Chromaticity measurement corresponding to Water Test Methods

November 12, 2020

Introduction

Quantitative chromaticity measurement is used to examine the water quality. This is the one of examination to analyze the coloration degree of water by humic acids which is created by microbe decomposition of plants. In Water Test Methods and ISO 7887 (Method C), the chromaticity is evaluated by absorbance using UV-Vis spectrophotometer around 390 nm and at 410 nm where the yellow color of humic acids is observed.

This article introduces JASCO’s chromaticity measurement system based on Water Test Methods. In addition, this report also shows the detection limit, the determination limit and the calibration curve using 100 mm optical path length cell of this system.

Experimental

Chromaticity test method
The water sample is put into 50 mm or 100 mm cell, and absorption measurement is carried out at 390 nm. In case of suspension, centrifuge or filtration is required.

Chromaticity measurement procedure
(1) Prepare the standard solution. The blank sample is purified water filtrated by 0.2 µm membrane filter.
(2) Create the chromaticity calibration curve by the above blank sample and standard solution.
(3) Pretreat the water sample. Conducting centrifuge separation or filtering with membrane filter as appropriate, the supernatant solution is extracted.
(4) The water sample (3) is injected to the cell and the absorbance measurement is carried out at the 390 nm. By using the calibration curve (2), the chromaticity of water sample can be calculated.

Standard sample
“Wako’s Color standard solution (100)”* is diluted by adding purified water to prepare the following chromaticity standard.
Color standard solution: 0, 0.1, 0.5, 1, 5, 10, 50, 100 degree

*The other procedure to prepare the chromaticity standard shows as below.
(1) Dissolve 2.49 g platinum chloride potassium and 2.02 g cobalt chloride with 200 ml hydrochloric acid.
(2) Add the purified water to the solution so that 1 L solution is created.
The chromaticity of this solution is defined as 1000 degree of chromaticity.

Measurement
(1) The blank measurement was carried out by ultrapure water.
(2) To check the measurement repeatability, the measurement of chromaticity 0 degree sample was carried out ten times.
(3) The absorbance measurement of each samples was carried out to create the calibration curve.

Figure 1. Absorption spectrum of standard sample (pathlength: 100mm)

<Measurement parameter>
UV/Vis bandwidth:  2.0 nm
Response:  0.96 sec

Keywords

Chromaticity, Water Test Methods, ISO 7887, detection limit, determination limit

Results

Table 1 shows the result of the measurement repeatability of chromaticity 0 degree. The values in the middle row are the absorbance, and the values in the right row are the chromaticity calculated by using the calibration curve.

Table 1. Measurement repeatability of chromaticity 0 degree

Absorbance Chromaticity
1 0.00006 0.00434
2 0.00012 0.00868
3 -0.00002 -0.00145
4 -0.00016 -0.01158
5 0.00014 0.01013
6 0.00025 0.01809
7 -0.00007 -0.00506
8 0.00012 0.00868
9 0.00026 0.01881
10 0.00008 0.00579
Ave. 0.00008 0.00564
S.D. 0.00013 0.00960

The table 2 and figure 2 show the absorbance of the standard sample and the calibration curve.

Table 2. Chromaticity and absorbanceof each standard sample

Chromaticity Absorbance
0 0.0016
0.5 0.0085
1 0.0146
5 0.0721
10 0.1429
50 0.6958
100 1.3742

Figure 2. chromaticity calibration curve

The obtained calibration curve has high correlation, whose coefficient of determination (R2) is more than 0.9999 within a range of 0.1 degree to 100 degree. The result of measurement repeatability with use of 100 mm pathlength cell indicates that the detection limit is 0.03 degree and determination limit is 0.1 degree*.

*The calculation of detection limit is based on 3.3σ and the determination limit is based on 10σ.
σ: Standard deviation in chromaticity 0 degree.

Conclusion

JASCO can provide the chromaticity measurement system consisting of  UV/Vis spectrophotometer, Long Path Cell Holder, integrating sphere and [Chromaticity/Turbidity Measurement] Program. You can apply this system to the turbidity measurement (JIS K 0101, JIS K 0400-9-10, ISO 7027 and ASTM D 7315) as well as the chromaticity measurement (Water Test Method, ISO 7887).

Figure 3. [Chromaticity/Turbidity Measurement] Program

About the Author

Spectroscopy Group