logging in or signing up CHM1222Chromatograph yTheory Arley33 Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINTLite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 1032 Category: Entertainment License: All Rights Reserved Like it (0) Dislike it (0) Added: October 16, 2007 This Presentation is Public Favorites: 1 Presentation Description No description available. Comments Posting comment... By: emymohamedaly (18 month(s) ago) i wanna to download this ppt please. Saving..... Post Reply Close Saving..... Edit Comment Close By: emymohamedaly (18 month(s) ago) its really very good Saving..... Post Reply Close Saving..... Edit Comment Close Premium member Presentation Transcript Introduction to Chromatography Theory: Introduction to Chromatography Theory Bioanalytical Chemistry Spring 2004The Theory of Chromatography: The Theory of Chromatography Plate theory - older; developed by Martin & Synge Rate theory - currently in use todayPlate Theory - Martin & Synge 1954 Nobel Laureates: Plate Theory - Martin & Synge 1954 Nobel Laureates View column as divided into a number (N) of adjacent imaginary segments called theoretical plates within each theoretical plate complete equilibration of analytes between stationary and mobile phase occursPlate Theory - Martin & Synge 1954 Nobel Laureates: Plate Theory - Martin & Synge 1954 Nobel Laureates Significance? Greater separation occurs with: greater number of theoretical plates (N) as plate height (H or HETP) becomes smaller L = N H or H = L / N where L is length of column, N is number of plates, and H is height of platesN can be Estimated Experimentally from a Chromatogram: N can be Estimated Experimentally from a Chromatogram N = 5.55 tr2 / w1/22 = 16 tr2 / w2 where: tr is retention time; w1/2 is full width at maximum w is width measured at baseline Choice of Column Dimensions: Choice of Column Dimensions Nmax = 0.4 * L/dp where: N - maximum column efficiency L - column length dp - particle size So, the smaller the particle size the higher the efficiency!Efficiency Relative to Analysis Time: Efficiency Relative to Analysis Time N Analysis Time, min 1970’s 300 mm L 10 um today 150 mm L 5 um today 90 mm L 3 um 10 100First Important Prediction of Plate Theory: First Important Prediction of Plate Theory Bandspreading - the width of bands increases as their retention time (volume) increasesProblem:: Problem: A band exhibiting a width of 4 mL and a retention volume of 49 mL is eluted from a column. What width is expected for a band with a retention volume of 127 mL eluting from the same analyte mixture on the same column? ANS: 10.4 mLSecond significant prediction of plate theory: Second significant prediction of plate theory The smaller HETP, the narrower the eluted peakPlate Theory - Practical Considerations: Plate Theory - Practical Considerations Not unusual for a chromatography column to have millions of theoretical plates Columns often behave as if they have different numbers of plates for different solutes present in same mixtureRate Theory: Rate Theory Based on a random walk mechanism for the migration of molecules through a column takes into account: band broadening effect of rate of elution on band shape availability of different paths for different solute molecules to follow diffusion of solute along lengthVan Deemter Equation: Van Deemter Equation H = A n1/3 + B/n + C n where: H is HETP (remember want a minimum!) n is mobile phase velocity A, B, and C are constants Van Deemter Equation: Van Deemter Equation H = A n1/3 + B/n + C n first term - rate of mobile phase movement through column (often just a constant) second term - longitudinal solute diffusion; solute concentration always lower at edges of column so solute diffuses longitudinally third term - equilibration is not instantaneous Resolution: Resolution Ideal chromatogram exhibits a distinct separate peak for each solute reality: chromatographic peaks often overlap we call the degree of separation of two peaks: resolution = peak separation average peak widthResolution: Resolution Resolution = D tr / wavg let’s take a closer look at the significance of the problem:Resolution: Resolution So, separation of mixtures depends on: width of solute peaks (want narrow) efficiency spacing between peaks (want large spacing) selectivityExample: Example What is the resolution of two Gaussian peaks of identical width (3.27 s) and height eluting at 67.3 s and 74.9 s, respectively? ANS: Resolution = 2.32 You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.
CHM1222Chromatograph yTheory Arley33 Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINTLite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 1032 Category: Entertainment License: All Rights Reserved Like it (0) Dislike it (0) Added: October 16, 2007 This Presentation is Public Favorites: 1 Presentation Description No description available. Comments Posting comment... By: emymohamedaly (18 month(s) ago) i wanna to download this ppt please. Saving..... Post Reply Close Saving..... Edit Comment Close By: emymohamedaly (18 month(s) ago) its really very good Saving..... Post Reply Close Saving..... Edit Comment Close Premium member Presentation Transcript Introduction to Chromatography Theory: Introduction to Chromatography Theory Bioanalytical Chemistry Spring 2004The Theory of Chromatography: The Theory of Chromatography Plate theory - older; developed by Martin & Synge Rate theory - currently in use todayPlate Theory - Martin & Synge 1954 Nobel Laureates: Plate Theory - Martin & Synge 1954 Nobel Laureates View column as divided into a number (N) of adjacent imaginary segments called theoretical plates within each theoretical plate complete equilibration of analytes between stationary and mobile phase occursPlate Theory - Martin & Synge 1954 Nobel Laureates: Plate Theory - Martin & Synge 1954 Nobel Laureates Significance? Greater separation occurs with: greater number of theoretical plates (N) as plate height (H or HETP) becomes smaller L = N H or H = L / N where L is length of column, N is number of plates, and H is height of platesN can be Estimated Experimentally from a Chromatogram: N can be Estimated Experimentally from a Chromatogram N = 5.55 tr2 / w1/22 = 16 tr2 / w2 where: tr is retention time; w1/2 is full width at maximum w is width measured at baseline Choice of Column Dimensions: Choice of Column Dimensions Nmax = 0.4 * L/dp where: N - maximum column efficiency L - column length dp - particle size So, the smaller the particle size the higher the efficiency!Efficiency Relative to Analysis Time: Efficiency Relative to Analysis Time N Analysis Time, min 1970’s 300 mm L 10 um today 150 mm L 5 um today 90 mm L 3 um 10 100First Important Prediction of Plate Theory: First Important Prediction of Plate Theory Bandspreading - the width of bands increases as their retention time (volume) increasesProblem:: Problem: A band exhibiting a width of 4 mL and a retention volume of 49 mL is eluted from a column. What width is expected for a band with a retention volume of 127 mL eluting from the same analyte mixture on the same column? ANS: 10.4 mLSecond significant prediction of plate theory: Second significant prediction of plate theory The smaller HETP, the narrower the eluted peakPlate Theory - Practical Considerations: Plate Theory - Practical Considerations Not unusual for a chromatography column to have millions of theoretical plates Columns often behave as if they have different numbers of plates for different solutes present in same mixtureRate Theory: Rate Theory Based on a random walk mechanism for the migration of molecules through a column takes into account: band broadening effect of rate of elution on band shape availability of different paths for different solute molecules to follow diffusion of solute along lengthVan Deemter Equation: Van Deemter Equation H = A n1/3 + B/n + C n where: H is HETP (remember want a minimum!) n is mobile phase velocity A, B, and C are constants Van Deemter Equation: Van Deemter Equation H = A n1/3 + B/n + C n first term - rate of mobile phase movement through column (often just a constant) second term - longitudinal solute diffusion; solute concentration always lower at edges of column so solute diffuses longitudinally third term - equilibration is not instantaneous Resolution: Resolution Ideal chromatogram exhibits a distinct separate peak for each solute reality: chromatographic peaks often overlap we call the degree of separation of two peaks: resolution = peak separation average peak widthResolution: Resolution Resolution = D tr / wavg let’s take a closer look at the significance of the problem:Resolution: Resolution So, separation of mixtures depends on: width of solute peaks (want narrow) efficiency spacing between peaks (want large spacing) selectivityExample: Example What is the resolution of two Gaussian peaks of identical width (3.27 s) and height eluting at 67.3 s and 74.9 s, respectively? ANS: Resolution = 2.32