EP0302912A4 - Verfahren zur herstellung monodispergierter, barium enthaltender ferrite. - Google Patents

Verfahren zur herstellung monodispergierter, barium enthaltender ferrite.

Info

Publication number
EP0302912A4
EP0302912A4 EP19880901364 EP88901364A EP0302912A4 EP 0302912 A4 EP0302912 A4 EP 0302912A4 EP 19880901364 EP19880901364 EP 19880901364 EP 88901364 A EP88901364 A EP 88901364A EP 0302912 A4 EP0302912 A4 EP 0302912A4
Authority
EP
European Patent Office
Prior art keywords
barium
particles
ferrite
dispersion
colloidal
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP19880901364
Other languages
English (en)
French (fr)
Other versions
EP0302912A1 (de
Inventor
Egon Matijevic
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Clarkson University
Original Assignee
Clarkson University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Clarkson University filed Critical Clarkson University
Publication of EP0302912A1 publication Critical patent/EP0302912A1/de
Publication of EP0302912A4 publication Critical patent/EP0302912A4/de
Withdrawn legal-status Critical Current

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C1/00—Magnetic separation
    • B03C1/005—Pretreatment specially adapted for magnetic separation
    • B03C1/01—Pretreatment specially adapted for magnetic separation by addition of magnetic adjuvants
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K9/00—Medicinal preparations characterised by special physical form
    • A61K9/48—Preparations in capsules, e.g. of gelatin, of chocolate
    • A61K9/50—Microcapsules having a gas, liquid or semi-solid filling; Solid microparticles or pellets surrounded by a distinct coating layer, e.g. coated microspheres, coated drug crystals
    • A61K9/5094—Microcapsules containing magnetic carrier material, e.g. ferrite for drug targeting
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G49/00—Compounds of iron
    • C01G49/0018—Mixed oxides or hydroxides
    • C01G49/0036—Mixed oxides or hydroxides containing one alkaline earth metal, magnesium or lead
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/26—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on ferrites
    • C04B35/2683—Other ferrites containing alkaline earth metals or lead
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/44—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of magnetic liquids, e.g. ferrofluids
    • H01F1/445—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of magnetic liquids, e.g. ferrofluids the magnetic component being a compound, e.g. Fe3O4
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/30—Particle morphology extending in three dimensions
    • C01P2004/38—Particle morphology extending in three dimensions cube-like
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/51—Particles with a specific particle size distribution
    • C01P2004/52—Particles with a specific particle size distribution highly monodisperse size distribution
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/42—Magnetic properties
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values

Definitions

  • This invention relates to a process and to the composition of matter resulting from this process. More specifically, this invention is directed to a process for the preparation of a colloidal dispersion of ferrite particles containing barium.
  • the particles produced by this process have a very narrow particle size distribution and are superparamagnetic in their response to a magnetic field. These particles are useful in magnetic recording media; in separation of various constituents of complex fluids (i.e. blood, cerebrospinal fluid or urine); and in certain diagnostic applications.
  • the precursors to the formation of the solid phase are, in most instances, one or more solute complexes.
  • This procedure is, thus, based upon the control of kinetics of the complexation reaction in order to achieve a single burst of nuclei, which are then allowed to grow uniformly, resulting in particles of narrow size distribution.
  • the constituent solutes are generated at the proper rate, their even distribution onto existing nuclei results in the least increase in total free energy of the dispersion, thus, controlling the growth of such particles by proper control of particle charge. Control of the charge on such particles is traditionally achieved by adjustment in pH or through the introduction of additives. In the absence of such control of charge, aggregation of such particles will result.
  • a precipitate is initially prepared.
  • the form of precipitate is generally other than in the desired colloidal form.
  • This precipitate is then subsequently changed, through crystallization, recrystallization or dissolution/ reprecipitation into the desired form of dispersed matter.
  • a most common example of this procedure is sol-gel transformation.
  • the mechanisms involved in these transformations are not generally well understood and, thus, the results are not readily predictable. It is also difficult to recognize if a phase transformation has in fact occurred since the initial state (form) of the dispersed matter may be either so short lived or so finely dispersed, the transition from one state to another is difficult to detect.
  • the literature does describe the preparation of spherical magnetite particles by phase transformation techniques.
  • colloidal particles Because of the nature of the colloidal particles, and the various methods used in their preparation, their physical properties are often unpredictable. For example, in the preparation of colloidal magnetite and ferrites, their • respective crystal structure can often vary and so to the response of such materials to magnetic fields.
  • the production of barium ferrite powders has traditionally involved the phase transformation of large particles of barium ferrite at elevated temperature, see for example Haneda, K, et al., J. Am. Cer. Soc. (1974) 57, 354. During production, the ferrite is milled and calcined at elevated temperatures to reduce particle size from multidomain to single-domain.
  • the above and related objects are achieved by providing a process for the preparation of well-defined monodispersed particles of barium containing ferrites.
  • This process involves the phase transformation of ferrous hydroxide gel, in a nonoxidizing atmosphere.
  • This gel is then contacted with barium nitrate solution.
  • the nitrate salt acts as a mild oxidizing agent, thus, promoting the phase transformation of the gel to barium containing ferrite particles.
  • barium is incorporated within the crystal lattice of the ferrite particle.
  • the resultant crystalline materials have a narrow particle size distribution, and a cubic morphology.
  • These crystalline particles are unique among ferrites in that they are readily dispersible in an aqueous medium and are superparamagnetic in response to magnetic fields.
  • the introduction of barium ions into the ferrite crystalline lattice is believed to attenuate the magnetic properties of these materials, thus, accounting for reduced particle/particle interactions (aggregation). This attenuation of magnetic properties of the ferrite can be controlled within limits, depending upon the relative concentration of barium ions introduced into these crystalline materials.
  • These modified ferrite particles have surface characteristics which are favorable for the adsorption of protein (i.e. cellular materials), and yet maintain the stability of the dispersion in aqueous fluids.
  • the adsorbed protein or cell can, thus, be separated along with the barium ferrite particle without alteration or destruction of the native physical and/or physiological characteristics of the adsorbed material.
  • the barium ferrite particle/protein complex can be redispersed in fluid media and subjected to quantitative or qualitative analysis.
  • the complex can be treated to effect dissociation of the adsorbed materials from the barium ferrite particles, and the particles thereupon separated from the fluid and recycled.
  • Fig. 1 is a reproduction of a photomicrograph depicting the monodispersed barium containing ferrite particles of this invention.
  • This invention provides a reproducible process for the synthesis of colloidal particles of narrow particle size distribution from barium salts and a ferrous hydroxide gel.
  • Colloidal particles are prepared from the above materials by phase transformation, in an inert atmosphere, of gelatinous ferrous hydroxide, in the presence of barium salts. This phase transformation is conducted under mild oxidizing conditions and in an aqueous environment.
  • This process initially involves the formation of ferrous hydroxide from a ferrous salt (i.e. ferrous chloride) and a stock solution of potassium hydroxide and potassium nitrate.
  • ferrous salt i.e. ferrous chloride
  • stock solution i.e. potassium hydroxide and potassium nitrate.
  • ferrous hydroxide gel suspension which is stable at a slightly acidic pH (approximately 6.4).
  • barium salts i.e. barium nitrate
  • the phase transformation of the gel to crystalline ferrite particles is initiated.
  • this gelatinous precipitate undergoes a phase transformation to produce ferrite particles containing barium with cubic crystal lattice.
  • the mildly acidic conditions affect the rate and degree of oxidation of the hydroxide gel to the corresponding crystalline ferrites.
  • the conditions prevailing during the initial formation of the hydroxide, and its subsequent phase transformation, are critical to the process of this invention in order to avoid the formation of hematite.
  • the gelatinous precipitate Once the gelatinous precipitate is formed, it is aged at elevated temperatures (approximately 90°C) to effect the phase transformation to the desired tolerance.
  • the magnetic particles which are ultimately recovered from the reaction mass are readily identifiable, easily redispersible in aqueous media, and have superparamagnetic properties in response to the magnetic field.
  • Ferrous hydroxide (Fe(OH)2) is initially formed by combining aqueous solutions of the ferrous salt with an aqueous solution containing a source of hydroxide ions. The quantity of ferrous salt solution combined with the alkali is carefully adjusted to produce a ferrous hydroxide solution of slightly acidic (pH approximately 6.4) character.
  • ferrous hydroxide solution is prepared, it is contacted with an aqueous solution of a suitable barium salt (i.e. Ba(N03)2).
  • a suitable barium salt i.e. Ba(N03)2.
  • the two solutions are combined in an inert atmosphere (e.g. argon or nitrogen) and permitted to interact at ambient (room) temperature. After about 30 minutes, the interaction of the barium salt solution and the ferrous hydroxide results in the incorporation of finite amounts of Ba ⁇ + ions within the ferrous hydroxide gel (presumably by ion exchange).
  • This suspension can thereafter be transferred to one or more sealed containers and aged at elevated temperatures until the phase transformation of the gel to the solid particles has been completed.
  • the solid particles are removed from the sealed containers, and washed by resuspension in water.
  • the magnetic properties of the colloidal particles permit their ready separation from other non-magnetic particles contained in the suspension. This separation is achieved by simply placing a magnet in contact with the side or bottom of the vessel containing the suspension, allowing the magnetic particles to collect on the interior of the vessel corresponding to the placement of the magnet and decanting the wash fluid containing the non-magnetic particles. This washing/decanting process can be repeated until essentially all non-magnetic particles and other water soluble materials are removed. The particles can thereafter be air dried or calcined. The particles obtained through this process in the foregoing manner are illustrated in Fig. 1.
  • These particles are uniform and of a relatively narrow size distribution.
  • the particle shape can vary from cuboidal to hexagonal, whereas relative size remains essentially uniform.
  • these particles are submicron in size and most preferably in the range of from 0.1 to 0.8 micrometers. As noted above, these particles, can be calcined in the conventional manner to modify one or more of their physical properties.
  • barium modified ferrite particles are, thus, capable of formation of stable colloidal dispersions in fluid media.
  • the surface characteristics of the particles of these colloidal dispersions have a natural affinity for adsorption of protein (i.e. cells, ligands, steroids, hormones, etc.). This adsorption is accomplished while maintaining the stability of the particle dispersion in the fluid medium.
  • the adsorption characteristics of the barium modified ferrites is essentially surface charge dependent.
  • the characteristic surface charge of these particles can be readily modified by adjustment in pH.
  • the variation in surface charge follows a characteristic signoid curve. At a pH above the particles isolectric point, the surface charge on these particles is positive; and at a pH below the isolectric point, the surface charge on these particles is negative.
  • these particles can rapidly and efficiently adsorb proteinaceous materials without adverse or destructive effect upon their physical and/or physiological properties.
  • This ability to effectively adsorb protein and its separation upon application of a magnetic field is unique to the barium modified colloidal particles of this invention.
  • the effective adsorption of protein without disruptive effect upon the other constituents of the fluid dispersion is of critical importance not only to preservation of the adsorbed species, but also to the particulates and dissolved matter which remain within the fluid.
  • This latter application involves the use of the colloidal particles as scavengers to remove undesirable components of a fluid sample (presumably interferents) prior to analysis of the residual material which remains in suspension.
  • the particles thus, have application in both industrial and biological environments, involving magnetic separation techniques of the type described in the following U.S. Patents: 4,001,288; 4,247,406; 4,018,886; 4,285,819; 4,147,767; 4,335,094; 4,152,210; 4,452,773; 4,169,804; 4,454,234; and 4,230,685 - all of which are hereby incorporated by reference in their entirety.
  • the barium modified ferrites of this invention thus provide, for the first time, a practical and efficacious material which can perform reliably in such separation systems and yet are compatible with relatively simple, straightforward methodologies.
  • the superparamagnetic colloidal barium ferrite particles obtained by this process can be used directly or modified by treatment with a binding material (i.e. antigen, antibody, binding protein, complement DNA), in accordance with conventional techniques described in the open literature.
  • a binding material i.e. antigen, antibody, binding protein, complement DNA
  • This treatment (coating) with these binding materials is performed under conditions which retain the desirable attributes of the barium ferrite particles.
  • These untreated or treated particles can thereafter be combined with an industrial or biological fluid having one or more constituents capable of binding to the particles. After a suitable incubation period, the particles, and presumably the constituents of the fluid for which they are 13
  • the barium ferrites prepared in this manner are also suitable in other industrial and biological applications, including the use as recording media, as delivery systems for therapeutics (ceramic composition and the like).
  • a reactive solution is initially prepared from appropriate volumes of 5 mol dm _ 3 KOH and 2 mol dm _ 3 KNO3 stock solutions.
  • the individual components of this reactive solution were combined in a two-necked round bottom flask, equipped with a gas -outlet and a gas-inlet.
  • Argon was bubbled for 2 hours through a solution of desired concentrations of KOH and KNO3 in oxygen free distilled water.
  • a calculated amount of a 1 mol dm"3 F Cl2 stock solution was added and bubbling of argon continued for 30 minutes. During this 30 minute period a dark green gelatinous precipitate is formed.
  • the solid reaction products obtained in the foregoing manner consisted predominantly of a mixture of particles, the main fraction of which was magnetic. To separate the latter, the precipitate was first agitated in an ultrasonic bath, then the magnetic particles were retained at the bottom of the test tube with the aid of a magnet, while the remaining suspension of nonmagnetic particles was decanted. The magnetic portion was resuspended again in doubly distilled water and the washing/decanting procedure repeated several times.
  • Magnetic properties were determined with a vibrating magnetometer on the original barium ferrite powders and on the annealed solids.
  • the coercivity before annealing ranged between 60 and 100 Oe and the saturation magnetization varied between 60 and 80 emu/g, while the squareness was between 0.12 and 0.18, depending on the sample.
  • the particles thus obtained could be physically modified by conventional treatment regimes.
  • the calcination was carried out at temperatures ranging between 300 and 900° C for 2-12 hours in air or in an air inert atmosphere (argon). This treatment brought about some rounding of the crystal edges.
  • the dried powders obtained by the foregoing procedures were readily redispersible in aqueous solutions. Their particle size ranged from between 0.1 and 0.8 mm (cubic edge) and the size could be altered by varying the concentrations of the solutions used in this synthesis (as illustrated in Tables I & II). As illustrated in these Tables, the chemical composition of the particles also varied with experimental conditions. Thus, the content of the barium within the ferrite could be varied between 1 to 7% by weight. As noted previously, the substitution of Ba ⁇ + for Fe ⁇ in the ferrite crystal lattice, at concentrations in the range of from about 1 to about 7% (w/w), is effective to alter the magnetic properties of these crystalline materials and, thus, substantially reduce particle to particle interaction.
  • a monoclonal antibody (MoAb) specific for a surface marker on human red blood cells is directly adsorbed onto the colloidal barium ferrite particles of Example I.
  • the particle size of the ferrite particle selected for use in the system was approximately 1.09 micrometers.
  • Sufficient MoAb was contacted with the colloidal particles to effect essentially complete saturations of the particle surface.
  • Antibody coated barium ferrite particles were then slurried with a whole blood sample for a brief incubation period, a magnet placed in contact with the bottom of the container and magnetic particles allowed to collect upon the inside surface of the container opposite the magnet. After a relative brief interval, the fluid phase of the sample is substantially depleted of both red blood cells and magnetic particles. The fluid phase is then aspirated from the sample container into a Coulter Model S-Plus cell counter and the sample subjected to analysis. The data available from such analysis permitted the identification of two discrete sub-populations of white blood cells. The ability to effectively separate erythrocytes from a whole blood sample in the above manner, without the resort to lytic reagents, offers significant advantages in the recovery of the leukocyte population.
  • the magnetic separation which is effected in the above manner has been achieved without substantial alteration in the physiological environment of the sample.
  • the leukocytes have retained their native physical, chemical and immunochemical properties. This can be critical in further differentiation of the leukocyte sub-populations from one another and in the continued vitality of these cells.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Health & Medical Sciences (AREA)
  • Organic Chemistry (AREA)
  • Bioinformatics & Cheminformatics (AREA)
  • Ceramic Engineering (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Medicinal Chemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Geology (AREA)
  • Pharmacology & Pharmacy (AREA)
  • Epidemiology (AREA)
  • Animal Behavior & Ethology (AREA)
  • Power Engineering (AREA)
  • Public Health (AREA)
  • Veterinary Medicine (AREA)
  • Manufacturing & Machinery (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Materials Engineering (AREA)
  • Structural Engineering (AREA)
  • Compounds Of Iron (AREA)
  • Colloid Chemistry (AREA)
EP19880901364 1987-01-16 1988-01-14 Verfahren zur herstellung monodispergierter, barium enthaltender ferrite. Withdrawn EP0302912A4 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US389987A 1987-01-16 1987-01-16
US3899 1987-01-16

Publications (2)

Publication Number Publication Date
EP0302912A1 EP0302912A1 (de) 1989-02-15
EP0302912A4 true EP0302912A4 (de) 1990-04-10

Family

ID=21708130

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19880901364 Withdrawn EP0302912A4 (de) 1987-01-16 1988-01-14 Verfahren zur herstellung monodispergierter, barium enthaltender ferrite.

Country Status (4)

Country Link
EP (1) EP0302912A4 (de)
JP (1) JPH01503623A (de)
AU (1) AU1222988A (de)
WO (1) WO1988005337A1 (de)

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5062991A (en) * 1990-06-04 1991-11-05 Coulter Corporation In situ use of gelatin in the preparation of uniform ferrite particles
US5240640A (en) * 1990-06-04 1993-08-31 Coulter Corporation In situ use of gelatin or an aminodextran in the preparation of uniform ferrite particles
DE4325071C2 (de) * 1993-07-19 1995-08-10 Lancaster Group Ag Präparat zur Durchblutungsförderung
EP2277544A1 (de) * 2009-07-08 2011-01-26 Nelica Ciobanu Biokompatible magnetische Nanocluster mit Eisenoxid bzw. Eisenoxid-Bor zur primären Verwendung in der magnetisch zielgerichteten Therapie und Bor-Neutronenerfassungstherapie
CN103801241B (zh) * 2014-02-27 2015-12-02 东华大学 利用微反应装置及外加磁场制备显色光子晶体微球的方法
CN105381780B (zh) * 2015-12-07 2017-10-31 中国科学院生态环境研究中心 一种吸附‑超导磁分离除砷锑的磁性吸附剂及其制备方法

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3634254A (en) * 1969-06-16 1972-01-11 Gen Motors Corp Method of coprecipitating hexagonal ferrites
JPS60137002A (ja) * 1983-12-26 1985-07-20 Toda Kogyo Corp 磁気記録用板状Ｂａフエライト微粒子粉末の製造法

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
JOURNAL OF CELLULOID AND INTERFACE SCIENCE, vol. 117, no. 2, June 1987, pages 593-595, Academic Press, Inc.; "Uniform colloidal barium ferrite particles" *
JOURNAL OF THE AMERICAN CERAMIC SOCIETY, vol. 71, no. 1, January 1988, pages C60-C62, Westerville, OH, US; X.-J. FAN et al.: "Preparation of uniform colloidal strontium ferrite particles" *
See also references of WO8805337A1 *

Also Published As

Publication number Publication date
WO1988005337A1 (en) 1988-07-28
EP0302912A1 (de) 1989-02-15
AU1222988A (en) 1988-08-10
JPH01503623A (ja) 1989-12-07

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