What are the advantages of glass chromatographic column
Glass chromatographic column, with large opening and fast feeding, does not need the cooperation of other instruments. The upper part can be made into a standard mouth to connect with other standard mouth glass instruments, but it is not easy to measure. There is a lot of liquid left under the screen, and the chromatographic speed is slow and inaccurate. It is generally used for experiments that require less precision.
The size of the chromatographic column is determined according to the amount of the separated substance, and the ratio of its diameter to its height is determined according to the separation difficulty of the separated mixture, generally between 1:8 and 1:50. The column body is thin and long, and the separation effect is good, but the amount of separation is small, and the separation time is long; The column body is short and thick, and the separation effect is poor, but more samples can be separated at one time, and the time required is short. If the components of the substance to be separated are difficult to separate, slender columns should be selected. If a large number of mixtures that are easy to separate or have low requirements for separation purity are to be processed, thick and short columns can be selected. The ratio of diameter to length of commonly used chromatographic columns ranges from 1:8 to 1:15.
The glass chromatographic column used in the laboratory has two forms: one is the glass tube with piston at the lower part, and the piston core is made of polytetrafluoroethylene, so that vacuum grease can not be applied to avoid polluting the product. If an ordinary glass piston is used, the vacuum grease should be carefully applied thinly and evenly. The other is to thin the lower end of the glass tube and cover it with a section of tube with good elasticity. This section of pipe must not be dissolved by eluent, and ordinary rubber pipe cannot be used for this purpose generally, because rubber is easily swollen by chloroform, benzene, THF and other solvents, while polyethylene pipe is inert to most solvents, so it is often used. A spiral clamp is used to control the flow rate. In addition, the film plastic column is used more and more widely due to its advantages such as convenient use, saving eluent and reducing evaporation. Film plastic columns are always stored in flat rolls, with deep creases on both sides. Before use, one end of a section of film tube cut shall be fastened, and the other end shall be sleeved on a section of glass tube and fastened with cotton thread. Pass the glass tube through a single hole plug. Then put the membrane tube into a thick and long glass tube with a thin lower end, so that the plug can tightly plug the mouth of the large glass tube. Pump air from the lower end of the large glass tube, and the membrane column will automatically circle because the internal pressure is greater than the external pressure. After the adsorbent is loaded, several small holes can be punched in the lower part of the adsorbent for use.