is the method of measuring the relative concentration of saturated hydrocarbons, aromatics, and olefins in a petroleum product (usually a solvent or light distillate), as determined by test method ASTM D 1319. The sample is passed through a column where it reacts with three dyes, each sensitive to one of the components. The relative concentration of the component is indicated by the length of the respective dyed zoned, viewed under ultraviolet light, which brings out the coloration of the dyes.