US3418152A - Method of making a chromatographic element containing a resinous binder and product produced thereby - Google Patents

Description

Dec. 24, 1968 w. J. STAUDENMAYER ET AL 3,418,152

METHOD OF MAKING A CHROMATOGRAPHIC ELEMENT CQNTAINING A RESINOUS BINDER AND PRODUCT PRODUCED THEREBY I Filed Aug. 1, 1966 HROMATOGRAPHICALLY ACTIVE LAYER F 3 fliflnvenfion) 9 8 g 7 H v g: 4 A (prior art) LU I {I 3 E R 2 2 I 5 4 5 TIME IN MINUTES WILLIAM J- STAUDENMAYER EDMOND S- PERRY United States Patent 3,418,152 METHOD OF MAKING A CHROMATOGRAPHIC ELEMENT CONTAINING A RESINOUS BINDER AND PRODUCT PRODUCED THEREBY William Joseph Staudenmayer and Edmond S. Perry, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Continuation-impart of application Ser. No. 450,362, Apr. 23, 1965. This application Aug. 1, 1966, Ser. No. 569,441

Claims. (Cl. 117-63) ABSTRACT OF THE DISCLOSURE A thin-layer chromatographic element made by coating on an inert support a dispersion of particulate finely-divided chromatographically-active adsorbent and particulate resinous binder in a liquid dispersing medium, removing the dispersing medium, and softening the particles of resinous binder to render them adherent and thereby form a continuous, coherent, porous layer. The support can be utilized as a permanent part of the chromatographic element or the coated layer can be stripped from the support and used as a self-supporting layer.

This application is a continuation-in-part of our US. patent application Ser. No. 450,362, filed Apr. 23, 1965, entitled, Chromatographic Sheets.

This invention relates to new chromatographic sheets for thin-layer chromatography and methods of making them; in one of its aspects it relates to a highly coherent chromatographic layer of excellent porosity, which can be self-supporting or bonded to a support which does not react with or absorb the developer (eluting solvent) or modify the chromatographic separation of the porous layer.

Thin-layer chromatographic techniques heretofore known in the art are becoming increasingly popular in analytical chemistry. Advantages include simplicity, speed, and applicability to a wide variety of separations. The large number of adsorbents available and ease of introducing other components such as fiuorescing or complexing agents or varying conditions such as eluting solvents present a number of parameters which may be manipulated to obtain the desired separation.

One major shortcoming stands in the way of more widespread acceptance of thin-layer chromatography: the tragility and abrasion propensity of such prior art thin-layer chromatographic elements. Conventional chromatographic elements comprise a glass plate bearing a thin layer of loosely adherent adsorbent powder. They are available commercially but since such preformed layers are fragile they are very prone to damage from the handling incident to packaging and shipping. Furthermore, they are inconvenient to store and generally unsuitable for record purposes because of their susceptibility to abrasion and breakage. Consequently the plates are more often coated by the user when he needs them.

It is an object of this invention to provide light, flexible, thin-layer chromatographic sheets which have the handling ease of a sheet of ordinary paper and which have outstanding resistance to abrasion.

It is another object to provide such chromatographic sheets which can be treated with alkaline eluting solvents without loss in quality of the resultant record.

It is another object .to provide such flexible thin-layer chromatographic sheets which can withstand chemical or oxidative charring as by sulfuric acid charring and provide an archival-quality record, without any detriment to the chromatographic and handling properties.

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It is another object to provide firmly bonded, thick, highly adsorbent, chromatographic layers of high porosity and good flexibility for preparative-scale chromatograph- 1c separation.

It is still another object to provide a method of preparing thin-layer chromatographic sheets which insures that the sheets will demonstrate excellent abrasion resistance, that the thin adsorbent layer will have a high degree of porosity, and that the adsorbent will retain its ability to adsorb chemicals.

It is a further object of this invention to provide strongly coherent, porous, flexible chromatographic layers which can be optionally self-supporting, loosely adherent to a temporary support, or strongly adherent to a permanent support.

Other objects of this invention will be apparent from the drawing and the following detailed disclosure.

The invention comprises a thin-layer chromatographic recording material having a continuous, coherent, porous layer of finely divided, discrete particles of chromatographic adsorbent bonded to associated particles of a resinous binder. In order not to impair the chromatographic activity of the adsorbent the quantity of binder is held low enough so as not to coat the chromatographic particles nor to completely fill the voids between the particles and the binder material. The binder particles adhere to portions of the surfaces of adjacent adsorbent particles to bind the chromatographic particles together in a layer of good mechanical strength. They also provide adhesion to the base when a supported layer is desired.

Coatings made according to the present invention are microscopically heterogeneous, particulate and porous. Under magnified viewing conditions, they present a sintered or spongelike appearance. Typically the layers of our invention are prepared by coating a dispersion of a mixture of fine particles of adsorbent and suitable resin binder, removing the liquid dispersing medium and then softening the resin sufliciently to insure adhesion to adjoining adsorbent particles and optionally to a support, by means of heat, pressure, solvent or the like.

The unique method of preparing the layer permits preparation of strong coherent, porous-layer coatings with chromatographic capacity of the same high order as that of binder-free prior art coatings. Since the layers of this invention are coherent, flexible and abrasion-resistant, it is not necessary to use glass plates or other rigid supports to provide strength and protection for the conventional chromatographic coatings. A flexible inert support can be employed or the porous chromatographic layer can be employed without a separate support.

If it was considered desirable to put these new porous layers on glass, it would be an improvement over the prior systems as the chromatographic layer can be precoated and handled in a routine manner without damaging it. :It also can be retained as permanent record.

Thin-layer chromatography is a separation technique having widespread utility with numerous unknowns and solvents. Since organic solvents are customarily employed in thin-layer chromatography, illustration of this invention will be p imarily concerned with binders which function in the desired manner with such solvents. However, this invention is equally applicable to less commonly used chromatographic elutants including aqueous liquids.

Typical thin-layer chromatographic elements have adsorbent layers about 10 mils thick. However, it is also an integral part of this invention to provide thicker chromatographic layers up to about 40 mils in thickness to facilitate the separation of larger amounts of single com pound. Previous attempts to make such thicker layers have generally resulted in coatings which break up even with very careful handling. With the new techniques for preparation disclosed in this invention and the fused particullate type of porous binder employed, we have successfully prepared thick chromatographic layers for use in the separation of relatively large amounts of material.

Until now, it has been impossible to obtain a visualized chromatographic separation which could withstand normal handling without abrading or destroying part of the record.

In the chromatographic separation of colorless compounds a technique called visualization is used. This consists of, e.g. sulfuric acid charring or similar treatment to show the chromatographic separation. The visualization of chromatograms by acid charring techniques is disclosed in the book, Thin-Layer Chromatography, by James M. Bobbit, and published by the Reinhold Publishing Corporation, New York, 1963, pages 85-86.

The thin-layer chromatographic layers of the present invention are conventionally coated on inert supports chosen so as not to affect the chromatographic activity of of the adsorbent. With our strongly coherent layers, a support is not necessary except as a temporary measure in preparing the initial coating. If desired after the coherent layer has been prepared, the temporary support can be stripped away. Where a permanent support is desired, the chromatographic layers of our invention can be coated on many surfaces and advantageously on plastic films, e.g., polyolefins, polyesters, olyolefin-subbed polyesters, polyamides, polycarbonates, cellulose esters, or on plastic coated paper, on aluminum or other metal films, or on glass. Polyolefin coated papers are especially attractive; they are much less expensive than an equivalent thickness of the polyolefin.

Our invention is not limited with respect to the adsorbent used. Any particulate adsorbent can be used such as alumina, silica gel, kieselguhr, polyamide, cellulose, etc. Advantageously, the particles should be fine enough to pass through a U.S. Standard 325 mesh screen. Additives such as phosphorescent or fluorescent compounds, and others which have been employed in prior art thinlayer chromatographic elements may be incorporated. These include calcium silicate, calcium metasilicate, and zinc silicate.

Separatory procedures in which currently available binder-free glass plate chromatographic elements have been used are facilitated by the use of the layers of our invention. Thus silver nitrate is frequently incorporated in the adsorbent layer to form weak complexes with olefinic groups to differentiate these materials. When silver nitrate is used with the binder-free elements of the prior art, it is added to the slurry of adsorbent prior to coating. This renders the already fragile powdery adsorbent coating even more fragile. However, the elements of our invention need merely be dipped into an alcoholic silver nitrate solution and dried prior to use. The treated elements retain their excellent coherence and abrasion resistance.

While it is not essential, the chromatographic elements of our invention can be activated in a known manner by heating before use. Our elements respond to such activation in substantially the same way as do the binderfree, thin-layer chromatographic elements showing substantially the same degree of improvement after heating for about one hour at 110 C. This further illustrates that the chromatographic properties of our layers do not suffer from the presence of a particulate binder which so greatly improves the mechanical properties of the material.

A wide choice of resinous binders is available which can be used in finely divided, particulate form to make the strong, highly adsorbent layers of our invention.

The resinous powder becomes tacky by application of heat, pressure or solvents or some combination of these. The particle size of the adsorbent and the resin, the ratio of adsorbent to resin, the selection of slurrying and coat ing vehicle and the degree of softening of the resin in the treatment after coating to prodpcg the desired layer coherence are all important and may be varied depending on particular conditions of use.

Typically a volume of powdered resin binder which is 10 per-cent to 50 percent of the volume of the chromatographic adsorbent, produces advantageous results although other ranges may be useful with particular combinations of adsorbent and resin.

The slurrying and coating vehicle is typically a liquid which is neither a solvent for, nor chemically reactive with, either adsorbent or resin. For ease in removal, volatile liquids, e.g., alcohol, water, ligroin, etc., are beneficial. The solvent can be selected to have just enough softening effect on the resin so that good adhesion between the resin and adsorbent particles is obtained without separate treatment. Alternatively, the slurrying and coating vehicle will be removed and the resin particles then softened enough to insure adhesion to the associated adsorbent particles and to the support, for example, by heating briefly to the softening point of the resin, typically to a temperature between and C. depending on the resin used. Alternatively a mist or vapor of a solvent for the resin may be used. Combinations of heat and solvent are useful and in some cases mechanical pressure can be combined with heat and/ or solvents to insure desired balance between porosity and abrasion resistance in the chromatographic layer.

For chromatographic sheet to be used with the acid charring technique, a preferred particulate binder is a polyolefin, particularly polyethylene and polypropylene. Both high and low density polyolefins give good results. A polyolefin film, or olyolefin-coated paper or resinous film of a different resin, provides an excellent base for such layers. The resin binder is selected to be inert to the solvents to be used in chromatographic development. Although it is unnecessary to provide a subbing layer between the support and the chromatographic layer, such snubbings may be advantageous in improving adhesion of the binder to the support or in insuring good stripping where a temporary and readily separated support is desired. Good adherence to a support for use in this system can also be obtained if the surface of the support is roughened by abrading it by applying a brush or abrasive to the surface.

The polymeric binders of our invention are mixed with the adsorbent in powder or granular form. The polymers of the parent application, U.S. Ser. No. 450,362, of which this application is a continuation-in-part, can be used, according to the technique described in this application. These binders include hydrophilic polymers such as polyvinyl alcohol and gelatin-polyvinyl alcohol mixtures, thermosetting polymers such as poly(vinyl acetal) resins and olefin polymers such as polyethylene and polypropylene.

Many natural or synthetic thermoplastic or solventsoftenable resins can be used in our layers. Examples of such resins include: polyvinyl chloride, polyolefins, polystyrene, polymethacrylates, styrene-methyl methacrylate copolymers, polyvinylacetate, 'butadiene-styrene copolymers, polyacrylates, and polyacrylic acid derivatives. Shellacand colophony and other natural resins may also be used but care must be taken to see that nonsolvents are used both in the preparation and separation stage to avoid destroying the porosity of the layer. These binders are incorporated in their particular form. Excellent results are for example obtained with powder, granules or pellets that pass through a U.S. Standard 325 mesh screen.

Alternatively the resinous binder may be used as an aqueous latex or emulsion of the resin. It is sometimes advantageous to employ combinations of two or more resins to enhance the porosity of the layer while improving the adhesion of the binder to the adsorbents and to the support.

Conventional coating methods and apparatus can conventionally be used to coat the adsorbent-binder mixture onto the support. Thus doctor-blade, air-knife, roll-coating and hopper-coating techniques are applicable.

A test which demonstrates the improvement in thinlayer chromatographic layers provided by our invention is one we designate as the Carnels Hair Brush Test. This consists of brushing a chromatographic element with a Camels hair brush for 50 strokes under mechanically controlled conditions of pressure and rate of application. With a conventional glass plate thin-layer chromatographic element complete removal of the material occurred with less than 50 strokes of the brush, frequently with the first or second stroke. Porous thin-layer chromatographic elements produced according to our invention showed no visible loss of material from the adsorbent layer after 50 strokes.

The invention can be readily understood with reference to the drawings.

FIG. 1 represents on an enlarged scale an elevational view looking at the edge of a thin-layer chromatographic sheet produced according to this invention wherein a particulate solid adsorbent and a particulate resinous binder 11 are coated on a polymeric film 13, the liquid vehicle removed, and the adhesion of the resulting porous layer enhanced by heat treatment.

FIG. 2 is a cross-sectional view through the sheet of FIG. 1, but with much greater magnification, showing that the layer 11 is made up of active particles interspersed with resinous binder particles 17.

FIG. 3 is a graph illustrating the rate of solvent migration for methanol in centimeters per minute for a binderless chromatographic layer A, representing the prior art, and for a layer B, representing our invention. The same adsorbent and concentration per unit area was used in the two materials. a

The invention will 'be more clearly recognized by reference to the following examples which are set forth to illustrate the invention, but not to limit it. As shown by these examples, satisfactory results are obtained when the binder is present in the dispersion in a proportion of from about 0.06 part per part by weight of the adsorbent (see Example XV) to about 1.6 parts per part by weight of the adsorbent (see Example VIII).

Example I 100 grams of neutral alumina, 65 grams of polyethylene powder (Microthene FNSlO, supplied by US. Industrial Chemicals, Div. of National Distillers and Chemicals Corp), and 115 ml. of ethyl alcohol were thoroughly mixed together and the suspension coated on a polyethylene coated paper stock. After evaporating the alcohol, the coating was heated for five minutes at 120 C., resulting in a porous, strongly adherent layer. A standard dye mixture was separated by the coating after ten minutes elution with toluene.

The dye mixture used was obtained from Brinkmann Instruments, Inc.; it contained 0.01 percent by weight of 4-dimethylaminoazo-benzene, indophenol, and Sudan Red G in benzene.

The alcohol was used merely to slurry the adsorbent and binder to facilitate application of an even coating. The heat treatment bonded the resin and adsorbent particles into a coherent layer and bonded the binder firmly to the support. The time and temperature of heating must be carefully controlled to insure that the polyolefin powder does not coalesce and surround the adsorbent, but only softens at the surface to insure adherence to joining particles thus preserving the porosity required for quick and efficient developer penetration.

Example II 36 grams of finely powdered cellulose, 24 grams of polyethylene powder, and 150 ml. of ethyl alcohol were slurried and coated on polypropylene film. The coating was heated for five minutes at 130 C. and then allowed to cool to room temperature. The resulting strong porous chromatographic layer satisfactorily separated a mixture of certified food colors after twenty minutes clution in an isopropanol ethanol-water mixture.

Example IH grams of finely powdered silica gel, 40 grams of polyethylene powder, 265 ml. of ethyl alcohol, and 140 ml. of water were thoroughly mixed together and coated on a polyethylene-coated paper. The coating was heated at C. for five minutes. The resulting abrasion-resistant chromatographic layer satisfactorily separated the standard Brinkmann test dye mixture after ten minutes using toluene as the elutant.

Example IV 80 grams of finely powdered silica gel, 40 grams of polyethylene powder, 265 ml. of ethyl alcohol and ml. of water were slurried and coated on a polypropylene film support. The coating was heated at 130 C. for five minutes. A strongly coherent chromatographic layer resulted which satisfactorily separated the standard Brinkmann test dye mixture after ten minutes using toluene as the elutant.

Example V 100 pounds of powdered nylon 11 polyamide adsorbent (Brinkmann, Instruments, Inc.), 65 pounds of finely powdered polypropylene and 13 gallons of ethyl alcohol were thoroughly blended together and coated on polyethylene film to obtain a dry thickness of about 40 mils. After heating the film for five minutes at 130 C., the coating adhered firmly to the support and resisted abrasion. A sample of the film separated the Desaga test dye mixture after ten minutes development using methyl isobutyl ketone as a solvent.

Example VI 100 pounds of aluminum oxide (alumina AG7, Bio- Rad Laboratories), 40 pounds of finely powdered polypropylene and 12 gallons of ethyl alcohol were mixed together thoroughly and coated on a polypropylene coated paper to obtain a dry thickness of about 5 mils. The dried coating was then heated at 130 C. The chromatographic element thus formed separated the standard Brinkmann test dye mixture, using toluene as the developing solvent in four minutes.

Example VII Example VIII 50 grams of finely powdered normal unsubstituted cellulose adsorbent (Cellulose MN300, Brinkmann Instruments, Inc.), 80 grams of polypropylene and 100 milliliters of ethyl alcohol were slurried and coated on clear polyethylene support. The coating was dried and heated for five minutes at 120 C. A sample of the coating was tested with a mixture of two food dyes as in Example VII. The dyes separated, using methanol as a development solvent, in four minutes.

Example IX grams of finely powdered silica gel, 100 grams of a finely powdered styrene-methyl methacrylate copolymer, 470 ml. of ethyl alcohol were thoroughly mixed together and coated on a polypropylene film support. The coating was heated after solvent removal in an oven for four minutes at 115 C. The resultant coating satisfactorily separated the standard test dye mixture after five minutes.

Example X 50 grams of finely powdered normal, unsubstituted, cellulose adsorbent, 70 grams of finely powdered polyethylene, 225 ml. of methyl alcohol, and 150 ml. of isopropyl alcohol were mixed and coated on a polypropylene film support. The coating was cured after solvent removal by heating it in an oven for five minutes at 150 C. The resultant coating satisfactorily separated the standard test dye mixture after ten minutes.

Example XI 130 grams of powdered nylon 11, 70 grams of finely powdered polyacrylic acid, 225 ml. of benzene, and 150' ml. of toluene were thoroughly mixed together and coated on a polypropylene film support. The coating was heated after removal of the liquid vehicle in an oven for five minutes at 130 C. The resultant coating satisfactorily separated the standard test dye mixture after ten minutes.

Example XII 150 grams of finely powdered silica gel, 100 grams of finely powdered polymethacrylate resin, 470 ml. of ethyl alcohol were thoroughly mixed together and coated on polypropylene-coated paper. The coating was dried and heated in an oven at 125 C. for eight minutes. The resultant coating satisfactorily separated the standard test dye mixture after five minutes.

Example XIII 80 grams of finely powdered silica gel, 50 grams of finely powdered polyvinyl chloride resin, 225 ml. of ethyl alcohol and 150 ml. of isopropyl alcohol were thoroughly mixed together and coated on polypropylene-coated paper. The coating was dried and heated in an oven at 125 C. for five minutes. The resultant coating satisfactorily separated the standard test dye mixture after five minutes.

Example XIV 80 grams of finely powdered silica gel, 40 grams of polyethylene powder, 265 ml. of ethyl alcohol, and 140 ml. of water were thoroughly mixed together and coated on an unsubbed polyethylene terephthalate film. The coating was heated at 115 C. for five minutes, cooled to room temperature and stripped from the polyethylene terephthalate film. This coating was equally as flexible as the previous coatings and satisfactorily separated the standard dye mixture after ten minutes.

Example XV A slurry containing 150 grams of microcrystalline cellulose, 9.4 grams of polyethylene powder, and 53 grams of 1,1,l-trichloroethane was coated on a clear polypropylene film to a dry thickness of 10 mils. The solvent was then evaporated from the film leaving behind an adherent, porous chromatographic element. Using methanol as the development solvent, a mixture of two food dyes as described in Example VII was separated in four minutes. This solvent fusing technique in obtaining a porous layer is useful, but the appropriate solvent must be found to soften but not dissolve the polymeric-particles so that, on drying, the adsorbent particles adhere to the polymer and the layer remains porous.

Example XVI 100 grams of neutral alumina, 65 grams of polyethylene powder and 115 ml. of ethyl alcohol were thoroughly mixed together and the suspension coated on a polypropylene-coated paper stock. After evaporating the alcohol, the coating was subjected to a mist spray of 1,1,1-trichloroethane for two minutes. The coating was then dried. The

coating was tested as in Example XV and it was found to separate the food dyes in four minutes.

Example XVII grams of finely powdered silica gel were added to a 40 percent latex of polystyrene in water, and thoroughly mixed. The mixture was coated on polyethylene coated paper and dried, the resultant coating was heated at 125 C. for five minutes, and then cooled to room temperature. The chromatographic element satisfactorily separated the standard test dye mixture after five minutes.

Example XVIII Example XVII was repeated except that a 45 percent latex of polyvinylidene chloride in water was used. The result was essentially the same as Example XVII.

Example XIX grams of neutral alumina (325 mesh) and 65 grams of polyethylene powder (325 mesh) were slurried in ml. of ethyl alcohol and the suspension coated on the polyethylene surface of a composite polyolefin-polyester support, consisting of a 7 mil. thick layer of polyethylene laminated to a 7 mil. thick layer of a poly(ethylene terephthalate). The alcohol was allowed to evaporate, and the coating was then cured for five minutes at C., resulting in a porous, strongly adherent layer. The coating was tested as in Example I with equivalent good results.

Example XX Naturally occurring or synthetic resins which become tacky when contacted with water as a result of being watersoluble or water-swellable (so-called water-soluble gums or mucilages) can be used to form the binder particles for the practice of our invention. The resulting chromatographic sheets can be used advantageously in thin layer chromatography with organic solvent solutions. Thus, use can be made of various starches, e.g., corn, potato, taroroot, locust bean starches and the like, mucilages and water-soluble gums, such as gelatin, tragacanth, karaya, acacia, alginic acids and deviratives, hydroxyethylcellulose, carboxymethylcellulose, hydroxyethylcarboxymethylcellulose, poly(methacrylic acid), polyvinyl alcohol, cellulose acetate phthalate and similar materials. These are hard, tough solid resinous materials in the dry state and can be ground to appropriate particle size for use in the practice of this invention. Cohesion of the resin particles and adhesion to the support and to the adsorbent particles can be effected by lightly wetting the surface. For example, granular powders of the adsorbent and a binderlike starch or gum arabic can be slurried in and coated from a non-solvent, such as Stoddard solvent. After removal of the carrier liquid, the required adhesion can be obtained by treatment with a mist of warm water, or application of an aqueous solution of alcohol, e.g., 30% solution of ethanol in water, or the like.

Example XXI 10 grams of locust bean starch ground to 5-10 micron particle size was thoroughly mixed with 85 g. of alumina of 1025 micron particle size, slurried in 200 cc. ligroin and coated to a dry thickness of 5 mils. on a PVA subbed cellulosic film. The ligroin was removed by drying with forced air at 95 F. and the coating fixed by treatment with a spray of 30% solution of isopropanol in water. A coating of good mechanical strength was obtained having a strong bond to the support. It was used in a chromatographic separation of a mixture of three dyes (sudan red, butter yellow, and indophenol blue) dissolved in benzene.

Example XXII 25 grams of granular hydroxyethylcellulose (average diameter 510 microns) were intimately mixed with 250 g. of silica gel (average diameter 10-25 microns), slurried in 320 ml. of deodorized kerosene and coated on a hydroxymethylcellulose-subbed cellulosic film support. The liquid carrier was removed in a warm air dryer at 140 F. and the coating was stabilized by cooling the coating to 35 F. and then passing it through a chamber containing air saturated with water vapor at 120 F.

The water which condensed on the coating softened the hydroxyethylcellulose granules and the subbing sufliciently to promote good adhesion to the support and to form a coating of adequate mechanical strength. The resulting sheet was used in chromatographic separation of the dye mixture of Example XXI. Good separation was obtained.

From the above description and examples, it is clear that the instant invention bestows a heretofore unobtainable usefulness upon the art and science of chromatography. The chromatographic sheets of the instant invention can be precoated to exacting and reproducible standards under mass production conditions. Thereafter, the sheets can be readily stored or transported without elaborate precautions or fear of damage. When using chromatographic sheets prepared according to the instant invention, those in the art will have the benefit of substantially all of the advantages of the currently available glass plate binder-free thin-layer chromatographic elements wherein the adsorbent is merely deposited on a glass plate support without a binder, while avoiding the serious disadvantages of such binder-free chromatographic elements. The thinlayer sheets of the instant invention display chromatoggraphic activity substantially equal to that of the binderfree elements without the fragile powdering of the binderfree glass plates. Instead of preparing an adsorbent mixture, hand coating the adsorbent mixture onto a bulky glass plate and drying the coated plate to render it useful, those practicing chromatography need only obtain a precoated thin-layer element according to the instant invention and proceed with the desired determination or separation.

We claim:

1. A method of making a chromatographic element adapted for use in thin-layer chromatography, which comprises preparing a dispersion consisting essentially of a particulate finely-divided chromatographically-active adsorbent and a particulate finely-divided resinous binder dispersed in a liquid dispersing medium, said binder being capable of being softened and made tacky by the action of heat or a solvent and said binder being present in said dispersion in a proportion of from about 0.06 to about 1.6 parts per part by weight of said adsorbent; coating said dispersion on an inert support; removing said liquid dispersing medium from said coating; and rendering said particles of resinous binder in said coating soft and tacky to a suflicient extent that they adhere to particles which are adjacent thereto and form upon subsequent hardening a continuous, coherent, porous, chromatographicallyactive layer capable of use as a self-supporting layer.

2. The method as described in claim 1 additionally comprising the step of stripping said porous chromatographically-active layer from said support.

3. The method as described in claim 1 wherein said resinous binder is a thermoplastic polymer and said particles of resinous binder are rendered soft and tacky by heating to the softening point.

4. The method as described in claim 3 wherein said particles of resinous binder are heated to a temperature 10 in the range between about C. and about C.

5. The method as described in claim 1 wherein said resinous binder is a resin which becomes soft and tacky when contacted with a solvent and wherein said particles of resinous binder are rendered soft and tacky by applyi g a solvent thereto.

6. The method as described in claim 5 wherein said liquid dispersing medium is a partial solvent for said resinous binder and serves to render said particles of resinous binder soft and tacky.

7. The method as described in claim 1 wherein said inert support is a polyester.

8. The method as described in claim 7 wherein said polyester is polyethylene terephthalate.

9. The method as described in claim 1 wherein said inert support is a polyolefin.

10. The method as described in claim 1 wherein said inert support is polyolefin coated paper.

11. The method as described in claim 1 wherein said inert support comprises a layer of polyethylene terephthalate carrying thereon a layer of polyethylene.

12. The method as described in claim 1 wherein said chromatographically-active adsorbent is selected from the group consisting of alumina, silica gel, kieselguhr, polyamide powder, and cellulose powder.

13. The method as described in claim 12 wherein said resinous binder is a polyolefin.

14. The method as described in claim 12 wherein said resinous binder is polyethylene.

15. The method as described in claim 12 wherein said resinous binder is polypropylene.

16. The method as described in claim 1 wherein the thickness of said porous chromatographically-active layer is in the range from about 10 to about 40 mils.

17. The method as described in claim 1 wherein said resinous binder is present in said dispersion in a proportion of from about 10 percent to about 50 percent based on the volume of said adsorbent.

18. The method as described in claim 1 wherein said resinous binder is the disperse phase of a resin latex.

19. A chromatographic element produced by the method of claim 1.

20. A chromatographic element produced by the method of claim 2.

References Cited UNITED STATES PATENTS 2,527,628 10/1950 Francis 264-122 X 2,707,703 5/1955 Dorst 117-132 2,759,847 8/1956 Frost et a1. 117-161 2,822,272 2/ 1958 Kosalek 9691 2,915,475 12/1959 Bugosh 2602.5 2,999,016 9/1961 Beeber et al 96--75 3,161,519 12/1964 Alsup 117-138.8 3,303,043 2/1967 Halpaap 117--33.5

WILLIAM D. MARTIN, Primary Examiner.

R. HUSAK, Assistant Examiner.

US. Cl. X.R.

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