WO1989007265A1

WO1989007265A1 - Chromatography using electrically conductive polymer stationary phase materials

Info

Publication number: WO1989007265A1
Application number: PCT/AU1989/000039
Authority: WO
Inventors: Gordon George Wallace
Original assignee: Wollongong Uniadvice Limited
Priority date: 1988-02-03
Filing date: 1989-02-03
Publication date: 1989-08-10

Abstract

A chromatographic stationary phase material comprising a mechanically stable substantially chemically inert substrate coated with an electrically conductive polymer by chemical or electrochemical deposition. Electrochemical control of chromatographic separation is effected by applying electric potential to the stationary phase material to control elution by means of changes in the chemical properties of the polymer dependent upon the applied potential. A cell for electrodeposition of conductive polymer on particles of mechanically stable substantially chemically inert substrates and an electrochemical chromatography column are also disclosed. The latter comprises a hollow auxiliary electrode (12) and a region (18) to be packed with particulate material. A perforated tube (24) to dispense fluid into region (18) extends substantially through the region and a working electrode contact (26) is helically wound around tube (24). A microporous film (21) is provided to insulate the particulate material from the auxiliary electrode. The stationary phase material may be prepared in the column.

Description

CHROMATOGRAPHY USING ELECTRICALLY CONDUCTIVE POLYMER STATIONARY PHASE MATERIALS

Technical Field

This invention relates to polymeric materials for use as a stationary phase for gas and liquid chromatography.

Background Art

Polymeric materials have been widely used as stationary phases for gas and liquid chromatography due to their physical and chemical stability. Suitable polymers have been disclosed by MacBlane, D., et al American Laboratory. 1987, 134-138; Baiulescu, G.B., Hie, V.A. "Stationary Phases in Gas Chromatography", Pergamon Press, 1975, Hungary, pp 295-312; Poole, C.F., Schuette, S.A. "Contemporary Practice of Chromatography", Elsevier, 1984, Netherlands, pp 68; and Parris, N.A. "Instrumental Liquid Chromatography", J. Chromatoαr Lib. V. 27, Elsevier, 1984, Netherlands, pp 44,219. Columns containing such polymers are usually prepared either by physical adsorption on a suitable support, such as silica or celite, or by packing polymeric beads.

The selectivity of known polymers used in chromatography columns can be modified by varying the nature of the coating on the beads, by copolymerisation or by bonding appropriate functional groups to the polymer matrix. Such modification of the selectivity requires the preparation of a polymer with the desired characteristics and a separate polymer must be prepared to change the selectivity characteristics.

Another problem associated with currently employed polymers in chromatography columns is that a column must be packed and prepared for every individual chromatography run, and reuse of the polymer is difficult as the column must be unpacked, the polymer washed, and the column repacked. This is time consuming and repacking often leads to aberrations in readings caused by uneven distribution of the polymer in the column caused by repacking.

Disclosure of Invention

It is an object of this invention to provide a chromatographic stationary phase material and a method of preparing such material which will overcome, or at least ameliorate, one or more of the above disadvantages. It is a further object of this invention to provide a method of electrochemically controlling chromatographic separation and an electrochemical chromatography column which will overcome, or at least ameliorate, one or more of the above disadvantages.

A further object of this invention is to provide a cell for electrodeposition of conductive polymer on particles.

Accordingly, in a first aspect this invention consists in a chromatographic stationary phase material comprising a mechanically stable substantially chemically inert substrate coated with an electrically conductive polymer by chemical or electrochemical deposition.

The stationary phase material of this invention can, for example, take the form of particulate material such as beads for packed columns, sheets of material for thin layer chromatography (TLC) and coatings on column walls for capilliary or open tubular type columns. In the case of the latter the substrate is preferably the column wall.

Suitable substrates for use in this invention include, for example, commercially available carbon particles such as graphite or crushed Reticulated Vitreous Carbon (RVC) for example obtained from Energy Research Corporation, metal substrates such as platinum and gold, metal amides and stainless steel. Non - A -

conducting substrates such as silica can also be em loyed.

Preferably, the electrically conductive polymer is an intrinsically conductive polymer. As used herein the term "intrinsically conductive polymer" refers to a polymer which is electrically conductive as synthesised, that is, without additional doping. Examples of such polymers are polypyrrole, polythiophene, polyaniline and polyfuran.

In a second aspect this invention consists in a method of preparing chromatographic stationary phase material comprising growing an electrically conductive polymer on a mechanically stable substantially chemically inert substrate by chemical or electro-chemical deposition.

Preferably, the stationary phase material is prepared in situ in an electrochemical chromatography column.

In a third aspect this invention consists in an electrochemical chromatography column comprising a hollow auxiliary electrode and having a region to be packed with particulate material, means to dispense fluid into said region, a working electrode contact for said particulate material extending substantially through said region and means to insulate said particulate material from said body. In some applications the auxiliary electorde can be formed by providing a conductive body for the column. In other applications a suitable hollow electrode, such as carbon fibre can be used.

The column according to this invention can be used to grow conductive polymer on a particulate substrate to form the stationary phase material according to this invention and can also be used to perform electrochromatography.

In a fourth aspect this invention consists in a method of electrochemically controlling chromatographic separation comprising applying an electrical potential to a stationary phase material including an electrically conductive polymer to control elution by means of changes in the chemical properties of the polymer dependant upon the applied potential.

In a fifth aspect this invention consists in a cell for electrodeposition of conductive polymer on particles of mechanically stable substantially chemically inert substrates, said cell comprising a reservoir for monomer solution, an auxiliary electrode disposed in said reservoir, a porous receptacle disposed in said reservoir to hold said particles, means to agitate said particles and a working electrode contact within said receptacle for contact with said particles, said working electrode contact being formed from a material having a higher over potential or less affinity for the polymer than said substrate.

This invention thus provides chromatographic stationary phase material which can be prepared in situ, thereby ameliorating the problem of tedious, costly and time consuming packing processes. Elution may be altered by applying a different potential gradient to the column, thus enabling the selectivity of the column to be changed for a subsequent use, or the elution profile to be changed during the run.

Conducting polymers suitable for use in this invention can be synthesised either chemically or electrochemically according to:

V C^~

where for example X = NH,S,0 and C^~ = counterion

The polymers most appropriately used in the present invention are those able to be prepared by electro chemical synthesis. Such polymers include polythiophene, polyaniline, polyfuran and polypyrrole, although others may also be employed. Such synthesis is disclosed in a number of references, including Tourllon, G., Gamier, F. J. Phvs. Chem.. 1983, 87, 2289-2292; Tourllon, G., Gamier, F. J. Electroanal. Chem.. 1982, 135, 173-178; Tourllon, G., Gamier, F. J. Electroanal. Chem.. 1984, 161, 407-414; Kobayashi, T. , Yaneyama, H. , Tamura, H. J. Electroanal. Chem.. 1984, 161, 419; Paul, E.W., Ricco, A.J., Wrightson, M.S. J.Φhvs. Chem.. 1985, 89, 1441-1447; Qian, Renyan, Qiu, Jinjin, Polymer. 1987, 19, 157-172;

Otero, T.F., Tejada, R. , Elola, A.S. Polymer. 1987 28, 651-658; Preja, J., Lundstrom, L., Skotheim, T. J. Electrochem Soc. 1982, 129, 1685-89; Murthy, A.S.N. , Shripal, Reddy, K.S., J. Material Sci. Letters. 1984, 3, 745-747; and Kanazawa, K.K., Diaz, A.F., Geiss, R.H., Gill, W.D., Dwak, J.F., Logan, J.A., Rabolt, J.F., Street, G.B. J.C.S. Chem. Comm.. 1979, 854.

Advantages of using electrochemically synthesised polymers in chromatography include:

(i) Rapid and easily achieved column preparation (ii) Synthesis of a wide range of materials is easily achieved, (iii) Easy modification of the stationary phase to change the chemical nature and hence the retention mode. For example, by switching the polymer from the conducting to less conducting state either chemically or electrochemically, counterions can be released from the polymer, (iv) Electrochemical control on retention selectivity can be achieved. For example, electrochemical control of solvent or analyte can be achieved using any conductive particles. Further, a range of chemical interactors such as ion exchange or hydropholin, can be electrochemically controlled, (v) Production of physically and chemically stable polymers (vi) Reproducible column production (vii) Accurate control of stationary phase thickness and composition (viii) Columns may be grown in situ (ix) Selectivity may be altered by varying constituents which are easily incorporated into the polymers. In particular a range of counterions can be incorporated into the conducting polymers so that the mode of chromatography can be selected by employing appropriate monomers and counterions. (x) Selectivity can be altered by electrochemical control which influences chemical interations on the polymers. Conducting polymers suitable for use in this invention can be synthesised chemically. In particular particles can be coated with polymer by the addition of an oxidant such as Cr² O ^2~ in the presence of a monomer whilst stirring the particles. Brief Description of Drawings

Figure 1 is a schematic cross sectional view of a cell for electrodeposition of polymer on conductive or non conductive particles according to this invention;

Figure 2 is a schematic cross sectional view of an electrochemical chromatography column according to this invention;

Figure 3 is a schematic representation of the arrangement for electrodeposition using the column of Figure 2.

Figure 4 is a schematic cross sectional view of a second electrochemical chromatography column according to this invention;

Figures 5a and 5b are chromatograms obtained using a column as shown in Figure 3 packed with polypyrrole on RVC particles. Figure 5a is for a sample containing NO^" and Figure 5b is for samples of (A) dichloroacetate; (B) NO^"; (C) NO^".

Figures 6a and 6b graphically demonstrate ion exchange chromatographic behaviour by way of plots of capacity factor against pH and buffer concentration of element for (A) NO^" 3; (B) NO^" Z; (C) dichloroacetate.

Figure 7 graphically demonstrates reversed phase chromatograhic behaviour by way of plots of capacity against method proportion of eluent for (A) quinoline; (B) quinaldine; (C) naphthalene; (C) iso-quinoline. Figure 8 graphically demonstrates separation of phthalates using the cell of Figure 3 packed with polypyrrole containing dodecyl sulfate on RVC particles. (A) Dimethylphthalate; (B) Diethylphthalate.

Figure 9 graphically demonstrates separation of (A), m-toluic acid; and (B) p-tolvic acid using the column as used to obtain the results of Figure 8.

Figure 10 graphically demonstrates chromatographic separation by way of plots of capacity factor against potential between packing and auxiliary electrode for (A) Caffeine; (B) Theophylline; (C) Benzoic acid; (D) M-Tolvic acid, using the column used to obtain the results of figures 8 and 9.

Modes for Carrying Out the Invention

This invention will now be described, by way of example only, with reference to the accompanying drawings and some examples.

Figure 1 shows a cell 1 for electrodeposition of polymer on conductive or non conductive packings. The cell 1 comprises a container 2 to hold a solution of monomer 3. A porous tube 4 is suspended in the monomer solution and contains a rotating electrode 5 which acts as a stirrer. Tantalum wire 6 is wound helically around the body of electrode 5 to form the electrical conductor. Conductive particles 7 onto which the polymer is to be grown are disposed within the tube 4 and separated therefrom by an ion exchange separator 8. A nickel-chromium wire coil 9 is wound around the outside of tube 4 to act as an auxiliary electrode. A reference electrode 10 is also suspended in the monomer solution 3.

The electrode material, in this example tantalum wire must have a higher over potential or less affinity for the polymer to be deposited than the substrate to be coated. This enables the cell of this invention to be used such than the electrode, for example tantalum wire initiates polymer growth on the substrate particles without being coated itself.

The stationary phase material is prepared by placing the substrate or articles 7 to be coated, for example crushed RVC, in cell 1 and applying a constant current to grow the polymer, for example polypyrrole, on the particles. The coated polymeric packings are then washed and used as stationary phase packing for a chromatography column. For example, the stationary phase packing can be packed into a cartridge suitable for use in conjunction with a device such as a Waters RCM-100 cartridge holder and compression chamber.

The particulate substrate can be prepared from Reticulated Vitreous Carbon (RVC) for example obtained from Energy Research Corporation. The RVC is crushed into small particles and classified by sieve. Useful particle include the ranges 125-80 urn, 45-63 μm, and < 45 μm. The RVC particles are rinsed with alcohol, pretreated by 6N HCl solution and then washed with water until no chloride is present before coating.

Tantalum wire and stainless steel substrates are prepared by polishing μsing sand paper and steel wool, wiping with tissue paper and washing with water.

Tin oxide film, gold film, carbon cloth and carbon fiber are prepared for polymer coating by rinsing with alcohol and then water.

It is also possible to coat non conductive particles such as silica-C18 using the cell of Figure 1 and a procedure similar to that described above.

Figure 2 shows an electrochemical chromatography column 11 according to this invention. This column is primarily used as an alternative to the cell of figure 1 for producing particulate stationary phase material according to this invention although it can also be used for chromatographic separation. The cell 11 comprises a hollow cylinderical stainless steel body 12 which serves as the auxiliary electrode.

One end of body 12 is provided with a screw fitting 13 to receive a fluid connection from a high pressure pump as will be described below. The other end of body 12 receives a screw threaded cap 14 which has an outlet 15 for discharge of fluid. A reference electrode Ag/AgCl (3M NaCl) 16 fits into a side arm 17 screwed into the body. A central region 18 of the body terminated by silicon rubber plugs 19 is packed with the conductive particulate substrate 20, for example crushed RVC, to be coated with polymer.

A microporous film 21 insulates the particles 20 from the body 12. The microporous film can, for example, be of the kind known as Celgard 5511 or Celanex (Registered Trade Marks). Glass wool 22 fills the area at each end of region 18, at one end between plug 19 and the end of the body 12 and at the other end between plug 19 and a further silicon plug 23. Fluid dispensing means in the form of a perforated teflon tube 24 extends coaxially through body 12. The perforates take the form of a regular. array of holes 25. A working electrode contact for the particulate material is formed by a tantalum wire coil 26 which is wound around the tube 24 and extends through the region 18. An electrical connection 27 is provided to coil via outlet 15 which contains suitable internal insulation (not shown) . Plug 23 is maintained in position by means of a length of plastics tubing 28 extending between cap 14 and plug 23.

It has been found that the use of the body 12 of the column as an auxiliary electrode and the use of a work electrode contact extending substantially through the region of packed particles is essential to minimise IR drops, minimise potential gradients, and minimise hydrogen evolution. Additionally the fluid dispensing tube extending through the region of packed particles improves percolation of monomer solution through the particles.

Figure 3 shows the arrangement for electrodeposition using the column 11 of Figure 2. The arrangement comprises a gas pressure pump 30 fitted to a container 31 of the reagent monomer 32. The reagent is pumped via line 33 to column 11. Overflow from the column 11 passes into a reservoir 34. EXAMPLE 1

Polypyrrole was grown on RVC particles using the column depicted in Figure 2 incorporated in the arrangement shown in Figure 3. RVC particles of less than 45 μm were packed into the cell. The column was then connected to a N pressure pump as shown before being washed with water. The reagent containing monomer was then pumped into the column using a flow rate in the range of 0.1 - 1 mL/min. A constant anodic current was applied. The packing was washed with water, removed and dried at about 70°C.

Polymer growth on other substrates was also investigated. Using the technique described above polymer formation on the substrates tantalum wire, carbon cloth, carbon films, tin oxide coated plastic film, gold coated plastic film and stainless steel were achieved using a 0.3M pyrrole solution containing 0.1M sodium dodecyl sulfate (SDS) as supporting electrolyte. Figure 4 shows a second electrochemical chromatograph column 40 according to this invention. This column is primarily for use in performing chromatographic separation although it can also be usfed to prepare the stationary phase material of this invention by coating of particles with conductive polymer.

The column 40 comprises a cylinderical teflon tube 41 fitted at one end by means of a teflon sleeve 42 to a stainless steel fitting 43 of a standard high pressure liqued chromatography (HPLC) pump (not shown) .

At the other end, tube 41 is similarly fitted by means of a teflon sleeve 44 to a first stainless steel fitting 45 provided with an end cap 46.

The stationary phase material 47 according to this invention is packed into tube 41 in a cartridge formed from an insulating ion exchange membrane 48 preferably by filter paper.

A hollow cylindrical carbon cloth auxiliary electrode 49 surrounds the membrane 48 immediately inside the teflon tube 41. A suitable electrical connection (not shown) is provided to the electrode. Filters 50 are placed at each boundary of the particulate material 47. A helical working electrode contact 51 extends substantially through the region containing the particulate stationary phase material 47. One end of column 40 is attached by means of a plastics tube 52 and suitable ferrule 53 and locknuts 54 to a T-piece 55. T-piece 55 also holds a reference electrode 56.

Outlet for the column 40 is provided by a further plastics tube 57 held in T-piece by suitable ferrule 53 and locknut 54. An electrical connection to contact 51 is provided by a wire 58 extending through plastics tube 52 and a further tube 59 secured to T-piece by locknut 54 and ferrule 53. EXAMPLE 2

A column as shown in Figure 4 was packed with polypyrrole coated RVC particles of less than 45μm and chromatograms obtained.

The detection method was UV absorption at 215nm. Figures 5a nd 5b show the results. In Figure 5a the eluent is 0.05M sodium acetate at a flow rate of 0.5mL/min with a sample of 10^~3M NO^". In Figure 5b the eluent is 0.0015M sodium acetate at a flow rate of 0.3 mL/min on a sample of

(A) dichloroacetic acid

(B) NO^"

(C) NO^"

The operation of the column of Figure 4 will be described in connection with several examples.

All reagents used in the examples were analytical reagent (AR) grade unless otherwise stated. LR grade pyrrol (Fluka) was redistilled before use. The aqueous solution used for polymer growth was 0.5 M KCl and 0.5 M pyrrole. In some instances 0.1 M sodium dodecyl sulfate (SDS) was used as the supporting electrolyte for growing polymer. Acetate buffer was prepared by dissolving sodium acetate into, water and then adjusting pH with acetic acid or sodium hydroxide. Methanol (HPLC grade) was obtained from BDH chemicals. Water was distilled and then purified by Milli-Q Water System (MILLIPORE) .

The chromatograhic column employed was that described with reference to Figure 4 packed with polymer coated RVC particles prepared using the apparatus of Figure 1 or Figures 2 and 3. The RVC particles were of a size less than 45μm.

In examples 5, 6 and 7 the solution employed in the electrochemical polymerization procedure was 0.2 M pyrrole and 0.1 M sodium dodecyl sulfate (SDS) in water. EXAMPLE 3 - ION EXCHANGE

Nitrate, nitrite and dichloroacetate acid ions were used as test compounds.

Using a column of the kind described with reference to Figure 4 packed polypyrrole coated RVC particles of less than 45um prepared according to this invention, behaviour characteristic of an anion exchange resin was observed. For the anions considered, the capacity factor decreases with increased pH and increased buffer concentration. This behaviour is typical of conventional ion exchange resins Snyder, L.R., Kirkland, J.J. "Introduction to Modern Liquid Chromatography" 2nd Ed. John Wiley & Sons, Inc., 1979. The separation factor(« ) differs markedly with pH. Once again, such behaviour is expected however, the selectivity series obtained from some anions was a little different from conventional ion exchange resins.

Figures 6a and 6b demonstrates ion exchange chromatographic behaviour by respective plots of capacity factor against pH and buffer concentration of eluent for:

(A) NO~

(B) NO^

(C) dichloroacetate EXAMPLE 4 - REVERSED PHASE

Reversed phase chromatography (RPC) was also investigated on the polypyrrole coated column material using naphthalene, isoquinnoline, quinoline and quinolidine as test compounds. The capacity factor value was found to be a function of methanol concentration in the eluent. The results are summarized in Figure 7 for:

(A) quinoline

(B) quinaldine

(C) naphathlene

(D) iso-quinoline

This behaviour is typical of that observed on conventional reversed phase columns. Separation factors for the isomers investigated were adequate to obtain separation.

EXAMPLE 5 - Separation of phthalates

Figure 8 graphically demonstrates the result of separation of the following phthalates using the column of Figure 4 packed with polypyrrole containing dodecyl sulfate on RVC particles of less than 45μm prepared according to this invention:

(A) Dimethyphthalate

(B) Diethylphthalate

EXAMPLE 6 - Separation of toluic acids

Figure 9 graphically demonstrates the result of separation of the following toluic acids using the column of Figure 4 packed with polypyrrole containing dodecyl sulfate on RVC particles of less than 45μm prepared according to this invention:

(A) m-toluic acid

(B) p-toluic acid EXAMPLE 7

Figure 10 graphically demonstrates the result of separation of the following compounds using the column of Figure 4 packed with polypyrrole containing dodecyl sulfate on RVC particles of less than 45um prepared according to this invention:

(A) Caffeine

(B) Theophylline

(C) Benzoic acid

(D) m-Toluic acid EXAMPLE 8

Separation of chiral molecules can be achieved by incorporating chiral discriminating species eg. a specific hand of Co (EDTA) or campher sulfuric acid into the polymer. Alternatively the monomer itself can be made chirally discriminating before polymerisation. EXAMPLE 9

Affinity purification of biologicial species can be achieved by incorporating either the antibody or antigen into the polymeric packing material.

Claims

1. A chromatographic stationary phase material comprising a mechanically stable substantially chemically inert substrate coated with an electrically conductive polymer by chemical or electro-chemical deposition.

2. A stationary phase material as claimed in claim 1 wherein said polymer is an intrinsically conductive poiymer.

3. A stationery phase material as claimed in claim 1 or claim 2 wherein said substrate is electrically conductive.

4. A stationary phase material as claimed in any one of claims 1 to 3 wherein said substrate is particulate.

5. A stationary phase material as claimed in claim 4 wherein said substrate is crushed reticulated vitrous carbon.

6. A stationary phase material as claimed in any one of claims 1 to 3 wherein said substrate is the wall of a chromatography column.

7. A stationary phase material as claimed in any one of claims 1 to 3 wherein said substrate is a planar sheet.

8. A stationary phase material as claimed in any one of claims 1 to 3 wherein said substrate is selected from the group comprising tantalum wire, stainless steel, tin oxide film, gold film, carbon cloth and carbon fibre.

9. A stationary phase material as claimed in claim 1 or claim 2 wherein said substrate is non electrically conductive.

10. A stationary phase material as claimed in claim 9 wherein said substrate is silica.

11. A stationary phase material as claimed in any one of claims 1 to 10 wherein said polymer is selected from the group comprising polythiphene, polyaniline, polyfuran and polypyrrole.

12. A method of preparing chromatographic stationary phase material comprising growing an electrically conductive polymer on a mechanically stable substantially chemically inert substrate by chemical or electro-chemical deposition.

13. A method as^" claimed in claim 12 wherein said polymer is an intrinsically conductive polymer.

14. A method as claimed in claim 12 or claim 13 wherein said substrate is electrically conductive.

15. A method as claimed in any one of claims 12 to 14 wherein said substrate is particulate.

16. A method as claimed in claim 15 wherein said substrate is crushed reticulated vitrous carbon.

17. A method as claimed in any one of claims 12 to 14 wherein said substrate is the wall of a chromatography colum .

18. A method as claimed in any one of claims 12 to 14 wherein said substrate is a planar sheet.

19. A method as claimed in any one of claims 12 to 14 wherein said substrate is selected from the group comprising tantalum wire, stainless steel, tin oxide film, gold film, carbon cloth and carbon fibre.

20. A method as claimed in claim 12 or claim 13 wherein said substrate is non electically conductive.

21. A method as claimed in claim 20 wherein said substrate is silica.

22. A method as claimed in any one of claims 12 to 21 wherein said polymer is selected from the group comprising polythiphene, polyaniline, polyfuran and polypyrrole.

23. A method as claimed in any on claims 12 to 22 when performed in situ in a chromatography column.

24. An electrochemical chromatography column comprising a hollow auxiliary electrode and having a region to be packed with particulate material, means to dispense fluid into said region, a working electrode contact for said particulate material extending substantially through said region and means to insulate said particulate material from said body.

25. An electrochemical chromatography column as claimed in claim 24 wherein the auxiliary electrode is formed by the column wall.

26. An electrochemical chromatography column as claimed in claim 24 or claim 25 wherein said mean to dispense fluid comprises a perforated tube extending substantially through said region.

27. An electrochemical chromatography column as claimed in claim 26 wherein said working electrode contact comprises a wire wound helically around said tube.

28. An electrochemical chromatography column as claimed in claim 24 wherein the auxiliary electrode is a hollow member disposed within the column wall.

29. An electrochemical chromatography column as claimed in claim 28 wherein said working electrode contact comprises a helically coiled wire.

30. A method of electrochemically controlling chromatographic separation comprising applying an electrical potential or current to a stationary phase material including an electrically conductive polymer to control elution by means of changes in the chemical properties of the polymer dependant upon the applied potential.

31. A method as claimed in claim 30 wherein elution is controlled by electrochemical control of solvent or analyte.

32. A method as claimed in claim 30 wherein a counterion is expelled from the polymer.

33. A method as claimed in claim 30 wherein elution is controlled by electochemical control of chemical interaction on the polymers.

34. A cell for electrodeposition of conductive polymer on particles of mechanically stable substantially chemically inert substrates, said cell comprising a reservoir for monomer solution, an auxiliary electrode disposed in said reservoir, a porous receptacle disposed in said reservoir to hold said particles, means to agitate said particles and a working electrode contact within said receptacle for contact with said particles, said working electrode contact being formed from a material having a higher over potential or less affinity for the polymer than said substrate.

35. A cell as claimed in claim 34 wherein an ion exchange separator is disposed to separate said particles and said receptacle.

36. A cell as claimed in claim 34 or claim 35 wherein a rotating electrode comprises said means to agitate the particles and said working electrode contact.

37. A cell as claimed in claim 36 wherin the elctrical conductor is formed by wire wound around said rotating electrode.

38. A cell as claimed in any one of claims 34 to 37 wherein said working electrode contact is formed from tantalum wire.