3.1. Appearance of Analysis
The reference and sample were visually assessed in a horizontal
direction in the light box with a white background. If the system
suitability criteria are met (i.e., the solution color must be such that
purified water is colorless) and the reference color solutions have
detectable color and can readily be distinguished in the relative color
intensities, we proceeded with the sample analysis. With the
prolongation of heat treatment time, changes to the appearance were
noted (Table 1).
Table 1. Analysis of sample appearance.