Application of 0901 solution color test method in 2020 edition of Chinese Pharmacopoeia in Shanghai

In the field of drug quality control, solution color inspection is an important link, which is related to the appearance quality and internal quality of drugs. The 0901 solution color test method in the 2020 edition of Chinese Pharmacopoeia provides a clear standard and standardized operating process for the detection of drug solution color. Shanghai Jiahang Instrument Co., Ltd. strictly follows the inspection method in the relevant business to ensure the accuracy and reliability of the test results.

I. Overview of solution color inspection method
The 2020 edition of Chinese Pharmacopoeia 0901 solution color test method aims to determine whether the color of the solution meets the standard by comparing the color of the drug solution with the specified standard colorimetric solution, or determining the absorbance at a specific wavelength. The test method gives a clear definition of "colorless" and "almost colorless", "colorless" means that the color of the test solution is the same as water or the solvent used, and "almost colorless" means that the color of the test solution is not darker than the corresponding tone 0.5 standard colorimetric solution.

2. Preparation of standard colorimetric solution
(A) various shades of standard reserve liquid
According to the pharmacopoeia, the colorimetric cobalt chloride liquid, colorimetric potassium dichromate liquid, colorimetric copper sulfate liquid and water were precisely measured according to a specific proportion, and the preparation was mixed and shaken well. Like the green and yellow standard storage solution, it is necessary to take 27ml cobalt chloride solution for coloration, 15ml potassium dichromate solution for coloration, and 58ml copper sulfate solution for coloration. During the preparation process, Shanghai Jiahang Instrument Co., Ltd. strictly controlled the accuracy of each solution, and adopted high-precision measurement equipment to ensure the accuracy of the composition of the standard stored liquid, laying the foundation for subsequent accurate testing.

(2) Standard colorimetric solution of various hue and color numbers
According to Table 2 of the pharmacopoeia, accurately measure the standard storage liquid and water of the color toning number, mix and shake well to obtain. If the standard colorimetric liquid of 0.2 color number is prepared, 0.25ml of the standard reserve liquid of the corresponding hue should be taken and 9.75ml of water should be added. The company records in detail the preparation of each batch of standard colorimetric solution, including solution source, measurement data, preparation time and other information, so as to facilitate traceability and quality control.

(3) Calibration of cobalt chloride liquid, potassium dichromate liquid and copper sulfate liquid for colorimetric use
Colorimetric cobalt chloride solution: Take about 32.5g cobalt chloride, add hydrochloric acid solution (1-40) and dissolve into 500ml. Accurately measure 2ml for titration operation, adjust the solution concentration according to the titration result, so that each 1ml solution contains 59.5mg CoCl₂ · 6H₂O.
Potassium bichromate solution for coloration: Finely weigh 0.4000g of reference potassium bichromate dried to constant weight at 120°C, place in a 500ml measuring bottle, dissolve with water and dilute to scale, then each 1ml solution contains 0.800mg K₂Cr₂O₇.
Colorimetric copper sulfate solution: Take about 32.5g copper sulfate, add hydrochloric acid solution (1-40) and dissolve into 500ml. 10 mL was precisely measured and titrated. Adjusted according to the titration result, the solution contained 62.4mg CuSO₄ · 5H₂O per 1ml.
In the calibration process, Shanghai Jiahang Instrument Co., Ltd. strictly implements the pharmacopoeia operation steps, strictly verifies the purity of the reagent used and the accuracy of the instrument to ensure the accuracy of the calibration results and ensure the quality of the standard colorimetric solution.

3. Inspection methods
(1) The first method (visual colorimetry)
Take the specified quantity of the test product, dissolve it with water, put it in 25ml Nassler colorimetric tube, and dilute it with water to 10ml. Take 10ml of standard colorimetric solution with specified tone and color number and place it in another colorimetric tube. Place the two tubes on the same white background and view them from top to bottom or at eye level. If the color of the test product is not darker than the care, it meets the standard. When it is difficult to distinguish the color depth visually, use the third method (color difference meter method). When performing visual colorimetry, Shanghai Jiahang Instrument Co., Ltd. strictly controls the observation environment to ensure that the background, light and other conditions meet the requirements and reduce human error.

(2) Second method (Ultraviolet-Visible Spectrophotometry)
Take the specified quantity of the test product, add water to dissolve and make 10ml solution, filter if necessary. The absorbance of filtrate shall be measured at the specified wavelength, and the absorbance shall not exceed the specified value. Before using the UV-VIS spectrophotometer for testing, the company calibrates the instrument and verifies the wavelength accuracy to ensure reliable testing data.

(3) The third method (color difference meter method)
1. Working principle: The color difference meter simulates the human vision system, uses the internal analog integrating optical system to integrate the tristimulus value of the spectral luminosity data, and calculates the color L*, a*, b value and color difference ΔE. In CIE Lab * uniform color space, brightness index, chromaticity index and color difference are calculated by correlation formulas to quantitatively analyze color.

2. Instrument requirements: Use a colorimeter with transmission measurement function, lighting observation conditions are 0/0 (vertical illumination/vertical reception), D65 light source lighting, 10° field of view conditions. When measuring transmission color, use a 1cm thick liquid tank unless otherwise specified. The instrument was comprehensively verified regularly and calibrated with water before each measurement. Under the condition of D65 light source and 10° field of view, the tristimulus value was X = 94.81, Y = 100.00 and Z = 107.32. Shanghai Jiahang Instrument Co., Ltd. is equipped with professional personnel responsible for instrument calibration and maintenance to ensure the stability of instrument performance.

3. Determination method: After calibrating the instrument with water, the test product solution and standard colorimetric solution are measured. The color difference between the test solution and water ΔE should not exceed the color difference between the standard colorimetric solution and water ΔE. If the actual color of the test solution is between the two specified tones, the color difference between it and water and the average value of the color difference between the standard color solution and water of the two tones shall not be deeper.

In the actual test, Shanghai Jiahang Instrument Co., Ltd. chooses the appropriate inspection method according to the characteristics of the test product and the pharmacopoeia regulations. For cases where visual colorimetry is difficult to judge, the color difference meter method is given priority to ensure that the test results are objective and accurate, and it strictly follows the requirements of the 0901 solution color inspection method of the 2020 edition of Chinese Pharmacopoeia to ensure the scientific and normative testing of drug quality.