tailieunhanh - Introduction to Modern Liquid Chromatography, Third Edition part 13

Introduction to Modern Liquid Chromatography, Third Edition part 13. 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. . | 76 BASIC CONCEPTS AND THE CONTROL OF SEPARATION Gradient elution refers to a continuous change in the mobile phase during separation such that the retention of later peaks is continually reduced that is the mobile phase becomes steadily stronger B increases as the separation proceeds. An illustration of the power of gradient elution is shown in Figure where all peaks for the sample of Figure b are separated to baseline in a total run time of slightly more than7nunutes with approximately constant peak widths and comparable detection senaitivityaar eaeh pesk aatamiaaa simiiardetactotrespanse for each swlt tee TheaOanuwaes aagiadientelutionfoo thissampleereobvious. Gradient elotionaltocan Us uaedto deaiwttheevtral ethes separation oroblems as discussed nfnrther aiscnsoionoS gaudiens eOution see Chapt i- 9. Peak Cnaacityandawa-d mensloualSepasation So far we haae escdcsiiical rctoletio. Rp os Aemetitre criterion is appaa iotswhen the peaks ofintereoo in echaamaloerpmcue th be le someoxeene and our goal is some minimum resolution for all peaks. Some samplaaeornmoso ma y sp n et. .howe that npmpracneal to a significaiicrcsolution forallpeaksof interest. Thenweneed adifferpnt measure of separation fewer farveeloun eonabneatie isof exeerimentaicon capacity ofa eeuoaatieoevfoesta thaootal numberofpseks tOaa canbefitima a chaomatoesam when eve. peakis e oan t edtat m aUjaceiit oeaks withRs t. An example isthawnin faaoaptentiuoaongauf 0 t atO and Na l 0. For isocraeia ttpaoaOon peekvoeueiey iogiveney a31 PC 1 WM - 14- 5log nû Vo where tR refers to the retention time of the last peak in the chromatogram. For typical separations with k 20 for the last peak and values of N as large as 20 000 PC 108. If we exclude peaks with k so that 4 20 the peak capacity drops to PC 93 if we require Rs 2 t e iiemberrA pcalct thaa fit between k and 20 drops to 47.