Investigación sobre el método de calibración del analizador de color de fármacos líquidos por el método de aberración cromática
This paper proposes a calibration method for drug color analyzers based on the working principle and main measurement characteristics of chromatic aberration method drug color analyzers. The method is scientific, reasonable, and applicable and can be used as a reference for relevant metrologists and instrument users.
With the further development of the economy, China’s medical career has also stepped on a new ladder. Drugs provide protection for people to prevent and treat diseases and have a close relationship with human health; therefore, good quality assurance of drugs plays an important role in safeguarding people’s health and life safety. In recent years, the quality of liquid drugs has received widespread attention. The solution color has a close relationship with the nature of the drug itself, the purity, and the content of impurities, and the change of the solution color is a visual manifestation of the change in the intrinsic quality of the drug. Liquid drug color analyzer mainly adopts the third method (i.e., colorimeter method) of solution color checking method in the Chinese Pharmacopoeia to detect the color and quickly measure the color number of the sample to be tested which is close to the standard colorimetric solution through the built-in software.
At present, colorímetro has been widely used. Liu Jundang et al. established a method to detect the color of Salvia divinorum polyphenolic acid solution through the principle of the colorimeter method, and the measurement results showed that the precision and repeatability items performed well. Liu Wei et al. established the corresponding relationship study on colorimeter and standard colorimetric liquid color, hue, and color difference. They used it for the color check of Qingkailing injection, which concluded that the solution color of injection could be checked accurately by the colorimeter method directly, suggesting that sensitive solution color determination is of practical significance for the safety control of traditional Chinese medicine injections. Kitamura Tomo et al. selected a specific component aqueous solution to determine the cause of drug color change. They predicted its solution color change under the addition of kinetics. Tong Baoguang et al. used the curve to determine the titration volume of the reaction endpoint, the curve endpoint using the color change before and after the reaction of loratadine, effectively avoiding the endpoint error caused by human vision. However, there are no corresponding national and local measurement specifications for the effective traceability of this type of equipment, so to ensure the accuracy and reliability of its measurement results, it is necessary to explore practical calibration methods.
1. Measuring principle of liquid drug color analyzer by color difference method
The principle of chromatic aberration liquid drug color analyzer is to use the colorimeter with transmission measurement function to directly determine the color of the solution of the transmission of the three stimulus values and quantitative expression and analysis of color. The analyzer has a built-in color database of the standard colorimetric solution of the Chinese Pharmacopoeia, which can quickly give the hue and color number of the standard colorimetric solution of the Chinese Pharmacopoeia that is the most similar to the sample. It can determine the color and the color difference quicker, more accurately, and quantitatively.
2. Colorimetric liquid drug color analyzer calibration method
Based on the measurement principle of the color difference method drug color analyzer, refer to JJG595-2002 “Colorimeter Calibration Regulations”, to determine the calibration items of the liquid drug color analyzer, i.e., instrument repeatability, instrument stability, instrument error, and the calibration method of each calibration item.
2.1 Standard substances for calibration
Standard colorimetric liquid: adopt the six color grades of yellow-green standard colorimetric liquid YG-1, YG-3, YG-5, YG-7, YG-9, and YG-11 in the Chinese Pharmacopoeia; use the blackboard for calibration.
2.2 Calibration items and calibration methods
2.2.1 Adjustment of the instrument before calibration
According to the requirements of the instrument manual, warm up the instrument first, and after the instrument is warmed up and stabilized, place the blackboard used for calibration in the test stand and cover the test cover, and then calibrate the instrument with the blackboard. After calibration, remove the blackboard, place the cuvette with distilled water (the amount of distilled water should be more than 2/3 of the total volume of the cuvette) in the test stand, and perform a blank calibration of the instrument.
2.2.2 Instrument error
After the blackboard and blank calibration of the instrument, take the yellow-green standard colorimetric solution YG-1, YG-3, YG-5, YG-7, YG-9, and YG-11 for testing and record the values of Y, x, y. Repeat the measurement 3 times, and the difference between the standard colorimetric solution’s average and standard values indicates an error. The measurement data of the signal value error of the instrument are shown in Table 1.
In the formula: Y0, x0, y0-standard colorimetric value of the standard colorimetric liquid; Y¯, x¯, y¯-measurement of the standard colorimetric liquid by the instrument to obtain the average value.
Table.1 YG-5 yellow standard colorimetric liquid colorimetric error measurement data
|Tristimulus||Test value1||Test value2||Test value3||Average value||Reference value||Indication error|
2.2.3 Instrument repeatability
To the requirements of the instrument manual, the instrument was turned on first to warm up. After the instrument was warmed up and stabilized, the YG-5 standard colorimetric liquid was selected. Then the color difference between the standard colorimetric liquid and pure water was measured (ΔE), and it was measured 7 consecutive times. The relative standard deviation of the measurement results was calculated according to equation (2), which is the instrument’s repeatability. The instrument repeatability measurement data are shown in Table 2.
In the formula: Sr-relative standard deviation of 7 measurements; ΔE-mean value of 7 measurements; ΔEi-the i-th measurement value.
Table.2 Instrument repeatability measurement data
|Number Of Tests||1||2||3||4||5||6||7|
|Valor de prueba||7.91||7.93||7.92||7.91||7.94||7.93||7.92|
|Relative Standard Deviation||0.14%|
2.2.4 Instrument Stability
Under the condition of repeatability measurement, YG-5 standard colorimetric liquid was selected to test the color difference between the standard colorimetric liquid and pure water. The color difference between the standard colorimetric liquid and pure water was tested every 5 min, and 7 consecutive measurements were made. The relative standard deviation of the measurement results was calculated according to the formula (3), which is the instrument’s stability. Instrument stability measurement data is shown in Table 3.
Table.3 Instrument stability measurement data
|Tiempo de prueba||0min||5min||10min||15min||20min||25min||30min|
|Relative standard deviation||0.17%|
2.2.5 Instrument Linearity
Adjust the parameters of the instrument to the best test state, use the YG-5 standard colorimetric solution as the reserve solution, measure different volumes of the reserve solution, dilute different concentrations of the working standard solution with pure water, take the proportion of the standard colorimetric solution in the working standard solution as the horizontal coordinate, and the value of the color difference as the vertical coordinate to calculate the linear regression equations and correlation coefficients. The instrumental linearity test data are shown in Table 4.
Linear regression equation:
In the equation: ΔEi-the color difference between the standard colorimetric solution and water for each measurement; ΔE¯-the average of the color difference between the standard colorimetric solution and water for 3 measurements; di-the ith colorimetric solution concentration; d¯-the average of the 3 times colorimetric solution concentration; d¯-the average of the 3 times colorimetric solution concentration; and d¯-the average of the 3 times colorimetric solution concentration. i-th colorimetric liquid concentration; the d¯-mean value of 3 times colorimetric liquid concentration; a-intercept of the working curve; b-slope of the working curve; r-linear correlation coefficient.
Table.4 Instrumental linearity test data
|Proportion of standard colorimetric solution||0.05||0.1||0.25||0.5||0.75|
|Color difference value||1.55||3.13||7.84||15.36||23.08|
|Linear regression equation||ΔEi=0.0672+30.681di|
|Linear correlation coefficient||1|
Solution color is an important indicator of drug quality; the state attaches great importance to it and has formulated national and industry standards on various color analysis methods. Meanwhile, the 2020 edition of Chinese Pharmacopoeia also gives the latest solution color-checking method. In this paper, the calibration method of colorimeter is studied, and the instrument users and metrologists can refer to this method to calibrate the relevant instruments and guarantee the traceability of the value of such instruments.
Author: Zhang Jin, Li Xianhong, Mo Hongbo