d. In Figure 4, each stationary phase shows some negative correlation between plate count and retention factor. In other words, as k' increases, N decreases. Explain this relationship between k' and N. Plate Count (N) 4000 3500 2500 2000 1500 1000 Figure 4. Column efficiency (N) vs retention factor (k') for 22 nonionizable solutes on FMS (red), PGC (black), and COZ (green). 3000 Eluent compositions (acetonitrile/water, A/W) were adjusted to obtain k' less than 15, which was achieved for most solutes as follows: FMS (30/70 A/W), PGC (60/40), COZ (80/20). Slightly different compositions were used for the most highly retained solutes. All columns were 50 mm × 4.6 mm id and packed with 5 um particles, except for COZ, which was packed with 3 um particles. All other chromatographic conditions were constant: column length 5 cm, column j.§. 4.6 mm, flow rate 2 mL/min, column temperature 40 °C, and injection volume 0.5 μL Log(k'x/K'ethylbenzene) FMS 1.5 1.0 0.5 0.0 ཐྭ ཋ ཤྩ བྷྲ ; 500 0 5 10 Retention Factor (k') 15 e. Figure 5 shows retention factor data for 16 solutes used in the hydrophobic subtraction model (HSM), which is used to characterize how ionizable solutes will behave on a new stationary phase. (You will notice that many of the HSM solutes are weak acids and/or weak bases.) Which stationary phase (FMS or C18) is better at retaining the HSM solutes? Why is this the case? 12 15 Figure 5. Retention of 16 HSM solutes relative to ethylbenzene -0.5 -1.0 1 -1.5 -2.0 -1.5 -1.0 -0.5 0.0 Log(k'x/k'ethylbenzene) Zorbax Rx-C18 14 16 on the FMS phase vs Zorbax Rx-C18. Data for the Rx-C18 phase were from Lloyd Snyder (personal communication). The dashed line has a slope of +1 and a y-intercept of 0. The R² value for this plot is 0.51. The Rx-C18 column was 150 mm × 4.6 mm id with 5 um particles, whereas the FMS column was 50 mm × 4.6 mm id with 5 um particles. All other chromatographic conditions were constant: mobile phase 50/50 ACN/60 mM potassium phosphate buffer at pH 2.8, flow rate 2 mL/min, column temperature 35 °C, and injection volume 10 ut Solutes: (1) N,N-dimethylacetamide, (2) N,N-diethylacetamide. (3) nortriptyline, (4) amitriptyline, (5) p- nitrophenol, (6) 5,5-diphenylhydantoin, (7) acetophenone, (8) benzonitrile, (9) 5-phenylpentanol, (10) anisole, (11) 4-n-butylbenzoic acid, (12) toluene, (13) cis-chalcone, (14) trans-chalcone, (15) mefenamic acid, and (16) ethylbenzene.

d. In Figure 4, each stationary phase shows some negative correlation between plate count and retention factor. In other words, as k' increases, N decreases. Explain this relationship between k' and N. Plate Count (N) 4000 3500 2500 2000 1500 1000 Figure 4. Column efficiency (N) vs retention factor (k') for 22 nonionizable solutes on FMS (red), PGC (black), and COZ (green). 3000 Eluent compositions (acetonitrile/water, A/W) were adjusted to obtain k' less than 15, which was achieved for most solutes as follows: FMS (30/70 A/W), PGC (60/40), COZ (80/20). Slightly different compositions were used for the most highly retained solutes. All columns were 50 mm × 4.6 mm id and packed with 5 um particles, except for COZ, which was packed with 3 um particles. All other chromatographic conditions were constant: column length 5 cm, column j.§. 4.6 mm, flow rate 2 mL/min, column temperature 40 °C, and injection volume 0.5 μL Log(k'x/K'ethylbenzene) FMS 1.5 1.0 0.5 0.0 ཐྭ ཋ ཤྩ བྷྲ ; 500 0 5 10 Retention Factor (k') 15 e. Figure 5 shows retention factor data for 16 solutes used in the hydrophobic subtraction model (HSM), which is used to characterize how ionizable solutes will behave on a new stationary phase. (You will notice that many of the HSM solutes are weak acids and/or weak bases.) Which stationary phase (FMS or C18) is better at retaining the HSM solutes? Why is this the case? 12 15 Figure 5. Retention of 16 HSM solutes relative to ethylbenzene -0.5 -1.0 1 -1.5 -2.0 -1.5 -1.0 -0.5 0.0 Log(k'x/k'ethylbenzene) Zorbax Rx-C18 14 16 on the FMS phase vs Zorbax Rx-C18. Data for the Rx-C18 phase were from Lloyd Snyder (personal communication). The dashed line has a slope of +1 and a y-intercept of 0. The R² value for this plot is 0.51. The Rx-C18 column was 150 mm × 4.6 mm id with 5 um particles, whereas the FMS column was 50 mm × 4.6 mm id with 5 um particles. All other chromatographic conditions were constant: mobile phase 50/50 ACN/60 mM potassium phosphate buffer at pH 2.8, flow rate 2 mL/min, column temperature 35 °C, and injection volume 10 ut Solutes: (1) N,N-dimethylacetamide, (2) N,N-diethylacetamide. (3) nortriptyline, (4) amitriptyline, (5) p- nitrophenol, (6) 5,5-diphenylhydantoin, (7) acetophenone, (8) benzonitrile, (9) 5-phenylpentanol, (10) anisole, (11) 4-n-butylbenzoic acid, (12) toluene, (13) cis-chalcone, (14) trans-chalcone, (15) mefenamic acid, and (16) ethylbenzene.

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

Chapter28: High-performance Liquid Chromatography

Section: Chapter Questions

Problem 28.7QAP

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