Difficulties in Preparing Dye Solutions For Accurate Strength Measurements.

An increasing use of spectrophotometric transmittance measurements to determine the relative dye strength of incoming shipments to a standard type has been noted for users of dyes. For many dyes, the results determined from solution measurements are in agreement with those determined by application tests on the intended substrate. The purpose of this paper is to point out the exceptions; i.e., those factors that affect the accuracy and precision of measuring dye concentrations in solution. The solution variables examined are categorized into three groups: group 1—effect of additives, concentration, dissolution aids, hydrogen ion activity and solvents on the absorption spectrum; group 2— effect of dye interaction, fluorescence, irradiation, plating, solution heating and temperature on the absorption spectrum; group 3—effect of hydrolysis, interfering ions, ionic strength, light fading and redox potential on the absorption spectrum. A brief description of each solution variable is included together with suggestions on methods of preparing the colorant solutions to avoid these effects. Illustrations of most of these solution effects on currently available dyes are included. [ABSTRACT FROM AUTHOR]