To calculate the signal-to-noise ratio, the signal was taken at the maximum absorbance of the amide I band between 1700 and 1600 cm1 for the whole bile and the aqueous phase, and at the maximum of the lipid band absorbance between 3120 and 2950 cm1 for the organic phase. Noise intensity was calculated in the 2100–2000 cm1 region for all three types of bile samples. Water vapour content was evaluated in the 1847–1837 cm1 region.