tailieunhanh - Introduction to Modern Liquid Chromatography, Third Edition part 43

Introduction to Modern Liquid Chromatography, Third Edition part 43. 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. . | 376 NORMAL-PHASE CHROMATOGRAPHY The detection of sample bands in TLC as in Figure normally requires the addition of a visualization agent to the plate. For different means of band detection in TLC see 10 . SELECTIVITY Changes in retention order as a result of a change in separation conditions can be quite pronounced when NPC is used with a silica column often much more so than in RPC. This ability to exert a greater control over relative retention with NPC is especially useful for preparative separations where large a values for a compound to be purified allow much larger sample weights and a corresponding reduction in the effort nndcost of sample purification . Solvcnf-StrnngthSelectivity An examph of y u c S telecehoy 1 0e 1 Kss v. sAIrrciigh rhe relative rerintsao cfpeaks 2 3t dovc opt change e M is varied peaks 1 and 4 shaded move toward the front of the chromatogram when B is increased. Iris signifioanrrhar mpleenles2 3 5 and 6 are each snbsritnred with the same potar group -N a wheaeanpeak 1 as 2-aminonaphthalene -NH2 and peak 4 is A-nitropheno -NO2 -0 thasis molecules of eolatee t nnd4 arc substituted r ydiSfsecnc po-argrovpt. Thechavpe in 4with B2vcoeaP4i2 .teater than for ornepermpeundtivthis ssmplc andthii cancearoviblydrsttriOutsd to the presence nttwo volac grouv-inihe molecule -NCh -N 6 comvaieC wille only a singie polas rroupShttfie other aompocndt -N oe-PhCe 2hat Ipw in Equation should vs ioino r peok 4 .so Hvr thp remaininopcoktlsand therefore itiec1en1ion sheoldchangemoretora eiven change in B. T e inmrwPan different behavios ofpeani compered with cvs 3 51and0inthiifesptcSmac be due to i22difSeceatSunc1iaha iiy a o l grovp is ak-l as osposed soa -P group for kv 2p h anV6. To summarice pnono2hprP ehkvg4S in rohtivn retnnti on wrth is hapgeid 0o0 solvent-str2nglhselecsivisa1 ore mote llkeIpfoshsamdle ohat cl 2tains coTpoeihs substitute by hiffeee2tphSar i upr ahPrtpeeialy foecompeimdsrPtn Ciller my numbers oS