Download Chromatographic Systems. Maintenance And Troubleshooting by John Q. Walker (Auth.) PDF

By John Q. Walker (Auth.)

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Some workers (3,4) claim that round and sharp bends in LC columns have advantages by decreasing the resistance to mass transfer of sample components passing through the column. Presumably, small voids and packing homogeneities are formed within the column which are virtually impossible to reproduce. If these columns are not excessively long, the overall efficiencies may be poor, yet reproducible, within certain limits. There are no advantages realized in reproducing poor efficiencies. For example, in using a narrow-bore column ten feet in length having two or three sharp bends and correspondingly two or three voids, it follows that column efficiency may be drastically impaired.

High pressure sample valve for liquid chromatography usable at pressures to 5000 psig. Connections are: (A) Mobile phase, (B) Chromatographie column, (C) Sample, (D) Drain, (E) and (F) Solenoid actuated 2-way pneumatic valve. Air source is 50-100 psig. (Courtesy of Hamilton Company) The sample injection system must be kept clean. Again, this is best accomplished via miscible solvents and may be carried out simultaneously with pump cleaning. The use of corrosive solvents should be eliminated as most injectors will be damaged by such treatment.

I. Halasz and M. Naefe, Anal. p. 76, 1972. , Vol. 44, LIQUID CHROMATOGRAPHY 61 QUESTIONS AND ANSWERS Question: Answer : Question: Answer : Question: Answer : Why does dead volume in the injector and column ends have more detrimental effects in LC than GC? Because in LC, the diffusion rates for liquids is 10 D times less than for gases and, hence, 10« the time duration of solutes in the void or dead volume area causes band broadening which lowers the efficiency. Of the modes possible in high speed LC, namely adsorption, partition, reversed-phase and ionexchange, which one seems to yield better quantitation?

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