TAILIEUCHUNG - Introduction to Modern Liquid Chromatography, Third Edition part 38

Introduction to Modern Liquid Chromatography, Third Edition part 38. 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. . | 326 IONIC SAMPLES REVERSED-PHASE ION-PAIR AND ION-EXCHANGE CHROMATOGRAPHY Inertsil ODS-3 bases 1-5 ---------- 10 Time min ses 1 5 0 2 Time min Figure7-9 Continued Other Conditions That Can Affect Selectivity Conditions that are less used today for the control of RPC selectivity include buffer type . phosphate acetate ammonium buffer concentration ammcmodificrs Buffer typeisnotcommonly .omidered asa meansof controlling selectivity for the separation of however buffer type can affect the effective pKiofavoSute which is equivalent to a change in pH. The largest changes m eolyneoeerynifgn will occur when a baste buffer . arnmouturn methylamine etc. replaces an acidic buffer such as phosphate or acetate and vice versa. Another wayinwhlcKbuSfertppe ceu comribute 70 seleatlvity ss by Inin pairing .Mote OeOuindoby luffeoesyshas srsfluoroaceiate TFA or especiu7u heptafluoroAutyrete UTFBA eos ion-aair wilhprytenuted baccsKH and 01 6 1116 ee ntk n SOhKhe stease inesteniion foraeotonateO bases incroyeec with ehe posftive sOargcon the aelutr moleuwSe cs m fhecete of peptidet whic4coweainmuhspielbcsioamino-ueidrsslPuef ihi . Soction . TheuseofTSK anPHFBAefbwefefsilPoisohAeftoproblemithefart common for otherion-oaieseparefionr . SEPARATION OF IONIC SAMPLES BY REVERS ED-PHASE CHROMATOGRAPHY RPC 327 Buffer concentration usually has only a minor effect on relative retention for separations at low pH on modern type-B alkylsilica columns 26 . However for separations at pH 6 and or older type-A columns Section protonated bases can be retain by ion exchange as a result of interaction with ionized silanols of silica-based column packings. Ion-exchange retention decreases as mobile-phase ionic strength ina-easesO i ois ri withtheresult thatan increase in buffer concentrationwilltendtodecreasetheretentionofprotonatedbases 31 . Aminenenditrers such as triethelamine

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