concentration of dye as a function of distance from the surface to the core of the polymer samples. A significant gradient of dye concentration normal to the surface, down to the depth of ca. 100 microm, has been observed. In addition, cross-sections of cut dyed polymer samples have been analysed using a conventional mapping approach. The comparison between confocal depth and conventional mapping approaches has demonstrated that the use of the oil objective can provide reliable qualitative information on dye distribution in these systems. These confocal Raman experiments demonstrate the potential of this method in applications to polymeric materials processed with supercritical fluids.

New opportunities in micro- and macro-attenuated total reflection infrared spectroscopic imaging: spatial resolution and sampling versatility

New opportunities exist to obtain chemical images using attenuated total reflection infrared (ATR-IR) spectroscopy. This paper shows the feasibility of obtaining FT-IR images with a spatial resolution of at least 3-4 microm using a Ge ATR objective coupled with an infrared microscope. The improved spatial resolution compared to FT-IR images obtained by the transmission method is due to the high refractive index of the ATR crystal, which gives a high numerical aperture and hence, a higher spatial resolution. FT-IR imaging with a conventional diamond ATR accessory has been investigated. This is the first time that FT-IR imaging is reported using such a versatile accessory based on a diamond ATR crystal. These results showed that a spatial resolution up to 13 microm can be achieved without the use of infrared microscope objectives. One advantage of the diamond element is that it allows pressure to be applied and hence, good contact to be obtained over the whole field of view.