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Application Notes

201

Gas phase diffusion studies of cyclohexane by infinite dilution inverse gas chromatography

Frank Thielmann, David Butler
Surface Measurement Systems Ltd, UK

Abstract

The shape of experimentally obtained IGC peaks is influenced by gas phase diffusion effects becoming stronger at smaller flow rates. At very high flow rates the assumption of equilibrium is no longer valid and adsorption will be less than in the equilibrium state.

This paper shows a way to find the best compromise between both influences. Elution studies were done on ¨¢-Lactose-Monohydrate with cyclohexane in the infinite dilution range.

202

Determination of the dispersive surface energy of Paracetamol by pulse inverse gas chromatography at infinite dilution

F. Thielmann, D. Butler
Surface Measurement Systems Ltd, UK

Abstract

The surface energy is a useful parameter describing the energetic properties of the surface of a solid sample. It can be determined in a fast and accurate way by IGC. This paper describes the measurement of the dispersive component of the surface energy of Paracetamol.

203

Heat of sorption studies on microcrystalline cellulose by pulse inverse gas chromatography at infinite dilution

F. Thielmann, D. Butler
Surface Measurement Systems Ltd, UK

Abstract

Inverse gas chromatography provides a fast and accurate method to measure the heat of sorption over different concentration and temperature ranges. Moreover IGC also allows the study of this parameter at different relative humidities. This paper describes the determination of the heat of desorption of octane on microcrystalline cellulose at infinite dilution and two different humidities.

204

Determination of the glass transition temperatures T_g of Maltose and its dependence on relative humidity by infinite dilution inverse gas chromatography (IGC)

F. Thielmann, D. Williams
Surface Measurement Systems Ltd, UK

Abstract

The glass transition temperature T_g is an important property for the characterisation of polymeric, food, pharmaceutical and many natural products. IGC can provide a fast and accurate determination of this property as well as its dependence on relative humidity. This paper describes the characterisation of maltose with decane at infinite dilution.

205

The Determination of the Solubility Parameter of Different Starch Types by Infinite Dilution Inverse Gas Chromatography

F. Thielmann, S. Reutenauer and V. McClean
Surface Measurement Systems Ltd, UK

Abstract

Solubility parameters are directly related to the cohesive energy density of a material. The latter is a measure for the strength of interaction between molecules and atoms; therefore, the solubility parameter can be used to predict the stability of food ingredients, polymers, drugs or excipients. Inverse Gas Chromatography provides a fast and sensitive route for the measurement of this parameter. This paper describes the determination of the solubility parameter of starch measured by water at infinite dilution.

206

Determination of diffusion coefficients of alkanes in polyethylene powder by infinite dilution inverse gas chromatography (IGC)

F. Thielmann, V. McClean
Surface Measurement Systems Ltd, UK

Abstract

The diffusion of solvent molecules in polymers can be measured rapidly and accurately by IGC at any concentration. At infinite dilution the van Deemter equation can be applied to obtain bulk diffusion coefficients. This paper demonstrates the performance of IGC measurements for the diffusion of octane in polyethylene.

207

Characterisation of drug polymorphs by Inverse Gas Chromatography

D. Butler¹, L. Mackin^2
1 Surface Measurement Systems Ltd, UK, ² Pharmacia, Chicago, USA

Abstract

Two polymorphs of the same active pharmaceutical material were characterised by infinite dilution inverse gas chromatography. Clear differences were observed in the surface properties despite the chemically identical nature of the samples. The sensitivity of the technique may be of considerable use in the identification of batch-to-batch variations, polymorphic forms being one cause of this problem.

208

The Measurement of Isotherms by Pulse Inverse Gas Chromatography

F. Thielmann* and I. Florian**
*Surface Measurement Systems Ltd, London, UK
**Porotec GmbH, Frankfurt, Germany

Abstract

Isotherm measurements provide the means to calculate BET surface areas and pore size distribution functions. Standard measurements at 77 K are restricted to very few probe molecules. Moreover, these temperatures cause long measurement times despite that they are less relevant in practical terms. Inverse Gas Chromatography provides a fast and accurate isotherm measurement in a wide temperature range and with various probe molecules. This is demonstrated in this paper by hexane and cyclohexane sorption measurements on different oxides.

209

An investigation of Chromosorb silicas as support materials for Inverse Gas Chromatography

David Butler and Frank Thielmann
Surface Measurement Systems Ltd, UK

Abstract

Chromosorb materials are interesting candidates for the support of viscous liquids in inverse gas-solid and gas-liquid chromatography. The tests conducted in this study include the determination of the material surface energy and its specific interaction with a range of polar probes.

210

Investigation of the Influence of Bleaching Conditions on Surface Properties of Standard Hair Samples by Inverse Gas Chromatography

F. Thielmann, D. Butler
Surface Measurement Systems Ltd, UK

Abstract

The surface energy is a useful parameter describing the energetic properties of the surface of a solid sample. It can be determined in a fast and accurate way by inverse gas chromatography (IGC). This paper describes the application of this approach for the investigation of how different bleaching conditions can cause changes on the surface of standard hair samples.

211

An Investigation of Minerals used in Asphalt by Inverse Gas Chromatography at Infinte Dilution

F. Thielmann, D. Pearse
Surface Measurement Systems Ltd, UK

Abstract

The affinity of minerals to bitumen is highly important for the quality of the asphalt composition. In order to predict this affinity a detailed knowledge of the physico-chemical properties of the mineral surface is required. Inverse Gas Chromatography (IGC) is a fast and sensitive method for the characterisation of solid powders. In the current study dispersive as well as acid-base properties have been investigated for different minerals.

213

Determination of Thermodynamic Parameters by Frontal Inverse Gas Chromatography at Infinite Dilution

F. Thielmann
Surface Measurement Systems Ltd, UK

Abstract

Strongly adsorbing materials are sometimes difficult to measure by pulse IGC since peaks become very broad and flat at infinite dilution conditions. An increase in temperature or concentration could change the surface thermodynamics significantly. An alternative method is the application of the frontal method at infinite dilution. This was until now difficult to realise since advanced instrumentation is required. This paper describes frontal measurements using the SMS-iGC at low concentration and temperature. The heat of sorption on carbon blacks is determined as an example for a typical infinite dilution property.

214

The determination of the permeability and the activation energy of diffusion of drug powders by infinite dilution inverse gas chromatography (IGC)

F. Thielmann¹⁾, V. McClean¹⁾, R. Willson²⁾ and T. Sokoloski^3)
1) Surface Measurement Systems Ltd, UK
²⁾ GlaxoSmithKline, UK
³⁾ GlaxoSmithKline, USA

Abstract

IGC provides an easy and quick route for the determination of diffusion coefficients of solvents in powders and films. The determination of the diffusion coefficient in drug powders is performed by applying the van Deemter approach at infinite dilution. A measurement of this property at different temperatures also provides the activation energy for the diffusion process.

215

Characterisation of Microporous Materials by Finite Concentration Inverse Gas Chromatography

F. Thielmann^a, E. Baumgarten^b
a Surface Measurement Systems Ltd., United Kingdom
^b Department of Physical Chemistry, Heinrich-Heine-Universitaet, Germany

Abstract

Finite concentration IGC is a useful tool for the investigation of surface and pore properties. A novel combination of finite concentration IGC and thermal desorption provides the possibility to separate micropore adsorption from surface and mesopore adsorption. This allows the calculation of BET values with physical relevance for highly microporous materials and the consideration of molecular sieve effects.

216

Characterisation of Surface Properties of Glass Fibres by Inverse Gas Chromatography

F. Thielmann*, S. Reutenauer* and A. Barbar**
*Surface Measurement Systems Ltd, UK
** ImperialCollege London, UK

Abstract

In the present paper dispersive surface energies and specific free energies have been calculated for different modified E-glass fibre surfaces. Both different sizing and different polymer coatings have been investigated to consider changes in the surface chemistry and surface energy during different fibre treatments.

218

The Determination of the Solubility Parameter of Polymethyl methacrylate by Infinite Dilution Inverse Gas Chromatography

Frank Thielmann and Majid Naderi
Surface Measurement Systems Ltd, UK

Abstract

Solubility parameters are directly related to the cohesive energy density of a material. The latter is a measure of the strength of interaction between molecules or atoms, therefore, solubility parameters are related to stability and other physical properties. Inverse Gas Chromatography provides a fast and reliable route for the measurement of these parameters. This paper describes the determination of the solubility parameter of PMMA and investigates the influence of different types of Chromosorb, which is used as a carrier for the coated polymer.

219

The Characterisation of Surface Area and Surface Heterogeneity Profiles of Hair by Inverse Gas Chromatography

Frank Thielmann*, Duncan Pearce* and Yash Kamath**
*Surface Measurement Systems Ltd, UK
**TRI Princeton, USA

Abstract

In the present paper the surface areas and adsorption potential distributions of nine different hair samples have been determined by Inverse Gas Chromatography (IGC). The distribution function reflects the energetic heterogeneity profile of a surface and provides interesting information on the nature and population of different surface sites. In this study IGC is shown to be a fast and accurate technique for the determination of these distribution functions.

220

The Characterisation of Cotton Fabrics and the Interaction with Perfume Molecules by Inverse Gas Chromatography

F. Thielmann and S. Reutenauer
Surface Measurement Systems Ltd, UK

Abstract

IGC is a versatile tool in the characterisation of textile products and the interaction with perfume molecules due to the wide range of physicochemical parameters, which can be determined by this technique. This is demonstrated by means of cotton wool and cotton fabrics. Alkanes, fragrance molecules and other polar probes have been used to measure interaction parameters such as dispersive surface energy and specific free energy. Experiments at different relative humidities gave additional information about the impact of water adsorption on the measured properties.

221

The Determination of Acid-Base Parameters by Inverse Gas Chromatography (IGC)

F. Thielmann, Majid Naderi and Daniel Burnett
Surface Measurement Systems

Abstract

The surface energy can be divided into a dispersive and specific component. Specific interactions consist mostly out of Lewis acid-base contributions. The latter are a useful descriptor for the acceptor and donor properties of surfaces. IGC is a very sensitive and accurate way of determining dispersive and specific interactions and has several benefits over common wettability techniques. In this study two different concepts (van Oss and Gutmann) have been applied to study the acid-base properties of three different kinds of microcrystalline cellulose.

222

The Determination of Surface Heterogeneity Profiles on Graphite by Inverse Gas Chromatography

F. Thielmann, D. Pearse
Surface Measurement Systems Ltd, UK

Abstract

In the present paper the adsorption potential distribution of two different graphite samples has been determined by Inverse Gas Chromatography (IGC). This distribution function reflects the energetic heterogeneity profile of a surface and provides therefore interesting information on the nature and population of different surface sites. In this study IGC is shown to be a fast and accurate technique for the determination of these energy distribution functions.

223

Determination of Energy Parameters of Highly Microporous Activated Carbons by Inverse Gas Chromatography

F. Thielmann*, S. Reutenauer* and G. Fowler**
*Surface Measurement Systems Ltd, UK
** Imperial College London, UK

Abstract

In the present paper the dispersive surface energy and specific energies of interaction for three microporous activated carbons have been calculated from IGC measurements. The enhanced adsorption potential in the micropores requires a measurement temperature of at least 350 ¡ãC to achieve equilibrium conditions.

301

iGC ¨C A new instrumental technique for characterising the phyisco-chemical properties of pharmaceutical materials

F. Thielmann and C. Levoguer
Surface Measurement Systems Ltd.

Abstract

The increasing sophistication of pharmaceutical drugs and drug delivery technologies has created the need for new techniques to measure the physico-chemical properties of a wide range of solid pharmaceutical ingredients and formulations. Inverse gas chromatography (IGC) is a gas phase technique, first developed over 40 years ago, to study the surface and bulk properties of particulate and fibrous materials. IGC has the potential to unlock some of the more difficult to measure physico-chemical properties of pharmaceutical materials such as powder surface energies, acid/base/polar functionality of surfaces, diffusion kinetics, solubility parameters, surface heterogeneity and phase transition temperatures/humidities. These properties affect both the performance and processing of many materials from active drug compounds to excipients and fillers. However, until recently, applications within the pharmaceutical industry have been limited to a few studies of properties such as the surface energy of simple powders. All of these studies have been carried out upon ¡®home-built¡¯ pieces of apparatus, often employing manual or semi-automated experimental methods. This has lead to a diversity of results in the literature, often seemingly contradictory, due to the differences in instrument design, methodology, sample preparation and individual operator skill.

Surface Measurement Systems (SMS), a small innovative scientific instrument manufacturer, noted for its expertise in the moisture sorption behaviour of pharmaceutical materials, has recently developed the world¡¯s first commercial inverse gas chromatography instrument ¨C iGC. This instrument, which has been developed in collaboration with a pharmaceutical academic/industrial consortium has been specifically designed to address many of the issues faced by physical properties researchers in the pharmaceutical industry, including fully automated operation and the ability to measure samples in a controlled humidity environment. This article gives a brief description of the technique, the instrument and some examples of its application within pharmaceutical physico-chemical analysis.

302

Characterisation of Strong Solid-Vapour Interactions by IGC

F. Thielmann
Surface Measurement Systems Ltd, UK

Abstract

Inverse Gas Chromatography (IGC) is a very versatile technique for the characterisation of different types of material. The solid material is characterised by a vapour or gas (probe molecule, adsorptive) with known physico-chemical properties. Depending on the activity of the surface and the probe molecule adsorption can occur as physisorption or chemisorption.

This paper focuses on the investigation of strong probe molecule ¨C surface interactions and describes appropriate IGC experiments for their investigation.

303

iGC ¨C A new instrument for characterising the physico-chemical properties of polymers.

F. Thielmann, C. Levoguer
Surface Measurement Systems Ltd, UK

Abstract

The surface properties of powders and fibres are an important parameter in the handling and performance of a wide range of solid materials. Inverse gas chromatography (IGC) is a gas phase technique, first developed over 40 years ago, to study the surface and bulk properties of particulate and fibrous materials. IGC has the potential to unlock some of the more difficult to measure physico-chemical properties of solid materials such as powder surface energies, acid/base/polar functionality of surfaces and phase transition temperatures/humidities. In addition kinetic effects such as diffusion and permeability may also be measured. However, until recently most IGC studies have been carried out upon ¡®home-built¡¯ pieces of apparatus, often employing manual or semi-automated experimental methods. This has lead to a diversity of results in the literature, often seemingly contradictory, due to the differences in instrument design, methodology, sample preparation and individual operator skill.

Surface Measurement Systems (SMS) has recently developed the world¡¯s first commercial inverse gas chromatography instrument ¨C iGC. This instrument has been specifically designed to address many of the issues faced by physical properties researchers, including fully automated operation and the ability to measure samples in a controlled humidity environment. This article gives a brief description of the technique, the instrument and some examples of its application to a range of polymeric materials analysis problems.

304

Characterization of Alumina and Related Surfaces by Inverse Gas Chromatography

F. Thielmann
Surface Measurement Systems Ltd., UK

Abstract

Aluminas as well as other metal oxides are of great importance in many applications in modern industry. These applications involve their use as catalyst supports, ceramics, and building materials, for example.

Therefore physico-chemical properties of these materials are the subject of innumerable studies by various techniques. Among all the different techniques measurements relying on the sorption of gaseous probe molecules belong to the most applied analytical methods.

In general sorption methods can be either dynamic or static. Standard procedures such as the determination of the surface area by nitrogen adsorption at 77 K are based on the latter. In recent years dynamic methods have become more and more important since they provide several advantages over common static techniques. For a dynamic measurement a carrier gas is used (instead of a vacuum) to transport the probe molecule (adsorptive) to the material under investigation (adsorbent). This allows faster equilibration under the experimental conditions.

The most common dynamic techniques are gravimetric methods and inverse gas chromatography (IGC). IGC exchanges the roles of the phases in classical gas chromatography. The adsorbent under investigation is placed into a column while a known adsorptive is used in the gas phase. As in analytical gas chromatography one obtains the retention time as a primary information. The retention time can be converted into a retention volume, which is directly related to various physico-chemical properties, which can be calculated from an IGC experiment. Those properties can be the surface energy or heat of sorption as examples for thermodynamic properties. Kinetic parameters such as the diffusion and the activation energy of diffusion are also available. Another possibility is the determination of the uptake both for physisorption and chemisorption. In the first case an isotherm results, which allows the computation of the surface area and porosity. In the latter case titration or thermal desorption techniques provide information about reversible and irreversible uptake.

The flexibility of the IGC method makes it a valid tool in the characterization of various materials. This is the reason for its frequent use in the characterization of metal oxides, especially for catalyst supports. A huge number of publications since the 50¡¯s proves this interest. This paper will give an overview of IGC application in the field of alumina and related oxides. It starts with a brief summary of the historical development. Subsequent chapters will give a few examples of important methods and actual advances.

305

The Application of Inverse Gas Chromatography in the Personal Care Sector

F. Thielmann and C. Levoguer
Surface Measurement Systems Ltd, UK

Abstract

The surface properties of powders and fibres are an important parameter in the handling and performance of a wide range of solid materials. Inverse gas chromatography (IGC) is a gas phase technique, first developed over 40 years ago, to study the surface and bulk properties of particulate and fibrous materials as well as their interaction with vapours such as flavour and fragrance molecules. IGC has the potential to unlock some of the more difficult to measure physico-chemical properties of solids due its unrivalled sensitivity. Such parameters include powder surface energies and enthalpies acid/base/polar functionality of surfaces, surface heterogeneity and phase transition temperatures / humidities. In addition kinetic effects such as diffusion and permeability may also be measured.

This article gives a brief description of the technique, the instrument and some examples of its application within physico-chemical analysis of personal care materials and products.

Case Studies

601

Identification of Batch-to-Batch variations in the dissolution rate of a pharmaceutical drug by Inverse Gas Chromatography

Simone Reutenauer¹, John Booth², Poul Bertensel^3
1 Surface Measurement Systems Ltd, UK
² Scientific & Medical, UK
³ Nycomed Danmark A/S, Denmark

Abstract

Nycomed Pharma (Denmark) supplied three different batches of the same active pharmaceutical material in order to have their surface properties investigated by infinite dilution Inverse Gas Chromatography (iGC). The final aim was to correlate the differences in surface properties between the three batches to observe differences in dissolution rates. The data showed that clear differences were observed in the surface properties despite the chemically identical nature of the samples. Indeed, the sensitivity of the iGC technique was shown to be of considerable use in the identification of batch-to-batch variations. In this particular case, a different surface chemistry was found for the different batches of the drug, which could be correlated to the different processing¡¯s and dissolution rates observed between the batches.

602

Investigation of the acid-base properties of an MCM-supported Ruthenium oxide catalyst by Inverse Gas Chromatography and Dynamic Gravimetric Vapour Sorption

Frank Thielmann, Majid Naderi, Dan Burnett, Helen Jervis
Surface Measurement Systems Ltd, UK

Abstract

Thermodynamic parameters of catalysts are highly relevant for practical applications. In particular, surface energies and acid-base properties of catalysts are of high interest since they reflect properties of active sites involved in the catalytic process and the initial adsorption step.

Dynamic vapour phase techniques are interesting tools for the determination of these properties. When compared to standard wettability experiments, they provide two main benefits. They can easily and reproducibly be applied to powders and a wide variety of probe molecules can be selected. In the current study dynamic gravimetric vapour sorption (DVS) and inverse gas chromatography (IGC) have been used to characterise the energetic and acid-base properties of a calcined ruthenium oxide / MCM41 catalyst as well as the corresponding MCM41 support.

603

Correlating Drug-Binder Adhesive Strengths Measured using Inverse Gas Chromatography with Tablet Performance

Frank Thielmann¹, Daniel Burnett², Kate Lusvardi³, and Thomas Durig³

¹Surface Measurement Systems Ltd, UK
²Surface Measurement Systems, Ltd, USA
³Aqualon Division, Hercules Incorporated, USA

Abstract

Drug-binder interactions have a significant impact on wet-granulation behaviour and product performance. Such interaction can be described by the work of adhesion between drug and binder. In this study, the work of adhesion is calculated from surface energy measurements carried out on the individual components by Inverse Gas Chromatography. The drugs Acetaminophen and Ibuprofen have been studied as well as the binders HPC, HPMC and PVP. HPC showed the strongest adhesion, followed by HPMC and PVP. This correlated well with the trends in tablet hardness and friability. The higher the work of adhesion the higher the tablet strength and the lower the friability.

604

Determination of Carbon Fibre-Polymer Interactions by Inverse Gas Chromatography

Frank Thielmann¹, Daniel Burnett², Alexander Bismark^3
1Surface Measurement Systems Ltd, UK
²Surface Measurement Systems, Ltd, USA
³Department of Chemical Engineering, Imperial College, UK

Abstract

The interaction between carbon fibres with different surface treatments and thermoplastic polymer matrices were investigated through thermodynamic, work of adhesion calculations and mechanical, practical adhesion measurements. The work of adhesion between the various carbon fibres and polymers were determined by measuring the dispersive and specific surface energetics of the individual components using Inverse Gas Chromatography (IGC). The mechanical adhesion measurements were performed by measuring the interfacial shear stress of the carbon fibre embedded in the polymer through single fibre pull-out testing. Oxidation of the PAN-based carbon fibres investigated caused an increase in the dispersive surface energy and a decrease in basicity. Work of adhesion values calculated from the surface energetics correlated well with the interfacial shear strength values of the composites. For all types of polymers used in this study there was an increase in both the work of adhesion and shear strength values on oxidation of the carbon fibre. Sizing does not significantly increase the shear strength despite a higher work of adhesion value, which may be caused by incompatibility of the polymers and epoxy-based sizing agent.

605

The effect of primary particle surface energy on agglomeration rate in fluidised bed wet

F. Thielmann¹, M. Naderi¹, M. Acharya¹, M. Ansari², F. Stepanek²

¹Surface Measurement Systems, Ltd., London

²Department of Chemical Engineering, Imperial College LondonUK

Abstract

The effect of primary particle surface wettability by a binder solution on the rate of agglomeration in a fluid-bed top-spray granulation process was investigated. A model system consisting of hydrophilic and hydrophobic spherical primary particles with a narrow size distribution, and an aqueous solution of hydroxy propyl-cellulose (HPC) as binder, was used. The surface energy of the primary particles was measured by inverse gas chromatography (IGC) and their wettability was characterised by contact angle experiments. Granulation was carried out in a desktop fluid-bed granulator and the resulting granule size distribution and granule microstructure were analysed. The hydrophobic particles gave a wider granule size distribution (larger maximum granule size) than hydrophilic ones under otherwise identical conditions, and the granules were notably rounder and more compact. SEM analysis of granule microstructure revealed that the hydrophilic particles were coated by the binder solution while all of the binder was found to form solid bridges for the hydrophobic primary particles. This behaviour suggests that the surface energy of the starting materials affects the outcome of the granulation significantly.

606

Correlating Surface Energies to Adhesion Data for Thermoplastic Polyolefins via Inverse Gas Chromatography Daniel Burnett1), Frank Thielmann2), Rose A. Ryntz3) 1) Surface Measurement Systems, 2222 South 12th Street, Suite D, Allentown, PA 18103, USA 2) Surface Measurement Systems UK, 5 Wharfside, Rosemount Road, London HA0 4PE, UK 3) Visteon Corporation, 401 Southfield, Dearborn, MI 48120, USA Abstract Polyolefins are used over a wide range of industries due to their low cost and adaptable mechanical properties. However, their low surface energy makes fabricating composites and applying coatings challenging. Therefore, various surface treatments have been utilized to enhance their adhesion properties. In this paper, the surface energies of various thermoplastic polyolefins (TPO) have been measured via Inverse Gas Chromatography (IGC). These surface energy values were correlated to mechanical adhesion testing of the painted polyolefins. The adhesive integrity of the painted TPO was determined by applying a comprehensive-shear load to the material. Higher surface energies measured by IGC lead to increased adhesion with the paint. The surface energies also correlate with TPO crystallinity, as determined by microhardness testing of the unpainted TPO.

Technical Notes

801

Reproducibility of the Dispersive Component of Surface Energy Measured by Inverse Gas Chromatography. Part I: Energetically Homogeneous Powders

Simone B. Reutenauer,
Surface Measurement Systems Ltd, UK.

Abstract

In this technical note, the experiment-to-experiment and column-to-column reproducibilities for inverse gas chromatography experiments performed with an SMS iGC have been investigated. 4-acetamidophenol, a readily available pharmaceutical ingredient, has been used as a representative material for the determination of the dispersive component of the surface energy by iGC. This material, in common with many pharmaceutical compounds, is expected to be energetically homogeneous. The aim of this study is to demonstrate the unrivalled performance of the SMS iGC instrument, as well as the effect of column-to-column variability on the results obtained.

802

Reproducibility of the Dispersive Component of Surface Energy Measured by Inverse Gas Chromatography. Part II: Highly Energetic Materials

Simone B. Reutenauer
Surface Measurement Systems Ltd, UK

Abstract

This technical note complements the Technical Note 801 [1] which investigated the experiment-to-experiment and column-to-column reproducibilities in the determination of the dispersive component of the surface energy of a low energetic material with an SMS iGC.
In this technical note, the same parameters have been investigated on a highly energetic material to demonstrate the performance of the SMS iGC instrument as well as the effect of column-to-column variability on the results obtained. GAC 1240, a readily available granulated activated carbon product, has been used as a representative material for the determination of the dispersive component of the surface energy by iGC.

803

Measuring Surface Energy for Viscous Fluids Using IGC

Armando R. Garcia
Surface Measurement Systems, Allentown, PA

Abstract

The measurement of surface energies of solids is a well proven technique using Inverse Gas Chromatography (IGC). There is a great deal of interest however in extending this valuable technique to liquids. This paper explores this possibility and provides data on techniques and results.

804

Influence of the Sample Mass on the Results obtained by
Inverse Gas Chromatography 


Frank Thielmann, Majid Naderi and Simone B. Reutenauer,
Surface Measurement Systems Ltd, UK.

Abstract

Inverse Gas Chromatography (IGC) is typically carried out at infinite dilution (low concentration of vapour). In this regime only few vapour probe molecules interact with the high energy sites on the surface of the solid material under investigation. If the concentration (partial pressure) of the vapour probe is increased (“finite dilution”) less active sites on the surface are also involved in the interaction and energetic parameters measured usually decrease in comparison to infinite dilution conditions. Whether a pulse experiment is carried out at infinite or finite concentration depends on the ratio between amount of sample (= mass) and amount of probe vapour (= concentration/volume) due to its discontinuous nature.
Given the above, it becomes obvious that the results of an IGC pulse experiment are dependent on the concentration regime and conditions must therefore be carefully controlled. In this study the effect of the sample mass on the surface and free energy of different pharmaceutical ingredients has been investigated.

805

The Influence of Packing Density and Column Diameter on the Results obtained by Inverse Gas Chromatography

Frank Thielmann and Daniel Burnett
Surface Measurement Systems Ltd, UK

Abstract

In this technical note, the effect of the column diameter on the results obtained by IGC has been investigated. In particular, the influence of the column diameter on the measurement of the dispersive component of the surface energy for alpha-lactose monohydrate is studied. In addition the effect of packing density is studied.