Laser-induced plasma emission spectrometric study of pigments and binders in paper coatings: Matrix effects

Laser-induced plasma emission spectroscopy (LIPS) has been used to study inorganic pigment and organic binder distributions in paper coatings, which are inhomogeneous and porous materials. The plasma was generated by focusing a pulsed XeCl excimer laser beam (diameter 100 pm, irradiance 0.3 GW/cm(2)) on the sample surface at atmospheric pressure. A gated intensified CCD detector was used to record time-delayed emission spectra. Linear correlations between the LIPS signals and the coat weight and the binder content of the coatings studied were obtained. Emission line intensities from ionic and neutral magnesium atoms were used to evaluate plasma temperature corrections in determining silicon and calcium in coatings. Self-absorption of the Ca(I) 423-mn line in air was observed for the coatings containing calcium carbonate. In an argon buffer, self-absorption was not present. Pigment and binder depth profiles of the coatings were studied for several coated paper samples. All samples studied indicated binder enrichment on the top layer of the coating.