Chromatographic Theory

Transcription

1 Updaed: 23 Ocober 204 Prin version CEE 772: Insruenal Mehods in Environenal Analysis Lecure #3 Gas Chroaography: asic Chroaographic Theory (Skoog, Chap. 26, pp ) (Harris, Chap. 238) ( ) David Reckhow CEE 772 #3 References: Chroaographic Theory Skoog, Principles of Insruenal Analysis 985 (3 rd ed): pars of Chaper (4 h ed): pars of Chaper (5 h ed): pars of Chaper 26 David Reckhow CEE 772 #3 2

2 Chroaography basics The basis for gas chroaography is he disribuion of a saple beween 2 phases, naely a saionary phase and a gas phase Gas Chroaography A echnique for separaing volaile subsances by pariioning beween he vapor phase and a dissolved or solid phase Gas Liquid Chroaography Saionary phase is a liquid. Gas Solid Chroaography Saionary phase is a solid. David Reckhow CEE 772 #3 3 Coponens of a Chroaographic Syse Source of Carrier Flow (obile phase) Cylinder of carrier gas or solven boles Injecion por (saple inle) Colun wih saionary phase Deecor(s) Signal Transducers & Daa Analyzers Recorders, inegraors Copuers for library aching Conrollers Teperaure conrols for injecors, coluns and deecor Flow conrollers and pressure regulaors David Reckhow CEE 772 #3 4 2

3 A Gas Chroaograph Three Heaed Zones Injecor Deecor Carrier Gas Colun Oven Daa Syse Gas Chroaograph David Reckhow CEE 772 #3 5 David Reckhow CEE 772 #3 6 3

4 The Colun Gas Chroaograph Saionary Phase Fused Silica Open Tubular Colun Colun Wall A A Gas Flow Mobile Phase David Reckhow CEE 772 #3 7 David Reckhow CEE 772 #3 8 4

5 saple obile phase A+ A A A David Reckhow CEE 772 #3 9 Solven Exracion: LLE & Chroaography Organic phase Aqueous phase A org A aq A aq A org K = [A] org [A] aq Chroaography: Mobile phase Saionary phase A A s A David Reckhow CEE 772 #3 0 A s A = Analye C = Concenraion of analye = obile phase s = saionary phase K = C s C 5

6 Two Measures of Reenion. Relaive reenion: = r2 r = 29 s 209 s = Capaciy facor: k = r - = = 3.98 David Reckhow CEE 772 #3 Linear Pariioning This equilibriu is governed by linear pariioning, where he raio of he concenraion of a solue in he saionary phase (C s ) o he concenraion in he obile phase (C ) is a consan, known as he saionary phase pariion coefficien, K S K S C C s David Reckhow CEE 772 #3 2 6

7 Reenion Tie The average rae a which a solue igraes along a colun, v-bar, is direcly proporional o he fracion of ie ha i spends in he obile phase.. This is dependen on he pariion coefficien u fracion of ie solue spends in obile phase # oles of solue in obile phase u oal # of oles of solue v u C CV V C V David Reckhow CEE 772 #3 3 s s v u And now we define, a capaciy facor C C s Which is equal o he ass of analye in he saionary phase o ha in he obile phase v u K S V s V Vs V k K S V s V David Reckhow CEE 772 #3 4 7

8 8 where is he residence ie of he obile phase in he colun David Reckhow CEE 772 #3 5 k u v v L R u L or k L L R David Reckhow CEE 772 #3 6 R k k u L R

9 Exaple I Sequenial counercurren exracions David Reckhow CEE 772 #3 7 Exaple II Separaion of Maleic acid fro fuaric acid using eher and 0.5 F HCl A. 0 ransfers. 25 ransfers C. 40 ransfers Fro: Pos, 987, pg.60 David Reckhow CEE 772 #3 8 9

10 Gaussian Concenraion Profile W David Reckhow CEE 772 #3 9 Theoreical Plae odel The plae odel supposes ha he chroaographic colun is conains a large nuber of separae layers, called heoreical plaes. Separae equilibraions of he saple beween he saionary and obile phase occur in hese "plaes". The analye oves down he colun by ransfer of equilibraed obile phase fro one plae o he nex. I is iporan o reeber ha he plaes do no really exis; hey are a figen of he iaginaion ha helps us undersand he processes a work in he colun.they also serve as a way of easuring colun efficiency, eiher by saing he nuber of heoreical plaes in a colun, N (he ore plaes he beer), or by saing he plae heigh; he Heigh Equivalen o a Theoreical Plae (he saller he beer). David Reckhow CEE 772 #3 20 0

11 If he lengh of he colun is L, hen he HETP is HETP L N The nuber of heoreical plaes ha a real colun possesses can be found by exaining a chroaographic peak afer eluion; where w /2 is he peak widh a half heigh. David Reckhow CEE 772 #3 2 To nex lecure David Reckhow CEE 772 #3 22