tailieunhanh - Introduction to Modern Liquid Chromatography, Third Edition part 28

Introduction to Modern Liquid Chromatography, Third Edition part 28. High-performance liquid chromatography (HPLC) is today the leading technique for chemical analysis and related applications, with an ability to separate, analyze, and/or purify virtually any sample. Snyder and Kirkland's Introduction to Modern Liquid Chromatography has long represented the premier reference to HPLC. This Third Edition, with John Dolan as added coauthor, addresses important improvements in columns and equipment, as well as major advances in our understanding of HPLC separation, our ability to solve problems that were troublesome in the past, and the application of HPLC for new kinds of samples. . | 226 THE COLUMN Phenyl columns Cyano column X OH OH w ww lwwy1 Othefcolumns Column type Embedded-polar-group ri I Fluoro columns X R-NH- C O -O- R-NH- C O -NH- R- C O -NH- Sub-type Carbamate . Urea Amide Perfluorophenyl PFP -CF2CF2CF3 h oroalkyl Figure RPC columns classified according to the ligand figures omit the connecting silane group -Si CH3 2- . simplified cartoons of Figure the SifCHs group is omitted in Fig. 5A9a-d . The ligand of a RPC column is often an alkyl group for example C3 Cg Cig Fig. .Alternatively the ligand may consistof phenylpropyl or phenylhexyl called pheytylco xxrnns . If the ligand is -C3-C N Fig. we have a cyano column. The alkyl group may also be substituted by other functional groups X Fig. and this fietr tisesylhe additiyoal column typeilistefas tOr b-kom of Figure 549. io-rallsd emeudOtd-aoiarggtooy EPG phystihavtboenarowiug in popularity bedduse ot stair oompylibilltywith low BmyOiie phaees drey-reduced silonoi h ten ctiei i trdisyiqud elecsit ity iSettion petk ihbpe for basic solufeuis usuallyqdte good withpiese coliuims. The iigandsinthesrphaset contain amidk cardamate nrea allof wOich yoertronfnyOeopen-bdPd brtor Or other poler fimisiobalgroeps emboadedwirhm lira lipandetruclyre. Some EPG COLUMN SELECTIVITY 227 packings tend to be less stable than comparable alkyl or aryl columns. The nature of the ligand mainly determines column selectivity which is the subject of following Section . COLUMMSELECTIVITY Column sekctivity can be important for different reasons. During method development a change of column may be necessary to improve selectivity and increase resolution Sections . For the latter application we must be able to identify a secondcolumn with quite z rmselectivity. When a routine RPC procedure is used at different times and places a replacement column from the same source may not be immeifcatslyavLitable locally ortoocsstly or impsK tKYlisr otherreasons .