tailieunhanh - Introduction to Modern Liquid Chromatography, Third Edition part 50

Introduction to Modern Liquid Chromatography, Third Edition part 50. 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. . | 446 GRADIENT ELUTION a change in k Eq. . For irregular samples this can result in changes in selectivity. As selectivity for a gradient method should have been optimized step 5 of Table prior to a change in column conditions it is important to maintain the same values of k and a when changing column conditions and N . This can be achieved by maintaining tcF L constant Eq. for example if column length is doubled gradienttime must also Ire doubled tuthot tG L staysconstant if flow rateis doubted- gaadienr time mostbadecraassd bs Oalf st as toksep toF constant. Forsxamples ol ibisapjcssaOi to optiimaingadr . As long as values oik aremasntainedfonstantinthis wny a changeinsflumn lenfth or flow rate hoe tUs some effectronruo time and satolution meiUserisocraOc ar gradient elo iom A miiiorrxoeutionto Oh cuIecagoxcurSoxahd esscSutie af -cute peaks in tbeshromotogram adrloearrvaluecoCOD regardas oXwhefoes tb is held constaua lt i ll Whep oh ma conbiifonsarechunged for u te msn-eh brudisu die isiw tseg for each segmen- mast aeaOjuarrd to a oa maintum SugFOO cun tant. Ooe example emsrldet -Pe the stuOlent isO 23S4O B in 0 32 C 8min. tSeoilmolenofowrre dbubleO foe Isirgth eachregmsiit tug would alss rrqmee doubliug othetthanewaradient would be 0 23 42 B in 0 64 76 min. De tamcioe Nngessary Cxiusen-SnsilibeationUime gSteg tl of Table After meahod development ls foe resulting HPLC procedme t column mu 7 washedbnweeiisuccessivegradmntruns tha snfficnmtpolnmc of mobile phase whose aompoostionmatchis thatoffonmolnile phase atthe start of the . 5 B in the examples of Fig. . This column-equilibration step is intdirded co slfowfo-SC the holduoaolume Vs uedwell-tlmo tD VD F of the gragianreobidmsots 2 xaUicctrauudinb Suction sU l Gow equilibrationotfocItctfongryphare temnvaI ul excise h-rotoenI wgeG swindling from high Uai thcmd etone usaOient isfow Batshe .