GB2142616A - Chromatography stationary phases and process for preparing the same - Google Patents

Chromatography stationary phases and process for preparing the same Download PDF

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Publication number
GB2142616A
GB2142616A GB08415957A GB8415957A GB2142616A GB 2142616 A GB2142616 A GB 2142616A GB 08415957 A GB08415957 A GB 08415957A GB 8415957 A GB8415957 A GB 8415957A GB 2142616 A GB2142616 A GB 2142616A
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Prior art keywords
chromatography
agent
acid
solution
ether
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GB08415957A
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GB8415957D0 (en
GB2142616B (en
Inventor
Giulio-Maria Gasparini
Giancarlo Torri
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Agenzia Nazionale per le Nuove Tecnologie lEnergia e lo Sviluppo Economico Sostenibile ENEA
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Agenzia Nazionale per le Nuove Tecnologie lEnergia e lo Sviluppo Economico Sostenibile ENEA
Comitato Nazionale per la Ricerca e per lo Sviluppo dell Energia
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Publication of GB8415957D0 publication Critical patent/GB8415957D0/en
Publication of GB2142616A publication Critical patent/GB2142616A/en
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/281Sorbents specially adapted for preparative, analytical or investigative chromatography
    • B01J20/286Phases chemically bonded to a substrate, e.g. to silica or to polymers
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/281Sorbents specially adapted for preparative, analytical or investigative chromatography
    • B01J20/282Porous sorbents
    • B01J20/283Porous sorbents based on silica
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/30Processes for preparing, regenerating, or reactivating
    • B01J20/32Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating
    • B01J20/3202Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating characterised by the carrier, support or substrate used for impregnation or coating
    • B01J20/3204Inorganic carriers, supports or substrates
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/30Processes for preparing, regenerating, or reactivating
    • B01J20/32Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating
    • B01J20/3231Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating characterised by the coating or impregnating layer
    • B01J20/3242Layers with a functional group, e.g. an affinity material, a ligand, a reactant or a complexing group
    • B01J20/3244Non-macromolecular compounds
    • B01J20/3246Non-macromolecular compounds having a well defined chemical structure
    • B01J20/3248Non-macromolecular compounds having a well defined chemical structure the functional group or the linking, spacer or anchoring group as a whole comprising at least one type of heteroatom selected from a nitrogen, oxygen or sulfur, these atoms not being part of the carrier as such

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Inorganic Chemistry (AREA)
  • Solid-Sorbent Or Filter-Aiding Compositions (AREA)
  • Silicon Compounds (AREA)
  • Treatment Of Liquids With Adsorbents In General (AREA)

Abstract

A process for preparing chromatographic stationary phases is characterized by the fact that the chromatography agent which may be an extractant, a complexant, an ion exchanger etc, insoluble in the mobile phase, is uniformly distributed in a silica matrix. The process comprises preparing a solution, emulsion, colloidal system or suspension of the agent in a liquid compound of silicic acid and hydrolysing or saponifying until a solid product is formed.

Description

SPECIFICATION Chromatography stationary phases and process for preparing the same The present invention relates to a process for preparing stationary phases for chromatographic columns and to such phasesperse.
The process of the present invention can be advantageously used for producing stationary phases to be employed in chromatography and particularly in extraction, partition or ion exchange chromatography and more generally in inverted phase chromatography.
Many chromatography processes are based on the transport of one or more chemical species between two phases: a moving one in which said chemical species are contained and a stationary one which comprises a chromatography agent which functions as extractant, complexant, ion exchanger and is immobilized on a suitable organic or inorganic support readily available on the market.
Up to now the methods for preparing chromatography stationary phases consist of chemically binding the chromatography agent to organic or inorganic matrices or of dissolving the chromatography agent in a suitable wetting agent usually comprising organic solvents capable of "wetting" the selected supports and subsequently immobilizing them by simply impregnating the either organic or inorganic supports with them.
The latter type of stationary phases are usually prepared at the very moment of their use due to the particular care required in preparing them.
It is an object of this invention to provide a method for preparing chromatographic stationary phases of novel character wherein the chromatography agent which must be insoluble in the mobile phase is held in an inorganic material matrix. Thus differently from the methods of the prior art, a direct contact is realized between the mobile phase which is usually in its liquid state and the chromatography agent; whereby a further organic phase comprising a wetting agent is eliminated. Furthermore in this way the exchange mechanisms between the phases are changed and consequently the chemico-physical behavious is changed in reference to the methods of the prior art, better extraction kinetics of metal ions from aqueous solutions being for instance obtained thereby.
According to a first aspect of the present invention there is provided a process for preparing a chromatography stationary phase consisting exclusively of a solid support and of a chromatography agent uniformly distributed in the whole mass of the support, which process includes the steps of: a) preparing a solution or an emulsion or a colloidal system or a suspension of a chromatography agent in a liquid compound of silicic acid which compound is hydrolyzable or saponifiable and capable of giving a solid product through hydrolysis or saponification; and b) allowing the hydrolysis or saponification process to evolve until a solid product is formed comprising silica and a chromatography agent uniformly distributed in the silica mass.
According to a second aspect of the present invention there is provided a chromatography stationary phase comprising a) a solid substance which functions as an inert support and b) a chromatography agent, characterized in that said agent is uniformly distributed in the whole mass of the inert support and is not chemically bound to said support.
The stationary phases as obtained by the method of this invention, when compared to the prior art, offer the following advantages: with respect to the prior art methods in which the chromatography agent is fixed on the support by means of the wetting agent, the process of this invention offers the advantage of fixing larger amounts of chromatography agent on the supporting means and of fixing it thereon in a more stable and reproducible manner. Furthermore the stationary phase 6f this invention, differently from the prior art, is more handleable, lends itself to commercial production and is adapted for long lasting storage.
Another advantage of the process of this invention is that the support means is produced concurrently with the addition of the chromatography agent into the whole mass of the same support whereby the preparation of the stationary phases - support plus chromatography agent - is reduced to a single process step while according to the processes of the prior art where a wetting agent is used, the support is first prepared and then the chromatography agent is fixed on the support surface.
Differently from the methods whereby the stationary phases are prepared by chemically binding the chromatography agents to organic or inorganic matrixes the method of this invention offers the advantage that the choice of the chromatography agents is not subject to limitations.
Therefore a stationary phase prepared by the method hereinafter particularly described can be advantageously employed when the support and the chromatography agent cannot be chemically bound together or when the fixing by impregnation of said agent on the support by means of a wetting agent is difficult to achieve in terms of the amount of chromatography agent fixedly contained in the end product which may be too small or in terms of the stability of the same which may be too low or further when problems arise for the transport of the chemical species between the mobile phase and the stationary one.
The process of this invention for preparing stationary phases is based on the hydrolysis or the saponification of the liquid compounds of silicic acid, for instance esters, chlorides etc. The tetraethyl ester of silicic acid, for instance, is a liquid capable of being hydrolyzed or saponified; it is unmiscible in water and gives therewith the following reaction: (C2H50)4Si +2H2Oo4C2HsoH+ SiO2 The hydrolysis or the saponification is speeded up by the presence of acids such as, for instance, HCI or HNO3 and of bases.
Among the products of the above reaction there is a solid vitreous material comprising silica which can effectively function as a support inasmuch as it is mechanically and chemically resistant and long lasting.
In those cases where a chromatography agent can form solutions, emulsions, colloidal systems, suspensions, a solid material is obtained of siliceous nature in whose structure the chromatography agent is incorporated.
Such solid material, after drying, grinding, sieving at the desired granulometry and washing is the end product that is the stationary phase and can be directly used in chromatography columns.
Therefore the process for preparing stationary phases according to this invention generally comprises the following steps.
a) Preparing a solution or an emulsion or a colloidal system or a suspension of a chromatography agent in a liquid compound of silicic acid which should be hydrolizable or saponifiable and capable of giving a solid product upon hydrolysis or saponification; b) contacting said solution, emulsion, colloidal system or suspension with water or solution of acids or bases which function as catalysts, the hydrolysis or saponification being continued until a solid product is obtained which comprises silica and the chromatography agent.In case the chromatography agent is effective for causing by itself hydrolysis or saponification the process can be continued subse quest to step a) until a product is obtained comprising silica and chromatography agent; c) drying the solid product obtained as above; d) grinding the solid product to the desired granularity; e) washing the dried, ground and shifted product.
The hydrolysis or the saponification can be carried out at various temperatures whereby for instance, in the case of solutions, the solubility of the chromatography agent in the silicic acid compound can be enhanced and consequently its content in the final product can be increased; furthermore the hydrolysis and the saponification proved to be reproducible and effective for imparting a high reactivity to the stationary phase thus produced.
The details of the process for preparing the above stationary phases according to this invention will be better illustrated by the following examples which however are not to be understood as limiting the practical extent of this invention or its applications.
Example I Tetraethylorthosilicate (C2H5O)4Si hereinafter referred to as TES was used as the compound of the silicic acid and tri-n-butylacetohydroxamic acid (C4H9)3CCONHOH hereinafter referred to as TBAH which is a known metal ion extractantfrom solutions was used as chromatography agent.
Process a) Preparing a solution of up to 1 M concentration of TBAH in TES.
Contacting said solution with a 1 M solution of HCI in water in a sealed vessel the ratio by volume of the first to the second solution being 2:1.
Two phases are immediately formed which are left to rest at room temperature until both the phases become first jelly and then solid. Subsequently the whole vessel content is dried, ground, sieved at the desired size and then washed.
The end product comprises a silica matrix in which the TBAH is incorporated in a stable reproducible and ready for use form. The amount of TBAH contained in the silica matrix has been found to be dependent on the initial concentration of TBAH in TES. With starting solutions in the range from 0.5 to 1 M of TBAH in TES, the amount of TBAH in the stationary phase is approximately from 0.4 to 1 m mole per gram.
Process b) A solution of TBAH in TES is prepared at a concentration higher than 1 M and left to rest in a sealed vessel until a solid phase is formed. Such phase after drying, grinding sieving and washing consists of a product in which TBAH is contained ready for use. The TBAH content in the stationary phase will be about 4 mmole/g with very good reproducibility.
Stationary phases obtained by such method have been found, by X ray spectrometry, to comprise a crystalline phase (TBAH) and an amorphous phase (SiO2).
In practice the stationary phase comprises a silica amorphous lattice in whose structure, the extractant is most stably enclosed while maintaining its extractive function.
Such stationary phases have been used for extracting Fe and Pu from nitric acid solutions.
Example 2 Tetraethylorthosilicate (TES) was used as silicic acid compound while as chromatography agent a series of large ring or macrocyclic ethers which are complexing agents selective for alkaline and alkaline earth metal ions were used. The following ethers named according to normally used nomenclature were used: 18 C 6, dicyclohexo 18 C 6, dibenzo 21 C 7, dibenzo 24 C 8, dibenzo 27 C 9.
The process is as follows.
A saturated solution is prepared of the macrocylic either in TES; such solution is contacted with a HCI 1 M water solution 4:1 by volume in a vessel of the Erlenmeyer flask type. The ester solution and the HCl water solution are immiscible, but after a certain lapse of time-which is dependent on the macrocyclic either kind - a solid phase is formed which after drying, grinding, sieving and washing gives a material which comprises silica with the macrocyclic ether held therein.
The solution can be prepared and also hydrolyzed or saponified at temperatures different from the ambient temperature whereby a higher solubility is attainable of the macrocyclic ethers in TES with a related increase of their amount per gram of stationary phase. Such amount is in fact dependent on the solubility of the macrocyclic ether in the starting solution.
Stationary phases obtained at ambient tempera turebytheuseofdicyclohexo 18 C 6 gave a 1 m mole/g average content of ether.
Stationary phases obtained at 45 C by the use of dibenzo 18 C 6 gave a 18 micromole/g average content of ether.
The above products have been used for extracting Cs from its aqueous solutions.

Claims (34)

1. A process for preparing chromatography stationary phases each of which consists exclusively of a solid support and of a chromatography agent uniformly distributed in the whole mass of the support, which process comprises the following steps: a) preparing a solution or an emulsion or a colloidal system or a suspension of a chromatography agent in a liquid compound of silicic acid which compound is hydrolyzable or saponifiable and capable of giving a solid product through hydrolysis or saponification; b) allowing the hydrolysis or saponification process to evolve until a solid product is formed comprising silica and a chromatography agent uniformly distributed in the silica mas; c) drying the solid product thus obtained; d) grinding and sieving the product to a desired granulometry; e) washing the dried, ground and sieved product.
2. A process as claimed in claim 1, which comprises the further step of adding H2O to the solution of the chromatography agent in the silicic acid compound priorto step b) of said claim.
3. A process as claimed in claim 1, which further comprises the step of adding an aqueous solution of an acid to the solution of the chromatography agent in the silicic acid compound prior to step b) of said claim.
4. A process as claimed in claim 1, which further comprises the step of adding an aqueous solution of a base to the solution of the chromatography agent in the silicic acid compound prior to step b) of said claim.
5. A process as claimed in any preceding claim, wherein said compound is an ether or chloride of silicic acid.
6. A process as claimed in claim 5, wherein the silicic acid liquid compound is tetraethylorthosilicate (C2H50)4Si.
7. A process as claimed in any one of claims 1 to 5, wherein the chromatography agent is tri-nbutylacetohydroxamic acid (C4H9)3CCONHOH.
8. A process as claimed in any one of claims 1 to 5, wherein the liquid compound of silicic acid is tetraethylorthosilicate (C2H5O)4Si and the chromatography agent is tri-n-butylacetohydroxamic acid (C4H9)3 CCONHOH.
9. A process as claimed in claims 1 and 3 wherein the silicic acid liquid compound is tetraethylorthosilicate (C2H5O)4Si and the chromatography agent is tri-n-butylacetohydroxamic acid (C4H9)3CCONHOH, the concentration of tri-nbutylacetohydroxamic acid in tetraethylorthosilicate is from 0.5 to 1 M, said acid is hydrochloric acid, the concentration of the aqueous solution of the latter is 1 M and the ratio by volume of the solution of tri-n-butylacetohydroxamic acid in tetraethylorthosilicate and the solution of hydrochloric acid is in the range from 2 to 1.
10. A process as claimed in claim 1 wherein said liquid compound of silicic acid is tetraethylorthosilicate (C2H50)4Si, the chromatography agent is tri-nbutylacetohydroxamic acid (C4H9)3CCONHOH and the concentration of the latter in the first is in the range from 1 M to 2M.
11. A process as claimed in any one of claims 1 to 5, wherein the chromatography agent is a large ring ether or macrocyclic ether.
12. A process as claimed in any one of claims 1 to 5, wherein the liquid compound of silicic acid is tetraethylorthosilicate and the chromatography agent is a large ring ether or macrocyclic ether.
13. A process as claimed in claim 12, wherein the macrocyclic ether is 18 C 6.
14. A process as claimed in claim 12, wherein the macrocyclic ether is dicyclohexo 18 C 6.
15. A process as claimed in claim 12, wherein the macrocyclic ether is dibenzo 18 C 6.
16. A process as claimed in claim 12, wherein the macrocyclic ether is dibenzo 24 C 8.
17. A process as claimed in claim 12, wherein the marocyclic ether is dibenzo 27 C 9.
18. A process as claimed in claim 12, wherein the marocyclic either is dibenzo 27 C 9.
19. A process as claimed in claims 3 and 12, wherein the solution of the macrocyclic ether in tetraethylorthosilicate is a saturated solution, said acid aqueous solution is a solution of hydrochloric acid at a concentration of 1 M and the ratio by volume of the ether solution in tetraethylorthosiicate and the aqueous solution of hydrochloric acid is in the range from 4 to 1.
20. A process for preparing a chromatography stationary phase comprising a solid support and a chromatography agent uniformly distributed in the whole mass of the support, which process includes the steps of: a) preparing a solution or an emulsion or a colloidal system or a suspension of a chromatography agent in a liquid compound of silicic acid which compound is hydrolyzable or saponifiable and capable of giving a solid product through hydrolysis or saponification; and b) allowing the hydrolysis or saponification process to evolve until a solid product is formed comprising silica and chromatography agent uniformly distributed in the silica mass.
21. A process according to claim 20 which includes the further steps of: c) drying said solid product; d) grinding and sieving the dried product to a desired granulometry; and e) washing the dried, ground and sieved product.
22. A process for preparing chromatography stationary phases, substantially as hereinbefore described with reference to the foregoing Example 1 or Example 2.
23. A chromatographic stationary phase produced by a process according to any one of the preceding claims.
24. A chromatography stationary phase comprising a) a solid substance which functions as an inert support and b) a chromatography agent, characterized in that said agent is uniformly distributed in the whole mass of the inert support and is not chemically bound to said support.
25. A chromatography stationary phase as claimed in claim 24, wherein the solid substance which functions as a suport is silica (SiO2).
26. A chromatography stationary phase as claimed in claim 24 or 25, wherein the chromatography agent comprises tri-n-butylacetohydroxamic acid.
27. A chromatography stationary phase as claimed in claim 24 or 25, wherein the chromatography agent comprises the macrocyclic ether 18 C 6.
28. A chromatography stationary phase as claimed in claim 24 or 25, wherein the chromatography agent comprises the macrocyclic ether dicyclohexo 18 C 6.
29. A chromatography stationary phase as claimed in claim 24 or 25, wherein the chromatogra phy agent comprises the macrocyclic ether dibenzo 18C6.
30. A chromatography stationary phase as claimed in claim 24 or 25, wherein the chromatography agent comprises the macrocyclic ether dibenzo 21 C7.
31. A chromatography stationary phase as claimed in claim 24 or 25, wherein the chromatography agent comprises the macrocyclic ether dibenzo 24C8.
32. A chromatography stationary phase as claimed in claim 24 or 25, wherein the chromatography agent comprises the macrocyclic ether dibenzo 27 C9.
33. A chromatography stationary phase, substantially as hereinbefore described with reference to the foregoing Example 1 or Example 2.
34. The features hereinbefore disclosed, or their equivalents, in any novel selection.
GB08415957A 1983-06-24 1984-06-22 Chromatography stationary phases and process for preparing the same Expired GB2142616B (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
IT48577/83A IT1197667B (en) 1983-06-24 1983-06-24 STATIONARY PHASES FOR CHROMATOGRAPHY AND PREPARATION PROCEDURE OF THE SAME

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GB8415957D0 GB8415957D0 (en) 1984-07-25
GB2142616A true GB2142616A (en) 1985-01-23
GB2142616B GB2142616B (en) 1987-03-25

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BE (1) BE899953A (en)
DE (1) DE3423171A1 (en)
FR (1) FR2549227B1 (en)
GB (1) GB2142616B (en)
IT (1) IT1197667B (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6303046B1 (en) * 1997-08-08 2001-10-16 William M. Risen, Jr. Aerogel materials and detectors, liquid and gas absorbing objects, and optical devices comprising same
CN103109182A (en) * 2010-09-24 2013-05-15 通用电气健康护理生物科学股份公司 Wetting of a plastic bed support for a chromatography column

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
IT1223582B (en) * 1987-12-22 1990-09-29 Eniricerche Spa PROCEDURE FOR THE PREPARATION OF SOLID DISPERSIONS OF ACID SALTS OF TETRAVALENT METALS WITH LAMELLAR STRUCTURE IN AN INORGANIC INERT MATRIX AND PRODUCTS SO OBTAINED

Citations (3)

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Publication number Priority date Publication date Assignee Title
GB1188873A (en) * 1967-01-27 1970-04-22 Ceskoslovenska Akademie Ved A Process of Producing Silicic Acid Gel with Active Charcoal Incorporated therein.
GB1371440A (en) * 1972-05-31 1974-10-23 Mo G Uni Im Mv Lomonosova Process for preparing a wide-pore adsorbent for use in chromato graphy
GB2118534A (en) * 1982-04-15 1983-11-02 South African Inventions Electronically conductive tectosilicates

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DE1000682B (en) * 1953-06-22 1957-01-10 Waldhof Zellstoff Fab Process for the production of absorbent paper for chromatographic purposes with special properties with regard to the separation effect
DE1517929B1 (en) * 1966-01-20 1971-11-18 Merck Patent Gmbh Sorbents for chromatography and processes for their preparation
LU73094A1 (en) * 1975-07-29 1977-03-24
JPS5817783B2 (en) * 1976-07-08 1983-04-09 日本曹達株式会社 Hetero-macrocyclic compounds supported on solid surfaces
DE2758415A1 (en) * 1977-12-28 1979-07-12 Fraunhofer Ges Forschung SILICIC ACID HETEROPOLYCONDENSATES, PROCESS FOR THEIR PRODUCTION AND THEIR USE AS MEMBRANES AND ADSORBENTS

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Publication number Priority date Publication date Assignee Title
GB1188873A (en) * 1967-01-27 1970-04-22 Ceskoslovenska Akademie Ved A Process of Producing Silicic Acid Gel with Active Charcoal Incorporated therein.
GB1371440A (en) * 1972-05-31 1974-10-23 Mo G Uni Im Mv Lomonosova Process for preparing a wide-pore adsorbent for use in chromato graphy
GB2118534A (en) * 1982-04-15 1983-11-02 South African Inventions Electronically conductive tectosilicates

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6303046B1 (en) * 1997-08-08 2001-10-16 William M. Risen, Jr. Aerogel materials and detectors, liquid and gas absorbing objects, and optical devices comprising same
US6602336B2 (en) 1997-08-08 2003-08-05 Brown University Research Foundation Printing medium comprising aerogel materials
US7037366B2 (en) 1997-08-08 2006-05-02 Brown University Research Foundation Printing medium comprising aerogel materials
US7147701B2 (en) 1997-08-08 2006-12-12 Brown University Research Foundation Printing medium comprising aerogel materials
CN103109182A (en) * 2010-09-24 2013-05-15 通用电气健康护理生物科学股份公司 Wetting of a plastic bed support for a chromatography column
CN103109182B (en) * 2010-09-24 2015-07-01 通用电气健康护理生物科学股份公司 Wetting of a plastic bed support for a chromatography column

Also Published As

Publication number Publication date
IT8348577A0 (en) 1983-06-24
FR2549227B1 (en) 1988-09-30
FR2549227A1 (en) 1985-01-18
GB8415957D0 (en) 1984-07-25
DE3423171A1 (en) 1985-01-03
GB2142616B (en) 1987-03-25
IT1197667B (en) 1988-12-06
BE899953A (en) 1984-10-15

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Effective date: 19940622