WO2006077406A1

WO2006077406A1 - Chromatographic material

Info

Publication number: WO2006077406A1
Application number: PCT/GB2006/000179
Authority: WO
Inventors: Linda Lucy Lloyd; Neil Thomson; Jane Louise Wheeler; Graham Ian Margetts
Original assignee: Polymer Laboratories Ltd
Priority date: 2005-01-19
Filing date: 2006-01-19
Publication date: 2006-07-27
Also published as: GB0501116D0

Abstract

The present invention provides novel surface modified chromatographic materials, based on chloromethylstyrene copolymer particles. Methods for preparing such materials and their use are also provided.

Description

CHROMATOGRAPHIC MATERIAL

The present invention relates to surface modified chloromethylstyrene copolymer particles for interactive/ reverse phase chromatographic applications utilising hydrophobic, hydrophilic and electrostatic interactions.

Interactive chromatography is a method whereby the separation of a mixture of solutes is achieved by differences in the degree of interaction between the solute and stationary phase. The greater the interaction the more the solute is retained by the packing and longer it takes to elute from the column. In reversed phase chromatography the eluent is polar and the stationary phase non-polar. Therefore in reversed phase chromatography non-polar molecules are attracted and interact with the stationary phase. Making the eluent more polar or making the stationary phase less polar increases the retention. It is clear that changing the polarity of the stationary phase whilst keeping the polarity of the eluent constant will alter the degree of interaction of the solute with the stationary phase and hence retention. This can be particularly advantageous where there are issues of solute solubility or stability in solution as the stationary phase hydrophobicity can be adjusted to give the required amount of retention with the optimum eluent conditions. Solute recovery can also be significantly influenced by the degree of hydrophobicity of the stationary phase since the eluent composition required to minimise interactions between the stationary phase and the solute may not provide for solubility of the solute. Changing the hydrophobicity of the stationary phase such that the solute is more soluble under the eluent conditions needed for elution can prevent precipitation and improve loading and recovery.

It is possible to choose conditions of stationary phase and eluent such that the solute adsorbs very strongly onto the packing material and is not eluted. Subsequent alterations to the eluent can then be made to modify these interactions and thereby elute the solute. This 'catch and release mechanism' can be a very efficient method to separate, purify or concentrate solutes of interest.

Chromatographic selectivity can in some cases be enhanced by the use of several different interactive modes such as in the case of affinity chromatography where the exceptional specificity is achieved by a combination of hydrophobic, hydrophilic and electrostatic interactions. This approach can also be taken with reversed phase materials where the introduction of a secondary mechanism can enhance or alter the selectivity.

Interactive high performance chromatography predominantly employs silica particles as the stationary phase. The silica surface is easily modified to produce a range of materials (C₄-Ci₈, amine, carboxyl etc) having specific separation characteristics. This is advantageous, allowing different mixtures to be optimally separated with different degrees of hydrophobicity or by different interactive mechanisms. However the chemical stability of silica particles is poor under certain conditions particularly across extremes of pH. Also surface modification must be complete as exposed silica can give rise to tailing peaks for basic compounds. To ensure complete modification an exhaustive reaction process must be employed.

Polymeric stationary phases can be used as an alternative to silica particles. These are predominantly styrenic based (styrene/divinylbenzene) crosslinked copolymers. The pH stability of the polymeric particles is excellent (typically pH 1-14). However because of their stability it is very difficult to modify the particle surface and vary the separation characteristics. The present invention describes chromatographic material comprising the copolymerisation of chloromethylstyrene and divinylbenzene to form particles and then subsequent chemical modification of the chloromethylstyrene functionality which can be used for interactive chromatographic applications. These may be in either column applications using medium or high pressure pumping systems, cartridge systems or syringe based systems or well plate systems or bulk extraction systems. In the un-modified form the chloromethylstyrene copolymer separation characteristics are very similar to standard styrene or divinylbenzene based materials. The use of the chloromethylstyrene group allows facile surface modification with the introduction of various ligands (C₄-Ci₈, amine, carboxyl, PEGs etc). The resultant groups are stable over a wide range of pH (1-14) and allow the separation characteristics to be varied considerably.

Detailed description

The invention relates to the use of materials comprising surface modified chloromethylstyrene/divinyl benzene copolymer particles in interactive chromatographic applications, in particular as the stationary phase in high performance liquid chromatography or solid phase extraction applications.

In the first aspect the present invention provides a chromatographic material comprising chemically modified chloromethylstyrene copolymer particles.

As used herein the term "chemically modified" means that chlorine molecules have been replaced with one or more ligands such that the specific separation characteristics of the material are altered. The general formula for the modified material is of the form: R,

Material -X- -Ri Material -N; or R₂

Wherein X is O or S;

Ri is a hydrocarbon chain or ring group;

R₂ and R₃ are each independently is H or Ri

As used herein, "hydrocarbon chain" includes C₂-Ci₈ alkyl, C2-Ci₈ alkenyl, or C₂-Ci_S alkynyl or Ci_-I8 alkanol.

The term "ring group" refers to C₅-Ci₈ cycloalkyl, C₆-Ci₈ aryl, C₅-C₁₈ heteroaryl, or C₅-Ci₈ heterocyclic, wherein N can optionally form part of said heteroaryl or said heterocyclic group.

For the purposes of this invention, the term alkyl relates to both straight chain and branched alkyl ligands of 1 to 18 carbon atoms, including but not limited to n-butyl, sec-butyl, isobutyl, tert-butyl n-pentyl and n-hexyl. The alkyl can contain 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 or 18 carbon atoms. The term also encompasses cycloalkyl radicals of 2 to 18 carbon atoms including but not limited to cyclobutyl, CH₂-cycloρropyl, CH₂-cyclobutyl, cyclopentyl or cyclohexyl.

When the ligand is an "alkenyl" this term relates to a straight chain or branched alkenyl radical of 2 to 18 carbon atoms containing one or more carbon-carbon double bonds and includes but is not limited to ethylene, n-propyl-1-ene, n- propyl-2-ene, isopropylene, etc. The alkenyl can contain 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 or 18 carbon atoms.

The term "alkynyl" means a straight chain or branched alkynyl radical of 2 to 18 carbon atoms containing one or more carbon-carbon triple bonds and includes but is not limited to ethynyl, 2-methylethynyl etc. The alkynyl can contain 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 or 18 carbon atoms.

The term "alkanol" refers to a straight chain or branched alkyl group attached to a hydroxy group, and includes but is not limited to methanol, ethanol, propanol, butanol, etc. .The alkanol can contain 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 or 18 carbon atoms.

The hydrocarbon chain can also contain S, O or NH in the backbone.

"Aryl" means an aromatic 6-18 membered hydrocarbon containing one ring or being fused to one or more saturated or unsaturated rings including but not limited to phenyl, naphthyl, anthracenyl or phenanthracenyl.

"Heteroaryl" means an aromatic 5-18 membered aryl containing one or more heteroatoms selected from N, O or S and containing one ring or being fused to one or more saturated or unsaturated rings .

The hydrocarbon chain or ring group can be optionally substituted with hydroxy, Ci_-i8 alkoxy, C_1-18 alkanol, SO_3, Ci-C₁₈ alkyl, or Si(O - alkyl)₃. Preferably the hydrocarbon chain is substituted with Si(O -alkyl)₃, more preferably Si(O -Et)₃. Preferably the ring group is substituted with hydroxy, C₁- C₁₈ alkyl , Ci_-18 alkanol, Ci_-18 alkoxy, or SO₃.

Most preferably R₁ is benzyl alcohol, phenyl- 3- sulfonic acid, n-butyl, phenyl- 3-t-butyl, n-octyl, phenyl-3-t-octyl, n-octadecyl, n-butylsilicate, and polyethyleneglycol (PEG). N and R₂ and R₃ together preferably form an amine group, more preferably a primary amine such as isoindole-1,3 (2H)- dione or a tertiary amine such as -N(CH₃)₂. Mixtures of groups can be employed to obtain desirable separation characteristics including mixed mode separations using two or more interactive modes of separation.

The particles in this invention are preferably composed of copolymers of chloromethylstyrene (CMS) and divinylbenzene (DVB). The DVB acts as crosslinking agent ensuring the particles are unable to dissolve or swell to significant amounts. The CMS content can vary between 90%wt/wt to l%wt/wt. The DVB is normally a mixture of various divinyl benzene isomers and ethyl vinyl benzene. Various grades can be employed from 96% divinyl content to 50% divinyl content. Pure para isomer or mixtures of isomers can be used. The divinyl content will control the degree of crosslinking, the CMS content will control the maximum degree to which the particles can be modified.

Polymerisation is achieved using a free radical process. The free radicals are generated by the thermal decomposition of a free radical initiator. Typical initiators are peroxides (benzoyl, dioctyl, lauryl, etc); azo initiators (AIBN) or other commonly used thermally decomposable molecules.

The particles are non-porous or porous in nature. Porosity is achieved by the use of inert diluents (Rohm and Haas, Patent GB 1389210). Typical diluents are toluene, diethyl benzene (DEB), hexanes, cyclohexanes, aliphatic or aromatic alcohols, aliphatic or aromatic acids or mixtures thereof. Polymeric diluents can also be employed for fine control of pore structure and pore size distribution. The choice of diluents or diluent mixtures will control the pore size. Pore sizes can range from IOA to IOOOOA but are most typically IOOA to 5OOθA. The diluents are removed after particle formation by a washing process. Non-porous particles are manufactured in the absence of inert diluents. The porous particles are manufactured using suspension polymerisation process. An oil phase consisting of monomers (CMS and DVB), oil soluble initiator and diluents are dispersed as droplets into an aqueous phase containing colloidal stabiliser. Typical stabilisers can be polyvinyl alcohol based (PVA), cellulose based stabilisers, sodium dodecyl sulphate (SDS) etc. The size of the droplets will determine the final bead size. Droplet formation can be achieved in a number of ways including simple stirring (most commonly used technique) or seeded swelling processes either with polymeric or monomeric seed particles (Sintef, US patent 4,459,378, T Nakashima et al, Key Engineering Materials 61&62, (1991) ρ513-516)). The droplets are heated to decompose the initiators, generating free radicals with subsequent polymerisation

Particle size can be varied between lμm and 300μm, more typically 2μm to 70μm particles are most useful. Non-porous particles can also be manufactured using a suspension process or a dispersion process. (Stover et al, Journal of Polymer Science, Part A, Polymer chemistry, 31, (1993), ρ3257-3263) The resultant particles are filtered or centrifuged and washed to remove any diluents and surfactants.

Typical chlorine content (chloromethylstyrene content 5wt%-60wt%) is 1-15%. The CMS functionality is distributed evenly about the bead and is present at both the pore/particle surface and within the polymer skeleton. Functional groups buried within the skeleton may not react during the surface modification and thus do not play a part in the chromatographic separation.

The chloromethyl group is easily reacted and allows facile introduction of ligands to modify the separation characteristics. Nucleophilic species will displace the chlorine group to introduce an alternate functionality. The δ

nucleophilic species has the formula HO Ri or HXR₂R₃ wherein X, Ri, R₂ and R₃ are as defined above.

The efficiency of the modification (displacement of chlorine groups) depends upon the reactivity and size of the ligand. The more nucleophilic the ligand the more facile the conversion. The larger the ligand the lower is the degree of conversion. Capping reactions with a suitable small nucleophile can be employed after the reaction of a large ligand to displace un-reacted, undesirable surface or submerged chlorine groups in the structure. Typically ammonia, methyl amine, dimethyl amine, alkali metal hydroxides, alkali metal methoxides are used for these capping processes.

After modification the particles are washed free of un-reacted ligands and dried. The particles can be used in many formats to achieve separations. Typically the particles are packed into stainless steel, glass or PEEK columns or cartridges and are used in conjunction with a gradient or isocratic pumping systems at high or medium differential pressures (100-2000 psi) to achieve flow.

Alternatively they may be packed into a fritted syringe, embedded within a sintered plug (Millennium pharmaceuticals, WO 00/21658) or dispensed into a fritted well plate and used at relatively low differential pressures (<100psi).

Low pressure systems are generally more applicable to a catch and release type mechanism.

Preferred features of each aspect of the invention are applicable to each other aspect mutatis mutandis.

The invention will now be described with reference to the following non- limiting examples which refer to the following figures: Figure 1 shows the separation of a mixture of standard peptides, oxytocin, angiotensin II, angiotensin I and insulin on a commercial PS/DVB material (PLRP-S), and a material modified with an alkyl ligand to reduce the effective hydrophobicity.

Figure 2 shows the separation of a mixture of standard peptides, oxytocin, angiotensin II, angiotensin I and insulin on a commercial PS/DVB material, PLRP-S, and a series of materials with different functional group loads.

Figure 3 shows the separation of a mixture of standard peptides, oxytocin, angiotensin II, angiotensin I and insulin on a commercial PS/DVB material, PLRP-S, and a series of materials with different functional group loads. The insulin peak has been circled for each material.

Figure 4 shows the separation of a mixture of standard peptides, oxytocin, angiotensin II, angiotensin I and insulin on a commercial PS/DVB material, PLRP-S, and a series of materials with different pore sizes and particle sizes.

Figure 5 shows the retention characteristics of lysozyme on two materials with different loadings of the acidic functionalities.

Examples

Example 1. Manufacture of 40% CMS particle using a stirred suspension polymerisation process.

600OmIs of R.O. water is added to a 1OL flanged topped reactor fitted with a nitrogen inlet, water condenser and high shear overhead stirrer. The water is purged with nitrogen gas for 2 hours at room temperature. The nitrogen purge is replaced with a nitrogen blanket and 30Og of Polyvinyl alcohol) (126,000 molecular weight, 88% hydrolyzed grade) added. The stirring is started and reaction mix heated to 8O⁰C. When the Polyvinyl alcohol) is completely dissolved the temperature is reduced to 65⁰C, whilst maintaining stirring.

A mixture of 300g of divinyl benzene (96% divinyl content), 20Og of chloromethyl styrene, 274g of 3-methyl-l-butanol, 281g of diethyl benzene and 2Og of benzoyl peroxide is prepared and added to the aqueous solution at 65⁰C. The stirring speed is adjusted to control droplet size, target size of 10-20μm. Once the approximate droplet size has been achieved the stirring rate is reduced and the temperature maintained at 65⁰C for 18 hours.

The reaction mixture is cooled and the polymerised particles are filtered from the aqueous continuous phase using a 5μm porous plate. The particles are washed with water to remove surfactants and then acetone to remove the pore forming diluents. The particles are dried under vacuum and air classified to produce a narrow particle size fraction with particle size mode of 13.8μm.

Yield 68g, Chlorine content from elemental analysis: 7.57%, SEC exclusion limit 184,000 polystyrene, chromatographic pore volume 56%, Surface area N₂ BET analysis 446m²/g, Pore volume N₂ BET analysis 1.43ml/g

Example 2. Manufacture of a 10% CMS particle using a polymer seeded polymerisation process.

600OmIs of a 0.2wt/wt% sodium dodecyl sulphate / 0.5wt/wt% polyvinyl alcohol) is added to a 1OL flanged topped reactor fitted with a nitrogen inlet, water condenser, PTFE anchor overhead stirrer and Ultra-Turrex homogeniser. A mixture of 45Og of divinyl benzene (96% divinyl content), 50g of chloromethyl styrene, 274g of 3-methyl-l-butanol, 281g of diethyl benzene and 2Og of benzoyl peroxide is prepared and added to the aqueous solution at room temperature. This dispersion is homogenised at high speed to produce a fine emulsion with a typical droplet size of 2μm. The homogeniser is then removed from the reactor.

85g of an aqueous dispersion containing 8.5g of linear polystyrene template particles (2.0μm diameter, 2.3%CV) is added to the 1OL reactor containing aqueous emulsion. The template particles are allowed to swell with the monomer / diluent mixture for 4 hours. The temperature is then increased to 65°C and maintained at this temperature with gentle stirring for 18 hours.

The reaction mixture is cooled and the polymerised particles are filtered from the aqueous continuous phase using a 5/mi porous plate. The particles are washed with water to remove surfactants and then tetrahydrofuan and finally acetone to remove the pore forming diluents. The particles are dried under vacuum. Modal particle size of final product is 9.2μm, CV of 3.2%.

Yield 454g, Chlorine content from elemental analysis: 1.78%, SEC exclusion limit 2,000,000 polystyrene, chromatographic pore volume 52%, Pore volume N₂ BET analysis 1.28ml/g

Example 3. Manufacture of a 30% CMS particle using a membrane emulsified seeded polymerisation process.

1200OmIs of a 0.2wt/wt% sodium dodecyl sulphate / 0.5wt/wt% polyvinyl alcohol) is added to a 2OL flanged topped reactor fitted with a nitrogen inlet, water condenser and PTFE anchor overhead stirrer and Ultra-Turrex homogeniser. A mixture of 70Og of divinyl benzene (96% divinyl content), 300g of chloromethyl styrene, 548g of 3-methyl-l-butanol, 562g of diethyl benzene and 4Og of benzoyl peroxide is prepared and added to the aqueous solution at room temperature. This dispersion is homogenised at high speed to produce a fine emulsion with a typical droplet size of 2μm. The homogeniser is then removed from the reactor.

1350g of an aqueous tetradecane seed dispersion produced using a membrane emulsification process (10wt% tetradecane, 0.5wt% polyvinyl alcohol, 0.2wt% sodium dodecyl sulfate, modal size 5.2μm) is added to the 2OL reactor containing the aqueous emulsion. The seed droplets are allowed to swell with the monomer / diluent mixture for 4 hours. The temperature is then increased to 65⁰C and maintained at this temperature with gentle stirring for 18 hours.

The reaction mixture is cooled and the polymerised particles are filtered from the aqueous continuous phase using a 5μm porous plate. The particles are washed with water to remove surfactants and then tetrahydrofuan and finally acetone to remove the pore forming diluents. The particles are dried under vacuum. Modal particle size of final product is 12.6μ,m, 95-5% span of 5.2μm.

Yield 948g, Chlorine content from elemental analysis: 5.13%, SEC exclusion limit 140,000 polystyrene, chromatographic pore volume 49%.

Example 4. Attachment of butyl amine

2Og of Chloromethyl styrene functional particles from example 1 are dispersed into a mixture of lOOmls of dimethyl acetamide and 52mls of n-butyl amine in a 250ml reactor fitted with a water condenser, nitrogen inlet and overhead stirrer. The reactor is heated to 9O⁰C and maintained at this temperature for 24hours under nitrogen. The reactor is cooled and particles filtered on a 5μm sinter. The particles are washed with fresh dimethyl acetamide, water, methanol and finally acetone before drying under vacuum at 4O⁰C. Product is light yellow in colour.

Yield: 19g, Nitrogen content from elemental analysis: 1.77%.

Example 5. Attachment of diethylene glycol.

lOOg of Chloromethyl styrene functional particles from example 1, lOOOmls of diethylene glycol and 70g of sodium methoxide are added to a 2L flanged topped reactor fitted with a nitrogen inlet, water condenser and high shear overhead stirrer. The reactor temperature is increased to 6O⁰C and a nitrogen blanket maintained throughout the reaction of 24hours. The reaction is cooled and the particles filtered in a 5L 5μm sinter. The particles are washed with water and then acetone to remove diethylene glycol and reaction products before drying under vacuum at 4O⁰C.

Yield: 95g, Chlorine content from elemental analysis: 1.79% (7.57% before reaction).

Examples of other ligands attached.

Examples of chromatographic separations.

Example 1. Figure 1 shows the separation of a mixture of standard peptides, oxytocin, angiotensin II, angiotensin I and insulin on a commercial PS/DVB material (PLRP-S), and a material modified with an alkyl ligand to reduce the hydrophobicity. There is a clear reduction in the retention of the four peptides with the three smallest peptides eluting as a group. The insulin peak has been circled in both chromatograms to show the reduction in retention but also the difference in selectivity between insulin and the three smaller peptides. It is clear that the functional group does indeed alter the retention and selectivity of the peptide separation.

Chromatographic conditions: column; 250x4.6mm, eluent A; 0.1% TFA in 20% acetonitrile, eluent B; 0.1% TFA in 50% acetonitrile, gradient; 0-100% B in 15 min, flow rate; l.Oml/min, detector; UV @220nm

Example 2. Figure 2 shows the separation of a mixture of standard peptides, oxytocin, angiotensin II, angiotensin I and insulin on a commercial PS/DVB material, PLRP-S, and a series of materials with different functional group loads. The insulin peak has been circled for each material. It is clear that the functional group load does indeed alter the retention of the peptides, in this examples the higher the load the lower the retention.

Chromatographic conditions: column; 250x4.6mm, eluent A; 0.1% TFA in 20% acetonitrile, eluent B; 0.1% TFA in 50% acetonitrile, gradient; 0-100% B in 15 min, flow rate; l.Oml/min, detector; UV @220nm Example 3. Figure 3 shows the separation of a mixture of standard peptides, oxytocin, angiotensin II, angiotensin I and insulin on a commercial PS/DVB material, PLRP-S, and a series of materials with different functional group loads. The insulin peak has been circled for each material. It is clear that the functional group load does in deed alter the retention of the peptides, in this examples the higher the load the lower the retention.

Chromatographic conditions: column; 250x4.6mm, eluent A; 0.1% TFA in 20% acetonitrile, eluent B; 0.1% TFA in 50% acetonitrile

Example 4. Figure 4 shows the separation of a mixture of standard peptides, oxytocin, angiotensin II, angiotensin I and insulin on a commercial PS/DVB material, PLRP-S, and a series of materials with different pore sizes and particle sizes. The insulin peak has been circled for each material. It is clear that the chemistry is suitable for a range of pore sizes and particle sizes.

Chromatographic conditions: column; 250x4.6mm, eluent A; 0.1% TFA in 20% acetonitrile, eluent B; 0.1% TFA in 50% acetonitrile, gradient; 0-100% B in 15 min, flow rate; l.Ornl/min, detector; UV @220nm

Example 5. Figure 5 shows the retention characteristics of lysozyme on two materials with different loadings of the acidic functionalities. Chromatogram A is an isocratic separation under reversed phase conditions, 0.1% TFA in 34% acetonitrile and chromatogram B the reversed phase with the addition of a salt gradient, 0 - 0.4M NaCl in 15 min. Indicative of both hydrophobic and electrostatic interactions with these materials.

Claims

1. A chromatographic material comprising chemically modified chloromethylstyrene copolymer particles.

2. The chromatographic material of claim 1 wherein said chloromethylstyrene copolymer is a chloromethylstyrene divinyl benzene copolymer.

3. The chromatographic material as claimed in claim 1 or claim 2 wherein said material has the general formula:

Material -X R₁

Wherein X is O or S;

Ri is a hydrocarbon chain or ring group; R₂ and R₃ are each independently is H or R_t

4. A chromatographic material as claimed in claim 3 wherein R₁ is selected from C₂-Ci₈ alkyl, C₂-C₁₈ alkenyl, C₂-C₁₈ alkynyl, C₅-Ci₈ cycloalkyl, C₂-Ci₈ alkanol, C₆-Ci₈ aryl, C₅-Ci₈ heteroaryl, or C₅-Ci₈ heterocyclic, wherein N can optionally form part of said heteroaryl or said heterocyclic group.

5. A method for forming a modified chloromethylstyrene copolymer chromatographic material comprising the step of:

(a) Reacting a chloromethylstyrene copolymer particle with at least one nucleophilic species.

6. The method as claimed in claim 5 wherein said nucleophilic species has the formula HNRi or HXR₂R₃, wherein X, Ri_, R_2i and R₃ are as defined in claim 3 or claim 4.

7. The method as claimed in claim 5 or claim 6 further comprising the step of :

(b) Reacting the chloromethylstyrene copolymer particle with a further nucleophile.

8. The method as claimed in claim 7 wherein said further nucleophile is selected from ammonia, methyl amine, dimethyl amine, alkali metal hydroxides, and alkali metal methoxides.

9. A chromatographic material comprising a modified chloromethylstyrene copolymer particle formed by a method as claimed in any one of claims 5 to 8.

10. The use of modified chloromethylstyrene copolymer material as claimed in any one of claims 1 to 4 or 9 in chromatographic applications.

11. The use as claimed in claim 10 wherein said material is the stationary phase in high performance liquid chromatography.

12. The use as claimed in claim 10 wherein said material is the stationary phase in solid phase extraction applications.