Theoretical study of system peaks and elution profiles of high concentration bands of binary mixtures eluted by a binary eluent containing a strongly retained additive

Abstract

A theoretical Investigation Is done of the phenomena that take place when a large sample of a binary mixture Is eluted by a mobile phase containing a strong solvent or additive which Is nearly as strongly or more strongly retained as the sample components. For this study we have assumed the competitive equilibrium Isotherms of the sample components and the strong solvent to be given by a competitive Langmuir model. The main parameter of the model Is the adsorption strength of the additive compared to that of the sample components. At low additive strength, the band profiles are very similar to those found with a pure mobile phase which would have the same elution strength. At high additive strength, the band profiles are reversed. They exhibit a smooth, diffuse front and a steep rear shock layer. When the two component bands Interfere, two new effects are observed, a retalnment effect and a pull-back effect. These effects are analogous to the displacement and the tag-along effects, respectively, which are observed with pure mobile phases but act In the opposite direction. Then the chromatogram looks as If the first component band displaces the second one and/or tags along It. At very high additive strength, very complex and unusual band profiles are observed, e.g., two Interfering bands exhibiting three maxima. If the additive strength Is equal to the strength of one of the components, the band of this component remains nearly Gaussian, while the band of the other one becomes unsymmetrlcal and a shock layer eventually appears on the side of the band directed toward the other band.

High-Concentration Band Profiles and System Peaks for a Ternary Solute System

“…This profile shape was obtained before in theoretical calculations. 6 The results obtained with a twice larger injection (1 mL) of the same mixture are shown in Figure 9. Although the same features of Figure 8 are maintained, there are some striking changes which would not arise in the case of a binary feed sample analyzed with a pure mobile phase, with Langmuirian isotherm behavior.…”

“…The band of PE also exhibits two small “hills” with a shallow valley between them. This profile shape was obtained before in theoretical calculations . The results obtained with a twice larger injection (1 mL) of the same mixture are shown in Figure .…”

“…The band profiles were calculated using the equilibrium-dispersive model of chromatography . Experimental studies , showed good qualitative agreement with the previous theoretical predictions. A quantitative comparison between experimental and theoretical results was not possible because of the lack of the relevant multicomponent adsorption equilibria in the systems under consideration.…”

High-Concentration Band Profiles and System Peaks for a Ternary Solute System

“…This profile shape was obtained before in theoretical calculations. 6 The results obtained with a twice larger injection (1 mL) of the same mixture are shown in Figure 9. Although the same features of Figure 8 are maintained, there are some striking changes which would not arise in the case of a binary feed sample analyzed with a pure mobile phase, with Langmuirian isotherm behavior.…”

“…The band of PE also exhibits two small “hills” with a shallow valley between them. This profile shape was obtained before in theoretical calculations . The results obtained with a twice larger injection (1 mL) of the same mixture are shown in Figure .…”

“…The band profiles were calculated using the equilibrium-dispersive model of chromatography . Experimental studies , showed good qualitative agreement with the previous theoretical predictions. A quantitative comparison between experimental and theoretical results was not possible because of the lack of the relevant multicomponent adsorption equilibria in the systems under consideration.…”

Tuneable Peak Deformations in Chiral Liquid Chromatography

“…When non-Langmuirian peaks are encountered, the classical explanation is that the solutes are governed by non-Langmuirian adsorption isotherms (type-II or type-III). We believe that the peak deformations in many modern chiral systems are due to the effects caused by strongly adsorbed additives. − In the present study, we will show that this theory applies to the chiral separation of β-blockers on an immobilized teicoplanin stationary phase (Chirobiotic T) when typical methanol/acetonitrile eluents with acetic acid/triethylamine additives are used. Detailed characterization by adsorption isotherm determination has been impossible with traditional methods, such as frontal analysis, because of the extraordinary system complexity.…”

Comparison of core‐shell versus fully porous particle packings for chiral liquid chromatography productivity

“…Since exactly the same behavior was observed with all three vancomycin columns, hardware artifacts were excluded. The peak splitting may be due to mianserin adsorption competition with TEA as studied previously [16–20]. The adsorption strength for the two enantiomers being different, the resulting peaks are different.…”

High-Concentration Band Profiles and System Peaks for a Ternary Solute System

“…This profile shape was obtained before in theoretical calculations. 6 The results obtained with a twice larger injection (1 mL) of the same mixture are shown in Figure 9. Although the same features of Figure 8 are maintained, there are some striking changes which would not arise in the case of a binary feed sample analyzed with a pure mobile phase, with Langmuirian isotherm behavior.…”

“…The band of PE also exhibits two small “hills” with a shallow valley between them. This profile shape was obtained before in theoretical calculations . The results obtained with a twice larger injection (1 mL) of the same mixture are shown in Figure .…”

“…The band profiles were calculated using the equilibrium-dispersive model of chromatography . Experimental studies , showed good qualitative agreement with the previous theoretical predictions. A quantitative comparison between experimental and theoretical results was not possible because of the lack of the relevant multicomponent adsorption equilibria in the systems under consideration.…”

Tuneable Peak Deformations in Chiral Liquid Chromatography

“…When non-Langmuirian peaks are encountered, the classical explanation is that the solutes are governed by non-Langmuirian adsorption isotherms (type-II or type-III). We believe that the peak deformations in many modern chiral systems are due to the effects caused by strongly adsorbed additives. − In the present study, we will show that this theory applies to the chiral separation of β-blockers on an immobilized teicoplanin stationary phase (Chirobiotic T) when typical methanol/acetonitrile eluents with acetic acid/triethylamine additives are used. Detailed characterization by adsorption isotherm determination has been impossible with traditional methods, such as frontal analysis, because of the extraordinary system complexity.…”

Comparison of core‐shell versus fully porous particle packings for chiral liquid chromatography productivity

“…Since exactly the same behavior was observed with all three vancomycin columns, hardware artifacts were excluded. The peak splitting may be due to mianserin adsorption competition with TEA as studied previously [16–20]. The adsorption strength for the two enantiomers being different, the resulting peaks are different.…”

High-Concentration Band Profiles and System Peaks for a Ternary Solute System

“…This profile shape was obtained before in theoretical calculations. 6 The results obtained with a twice larger injection (1 mL) of the same mixture are shown in Figure 9. Although the same features of Figure 8 are maintained, there are some striking changes which would not arise in the case of a binary feed sample analyzed with a pure mobile phase, with Langmuirian isotherm behavior.…”

“…The band of PE also exhibits two small “hills” with a shallow valley between them. This profile shape was obtained before in theoretical calculations . The results obtained with a twice larger injection (1 mL) of the same mixture are shown in Figure .…”

“…The band profiles were calculated using the equilibrium-dispersive model of chromatography . Experimental studies , showed good qualitative agreement with the previous theoretical predictions. A quantitative comparison between experimental and theoretical results was not possible because of the lack of the relevant multicomponent adsorption equilibria in the systems under consideration.…”

Tuneable Peak Deformations in Chiral Liquid Chromatography

“…When non-Langmuirian peaks are encountered, the classical explanation is that the solutes are governed by non-Langmuirian adsorption isotherms (type-II or type-III). We believe that the peak deformations in many modern chiral systems are due to the effects caused by strongly adsorbed additives. − In the present study, we will show that this theory applies to the chiral separation of β-blockers on an immobilized teicoplanin stationary phase (Chirobiotic T) when typical methanol/acetonitrile eluents with acetic acid/triethylamine additives are used. Detailed characterization by adsorption isotherm determination has been impossible with traditional methods, such as frontal analysis, because of the extraordinary system complexity.…”

Comparison of core‐shell versus fully porous particle packings for chiral liquid chromatography productivity

“…Since exactly the same behavior was observed with all three vancomycin columns, hardware artifacts were excluded. The peak splitting may be due to mianserin adsorption competition with TEA as studied previously [16–20]. The adsorption strength for the two enantiomers being different, the resulting peaks are different.…”