tailieunhanh - Introduction to Modern Liquid Chromatography, Third Edition part 32

Introduction to Modern Liquid Chromatography, Third Edition part 32. 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. . | 266 REVERS ED-PHASE CHROMATOGRAPHY FOR NEUTRAL SAMPLES mobile phases will often provide a better separation. This proved to be the case for the present sample. A 1 1 blend of the mobile phases of Figure 46 ACN and Figure 61 MeOH was prepared and used to obtain the separation of Figure new mobile phase containing 23 ACN - 30 MeOH provides baseline resolution Rs . Figure Variation of log k with B for regular and irregular samples. Regular sample a mixture of herbicides 24 separated on a Cig column with methanol-water as mobile phase see Fig. for other conditions b plot of values of S versus log kw for data of a c irregular sample of Figure conditions as in Figure d plot of values of S versus log for data of c . a b Adapted from 25 . SELECTIVITY 267 Figure Continued While the separation of Figure is much improved further variation in the proportionsole mob ilephasefrom Figure 46 ACN and Figure 61 MeOH may provide some more resolution. Peaks 1 to 4 in Figure are less resolved than remaining peaks 5 to 10 . peaks 1-4 are critical so we will limit our discussion to these peaks. Figures replicate earlier chromatograms for peaks 1 to 4 for changesin therelativeproportions of ACN . As MeOHrspiaceeACNot roingfrom t-Of ir is seen thatpeaks hsnd3 thpded mhvetowerp thafrostof the chramat gtam. In Figure from Pig. c the critrcai least resolved peek-w or it 2 3 andwt cat imptovett tesriroinn byr tustPtsmpvemene 268 REVERSED-PHASE CHROMATOGRAPHY FOR NEUTRAL SAMPLES 46 ACN k FL 5 0 2 4 6 8 10 12 14 Time min b 34 ACN 2 k 14 Rs 1 2 5L 8 a9- I I I I I 0 20 40 Time min Figure Separation of a mixture of substituted benzenes as a function of solvent strength B . Sample 1 p-cresol 2 benzonitrile 3 2-chloroaniline 4 2-ethylaniline 5 3 4-dichloroaniline 6 2-nitrotoluene 7 3-nitrotoluene 8 toluene 9 3-nitro-o-xylene 10