1
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Meng F, Zhou X, Hou Y, Zhao H, Zhang J, Huang Q, Zhang M, Adams E, Yuan Y, Shi HW. Characterization of ribostamycin and its impurities using a nano-quantity analyte detector: Systematic comparison of performance among three different aerosol detectors. Talanta 2024; 277:126359. [PMID: 38852340 DOI: 10.1016/j.talanta.2024.126359] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2024] [Revised: 05/17/2024] [Accepted: 06/03/2024] [Indexed: 06/11/2024]
Abstract
Characterization of aminoglycoside antibiotics like ribostamycin is important due to the complex composition and common toxic impurities. Aerosol detectors are often employed for determination of these non-absorbent analytes. In this work, a robust and cost-effective method was developed for simultaneous detection of ribostamycin and its related substances using high-performance liquid chromatography (HPLC) with a relative new aerosol detector named nano-quantity analyte detector (NQAD). With the introduction of less toxic but more compatible ion-pairs pentafluoropropionic acid (PFPA) and trifluoroacetic acid (TFA) in the eluent, an optimized separation effect was achieved. Compared with the other two aerosol detectors namely ELSD (evaporative light scattering detector) and CAD (charged aerosol detector), method verification and quantitative detection results revealed that NQAD had higher sensitivity than ELSD with a 0.8 μg/mL limit of detection, as well as wider linear range (from 2 μg/mL to 1000 μg/mL) than both CAD (from 2 μg/mL to 200 μg/mL) and ELSD (from 8 μg/mL to 200 μg/mL) detector. The performance of NQAD helped to realize detection of ribostamycin and its impurities with significant concentration differences in a single run. With a cation suppressor to eliminate the ion-suppression caused by the ion-pairs in the eluent, the structure of nine impurities in ribostamycin sample was characterized by liquid chromatography-mass spectrum (LC-MS). Both external standard and area normalization calculation were investigated, and NQAD obtained more accurate results due to its full-range linear response-to-concentration relationship, providing an alternative for routine quality control of multi analyte systems.
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Affiliation(s)
- Fei Meng
- Jiangsu Institute for Food and Drug Control, Nanjing, 210019, China; NMPA Key Laboratory for Impurity Profile of Chemical Drugs, Nanjing, 210019, China; School of Pharmacy, Nanjing University of Chinese Medicine, Nanjing, 210046, China
| | - Xiaohua Zhou
- Jiangsu Institute for Food and Drug Control, Nanjing, 210019, China; NMPA Key Laboratory for Impurity Profile of Chemical Drugs, Nanjing, 210019, China
| | - Yurong Hou
- Jiangsu Institute for Food and Drug Control, Nanjing, 210019, China; NMPA Key Laboratory for Impurity Profile of Chemical Drugs, Nanjing, 210019, China
| | - Haodong Zhao
- Jiangsu Institute for Food and Drug Control, Nanjing, 210019, China; NMPA Key Laboratory for Impurity Profile of Chemical Drugs, Nanjing, 210019, China
| | - Jinlin Zhang
- Jiangsu Institute for Food and Drug Control, Nanjing, 210019, China; NMPA Key Laboratory for Impurity Profile of Chemical Drugs, Nanjing, 210019, China
| | - Qing Huang
- Jiangsu Institute for Food and Drug Control, Nanjing, 210019, China; NMPA Key Laboratory for Impurity Profile of Chemical Drugs, Nanjing, 210019, China
| | - Mei Zhang
- Jiangsu Institute for Food and Drug Control, Nanjing, 210019, China; NMPA Key Laboratory for Impurity Profile of Chemical Drugs, Nanjing, 210019, China
| | - Erwin Adams
- Department of Pharmaceutical and Pharmacological Sciences, Pharmaceutical Analysis, KU Leuven, Herestraat 49, O&N2, PB 923, B-3000, Leuven, Belgium
| | - Yaozuo Yuan
- Jiangsu Institute for Food and Drug Control, Nanjing, 210019, China; NMPA Key Laboratory for Impurity Profile of Chemical Drugs, Nanjing, 210019, China.
| | - Hai-Wei Shi
- Jiangsu Institute for Food and Drug Control, Nanjing, 210019, China; NMPA Key Laboratory for Impurity Profile of Chemical Drugs, Nanjing, 210019, China.
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2
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Scrosati PM, Konermann L. Atomistic Details of Peptide Reversed-Phase Liquid Chromatography from Molecular Dynamics Simulations. Anal Chem 2023; 95:3892-3900. [PMID: 36745777 DOI: 10.1021/acs.analchem.2c05667] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Peptide separations by reversed-phase liquid chromatography (RPLC) are an integral part of bottom-up proteomics. These separations typically employ C18 columns with water/acetonitrile gradient elution in the presence of formic acid. Despite the widespread use of such workflows, the exact nature of peptide interactions with the stationary and mobile phases is poorly understood. Here, we employ microsecond molecular dynamics (MD) simulations to uncover details of peptide RPLC. We examined two tryptic peptides, a hydrophobic and a hydrophilic species, in a slit pore lined with C18 chains that were grafted onto SiO2 support. Our simulations explored peptide trapping, followed by desorption and elution. Trapping in an aqueous mobile phase was initiated by C18 contacts with Lys butyl moieties. This was followed by extensive anchoring of nonpolar side chains (Leu/Ile/Val) in the C18 layer. Exposure to water/acetonitrile triggered peptide desorption in a stepwise fashion; charged sites close to the termini were the first to lift off, followed by the other residues. During water/acetonitrile elution, both peptides preferentially resided close to the pore center. The hydrophilic peptide exhibited no contacts with the stationary phase under these conditions. In contrast, the hydrophobic species underwent multiple transient Leu/Ile/Val binding interactions with C18 chains. These nonpolar interactions represent the foundation of differential peptide retention, in agreement with the experimental elution behavior of the two peptides. Extensive peptide/formate ion pairing was observed in water/acetonitrile, particularly at N-terminal sites. Overall, this work uncovers an unprecedented level of RPLC molecular details, paving the way for MD simulations as a future tool for improving retention prediction algorithms and for the design of novel column materials.
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Affiliation(s)
- Pablo M Scrosati
- Department of Chemistry, The University of Western Ontario, London, Ontario, N6A 5B7, Canada
| | - Lars Konermann
- Department of Chemistry, The University of Western Ontario, London, Ontario, N6A 5B7, Canada
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3
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Chester TL. The combination of partition, size exclusion, and hydrodynamic models in chromatography, and application to bonded phases on porous supports. J Chromatogr A 2020; 1620:461011. [PMID: 32284152 DOI: 10.1016/j.chroma.2020.461011] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2020] [Revised: 03/02/2020] [Accepted: 03/05/2020] [Indexed: 11/26/2022]
Abstract
Liquid-liquid partition chromatography has been used for many years as a model and teaching introduction to column chromatography. However, the partition model does not describe separations on bonded phases with porous supports particularly well, especially regarding the thermodynamics controlling solute distribution. Further difficulties arise when more than one mechanism is involved in solute retention. Nomenclature is not perfectly aligned with the underlying thermodynamic descriptors and is inconsistently applied over various chromatographic techniques. Presented here is a general description of retention that spans partition, size exclusion, and hydrodynamic separation processes, and is then applied to bonded-phase separations on porous supports. The model provides a general description applicable to adsorption, reversed-phase, hydrophilic interaction, size-exclusion, hydrodynamic chromatography, and any combination of these techniques including liquid chromatography at the critical condition. Further expansion to include retention by ion-exchange and field-flow fractionation appears to be possible. Recommendations on retention factor definition and evaluation are given.
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Affiliation(s)
- T L Chester
- Department of Chemistry, University of Cincinnati, PO Box 210172, Cincinnati, Ohio 45221-0172, United States.
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4
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Simulation and theory of open-tube dispersion in short and long capillaries with slip boundaries and retention. J Chromatogr A 2018; 1588:85-98. [PMID: 30685185 DOI: 10.1016/j.chroma.2018.12.040] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2018] [Revised: 12/15/2018] [Accepted: 12/19/2018] [Indexed: 12/11/2022]
Abstract
Using random walk techniques, high resolution simulations of zone shape are conducted in open capillary tubes for short and long tube conditions. Finite size solutes are used as tracers in this treatment. Slip flow boundary conditions and wall retention are utilized as needed. These simulations are able to reproduce previous work in short and long tubes. For the short tube case where dispersion does not asymptotically approach the classic Taylor-Aris and Golay solutions, the effect of slip flow boundaries in the transient region shows zone shapes with abbreviated tails where the larger slip flow values cause zone compression. The use of slip flow to lower dispersion in capillary-based, wall-coated separations is shown to favor long tube behavior. This is because slip flow is relevant for cases where slip lengths are fractions of small capillary tube diameters. Incorporating slip flow into transport in capillaries favors a very small capillary radius where the cross-sectional diffusion length is very small and sampling times are fast. The purely convective zone shape with slip flow boundaries is derived analytically. Applications for this type of separation, guided by both analytical theory and simulation, show the potential for nano-sized capillary tubes less than 1 μm in diameter and favor very fast isocratic separations. Using long tube retention theory with slip boundaries shows that the dispersion-reducing region is most important in the range 0 ≤ k' ≤ 1, a relatively small retention window. Further discussion of the gradient elution technique and dispersion in packed beds suggests that the general usage of slip flow boundaries is restricted in liquid phase separation systems.
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5
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Liu CW, Kuo BC, Liu MH, Huang YR, Chen CL. Computer simulation for the study of the liquid chromatographic separation of explosive molecules. J Mol Graph Model 2018; 85:331-339. [PMID: 30292170 DOI: 10.1016/j.jmgm.2018.09.009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2018] [Revised: 08/17/2018] [Accepted: 09/18/2018] [Indexed: 10/28/2022]
Abstract
The application of high performance liquid chromatography (HPLC) to separate explosive chemicals was investigated by molecular dynamics (MD) simulations. The explosive ingredients including NG, RDX, HMX and TNT were assigned as solutes, while methanol (CH3OH) and acetonitrile (CH3CN) were assigned as solvents in the solution system. The polymeric-molecular siloxanes (SiC8) and poly-1,2-methylenedioxy-4-propenyl benzene (PISAF) compounds were treated as stationary phase in the simulation. The simulation results showed that the different species of explosive ingredients were separated successfully in the solutions by each of the constructed stationary phase of SiC8 and PISAF after a total simulation time of 12.0 ps approximately, which were consistent with the experimental analysis of HPLC spectra. The origin for the separation was found due to the electrostatic interactions between polymer and explosives.
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Affiliation(s)
- Chuan-Wen Liu
- Department of Chemical and Materials Engineering, Chung-Cheng Institute of Technology, National Defense University, Taoyuan, 335, Taiwan, ROC
| | - Bing-Cheng Kuo
- Department of Chemistry, National Sun Yat-sen University, Kaohsiung, 804, Taiwan, ROC
| | - Min-Hsien Liu
- Department of Chemical and Materials Engineering, Chung-Cheng Institute of Technology, National Defense University, Taoyuan, 335, Taiwan, ROC
| | - Yu-Ren Huang
- Department of Applied Science, Naval Academy, Zuoying District, Kaohsiung City, 813, Taiwan, ROC
| | - Cheng-Lung Chen
- Department of Chemistry, National Sun Yat-sen University, Kaohsiung, 804, Taiwan, ROC.
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6
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Bocian S. Solvation processes in liquid chromatography: The importance and measurements. J LIQ CHROMATOGR R T 2016. [DOI: 10.1080/10826076.2016.1242494] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Affiliation(s)
- Szymon Bocian
- Chair of Environmental Chemistry and Bioanalytics, Faculty of Chemistry, Nicolaus Copernicus University, Toruń, Poland
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7
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Kulsing C, Yang Y, Sepehrifar R, Lim M, Toppete J, Matyska MT, Pesek JJ, Boysen RI, Hearn MTW. Investigations into the separation behaviour of perfluorinated C8 and undecanoic acid modified silica hydride stationary phases. Anal Chim Acta 2016; 916:102-11. [PMID: 27016444 DOI: 10.1016/j.aca.2016.02.013] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2015] [Revised: 02/12/2016] [Accepted: 02/14/2016] [Indexed: 11/25/2022]
Abstract
In this study, the surface charge properties of perfluorinated C8 (PerfluoroC8) and undecanoic acid (UDA) modified silica hydride stationary phases have been investigated. The zeta potential values of these stationary phases were measured in aqueous/acetonitrile mobile phases of different pH, buffer concentrations and acetonitrile contents. The retention behaviour of several basic, acidic and neutral compounds were then examined with these two stationary phases, with U-shaped retention dependencies evident with regard to the organic solvent content of the mobile phase. Plots of the logarithmic retention factor versus buffer concentration revealed slopes ≥ -0.41 for both stationary phases, indicating the involvement of mixed mode retention mechanisms with contributions from both ionic and non-ionic interactions. Using a linear solvation energy relationship approach, the origins of these interactions under different mobile phase conditions were differentiated and quantified. The PerfluoroC8 stationary phase exhibited stronger retention for basic compounds under high acetonitrile content mobile phase conditions, whilst stronger retention was observed for all compounds with the UDA stationary phase under high aqueous content mobile phase conditions. The more negative zeta potentials of the UDA stationary phase correlated with higher total charge density, surface charge density and charge density at the beta plane (the outer plane of the double layer) compared to the PerfluoroC8 stationary phase. With mobile phases of low buffer concentrations, more negative zeta potential values were unexpectedly observed for the PerfluoroC8 stationary phase with slight increases in the C descriptor value, reflecting also the greater accessibility of the analytes to the stationary phase surface. Comparison of the retention behaviours on these phases with other types of silica hydride stationary phases has revealed different patterns of selectivity.
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Affiliation(s)
- Chadin Kulsing
- Australian Centre for Research on Separation Science (ACROSS), School of Chemistry, Monash University, Melbourne, Victoria 3800, Australia
| | - Yuanzhong Yang
- Australian Centre for Research on Separation Science (ACROSS), School of Chemistry, Monash University, Melbourne, Victoria 3800, Australia
| | - Roshanak Sepehrifar
- Australian Centre for Research on Separation Science (ACROSS), School of Chemistry, Monash University, Melbourne, Victoria 3800, Australia
| | - Michael Lim
- Department of Chemistry, San Jose State University, San Jose, CA 95192, USA
| | - Joshua Toppete
- Department of Chemistry, San Jose State University, San Jose, CA 95192, USA
| | - Maria T Matyska
- Department of Chemistry, San Jose State University, San Jose, CA 95192, USA
| | - Joseph J Pesek
- Department of Chemistry, San Jose State University, San Jose, CA 95192, USA
| | - Reinhard I Boysen
- Australian Centre for Research on Separation Science (ACROSS), School of Chemistry, Monash University, Melbourne, Victoria 3800, Australia
| | - Milton T W Hearn
- Australian Centre for Research on Separation Science (ACROSS), School of Chemistry, Monash University, Melbourne, Victoria 3800, Australia.
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8
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Sykora D, Vozka J, Tesarova E. Chromatographic methods enabling the characterization of stationary phases and retention prediction in high-performance liquid chromatography and supercritical fluid chromatography. J Sep Sci 2015; 39:115-31. [DOI: 10.1002/jssc.201501023] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2015] [Revised: 10/08/2015] [Accepted: 10/08/2015] [Indexed: 11/11/2022]
Affiliation(s)
- David Sykora
- Department of Analytical Chemistry; University of Chemistry and Technology; Prague Czech Republic
| | - Jiri Vozka
- Department of Analytical Chemistry; University of Chemistry and Technology; Prague Czech Republic
- Department of Physical and Macromolecular Chemistry, Faculty of Science; Charles University in Prague; Prague Czech Republic
| | - Eva Tesarova
- Department of Physical and Macromolecular Chemistry, Faculty of Science; Charles University in Prague; Prague Czech Republic
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9
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Socia A, Foley JP. Sequential elution liquid chromatography can significantly increase the probability of a successful separation by simultaneously increasing the peak capacity and reducing the separation disorder. J Chromatogr A 2014; 1324:36-48. [DOI: 10.1016/j.chroma.2013.11.016] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2013] [Revised: 10/29/2013] [Accepted: 11/12/2013] [Indexed: 10/26/2022]
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10
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Lindsey RK, Rafferty JL, Eggimann BL, Siepmann JI, Schure MR. Molecular simulation studies of reversed-phase liquid chromatography. J Chromatogr A 2013; 1287:60-82. [PMID: 23489490 DOI: 10.1016/j.chroma.2013.02.040] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2013] [Revised: 02/10/2013] [Accepted: 02/11/2013] [Indexed: 11/28/2022]
Abstract
Over the past 20 years, molecular simulation methods have been applied to the modeling of reversed-phase liquid chromatography (RPLC). The purpose of these simulations was to provide a molecular-level understanding of: (i) the structure and dynamics of the bonded phase and its interface with the mobile phase, (ii) the interactions of analytes with the bonded phase, and (iii) the retention mechanism for different analytes. However, the investigation of chromatographic systems poses significant challenges for simulations with respect to the accuracy of the molecular mechanics force fields and the efficiency of the sampling algorithms. This review discusses a number of aspects concerning molecular simulation studies of RPLC systems including the historical development of the subject, the background needed to understand the two prevalent techniques, molecular dynamics (MD) and Monte Carlo (MC) methods, and the wealth of insight provided by these simulations. Examples from the literature employing MD approaches and from the authors' laboratory using MC methods are discussed. The former can provide information on chain dynamics and transport properties, whereas the latter techniques are uniquely suited for the investigation of phase and sorption equilibria that underly RPLC retention, and both can be used to elucidate the bonded-chain conformations and solvent distributions.
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Affiliation(s)
- Rebecca K Lindsey
- Department of Chemistry and Chemical Theory Center, University of Minnesota, 207 Pleasant Street SE, Minneapolis, MN 55455-0431, USA
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11
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Gupta PK, Meuwly M. Dynamics of Water/Methanol Mixtures at Functionalized Chromatographic Interfaces. J Phys Chem B 2012; 116:10951-9. [DOI: 10.1021/jp305351f] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Prashant Kumar Gupta
- Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056 Basel, Switzerland
| | - Markus Meuwly
- Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056 Basel, Switzerland
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12
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Hall K, Ashtari M, Cann NM. On simulations of complex interfaces: Molecular dynamics simulations of stationary phases. J Chem Phys 2012; 136:114705. [DOI: 10.1063/1.3693516] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
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13
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Rafferty JL, Siepmann JI, Schure MR. A molecular simulation study of the effects of stationary phase and solute chain length in reversed-phase liquid chromatography. J Chromatogr A 2012; 1223:24-34. [DOI: 10.1016/j.chroma.2011.11.039] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2011] [Revised: 11/17/2011] [Accepted: 11/20/2011] [Indexed: 10/15/2022]
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14
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Rafferty JL, Siepmann JI, Schure MR. Molecular simulations of retention in chromatographic systems: use of biased Monte Carlo techniques to access multiple time and length scales. Top Curr Chem (Cham) 2012; 307:181-200. [PMID: 21898207 DOI: 10.1007/128_2011_210] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The use of configurational-bias Monte Carlo simulations in the Gibbs ensemble allows for the sampling of phenomena that occur on vastly different time and length scales. In this review, applications of this simulation approach to probe retention in gas and reversed-phase liquid chromatographic systems are discussed. These simulations provide an unprecedented view of the retention processes at the molecular-level and show excellent agreement with experimental retention data.
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Affiliation(s)
- Jake L Rafferty
- Department of Chemistry and Chemical Theory Center, University of Minnesota, 207 Pleasant Street SE, Minneapolis, MN 55455-0431, USA
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15
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Separation of imidacloprid and its degradation products using reversed phase liquid chromatography with water rich mobile phases. J Chromatogr A 2011; 1218:9221-6. [DOI: 10.1016/j.chroma.2011.10.057] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2011] [Revised: 10/18/2011] [Accepted: 10/21/2011] [Indexed: 11/18/2022]
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16
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Rafferty JL, Siepmann JI, Schure MR. Retention mechanism for polycyclic aromatic hydrocarbons in reversed-phase liquid chromatography with monomeric stationary phases. J Chromatogr A 2011; 1218:9183-93. [DOI: 10.1016/j.chroma.2011.10.043] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2011] [Revised: 10/11/2011] [Accepted: 10/17/2011] [Indexed: 10/15/2022]
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17
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Ashtari M, Cann N. Proline-based chiral stationary phases: A molecular dynamics study of the interfacial structure. J Chromatogr A 2011; 1218:6331-47. [DOI: 10.1016/j.chroma.2011.06.096] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2011] [Revised: 06/24/2011] [Accepted: 06/27/2011] [Indexed: 10/18/2022]
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18
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Rafferty JL, Siepmann JI, Schure MR. Mobile phase effects in reversed-phase liquid chromatography: A comparison of acetonitrile/water and methanol/water solvents as studied by molecular simulation. J Chromatogr A 2011; 1218:2203-13. [DOI: 10.1016/j.chroma.2011.02.012] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2010] [Revised: 01/28/2011] [Accepted: 02/05/2011] [Indexed: 11/16/2022]
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19
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Li Y, Liu D, Wang P, Zhou Z. Computational study of enantioseparation by amylose tris(3,5-dimethylphenylcarbamate)-based chiral stationary phase. J Sep Sci 2011; 33:3245-55. [PMID: 20839235 DOI: 10.1002/jssc.201000266] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The mechanism of chiral separation on amylose tris(3,5-dimethylphenylcarbamate) is studied with docking simulations of enantiomers by molecular dynamics. All-atom models of amylose tris(3,5-dimethylphenylcarbamate) on the modified silica gel surface were constructed for the docking simulations of metalaxyl and benalaxyl. The elution orders and energetic differences were also predicted based on the intermolecular interactions, which were in agreement with the experimental results. The radial distribution function was employed to analyze the structural features of the enantiomer-chiral stationary phase complex and used to elucidate the mechanism of chiral separation. The separation of metalaxyl and benalaxyl is mainly controlled by the hydrogen bond. And the binding sites had slight differences for the pair of enantiomers, but obvious differences between different chemicals.
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Affiliation(s)
- Yangyang Li
- Department of Applied Chemistry, College of Science, China Agricultural University, Beijing, PR China
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20
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Allmon SD, Dorsey JG. Properties of subcritical water as an eluent for reversed-phase liquid chromatography—Disruption of the hydrogen-bond network at elevated temperature and its consequences. J Chromatogr A 2010; 1217:5769-75. [DOI: 10.1016/j.chroma.2010.07.030] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2010] [Revised: 06/15/2010] [Accepted: 07/13/2010] [Indexed: 10/19/2022]
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21
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Buszewski B, Bocian S, Nowaczyk A. Modeling solvation on the chemically modified silica surfaces. J Sep Sci 2010; 33:2060-8. [DOI: 10.1002/jssc.201000101] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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22
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23
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The effects of chain length, embedded polar groups, pressure, and pore shape on structure and retention in reversed-phase liquid chromatography: Molecular-level insights from Monte Carlo simulations. J Chromatogr A 2009; 1216:2320-31. [DOI: 10.1016/j.chroma.2008.12.088] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2008] [Revised: 12/22/2008] [Accepted: 12/29/2008] [Indexed: 11/22/2022]
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24
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Retention models for isocratic and gradient elution in reversed-phase liquid chromatography. J Chromatogr A 2009; 1216:1737-55. [DOI: 10.1016/j.chroma.2008.09.051] [Citation(s) in RCA: 115] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2008] [Revised: 09/11/2008] [Accepted: 09/12/2008] [Indexed: 11/20/2022]
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25
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Gritti F, Guiochon G. Adsorption mechanism of acids and bases in reversed-phase liquid chromatography in weak buffered mobile phases designed for liquid chromatography/mass spectrometry. J Chromatogr A 2009; 1216:1776-88. [DOI: 10.1016/j.chroma.2008.10.064] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2008] [Revised: 10/10/2008] [Accepted: 10/14/2008] [Indexed: 11/28/2022]
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26
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Rafferty JL, Siepmann J, Schure MR. Influence of bonded-phase coverage in reversed-phase liquid chromatography via molecular simulation. J Chromatogr A 2008; 1204:11-9. [DOI: 10.1016/j.chroma.2008.07.037] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2008] [Revised: 06/24/2008] [Accepted: 07/04/2008] [Indexed: 10/21/2022]
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27
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Rafferty JL, Siepmann JI, Schure MR. Molecular-Level Comparison of Alkylsilane and Polar-Embedded Reversed-Phase Liquid Chromatography Systems. Anal Chem 2008; 80:6214-21. [DOI: 10.1021/ac8005473] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Jake L. Rafferty
- Departments of Chemistry and of Chemical Engineering and Material Science and the Minnesota Supercomputing Institute, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, and Theoretical Separation Science Laboratory, Rohm and Haas Company, 727 Norristown Road, Box 0904, Spring House, Pennsylvania 19477-0904
| | - J. Ilja Siepmann
- Departments of Chemistry and of Chemical Engineering and Material Science and the Minnesota Supercomputing Institute, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, and Theoretical Separation Science Laboratory, Rohm and Haas Company, 727 Norristown Road, Box 0904, Spring House, Pennsylvania 19477-0904
| | - Mark R. Schure
- Departments of Chemistry and of Chemical Engineering and Material Science and the Minnesota Supercomputing Institute, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, and Theoretical Separation Science Laboratory, Rohm and Haas Company, 727 Norristown Road, Box 0904, Spring House, Pennsylvania 19477-0904
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28
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Mountain RD, Lippa KA. Solvation of Perfluorooctane and Octane in Water, Methanol, Acetonitrile, and Aqueous Mixtures of Methanol and Acetonitrile. J Phys Chem B 2008; 112:7785-93. [DOI: 10.1021/jp0774802] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Raymond D. Mountain
- Physical and Chemical Properties Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8380, and Analytical Chemistry Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8392
| | - Katrice A. Lippa
- Physical and Chemical Properties Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8380, and Analytical Chemistry Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8392
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29
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Liao Z, Pemberton JE. Structure−Function Relationships in High-Density Docosylsilane Bonded Stationary Phases by Raman Spectroscopy and Comparison to Octadecylsilane Bonded Stationary Phases: Effects of Common Solvents. Anal Chem 2008; 80:2911-20. [DOI: 10.1021/ac702270b] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Zhaohui Liao
- Department of Chemistry, University of Arizona, 1306 East University Boulevard, Tucson, Arizona 85721
| | - Jeanne E. Pemberton
- Department of Chemistry, University of Arizona, 1306 East University Boulevard, Tucson, Arizona 85721
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30
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Zhao CF, Cann NM. Molecular Dynamics Study of Chiral Recognition for the Whelk-O1 Chiral Stationary Phase. Anal Chem 2008; 80:2426-38. [DOI: 10.1021/ac702126y] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- C. F. Zhao
- Department of Chemistry, Queen's University, Kingston, Ontario, Canada K7L 3N6
| | - N. M. Cann
- Department of Chemistry, Queen's University, Kingston, Ontario, Canada K7L 3N6
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31
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Felinger A. Molecular dynamic theories in chromatography. J Chromatogr A 2008; 1184:20-41. [DOI: 10.1016/j.chroma.2007.12.066] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2007] [Revised: 12/10/2007] [Accepted: 12/20/2007] [Indexed: 10/22/2022]
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32
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Han A, Qiao Y. Effects of nanopore size on properties of modified inner surfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2007; 23:11396-11398. [PMID: 17929956 DOI: 10.1021/la702606s] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
By analyzing sorption isotherm curves of surface treated MCM-41 samples, it is noticed that if the nanopore size is relatively small, the end group dominates the solid-liquid interaction and the influence of the side group is relatively weak, which can be attributed to the confinement effect of nanopore walls.
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Affiliation(s)
- Aijie Han
- Department of Structural Engineering, University of California-San Diego, La Jolla, California 92093-0085, USA
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33
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Fouqueau A, Meuwly M, Bemish RJ. Adsorption of Acridine Orange at a C8,18/Water/Acetonitrile Interface. J Phys Chem B 2007; 111:10208-16. [PMID: 17685640 DOI: 10.1021/jp071721o] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Fully atomistic simulations are used to characterize the molecular dynamics (MD) of acridine orange (3,6-dimethylaminoacridine) at a chromatographic interface. Multiple 1 ns MD simulations were performed for acridine orange at the interface between three different acetonitrile/water mixtures (0/100, 20/80, and 50/50) with C8 and C18 alkyl chains. The diffusion coefficient, D, of acridine orange in pure solvent was found to be 4 times smaller at the water/C18 interface (D = 0.022 x 10(-4) cm2/s) than in bulk water (D = 0.087 x 10(-4) cm2/s), in qualitative agreement with experiment. Rotational reorientation times were 20 and 700 ps, which also agree favorably with the measured time scales of 130 and 740 ps. Contrary to experiment, the simulations found that for increasing surface coverage, the diffusion coefficient for acridine decreased. Detailed analysis of the solvent structure showed that the transport properties of acridine were primarily governed by the solvent distribution above the functionalized surface. The solvent structure, in turn, was largely determined by the surface consisting of the silica layer, the alkyl chains, and their functionalization.
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Affiliation(s)
- Antony Fouqueau
- Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056 Basel, Switzerland
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34
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Rafferty JL, Zhang L, Siepmann JI, Schure MR. Retention Mechanism in Reversed-Phase Liquid Chromatography: A Molecular Perspective. Anal Chem 2007; 79:6551-8. [PMID: 17668929 DOI: 10.1021/ac0705115] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A detailed, molecular-level understanding of the retention mechanism in reversed-phase liquid chromatography (RPLC) has eluded analytical chemists for decades. Through validated, particle-based Monte Carlo simulations of a model RPLC system consisting of dimethyloctadecylsilanes at a coverage of 2.9 micro mol/m2 on an explicit silica substrate with unprotected residual silanols in contact with a water/methanol mobile phase, we show that the molecular-level retention processes for nonpolar and polar analytes, such as alkanes and alcohols, are much more complex than what has been previously deduced from thermodynamic and theoretical arguments. In contrast to some previous assumptions, the simulations indicate that both partitioning and adsorption play a key role in the separation process and that the stationary phase in RPLC behaves substantially different from a bulk hydrocarbon phase. The retention of nonpolar methylene segments is dominated by lipophilic interactions with the retentive phase, while solvophilic interactions are more important for the retention of the polar hydroxyl group.
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Affiliation(s)
- Jake L Rafferty
- Department of Chemistry and of Chemical Engineering, University of Minnesota, Minneapolis, MN 55455-0431, USA
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35
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Coym JW, Roe BW. Effect of temperature on gradient reequilibration in reversed-phase liquid chromatography. J Chromatogr A 2007; 1154:182-8. [PMID: 17412352 DOI: 10.1016/j.chroma.2007.03.075] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2006] [Revised: 03/15/2007] [Accepted: 03/21/2007] [Indexed: 11/29/2022]
Abstract
The effect of mobile phase modifier and temperature on gradient reequilibration is examined using three different stationary phases. The stationary phases studied are a traditional C18 phase, a polar endcapped C18 phase, and an alkyl phase with a polar embedded group. It was observed that both temperature and choice of mobile phase organic modifier had an effect on gradient reequilibration volume on both the traditional C18 stationary phase and the polar endcapped phase. On both these phases, at any given temperature, the reequilibration volume was generally smaller when methanol was used as the mobile phase modifier as compared to acetonitrile. As the temperature is increased from 10 to 50 degrees C, significant reductions in reequilibration volume were observed with both mobile phase modifiers. In contrast, neither temperature nor choice of modifier appeared to have much effect on reequilibration volume when the polar embedded group stationary phase was considered.
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Affiliation(s)
- Jason W Coym
- Department of Chemistry, The University of South Alabama, Mobile, AL 36688-0002, USA.
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36
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Neue UD, Méndez A. Selectivity in reversed-phase separations: General influence of solvent type and mobile phase pH. J Sep Sci 2007; 30:949-63. [PMID: 17566327 DOI: 10.1002/jssc.200600451] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The influence of the mobile phase on retention is studied in this paper for a group of over 70 compounds with a broad range of multiple functional groups. We varied the pH of the mobile phase (pH 3, 7, and 10) and the organic modifier (methanol, acetonitrile (ACN), and tetrahydrofuran (THF)), using 15 different stationary phases. In this paper, we describe the overall retention and selectivity changes observed with these variables. We focus on the primary effects of solvent choice and pH. For example, transfer rules for solvent composition resulting in equivalent retention depend on the packing as well as on the type of analyte. Based on the retention patterns, one can calculate selectivity difference values for different variables. The selectivity difference is a measure of the importance of the different variables involved in method development. Selectivity changes specific to the type of analyte are described. The largest selectivity differences are obtained with pH changes.
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Affiliation(s)
- Uwe D Neue
- Waters Corporation, 34 Maple St., Milford, MA 01757, USA.
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37
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Sun L, Siepmann JI, Schure MR. Monte Carlo Simulations of an Isolated n-Octadecane Chain Solvated in Water−Acetonitrile Mixtures. J Chem Theory Comput 2007; 3:350-7. [DOI: 10.1021/ct600239z] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Li Sun
- Departments of Chemistry and of Chemical Engineering and Materials Science, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, and Theoretical Separation Science Laboratory, Rohm and Haas Company, 727 Norristown Road, P.O. Box 0904, Spring House, Pennsylvania 19477
| | - J. Ilja Siepmann
- Departments of Chemistry and of Chemical Engineering and Materials Science, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, and Theoretical Separation Science Laboratory, Rohm and Haas Company, 727 Norristown Road, P.O. Box 0904, Spring House, Pennsylvania 19477
| | - Mark R. Schure
- Departments of Chemistry and of Chemical Engineering and Materials Science, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, and Theoretical Separation Science Laboratory, Rohm and Haas Company, 727 Norristown Road, P.O. Box 0904, Spring House, Pennsylvania 19477
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38
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Zhao C, Cann NM. Solvation of the Whelk-O1 chiral stationary phase: A molecular dynamics study. J Chromatogr A 2006; 1131:110-29. [PMID: 16950326 DOI: 10.1016/j.chroma.2006.07.085] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2006] [Accepted: 07/14/2006] [Indexed: 11/29/2022]
Abstract
Density functional theory calculations and molecular dynamics simulations are employed to explore the solvation of the Whelk-O1 chiral stationary phase. First, a semi-flexible representation of the Whelk-O1 selective molecule is extracted from an extensive series of B3LYP/6-311+ G(2d,p) calculations. The resulting model is used to build a chiral surface, including end-caps, for molecular dynamics study of the interface between solvent and Whelk-O1. Three solvent environments in common use for Whelk-O1 HPLC have been examined: a normal-phase solvent of n-hexane/2-propanol; a reversed-phase solvent of water/methanol; and a supercritical solvent of CO(2) and methanol. In each case, we analyze the interface with an emphasis on solvent composition and solvent hydrogen bonding to the Whelk-O1 selector.
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Affiliation(s)
- Chunfeng Zhao
- Department of Chemistry, Queen's University, Kingston, Ontario K7L 3N6, Canada
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39
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Zhang L, Rafferty JL, Siepmann JI, Chen B, Schure MR. Chain conformation and solvent partitioning in reversed-phase liquid chromatography: Monte Carlo simulations for various water/methanol concentrations. J Chromatogr A 2006; 1126:219-31. [PMID: 16820151 DOI: 10.1016/j.chroma.2006.06.003] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2006] [Revised: 05/24/2006] [Accepted: 06/01/2006] [Indexed: 11/25/2022]
Abstract
Many structural models for the stationary phase in reversed-phase liquid chromatography (RPLC) systems have been suggested from thermodynamic and spectroscopic measurements and theoretical considerations. To provide a molecular picture of chain conformation and solvent partitioning in a typical RPLC system, a particle-based Monte Carlo simulation study is undertaken for a dimethyl octadecyl (C(18)) bonded stationary phase on a model siliceous substrate in contact with mobile phases having different methanol/water concentrations. Following upon previous simulations for gas-liquid chromatography and liquid-liquid phase equilibria, the simulations are conducted using the configurational-bias Monte Carlo method in the Gibbs ensemble and the transferable potentials for phase equilibria force field. The simulations are performed for a chain surface density of 2.9 micromol/m(2), which is a typical bonded-phase coverage for mono-functional alkyl silanes. The solvent concentrations used here are pure water, approximately 33 and 67% mole fraction of methanol and pure methanol. The simulations show that the chain conformation depends only weakly on the solvent composition. Most chains are conformationally disordered and tilt away from the substrate normal. The interfacial width increases with increasing methanol content and, for mixtures, the solvent shows an enhancement of the methanol concentration in a 10 Angstrom region outside the Gibbs dividing surface. Residual surface silanol groups are found to provide hydrogen bonding sites that lead to the formation of substrate bound water and methanol clusters, including bridging clusters that penetrate from the solvent/chain interfacial region all the way to the silica surface.
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Affiliation(s)
- Ling Zhang
- Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, MN 55455-0431, USA
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40
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Lippa KA, Sander LC. Identification of isolated cavity features within molecular dynamics simulated chromatographic surfaces. J Chromatogr A 2006; 1128:79-89. [PMID: 16846606 DOI: 10.1016/j.chroma.2006.06.043] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2006] [Revised: 06/06/2006] [Accepted: 06/13/2006] [Indexed: 10/24/2022]
Abstract
Highly ordered morphological features were characterized for molecular dynamics simulated alkyl-modified silica models that represent chromatographic materials with enhanced shape recognition capability. Deep cavities (8-10A wide) within the alkyl chains were identified for C18 polymeric models corresponding to shape-selective RPLC stationary phases. The all-trans conformational distal-end segments of these isolated cavities averaged over a 100 ps simulation time interval were observed to increase (up to 15 A) in models with an increase in both surface coverage and corresponding shape selectivity. Similar-structure cavities with significant alkyl chain ordered regions (>11A) were isolated from two independent C18 models (differing in bonding chemistry, density and temperature) that represent highly shape-selective materials. The size and depth of these ordered regions increased (up to 28 A) for the extended-length C30 alkyl phase models. These initial results offer a physical representation of alkyl-modified surfaces that may facilitate the identification of potential molecular features that may be involved in the shape-selective retentive processes, as well as illustrating the potential for such computational techniques to predict the molecular recognition capabilities of novel analyte-specific sorbents.
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Affiliation(s)
- Katrice A Lippa
- Analytical Chemistry Division, Chemical Science and Technology Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD 20899, USA.
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41
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Gritti F, Guiochon G. Adsorption mechanism in reversed-phase liquid chromatography. J Chromatogr A 2006; 1115:142-63. [PMID: 16580678 DOI: 10.1016/j.chroma.2006.02.095] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2006] [Revised: 02/21/2006] [Accepted: 02/28/2006] [Indexed: 11/22/2022]
Abstract
The effect of the bonding density of the octadecyl chains onto the same silica on the adsorption and retention properties of low molecular weight compounds (phenol, caffeine, and sodium 2-naphthalene sulfonate) was investigated. The same mobile phase (methanol:water, 20:80, v/v) and temperature (T = 298 K) were applied and two duplicate columns (A and B) from each batch of packing material (neat silica, simply endcapped or C1 phase, 0.42, 1.01, 2.03, and 3.15 micromol/m2 of C18 alkyl chains) were tested. Adsorption data of the three compounds were acquired by frontal analysis (FA) and the adsorption energy distributions (AEDs) were calculated using the expectation-maximization method. Results confirmed earlier findings in linear chromatography of a retention maximum at an intermediate bonding density. From a general point of view, the saturation capacity of the adsorbent tends to decrease with increasing bonding density, due to the vanishing space intercalated between the C18 bonded chains and to the decrease of the specific surface area of the stationary phase. The equilibrium constants are maximum for an intermediary bonding density (approximately 2 micromol/m2). An enthalpy-entropy compensation was found for the thermodynamic parameters of the isotherm data. Weak equilibrium constants (small deltaH) and high saturation capacities (large deltaS) were observed at low bonding densities, higher equilibrium constants and lower saturation capacities at high bonding densities, the combinations leading to similar apparent retention in RPLC. The use of a low surface coverage column is recommended for preparative purposes.
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Affiliation(s)
- Fabrice Gritti
- Department of Chemistry, University of Tennessee, Knoxville, TN 37996-1600, USA
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42
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43
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Srinivasan G, Müller K. Influence of solvents on the conformational order of C18 alkyl modified silica gels. J Chromatogr A 2006; 1110:102-7. [PMID: 16464463 DOI: 10.1016/j.chroma.2006.01.095] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2005] [Revised: 01/11/2006] [Accepted: 01/19/2006] [Indexed: 12/01/2022]
Abstract
The influence of solvents on the conformational order of C(18) alkyl modified silica gels is studied by means of variable temperature FTIR spectroscopy. Symmetric and anti-symmetric CH(2) stretching modes were utilized for getting qualitative information about the changes in alkyl chain conformational order as a function of both protonated and perdeuterated solvents. It was found that interaction between the C(18) alkyl modified silica gels and the mobile phase results in pronounced changes of the alkyl chain conformational order. Furthermore, it was observed that some perdeuterated solvents exhibit isotope effects, which again is reflected by a different alkyl chain conformational order as compared to the corresponding stationary phases with protonated solvents.
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Affiliation(s)
- Gokulakrishnan Srinivasan
- Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
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44
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Lippa KA, Sander LC, Mountain RD. Molecular Dynamics Simulations of Alkylsilane Stationary-Phase Order and Disorder. 1. Effects of Surface Coverage and Bonding Chemistry. Anal Chem 2005; 77:7852-61. [PMID: 16351130 DOI: 10.1021/ac0510843] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
"Shape-selective" polymeric alkylsilane stationary phases are routinely employed over the more common monomeric phases in reversed-phase liquid chromatography (RPLC) to improve the separation of geometric isomers of shape-constrained solutes. We have investigated the molecular dynamics of chromatographic models that represent both monomeric and polymeric stationary phases with alkylsilane surface coverages and bonding chemistries typical of actual materials in an effort to elucidate the molecular-level structural features that control shape-selective separations. The structural characterization of these models is consistent with previous experimental observations of alkyl chain order and disorder: (1) alkyl chain order increases with increased surface coverage; and (2) monomeric and polymeric phases with similar surface coverages yield similar alkyl chain order (although subtle differences exist). In addition, a significant portion of the alkyl chain proximal to the silica surface is disordered (primarily gauche conformations) and the distal end is most ordered. Models that represent shape-selective RPLC phases possess a significant region of distal end chain order with primarily trans dihedral angle conformations. This is consistent with the view that the alkyl chains comprising polymeric stationary phases contain a series of well-defined and rigid voids in which shape-constrained solutes can penetrate and hence be selectively retained.
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Affiliation(s)
- Katrice A Lippa
- Analytical Chemistry Division and Physical and Chemical Properties Division, Chemical Sciences and Technology Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899, USA.
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45
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Sun L, Wick CD, Siepmann JI, Schure MR. Temperature Dependence of Hydrogen Bonding: An Investigation of the Retention of Primary and Secondary Alcohols in Gas−Liquid Chromatography. J Phys Chem B 2005; 109:15118-25. [PMID: 16852913 DOI: 10.1021/jp0512006] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Configurational-bias Monte Carlo simulations in the Gibbs Ensemble were carried out to investigate the analyte partitioning of n-pentane, n-hexane, n-heptane, 1-propanol, and 2-propanol into a dioctyl ether retentive (stationary) phase used in gas-liquid chromatography. The united-atom version of the TraPPE (transferable potentials for phase equilibria) force field was used to model all analytes and the solvent. The analyte partition coefficients, Gibbs free energies of transfer, and Kovats retention indexes were calculated at four different temperatures ranging from 303.15 to 348.15 K. Although hydrogen bonding is a major contributor to the retention of the alcohol analytes over the entire temperature range, its importance for the separation factor between the primary and secondary alcohol decreases substantially with increasing temperature. The enthalpies and entropies for hydrogen bond formation were also estimated from the temperature dependence of the corresponding equilibrium constants. In agreement with experimental measurements, it is observed that the hydrogen bond involving 1-propanol is enthalpically favored, but entropically disfavored compared to 2-propanol.
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Affiliation(s)
- Li Sun
- Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, USA
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