Quantitative infrared spectroscopy of formalin-fixed, paraffin-embedded tissue specimens: paraffin wax removal with organic solvents.

Formalin-fixed, paraffin-embedded tissue specimens form the basis for diagnostic histopathology. Although adequate for morphologic visualization, clinical variability in preparation of formalin-fixed, paraffin-embedded clinical specimens represents an obstacle to quantitative molecular genetic analysis in areas such as genomics and proteomics. A quantitative reexamination of classical histopathology tissue preparation methods was initiated to determine which protocol steps might improve molecular analysis, beginning with deparaffinization. Infrared spectroscopy in the spectral region above 2000/cm of fixed sectioned model cell cultures through glass microscope slides showed all solvents remove over 97% of paraffin. To further compare extractions among solvents xylene, hexane and limonene, the correlation coefficients between the spectrum of paraffin and the spectra of the mounted extracted model tissue sections across the spectral interval containing the prominent CH stretching bands of paraffin were calculated. The correlation coefficients allow different extraction methods to be ranked in terms of how much paraffin remains. The results indicate that among 3 model tissue sample types, xylene extraction removes more paraffin than hexane or limonene. More importantly, these results establish a starting point from which further analysis of preanalytical processing methods can proceed.