Photoacoustic spectroscopy on coloured and lightscattering liquids

Experiments show that photoacoustic spectroscopy (PAS) allows to record spectra equivalent to or even better than photometry. This could be demonstrated on measurements at water soluble systems. Measurements on disperse dyestuff systems and unfiltered fruit juices resulted in qualitative spectra which are not or only a little effected by light scattering. In contrast to photometry, PAS recorded spectra have pronounced structures in the entire wavelength range. This is further proved by concentration dependent PA-measurements with disperse dyestuff. These spectra have no offset in the wavelength range where no absorption takes place. Photometrical measurements of disperse dyestuff extracted from textiles yield spectra which are equivalent to spectra measured with PAS on disperse systems. The evaluation and standardization procedure is still critical. This is due to the instability of the light source and also of the qualitative behaviour of the transients for different concentrations.