Analysis of nanogram spots of ink by fourier transform infrared microscopy and spectral stripping

Abstract

Dot matrix printing inks for industrial printers consist of solvent, binder, dye and various minor additives. We have used FTIR microspectroscopy to examine the composition of these inks from the analysis of single dots of less than 1 mm diameter. Good spectra were obtained by reflection–absorption on metal surfaces and by ATR on plastic surfaces. Paper substrates have proved more troublesome. Analysis of the printed inks was performed by an iterative process of component identification through library searching and spectral subtraction. Some bandshifts were observed which complicated this process, but two or three successive identification–subtraction cycles could often be made. A comparison of real sample spectra with synthetic spectra produced by addition of pure component spectra was also useful in highlighting spectral differences indicating component interactions in the formulated inks.