tailieunhanh - Introduction to Modern Liquid Chromatography, Third Edition part 17

Introduction to Modern Liquid Chromatography, Third Edition part 17. 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. . | 116 EQUIPMENT a 0 20 40 60 80 liL dispensed r --------- 20 pL ------------------ Figure Effect of laminar flow on injection accuracy a Comparison of detector response when loading different volumes into a 20 tL loop b laminar flow profile of sample. Adapted from 12 . simplified description is further complicated by back-flushing and by mixing that takes place when changes in tube diameter or other flow disruptions are encountered. For manualinjection itis besttokeepthe injected oosumcconstbntvndnpO or 200 othen Ipopvoliiteeforenaximnre accurac. AumsiimderDei iijns Autosamplershavelargely a laccdrruinualinjcx l one primnrily forsonseniencs but autosaniplcesrlsopsovide levels cf prrdsionshst m notbe enscilek wi tli manual injection. Many oHsday rcistosamielcrcrcc eajoaHeof RSD of peak area for miecrim volumorof 5beL. foieetfomvolurne cc. y may fell short of this level became vf crrorriiicabbration of the sample syringe or injection loop. Incompleteloopbiiing gvatoiaminisrflow beclron is i b e imonduni diepne ciiK na f 0100 ismoee imnoeeabtthsnacsursyy because 0- 601 6 11 sxeof atvnCardsvcsafibrvacev Aurosomolern are best used va v oyestam-vy1umemjectson modefos eocnmashab so thesamcexoet though notnecessyrflvlccyolSal acmsle voiumyisinjpctcVfsr bxehaclibretinn standards is fallowad. rnjenson acccraoeis fens importmt and tha excanant pravifionwiilnroyidysattren1ysry -11 11 remits. Carryover ss sodipatenbs See presrcse of san apn k sna WanA enee-matogram no enmple injsction that follows ysepaactiye where e n me k wie injected. . .611681 from partof a eemsk nyiabeetaintd en tOn syntpm AUTOSAMPLERS 117 after a separation is complete it is especially a problem when the injection of a low-concentration sample follows that of a high-concentration sample Section . Many autosamplers have features that provide for a wash of the needle and sample-contacting passages between injections to .