PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Column ChromatographySlide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Separation Methods Based on Distributions in Discrete Stages (9/23/13)1. Chemical Separations: The Big Picture Classification and comparison of methods2. Fundamentals of Distribution Separations3. Separation Methods Based on Distributions in Discrete Stages Such as solvent extraction and distillation4. Introduction to Distribution Separations in chromatographic methods. The plate theory, the rate theory; van Deemter's equation.1A. Chromatography vs. Countercurrent distribution1. Both techniques involve the interaction of solutes with a mobile phase and stationary phase Countercurrent distributionstationary phase mobile phaseChromatographystationary phasemobile phase2. Countercurrent distribution is based on a well-defined number of contacts between the mobile and stationary phases (i.e. discrete contact method) Chromatography involves continuous contact between the mobile and stationary phase (i.e. continuous contact method)Basics of Chromatography23. Separation of solution in both methods depends on a. differences in the retention of solute (i.e. their interaction with mobile and stationary phase, distribution coefficients). b. The efficiency of the the system (i.e., the number of transfers or the width of the solute peaks).B. Type of Chromatography1. Based on type of mobile phase: a. Gas chromatography b. Liquid chromatography c. supercritical fluid chromatography2. Based on type of support a. Packed bed (column) chromatography b. Open tubular (capillary) chromatography c. Open bed (planar) chromatography3. Based on the elution method: a. Constant column condition (e.g., isocratic conditions = constant mobile phase composition, isothermal conditions (T), or isobaric conditions (pressure). b. Variable column conditions (e.g., gradient elution, stepwise elution, temperature programming, pressure programming).34. Based on the type of sample development:Frontal developmentDisplacement developmentElution development(under equilibrium)(with displacer in theMobile phase)(solutes continuously Introduced with mobilephase). The Essence of Chromatography: p64C. Chromatography Parameters:(1) Time vs. detector response:Where: tR = Retention time tM= Void time (or dead time, hold-up time) time for mobile phase entering column reach the detector. Wb = Baseline width of the peak (in time units) Wh = Half-height width of the peak (in time units)(2) Volume vs. detector response:Where: VR = Retention volume VM= Void volume of mobile volume (volume of mobile phase filling the column) Wb = Baseline width of the peak (in volume units) Wh = Half-height width of the peak (in volume units)The Essence of Chromatography: p85Column ChromatographyColumn ChromatographyChromatogramDilution &Peak broadening!6(3) Relationship of volume and time response:VR = tR X FVM = tM X FWhere: F = Flow-rate of solvent through the column(4) Adjust retention times and volumes Adjusted retention time (tR’) = tR – tM Adjusted retention Volume (VR’) = VR - VMThese adjusted parameters are useful in that they better reflect the true retention of solute one the system (i.e. they correct for the void time contribution to the solute’s total elution time).7D. Solute Retention:(1) A solute’s retention time or volume is important since it is related to the strength of a solute’s interactions with the mobile and stationary phases.(2) The capacity factor (k) is commonly used in chromatography as a measure of solution retention, where k = = q / pMoles Astationary phaseMoles Amobile phase(3) k can be experimentally related to tr’ or Vr’ by the following equations:k = tR’/tM = (tR – tM)/tM k = VR’/VM tR = tM(1+k) = (L/u)*(1+k)L : length of columnu: the average mobile phase velocity8E. Efficiency of Chromatography and Plate Theory: 1. Efficiency in chromatography is related experimentally to solute’s peak width (e.g., an efficient system will present narrow peaks)2. Efficiency in Chromatography is related theoretically to various kinetic and thermodynamic process occurring in the column: e.g., equilibrium, diffusion, and fluid (mobile phase) flow. 3. Plate theory for describing the efficiency of chromatography (proposed by Martin and Synge). Plate theory has contributed significantly in understanding the formation of bands and band broadening. Assumptions: a. Chromatography column can be divided into s number of volume elements or imaginary sections, called plates. b. At each plate the partitioning of the solute between stationary and mobile phase is rapid and equilibrium reached before the solute goes to the next plate. c. The solution distribution is constant and is independent with the solute concentration.This theory has been replaced by rate theory. However, the number of plats (N) and plate height (H) are stilled used to evaluate the efficiency of chromatography.The Essence of Chromatography: p269Lstationary phase mobile phaseCraig apparatus(a) After given number of transfers (r), the relative amount of A in any tube n is Pr,n =r!n! (r-n)!pn qr-nWhere: Pr,n = Fraction of A in tube n after transfer r.(b) The binomial can be expended as Gaussian distribution when n larger than 20 (rpq>3).Pr,n =2πrqp*1Exp [-(n-rp)2/2rpq)]Where: Pr,n = Fraction of A in tube n after transfer r.Column104. Properties of Gaussian curve. y= y0 Exp[-x2/2σ2]Where: y = Height of curve at position x y0 = Maximum height of the curve (at x = 0) σ = standard deviation of the curve(a). The general form of a Gaussian curve is shown below:(b). Measures of σ in Gaussian curves.Wi = 2 σ (width at peak’s inflection points, y = 0.607 y0)Wh = 2.354 σ (width at half-height of the peak. y = 0.5 y0)Wb = 4 σ (measured by drawing tangents to the curve at peak’s inflection points. and measuring the peak width where they intersect the baseline.The Essence of Chromatography: p25115. Theoretical plates(a). The peak width, or variance, is related to column efficiency, but also increase with solutes retention (i.e., k, tR, or VR).(b). To compare the efficiencies of the solute with different retentions, the number of theoretical plates (N) is often used, whereN = (tR/ σt)2Wb = 4 σWh = 2.354 σN =