tailieunhanh - Introduction to Modern Liquid Chromatography, Third Edition part 33

Introduction to Modern Liquid Chromatography, Third Edition part 33. 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. . | 276 REVERS ED-PHASE CHROMATOGRAPHY FOR NEUTRAL SAMPLES We presently have a more complete understanding of the basis of column selectivity than for other kinds of selectivity solvent strength solvent type temperature etc. . As discussed in Section column selectivity can be quantitatively defined by five different characteristics column hydrophobicity coli n siaoicrosisiance O column hydrogen-bond acidity 51 colnmnltychogen-bondbaoiohy B column cation-eochiuigeoapabisn C For the case of iibritealsaniplcs oolythe first four column parameters H S A B are important. Theelif n iirci ii iclodtivii of two columns for a neutral sample can be charactericrdey aidlecclvityfudclion Fft -C that is defined by Equation below Secticc S-SoU scoalsc . For the columns of Ftgure compared to the Symmetry column values of Fs C are equal to 26 for the Alltima wFiirnio 12 fortOeLuna velrmn onf Oh foo thrOpheeisosbvoiemn. A value of F--Cl ScanSeadio pocentiolly signihcans nhanges mreletive rotvnslon as observeyfoitdisoxampla. Linger chcnnes inoelatiue retentiooas a asulloln change in columnare ohcerved forioniasvmplesbroause the colnmnparemescr Si has a rnu 1 101 101 11 on coiemnsoiectivitySor sunhsamplee. Isomer Ceperani on u Compounds thal resemHeevoh olOars1 nctusclly tenStahyvesimiloa brinesorV and are often moredifficclt to c t ruc. l eRi Cc pai nC c n nCisomericoompounds is therefore commonly regarded as challenging. While this may be somewhat true general one r evemof uhdRPCsepararron of 137 different isomer-parrs with alkylsilica columns 37 fouiidthat90 of these samples could be separated wtth Rs bysimpSuoptiiinzingS yB 12 wirl i sc by i -foOi ami temaeratore T varied 0 as much os 2 S fil. An ooavoylo is ahowy oi spo che separationoS1hrechbProoyseafoo1ctodeisomsrt ooaC18Oo1umn es n ftmiC ioh of tempers 4P0allthree noimTowmhm wudX C. the threeisnmersare separated weth Sis m genercClySavooa bettersepdry1iony0