High performance capillary electrophoresis - T.E.A.M.
High performance capillary electrophoresis - T.E.A.M. High performance capillary electrophoresis - T.E.A.M.
Principles the exact pI of fused silica is difficult to determine, EOF becomes significant above pH4. Nonionic materials such as Teflon also exhibit EOF, presumably resulting from adsorption of anions. Counterions (cations, in most cases), which build up near the surface to maintain charge balance, form the doublelayer and create a potential difference very close to the wall (figure 5b). This is known as the zeta potential. When the voltage is applied across the capillary the cations forming the diffuse double-layer are attracted toward the cathode. Because they are solvated their movement drags the bulk solution in the capillary toward the cathode. This process is shown in schematic form in figure 5c. The magnitude of the EOF can be expressed in terms of velocity or mobility by or v EOF = (e z / h) E (7) m EOF = (e z / h) (8) where: v EOF = velocity m EOF = EOF “mobility” z = zeta potential e = dielectric constant. (note the independence of mobility on applied electric field) The zeta potential is essentially determined by the surface charge on the capillary wall. Since this charge is strongly pH dependent, the magnitude of the EOF varies with pH. At high pH, where the silanol groups are predominantly deprotonated, the EOF is significantly greater than at low pH where they become protonated. Depending on the 20
a) Principles b) c) Figure 5 Development of the electro-osmotic flow: a) negatively charged fused silica surface (Si-O - ) b) hydrated cations accumulating near surface c) bulk flow towards the cathode upon application of electric field 21
- Page 1: An introduction High performance ca
- Page 4 and 5: Copyright © 2000 Agilent Technolog
- Page 6 and 7: Foreword Capillary electrophoresis
- Page 8 and 9: Table of content Foreword .........
- Page 10 and 11: Scope The purpose of this book is t
- Page 12 and 13: Introduction 1.1 High performance c
- Page 14 and 15: Introduction sis, methods for on-ca
- Page 16 and 17: Principles 2.1 Historical backgroun
- Page 18 and 19: Principles that ion. The mobility i
- Page 22 and 23: Principles µ EOF × 10 -4 (cm 2 /
- Page 24 and 25: Principles For the analysis of smal
- Page 26 and 27: Principles µ EOF ( × 10 -4 cm 2 /
- Page 28 and 29: Principles Total length Effective l
- Page 30 and 31: Principles Note that equation (15)
- Page 32 and 33: Principles determined by the capill
- Page 34 and 35: Principles Current (uA) 300 250 200
- Page 36 and 37: Principles The contribution of inje
- Page 38 and 39: Principles k' H N H, µm 0.001 0.58
- Page 40 and 41: Principles Figure 19 Electrodispers
- Page 42 and 43: Principles rapidly eluting ions, th
- Page 44 and 45: Principles 44
- Page 46 and 47: Modes Mode Capillary zone electroph
- Page 48 and 49: Modes 3.1.1 Selectivity and the use
- Page 50 and 51: Modes Name pK a Phosphate 2.12 (pK
- Page 52 and 53: Modes EOF No flow Figure 22 Elimina
- Page 54 and 55: Modes Absorbance 214 nm 0.05 0.04 0
- Page 56 and 57: Modes Type Comment Silylation coupl
- Page 58 and 59: Modes Type Result Comment Extremes
- Page 60 and 61: Modes Figure 29 CZE of reversed pha
- Page 62 and 63: Modes Figure 33 Ion analysis of fer
- Page 64 and 65: Modes The separation mechanism of n
- Page 66 and 67: Modes the stationary phase in LC. S
- Page 68 and 69: Modes Amplitude 2 a) with a migrati
a)<br />
Principles<br />
b)<br />
c)<br />
Figure 5<br />
Development of the electro-osmotic flow:<br />
a) negatively charged fused silica surface (Si-O - )<br />
b) hydrated cations accumulating near surface<br />
c) bulk flow towards the cathode upon application of electric field<br />
21
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