FTIR-PAS offers some unique advantages for microsample analysis over FTIR microscopy:

1. No pressing of samples is required to reduce optical density. This avoids the destruction of evidence in forensic analyses, and questions of reproducibility and sample alteration posed by the pressing operation. The nondestructive character of FTIR-PAS allows analyses confirmation by other techniques such as optical or electron microscopy.
2. The delicate optical alignment and aperturing of FTIR microscopy is avoided because FTIR-PAS microsampling can be done with a beam focal spot size that is much larger than the sample since only the portion of the beam that impinges on the sample generates a photoacoustic signal.
3. The spectral range of measurements is not limited by the cut-off of narrow band MCT detectors commonly used in FTIR microscopy. The extended spectral range of FTIR-PAS microsample spectra allows better spectral differentiation between difficult samples such as nylons.
4. FTIR-PAS spectra of fibers have more easily discernible detail because normally weak but definitive bands are more prominent due to truncation of strong bands by photoacoustic signal saturation and to enhanced structure at low wavenumbers from more efficient signal generation at low frequencies.

A key consideration in FTIR-PAS microsample analyses is mounting the sample so that it is surrounded by helium gas for efficient signal generation. Fig. 14 shows devices supplied by MTEC that are used to mount single fibers and particles for FTIR-PAS analyses. Tweezers are used to mount fibers in spring loaded split rings before placement in the sample cup. In front of the sample holder is a fixture which holds the ring with either a white or black centering pin to provide a contrasting background during mounting of fibers. In the procedure, fibers are either attached by pressure sensitive adhesive to the arms of the device shown in Fig. 14 in front of the ring fixture, or fibers can be manipulated with tweezers during mounting. This operation can be done using an illuminated bench magnifier with a contrasting background. A microscope is not required. In Fig. 15 a black thread depicts a fiber being mounted and placed in the sample holder over a covered desiccant cup. The desiccant cup is shown in Fig. 14 on the left side of the ring fixture. A magnesium perchlorate desiccant and a dry helium gas atmosphere are required in micro- sampling because otherwise the water vapor signal, which is out-of-phase with the sample signal, can dominate the sample signal and seriously degrade the spectrum.