tailieunhanh - HPLC A Praactical User'S Guide Part 5

Tham khảo tài liệu 'hplc a praactical user's guide part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | COLUMN SELECTION 71 1-3 cm in length they can be inverted and backwashed without causing them to void. Please do not wash the guard column down the main column. Disconnect and reverse it reconnect and use the pump to pump a strong solvent through it into a beaker. This may seem obvious but I had to troubleshoot a persistent detector problem that turned out to be caused by a chromatographer who washed a guard column into his main column. Since the guard column is placed in the injector column path it does contribute to the separation. Methods development should be completed with the guard column in place. The increased separating length usually overcomes the effect of extra tubing as long as the connecting tube between the guard and analytical columns is kept as short and as fine as possible. The wrong diameter tubing can really mess up a separation. Changing guard columns in the middle of a series of runs generally has little effect on the separation. However it is usually a good idea to follow the change with a standard QA run as a check. The other type of protective in-line column is the saturation column. This column is used when operating conditions tend to dissolve the main column bed . high pH high temperature etc. . In theory the packing in the saturation column dissolves first and protects the main column packing. As long as the same bonded phase is used in the pre-column the column running character does not seem to change. Using this technique I had a customer who ran taurine separations at pH 12 for a year on the same C18 column. Care must be taken that the saturation column does not break through erosion of the main column will begin immediately if this happens. A guard column will serve as a saturation column but is not recommended since the pre-column bed is consumed and band spreading will occur. Usually the saturation column is placed in the flow from pump to injector. At this point the column to be used can be slurry packed with no regard given