The feature that a substance can coincide with its mirror image is called chirality.
The condition that a molecule is chirality:
1. There must be an axis of symmetry.
2. Other deformations must be consistent with the mirror image after rotation. [1]
The term chirality means that an object cannot coincide with its mirror image. For example, our hands, the left hand and the right hand that mirror each other do not coincide.
The word chirality is more commonly used in the field of chemical medicine. A chiral molecule does not coincide with its mirror image. The chirality of a molecule is usually caused by asymmetric carbon, that is, the four groups on a carbon are different from each other. It is usually identified by (RS), (DL) and (±).
Chirality also exists widely in nature. Chirality is a basic attribute of nature.
Chiral molecule and chiral carbon have been widely used since the 1970s, enabling Plane polarized light Materials that rotate left or right are called optically active substances (or photoactive substances). Chiral molecule means that a molecule cannot coincide with its mirror image. Chiral molecules must be photoactive substances.
Enantiomer : The two are mirror images of each other, but cannot coincide. They are two different compounds. The optical rotation ability is the same, but the direction is opposite, just like the left and right hands. To investigate whether a molecule is chiral, we can start from the presence or absence of chiral carbon, but the most fundamental is to look at the molecular symmetry.
Necessary and sufficient conditions for chiral molecules:
① No symmetry plane; ② No symmetrical center; ③ No axis of symmetry is exchanged.
One of the three is indispensable, but generally speaking, it only requires whether the molecule has a symmetry plane or a symmetry center. (Note: The axis of symmetry cannot be used as a criterion.) [1]
HPLC Chiral stationary phase Chiral stationary phase (CSP) method is one of the important methods for the analysis of chiral drugs in vivo. However, due to the low selectivity of CSP, the CSP method is often unable to be directly used for the analysis of chiral drugs in vivo, and the use of the non chiral column chiral column coupling technology can overcome this shortcoming. The direct injection method has made some initial progress in the automation of chiral drug analysis in vivo. Chiral column chiral column coupling technology
Based on biological samples Endogenous substance The internal standard substance is easy to interfere with the separation of the chiral drug to be measured and the interaction between the chiral drug to be measured and its chiral metabolites. In many cases, the CSP method cannot be directly applied to the analysis of chiral drugs in vivo. The combination technology of chiral column and non chiral column can not only improve the Chiral stationary phase The separation capacity can make up for the above shortcomings and extend the service life of CSP column. Chiral column chiral column coupling technology refers to the technology that connects the chiral column with the chiral column in a certain way. After the sample is injected into the pretreated sample, it is first loaded onto the chiral column along with the mobile phase. The measured chiral drug is separated from the interfering component or multiple chiral drugs are separated from each other, and then the measured chiral drug enters the chiral column to be separated or separated independently without interference, They do not interfere with each other. Generally, there are two connection modes: column switching system and direct connection system. [2] 1 Achiral column chiral column switching system
1.1 Column switching mode Since Edholm et al first used column switching mode to analyze chiral drugs in biological samples, the switching mode of non chiral column chiral column has little change. Generally, six way valves are used to connect the two columns, and a spiral tube or concentration precolumn is added, or the direct transfer method is used. The main change is the number of detectors and their positions. Initially, only a single detection was placed behind the chiral column to detect the enantiomeric ratio. When determining the absolute amount of enantiomers, another separate non enantioselective HPLC system is required for the determination of the total amount of enantiomeric mixture, and then calculate the absolute amount of each enantiomer according to the percentage method. Wainer et al. put another detector at the outlet of the mobile phase of the non chiral column to determine the total amount of the enantiomeric mixture. In this way, no additional HPLC system is required for the determination of the absolute amount of enantiomers, but two injections are required. Gimenez et al. put the above detector directly on the non chiral column, and measured the total amount of enantiomer mixture and the enantiomer ratio with only one sample injection, thus obtaining the absolute amount of enantiomer. Gimenez and others further improved the above system, using only a single detector to simultaneously measure the total amount of enantiomer mixture and the enantiomer ratio, but using a double switching valve.
1.2 Flow matching in the column switching mode One of the preconditions for using the column switching mode is that the two column flows are correspondingly similar and compatible. CSP often has various restrictions on mobile phase. Some CSPs can only be used for normal phase, and some cannot tolerate higher concentrations of organic solvents. In fact, it is not always possible to find similar compatible mobile phases. One solution is to use mobile phase transformation technology. Oda et al. added a concentration column and a dilution tube between the chiral column and the chiral column. When the measured chiral drug enters the spiral tube, use another mobile phase 2 (M2) compatible with the chiral column (C3) mobile phase 3 (M3) to dilute and transfer the mobile phase 1 (M1) containing the measured substance to the concentration column (C2). By controlling the flow rate of mobile phase 2 (M2), the mobile phase 1 (M1) of the chiral column (C1) is greatly diluted and almost completely changed into mobile phase 2 (M2), thus overcoming the problem that M1 and M3 are incompatible and difficult to separate. This technology is applied to Verapami Determination of enantiomers of ketoprofen, fluranil and their chiral metabolites. 1.3 Peak broadening is inevitable during column switching. Therefore, although column switching increases the non stereoselectivity of CSP, it often reduces the enantioselectivity of CSP, which may make the two enantiomers unable to achieve baseline separation, thus affecting the detection sensitivity. Therefore, it is necessary to minimize peak broadening to improve detection sensitivity.
2 Achiral column chiral column direct connection system
Without switching valve, the method of direct connection between the chiral column and the non chiral column can improve the peak broadening caused by the column switching to a certain extent and reduce the analysis time, but it is more strict with the mobile phase requirements, because the two columns need the same mobile phase, and can not selectively switch the measured substances like the column switching mode.
Application of Chiral Column Chiral Column Coupled Technique
Chiral column - chiral column coupled technique has been applied to the in vivo analysis of many chiral drugs. as Terbutaline (phenyl column - β - cyclodextrin column), folinic acid (phenyl column BSA column), mefloquine (cyano column - (S) - naphthylurea column, cyanopropyl column - (S) - naphthylurea column), Verapami (ODS column OVM column), ketoprofen (ODS column OVM column), verapamil and norverapamil (di alcohol column Chi rapak AD column). [2] 
