Chiral drugs refer to a class of drugs in which the three-dimensional structure of the molecule and its mirror images cannot overlap each other. A pair of drug structures that are mirror images of each other but cannot overlap are called enantiomers. Enantiomers have different degrees of optical rotation: left-handed, right-handed, and racemic. The chiral labeling of drug molecules is usually R/S labeling.
Analysis methods and techniques
One of the most critical items in manual analysis is the choice of mobile phase. Normally, normal phase is used for manual analysis. The most used mobile phases are n-hexane, n-heptane, alcohol and isopropanol. The mobile phases for elution were ethanol and isopropanol, and n-hexane and n-heptane were used to adjust the elution strength of the mobile phase. N-heptane and n-heptane have little effect on sample separation and will not change the selectivity and resolution. They can usually be mixed. However, n-heptane is much less harmful to human body than n-heptane, but the price It is twice that of the latter, so many large pharmaceutical companies in Europe and the United States use n-heptane more, while domestic use more n-heptane.
Alcohol and isopropanol play a key role in the separation of samples. Different alcohols have different selectivities. Changing the type of alcohol can change the selectivity. The commonly used alcohols are alcohol and isopropanol. Methanol cannot be used. Because it is immiscible with n-hexane and n-heptane, and the viscosity of tert-butanol is too high, it is generally used as an additive with a small amount of alcohol or isopropanol to provide special selectivity and usually have unexpected effects.
It is often necessary to add acid or base to the mobile phase to adjust the peak shape. Common acids are trifluoroacid, nitric acid and methanesulfonic acid. For isobutylamine, the concentration of acid and base added to the mobile phase is generally required to be controlled below 0.2% (volume ratio). Yes, it contains acidic groups and basic groups. It depends on which group has a stronger effect. For some amphoteric samples containing amino groups, such as phenylalanine, methanesulfonic acid is a very good solution. The sulfonic acid group can inhibit the basicity of the amino group and provide an acidic mobile phase environment, so that the sample can be well separated and symmetrical peak shape can be obtained.
Generally, when we do purity analysis to detect impurity content, we need to use low wavelength as much as possible to make as many impurities as possible to have UV absorption, and when doing manual analysis, we need to use the highest possible wavelength to remove the impurities at low wavelengths. There is interference from absorbing impurities. As a general principle, try to choose the place with the best UV absorption of the sample to obtain higher sensitivity. However, adding amine to the mobile phase will cause the baseline fluctuation to become larger at low wavelengths, making the system difficult to In this case, it is generally necessary to increase the detection wavelength. During the actual operation, some samples have very poor absorption at high wavelengths, and can only be detected at low wavelengths. For such samples, try adding an excess amount when the sample is diluted. Diamine (but not too much) and neutral mobile phase to obtain satisfactory analytical results.
For some samples, the effect of adding only alkali or acid is not good. You can try to add acid or alkali to the sample at the same time. I have encountered such a sample, and only adding acid or alkali is tailing, and the baseline separation cannot be achieved. In this case By adding acid and base at the same time, a very nice peak shape and good resolution were finally obtained. In practice, some samples are too alkaline, and there is no peak at all after injection. If you look closely at low wavelengths, you can feel that the baseline has been drifting. At the beginning, it is suspected that the sample concentration is not enough. After increasing the sample concentration, the sample peak cannot be seen. , adding diamine or triamine to the mobile phase and then injecting the sample, adding acid or base to the mobile phase basically does not provide additional selectivity, but it can improve the resolution.