Chromatographic mode sequencing

Procedure. One chromatographic mode was used throughout, but a change in uffer and/or column at each step was used to effect purification. Alternatively, Hez-PBAN was purified by a sequence of three HPLC (RP-HPLC = HP-SEC => RP-HPLC) steps. In this case, changes in chromatographic mode, in addition to changes in buffer and/or column, were used to achieve purification in only three steps. The purity of the product isolated by either procedure was comparable. Similar multi-step procedures have been employed in the isolation of insect neuropeptides in the AKH/RPCH-family (3, 10, 11) and in the isolation of mammalian neu eptides from brain and hippocampus (12). 

An efficient purification process for a given biological usually consists of several consecutive steps, comprising a combination of the different chromatographic modes described above. Only a sequence of separations according to different separation principles can assure that the required... 

It should be pointed out at this point that the isomer distribution presented here fits the experimental observations, but that there still remains uncertainty regarding the sequence of elution of the various isomers except for those in the respective centre peaks of Gl, G2 and G3. Due regard should be given to the fact that iotrolan represents a mixture of racemates and conformers which differ in their physicochemical properties as is demonstrated by their chromatographic separation. For the same reasons, the mode of preparation and purification may influence the composition of a given sample to some extent, but is not believed to bear significantly on the principles outlined herein. 

Agilent GC-MS ChemStation System equipped with capillary gas chromatograph HP 5972,5973, or 6890 series Agilent 6890 series autosampler. The GC-MS system is operated in the positive-ion, chemical-ionization mode the reagent gas is ammonia. The chromatographic parameters of the acquisition method, the sequence of SIM windows, and the ion species being monitored are listed in Tables 3.1.8 and 3.1.9. The total run time is 17.88 min. 

The delicate structure of proteins makes it difficult to achieve all goals of a separation procedure simultaneously. At the moment, the best approach is to find the main goal of a separation and to set the chromatographic conditions according to it. Protein mapping for identification and analytical information, or the isolation of proteins for subsequent chemical analysis of the ratio and sequence of the amino acids can be conducted under conditions that violate the tertiary structure. Separations for this purpose can be performed in reversed-phase mode using organic solvents. 

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