The colorimeter is an essential analytical instrument in drug analysis. We now give some suggestions to the operator on the problems encountered in the installation, debugging, maintenance, and testing of the instrument.
Issues that should be noted
Linearity of instrument photometric
It is well known that light absorption analysis must conform to the linear relationship of the Lambert-Beer law. The degree of photometric linearity of the instrument is related to the strength of the light source energy, the minimum detection limit of the receiver optical signal, the highest receiving ability and the quality and performance of the monochromatic color.
The photometric accuracy
Hotometric error In daily use, it is often difficult to test the photometric accuracy and reproducibility. To measure correct and reliable data depends on :① the source of the sample. ②Sample preparation technology (including weighing, volume, solvent reagents, pH value, time, temperature, etc.) ③Sample cell quality (sample holder position, cell quality, etc.). ④ The performance of the instrument itself (optical system performance, amplifier stability and linearity, receiver linearity and noise level, mechanical system or computer control ability of the instrument, etc.). ⑤ Instrument operation (baseline zero calibration blank control, etc.).
Quantitative analysis method: choose a suitable calculation method, especially in the calculation method, there are derivatives, simultaneous equations, etc., The most commonly used cup calibration curve method uses this method because the sample linearity is poor, and its influencing factors are many, such as in the wavelength The standard curve method is only used when the variation is in a considerable range and it is easy to produce large errors. If for no standard or other reasons, the standard curve measured by others in other environments and other instruments is used for direct reference, then the error is conceivable.
There are some suggestions
In quantitative analysis, there are calculation method reference substance method and absorption coefficient method calculation method, which should be clear in concept. The pocket colorimeters given by the intelligent instrument should be reasonably selected to avoid the substitution of systematic errors; the reference substance method is to compare the reference substance with the test sample. , The operation is simple, the operational requirements of the instrument are not high, and even sometimes the requirements for the blank control are very small. Under the same conditions, the error of the measurement results is small, the source standardization and recognition of the reference substance are high, and the sampling volume and dilution factor are required. Not too small;
In conclusion
In short, for the use of colorimeter, in addition to the use of qualified metrological verification instruments, it is necessary to understand the performance of this instrument and the degree of adaptability to the tested samples, in order to be used in drug research, drug standard formulation, standard modification and inspection. There is no large error in the results due to improper use in the process. As long as you pay attention and read the instruction manual carefully, you can avoid some unnecessary errors and make the test data correct and reliable.