The following data were obtained for four compounds separated Compound on a 20-m capillary column. t. (min) W (min) А 8.04 0.15 B 8.26 0.15 8.43 0.16 Calculate the selectivity factor for compound A and B. b. What is the average number of theoretical plates for the column? Calculate the resolution and selectivity factors for compounds A and B. а. с.

The following data were obtained for four compounds separated Compound on a 20-m capillary column. t. (min) W (min) А 8.04 0.15 B 8.26 0.15 8.43 0.16 Calculate the selectivity factor for compound A and B. b. What is the average number of theoretical plates for the column? Calculate the resolution and selectivity factors for compounds A and B. а. с.

Principles of Instrumental Analysis

7th Edition

ISBN:9781305577213

Author:Douglas A. Skoog, F. James Holler, Stanley R. Crouch

Publisher:Douglas A. Skoog, F. James Holler, Stanley R. Crouch

Chapter26: An Introduction To Chromatographic Separations

Section: Chapter Questions

Problem 26.18QAP

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A molecular exclusion column has a diameter of 7.8 mm and a length of 30 cm. The solid portion of the particles occupies 20% of the volume, the pores occupy 40%, and the volume between particles occupies 40%. (a) At what volume would totally excluded molecules be expected to emerge? (b) At what volume would the smallest molecules be expected? (c) A mixture of polymers of various molecular masses is eluted between 23 and 27 mL. What does this imply about the retention mechanism for these solutes on the column?
The following data give the recovery of bromide from spiked samples of vegetable matter, measuredusing a gas–liquid chromatographic method. The same amount of bromide was added to each specimen(Roughan, J.A., Roughan, P.A. and Wilkins, J.P.G., 1983, Analyst, 108: 742).Tomato: 777 790 759 790 770 758 764 ug/gCucumber: 782 773 778 765 789 797 782 ug/g(a) Test whether the recoveries from the two vegetables have variances which differ significantly.(b) Test whether the mean recovery rates differ significantly.
hree components in a mixture have varying distribution constants between the mobile phase and the stationary phass One of the components has a very low distribution constant, Would this component likely elute first or last and how would you design an experiment or modify the components of the separation to make it perform in the opposite manner?
(i) Calculate the capacity factors (k') for both compounds A and B and the selectivity factor (a) between them, commenting on the values. (ii) Calculate the resolution between A and B and comment on it. (iii) Using the peak for A, calculate the number of theoretical plates for the GC column and comment on the quality of the column.
(h) Describe a chromatographic technique that could be suitable for studying the molecular weight distribution of poly(phenylenevinylene) derivatives that are soluble in organic solvents. Explain the physical basis on which separation could occur and suggest how the polymers could be detected after elution.
Two species A and B are known to have water/hexane partition coefficient of 5.99 and 6.16. They are separated by elution on silica gel with hexane as eluent. The ratio for the packing VS/VM =0.425a) What column length should be used to provide a resolution of 1.5 if the plate height ofthe packing is 1.5 ×10-3 cm? b) If the flow rate is 6.75 cm min-1, how long will it take to elute the two species?
What effect will the following have on plate height (H). Make sure to explain your full and complete reasoning. Reducing the rate of sample injection.
Benzene and toluene, when analysed isothermally on a 25 m × 0.25 mm i.d. capillary GC column, were found to have retention times of 8.56 and 8.67 min, respectively. An unretained solvent passed through the column in 4.10 min in the same analysis. The peak widths at half height for benzene and toluene were 4.2 and 4.3 seconds, respectively. Calculate: a) The capacity factor for each of these compounds b) The selectivity factor for the separation c) The average number of plates for the column d) The resolution between benzene and toluene. Are they completely separated under these conditions? e) What is the plate height (H) for this column? What can you say about the efficiency of this column? Explain f) The dimensions of a column with the same phase ratio required to obtain a resolution of 1.5 under otherwise identical conditions
State TWO benefits of the mobile phase being prepared by the instrument rather than having to be prepared manually by the lab technician.
Which statements are true for molecular exclusion chromatography?I Molecular exclusion chromatography separates on the basis of size.II Small molecules can fit in the pores of the stationary phase and effectively pass through a larger volume, and elute last.III The pores in the stationary phase are too small for large molecules to pass through, so large molecules elute first.IV Molecular exclusion chromatography with a hydrophilic stationary phase and an aqueous solvent is called gel permeation chromatography. A. I, II, III B. III and IV C. II only D. I and II only E. I, III, and IV
Two species A and B are known to have water/hexane partition coefficient of 5.99 and 6.16.They are separated by elution on silica gel with hexane as eluent. The ratio for the packingVS/VM =0.425a. Calculate the retention factor for each soluteb. Calculate the selectivity factorc. How many plates are needed to provide a resolution of 1.5?d. What column length should be used to provide a resolution of 1.5 if the plate height ofthe packing is 1.5 ×10-3cm?e. If the flow rate is 6.75 cm min-1, how long will it take to elute the two species? (the question wanted to be answered)
Structural elucidation of a sample component is possible through point estimation of its components with modern instrumentation methodologies. Additionally, characterization of their chemical nature is possible through qualitative analytical methods. A - If the first statement is TRUE and the second statement is FALSEB - If the first statement is FALSE and the second statement is TRUEC - If both statements are TRUED - If both statements are FALSE