Annex A (Normative) Determination of color

A.1 Principal

The absorbance of a series of standard Pt-Co color calibration solutions is measured at 373 nm by spectral photometer and standard calibration curve is made. The absorbance spectrum of industrial lineal alkylbenzene is similar to that of Pt-Co color solution. Measure the absorbance of sample liquid the same wave length as that of standard solution, and calculate the hazen value via calibration curve.

Hazen: unit of color, the color of an aqueous solution containing 1mg of Pt (K2PtCl6) and 2 mg of Co (CoCl2·6H2O)per litre.

A.2 Chemical reagent

A.2.1 K2PtCl6

A.2.2 CoCl2 · 6H2O

A.2.3 Hydrochloric acid, G.R. ρ20=1.19

A.3 Apparatas

Ordinary laboratory apparatus and

A.3.1 Spectrophotometer, capable of measure thetransparency at 373 nm, 430 nm, 455 nm, 480 nm, 510 nm, up to reading 0.005.

A.3.2 Glass cell 1 cm, 5 cm, 10 cm.

A.4 Procedure

A.4.1 Preparation of Pt-Co standard stock solution

Weigh 1.245 g of K2PtCl6(A.2.1) and 1.000 g of CoCl2· 6H2O (A.2.2) into a beaker, add 100 mL of water to dissolve. Then, add 100 mL of Hydrochloric acid (A.2.3)to beaker to dissolve the solid completely. Quantitatively transfer the solution to a 1,000 mL volumetric flask, make up to volume with water, shake well.

Pippette the stock solution into 10 cm cell, measure the absorbance at 373 nm, 430 nm, 455 nm, 480 nm, 510 nm by specturmphotometer (A.3.1), respectively. The test value shall be in accordance with the range specified in Table 1.

Table 1. The allowed range of transparency and absorbance of color stock solution with 500 Hazen

A.4.2 Preparation of Pt-Co standard calibration solution

Transfer appropriate volume of stock solution according to Table 2. to 100 mL volumetric flasks, respectively, dilute to the mark with water. These are standard calibration solutions.

Table 2. Standard calibration solution

Use semi micro burette, when measure precisely the light color under 15 Hazen, to pipette carefully the stock solution according to volume specified in Table 3, into 100 mL volumetric flasks, respectively, dilute to the mark with water. These 15 flasks form the standard calibration solutions.

Table 3. Standard calibration solution with light color

A.4.3 Test of standard

Measure the absorbance of prepared solution at 373nm against water, use 1 cm or 5 cm cell (use 5 cm cell for solutions Hazen ＜100; otherwise, use 1 cm cell.). Draw a calibration graph, Hazen as X-axis and Absorbance as y-axis.

A.4.4 Test of sample

Fill the cell with sample liquid, light colored sample in 5 cm cell and dark colored in 1 cm cell. Measure the absorbance at 373 nm against water. Find the corresponding hazen on the curve as the sample color.

A.5 Precision

The absolute difference between two independent single test results, obtained using the same method on identical test material in the same laboratory by the same operator using the same equipment within a short interval of time, will not exceed the repeatability limit (r) in more than 5% of cases. R expected to be less than 8.