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Bawazeer S.,Strathclyde Institute of Pharmacy and Biomedical science | Sutcliffe O.B.,Manchester Metropolitan University | Euerby M.R.,HiChrom Ltd. | Watson D.G.,Strathclyde Institute of Pharmacy and Biomedical science
Journal of Chromatography A | Year: 2012

The retention properties of a silica gel column and a type C silica (silicon hydride) column for bases, sugars and polar acids were compared in hydrophilic interaction chromatography (HILIC) mode with formic acid or ammonium acetate as aqueous phase modifiers. The type C silica column was much more retentive for a series of model bases than the silica gel column and, surprisingly, retention of bases increased on the type C silica column when, the higher pH, ammonium acetate containing mobile phase was used. The retention of sugars was greater on the type C silica column than on the silica gel column and also increased on the type C silica column with increased pH suggesting either a silanophilic mechanism of retention or some unknown mechanism. Three type C silica based columns, type C silica, cogent diamond hydride and a β-pinene modified column, which it was hoped might exert some additional stereochemical discrimination, were tested for metabolomic profiling of urine. In general the unmodified type C silica column gave the strongest retention of the many polar metabolites in urine and could provide a useful complement to established HILIC methods for metabolomic profiling. © 2012 Elsevier B.V.


Miserez B.,Ghent University | Lynen F.,Ghent University | Wright A.,Pfizer | Euerby M.,Hichrom Ltd. | Sandra P.,Ghent University
Chromatographia | Year: 2010

Poly(N-vinylcaprolactam) (PVCL) connected to aminopropyl silica is a new stationary phase for temperature responsive liquid chromatography (TR-LC). PVCL shows a transition from hydrophilic to hydrophobic interaction between 30 and 40 °C. The synthesis is described in detail. The temperature responsive characteristic of the phase is illustrated with a mixture of steroids using pure water as mobile phase. An increase in retention is observed when raising the temperature. H-u plots at different temperatures were constructed. Below the lower critical solution temperature (LCST), no optimal velocity could be measured because of substantial resistance to mass transfer. Above the LCST, u opt was ca. 0.3 mm s -1 with reduced plate heights from 4 at 45 °C to 3 at 65 °C. The temperature responsive nature of the polymer is lost in green chromatography with ethanol as modifier in concentrations above 5%. © 2009 Vieweg+Teubner | GWV Fachverlage GmbH.


Euerby M.R.,Hichrom Ltd | James M.,Hichrom Ltd | Axelsson B.-O.,Novo Nordisk AS | Rosen O.,Umetrics AB | Petersson P.,Novo Nordisk AS
Journal of Separation Science | Year: 2012

The validity of the extended Tanaka column characterization procedure against the retention behavior of 101 analytes of widely differing properties chromatographed on five differing stationary phase chemistries has been established using a chemometric technique called principal component analysis (PCA). It was concluded that the simple and conveniently determined column characterization parameters covered the same space in the PCA loading plot as the retention times for the 101 differing analytes. This confirms that the ten column characterization parameters of the extended Tanaka protocol encode the same information as the retention times of the 101 analytes. Significant selectivity differences were observed between stationary phases and the mobile-phase modifiers - MeOH and MeCN. PCA contribution plots served as a convenient way to highlight specific selectivity differences between stationary phases. logD values exhibited a poor correlation with retention indicating that retention in RP-LC is not solely dictated by the analyte's hydrophobicity. The use of MeOH was found to generate greater selectivity differences with the five stationary phases than when MeCN is used. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Euerby M.R.,Hichrom Ltd | James M.A.,Hichrom Ltd | Petersson P.,Novo Nordisk AS
Analytical and Bioanalytical Chemistry | Year: 2013

This paper reports the influence of a diverse range of stationary phases and differing mobile phase modifiers on pressure-induced retention changes in reversed-phase liquid chromatography (RP-LC). The practical implications of these effects in the Tanaka column characterization using ultra high-performance liquid chromatography (UHPLC) conditions, and implications for HPLC to UHPLC translations in order to increase productivity and resolution are investigated. The stationary and mobile phase combinations responded to a similar degree to elevated pressure; hence, the authors believe that reliable column characterization parameters should be obtainable when UHPLC format columns are evaluated using the Tanaka approach. Analytes exhibited differing pressure-induced retention changes even for only modest increases in pressure (i.e. ΔP total 85 bar as shown when one transfers from a 3- to 2-μm particle). The degree of pressure-induced retention changes correlated with the analyte's molar volume and refractivity. The hydrophobicity of the analytes, as measured by logD, only exhibited a weak correlation. Hence, translating a RP-LC methodology from large to smaller particle size material of the same type may result in an increased or decreased selectivity and hence resolution between two analytes depending on their differing response to the pressure-induced retention changes. This potentially has a major impact on LC method development/optimization strategies and LC method translations. [Figure not available: see fulltext.] © 2013 Springer-Verlag Berlin Heidelberg.


Euerby M.R.,Hichrom Ltd | James M.,Hichrom Ltd | Petersson P.,Novo Nordisk AS
Journal of Chromatography A | Year: 2012

The practical implications of performing column characterization protocols (i.e. Tanaka) and their resultant chromatographic selectivity parameters using small dimension columns (i.e. 50×2.1mm I.D.) at high pressures have been critically compared to those obtained using conventional LC methodology. Retention factors should be corrected for the system extra column volume even when determined on ultra high performance liquid chromatographic (UHPLC) systems with low system volumes. An increase in pressure resulted in a general increase in the retention factor for most analytes, the degree being dependent on the physico/chemical properties of each analyte and the chromatographic conditions employed. However, analytes chromatographed at pH values close to their pK a values exhibited a substantial decrease in retention factor. Performing the Tanaka and extended column characterization procedures at pressures that would be encountered during the characterization of small particle sizes packed into 50×2.1mm I.D. column formats at a constant linear velocity according to standard protocols, resulted in comparable chromatographic selectivity parameters to those determined using standard HPLC systems and column formats. However, due to the wide structural diversity of analytes employed in other popular column characterization protocols, it is imperative to demonstrate comparable results when small columns packed with small particle sizes are chromatographed at increased pressure and compared to standard column formats - otherwise erroneous comparisons and conclusions may be made. © 2011 Elsevier B.V.


Borges E.M.,University of Campinas | Euerby M.R.,Hichrom Ltd | Collins C.H.,University of Campinas
Analytical and Bioanalytical Chemistry | Year: 2012

A novel stationary phase prepared by the thermal immobilization of poly(dimethylsiloxane) onto the surface of silica (PDMS-SiO 2) has been described, evaluated and compared with 229 commercially available RP-LC stationary phases using the Tanaka column classification protocol. The phase exhibited many unique chromatographic properties and, based on the phases in the database, was most similar to the fluoroalkylated phases (aside from the obvious lack of fluoro selectivity imposed by the C-F dipole). The phase exhibited classic reversed-phase behaviour in acid mobile phase conditions and mixed-mode reversed-phase/cation-exchange retention behaviour in neutral mobile phase conditions. The phase exhibited acceptable stability at both low and intermediate pH, conditions which should impart optimum chromatographic selectivity to the phase. Retention of basic analytes was shown to occur by a "three site model" as proposed by Neue. This new PDMS-SiO 2 stationary phase is extremely interesting in that the dominancy of its hydrophobic and ion-exchange interactions can be controlled by the influence of mobile phase pH, buffer type and concentration. The PDMS-SiO 2 stationary phase may provide a complementary tool to reversed-phase and HILIC stationary phases. The present results highlight the fact that the type of buffer, its concentration and pH can not only affect peak shape but also retention, selectivity and hence chromatographic resolution. Therefore, in method development and optimization strategies it is suggested that more emphasis should be given to the evaluation of these mobile phase operating parameters especially when basic solutes are involved. © 2012 Springer-Verlag.


Borges E.M.,University of Campinas | Euerby M.R.,Hichrom Ltd | Collins C.H.,University of Campinas
Analytical and Bioanalytical Chemistry | Year: 2012

Stationary-phase evaluation in reversed-phase liquid chromatography (RP-LC) is not a straightforward process. A number of tests to characterize and classify stationary phases have been suggested. The results of these various tests, however, do not always describe the real properties of the stationary phase. This study critically compares several tests for RP-LC stationary phases, including the Engelhardt, Tanaka, and SRM 870 tests, as well as an in-house test, with emphasis on the stationary-phase descriptors of hydrophobicity and silanol activity. The stationary phases were prepared by thermal immobilization of poly(methyloctylsiloxane) onto silica. Hydrophobicity data fromthe tests were generally good and interchangeable between the several tests. In contrast, the silanol activity results of the various tests differ significantly. As a consequence, stationary phase classification with respect to silanol activity depends considerably on the test method applied. A new classification method for silanol activity is proposed. © Springer-Verlag 2012.


Schad G.J.,University of Strathclyde | Euerby M.R.,Hichrom Ltd | Skellern G.G.,University of Strathclyde | Tettey J.N.A.,University of Strathclyde | Tettey J.N.A.,Policy Analysis and Research Branch
Analytical and Bioanalytical Chemistry | Year: 2012

This paper describes the reversed-phase liquid chromatographic behaviour of the trypanocidal quaternary ammonium salt isometamidium chloride and its related compounds on a range of liquid chromatographic phases possessing alkyl and phenyl ligands on the same inert silica. In a parallel study with various extended polar selectivity phases which possessed different hydrophobic/ silanophilic (hydrogen bonding) activity ratios, the chromatographic retention/ selectivities of the quaternary ammonium salts was shown to be due to a co-operative mechanismbetween hydrophobic and silanophilic interactions. The highly aromatic and planar isometamidium compounds were found to be substantially retained on stationary phases containing aromatic functionality via strong π-π interactions. The chemometric approach of principal component analysis was used to characterise the chromatographic behaviour of the isometamidium compounds on the differing phases and to help identify the dominant retention mechanism(s). Two-dimensional (temperature/gradient) retention modelling was employed to develop and optimise a rapid liquid chromatography method for the separation of the six quaternary ammonium salts within 2.5 min which would be suitable for bioanalysis using liquid chromatography-mass spectrometry. This is the first reported systematic study of the relationship between stationary phase chemistries and retention/selectivity for a group of quaternary ammonium salts. © Springer-Verlag 2012.


De Matteis C.I.,University of Nottingham | Simpson D.A.,University of Nottingham | Euerby M.R.,Astrazeneca | Euerby M.R.,Hichrom Ltd. | And 3 more authors.
Journal of Chromatography A | Year: 2012

The retention behaviour of a series of 28 monosubstituted benzenes, representing a diverse range of functional groups and substituent shape, were investigated using porous graphitic carbon (PGC) and octadecyl-bonded silica (ODS) stationary phases. For the majority of analytes retention on PGC was greater than on ODS, and in most cases this effect occurred at both pH 2.5 and 7.0. The main trends observed on PGC (in comparison with ODS) were: (i) similar or reduced retention of low polarity molecules such as the hydrocarbon and halogenated analytes; (ii) increased retention of conjugated analytes with extended planarity; (iii) increased retention of polar and charged species; and (iv) substantial increases in retention for selected polar and negatively charged analytes, including some ionised and unionised acid analytes. Poor retention of positively charged analytes was observed on both stationary phases. Molecular modelling studies have explored the geometry of π- π stacking interactions in retention on PGC and have highlighted the strong retention of large conjugated analytes, with extended planar conformations, which can interact with the graphite surface with cofacial geometry. Quantitative structure-retention relationships showed the importance of hydrophobic (π) and electronic factors (e.g. mean polarisability and LUMO energy) in retention on PGC, whilst retention on ODS was correlated to hydrophobicity (log. P and π). © 2012 Elsevier B.V.


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Hichrom Ltd | Date: 2012-01-19

chromatography grade silica. chromatography columns.

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