PURPOSE: To simplify the analysis of chromate treating liquid composition element, by a method wherein after the total Cr in the treating liquid is determined, Cr 6+ is settled from the treating liquid separately to determine Cr 3+ from the residual solution and then, the value of Cr 3+ is subtracted from the total Cr value to obtain Cr 6+ .
CONSTITUTION: When a chromate treatment of a Zn plated steel plate is carried out by a chromate treating liquid, the composition elements are analyzed. Here, first, a raw chromate treating liquid undergoes an X ray fluorescence analysis to determined the total amount of Cr. Separately, BaCl 2 or the like is added to the raw chromate treating liquid and made to react with only Cr 6+ to be settled as BaCrO 4 while Cr 3+ and Zn 2+ left as intact without being settled. The balance of the solution undergoes X ray fluorescence analysis to determine the amount of Cr 3+ and Zn 2+ . Then, the amount of Cr 6+ is determined by subtracting the amount of Cr 3+ from the total amount of Cr. Thus, the addition of a simple chemical pretreatment to the X ray fluorescence analysis eliminates the need for any costly apparatus to enable the determination of Cr at a high accuracy by patterns while permitting automatic analysis online.