Heterogeneity studies of a single particle fiber by using Fourier transform infrared micro-sampling photoacoustic spectroscopy

This paper reports the first investigation of the micro-sampling possibilit y of Fourier transform infrared photoacoustic spectroscopy (FT-IR PAS) in d epth profiling of a single particle and a single fiber. The samples studied in this paper include a Bio-Bead(TM) (150 mu m in diameter) coated with co mmercial strawberry flavor oil, a nylon wire with grease coating, and a pie ce of natural human hair (60 mu m in diameter and 7 mm in length) with gel- coating. Major FTIR PAS operation modes utilized in depth profiling of hete rogeneous/layered macro-samples reported previously, such as (continuous-) rapid-scan, phase-, and nonphase modulation step scans, were used in this s tudy. The software-based digital signal processing (DSP) algorithms for ste p-scan photoacoustic (fundamental and harmonic) signal modulation/demodulat ion were employed in the phase modulation experiments. Both modulation freq uency variation and photoacoustic signal phase analysis methods were applie d to elucidate detailed spectral depth profiling information from the raw d ata of these micro-samples. The results conclude that FT-IR micro-PAS offer s a unique and complementary method in analysis of heterogeneous micro-samp les with nondestructive, noncontact, and cost-effective advantages compared with conventional FT-IR micro-transmission/reflection/ATR approaches.