Separation materials for thin layer chromatography

New separation materials for thin layer chromatography are based on carrier materials coated with an adsorbent silica gel layer which has been surface-modified by a silanizing agent after the coating step. The degree of covering of the modifying reagent can be adjusted in a defined and controllable manner, e.g., from 0.15 to 0.8 .mu.mol/m.sup.2 in the case of reversed phase materials and 1.2 to 2.5 .mu.mil/m.sup.2 in the case of hydrophilic materials. A process for the preparation of these separation materials is also provided.

BACKGROUND OF THE INVENTION 
Because of its speed, thin layer chromatography (TLC) is a widely used 
analytical method. It has been possible to increase its efficiency 
constantly by continuous further developments and improvement. With the 
HPTLC technique (high performance thin layer chromatography), it has been 
possible to achieve results which largely are analogous to those of high 
pressure liquid chromatography (HPLC). It is thus a rapid and inexpensive 
alternative to the more time-consuming HPLC analysis, which required more 
expenditure of equipment. In the end, the advances in the TLC/HPTLC 
technique are based on improved porous silica gels, which are chiefly used 
as adsorbents and carrier materials in thin layer chromatography. 
In particular, the introduction of silica gel surfaces chemically modified 
with organic groups (for example, as described in Journal High Resol. 
Chromatogr. Comm. 3; 215-240, 1980) led to a considerably wider range of 
applications. It thereby became possible to react the Si--OH groups of the 
silica gel, which are polar by nature, with suitable Lipophilic or 
partially Lipophilic organic molecules in a chemical reaction, i.e., to 
convert them into hydrophobic (reversed phase) or partially hydrophobic 
groups. 
A further enrichment of the TLC technique is in situ modification, that is 
to say chemical modification on a finished layer of silica gel, for 
example, as has been described in German Patent Specification No. 
2,712,113 or German Patent Specification No. 2,809,137. It is thereby 
possible to produce, inter alia, homogeneous packing and coating surface 
structures and purer layers. 
In the known preparation processes for chemically modified silica gel, the 
particular degree of covering of the modified adsorbent with organic 
groups is predominantly determined by the nature of the groups in the 
modifying reagent which are capable of undergoing reaction with the Si--OH 
groups of the silica gel skeleton. To obtain the highest possible degrees 
of conversion, correspondingly substituted reactive halogenosilanes are 
usually employed as the modifying reagent. The use of alkoxysilanes which 
are in themselves slow to react can evidently, according to German Patent 
Specification No. 2,426,306, lead to quite high degrees of covering of the 
silica gel surface if catalysts are simultaneously present during the 
silanization. Although the high degrees of conversion guarantee a good 
interaction between the hydrophobic carrier matrix and the hydrophobic 
substance, they mean that the hydrophobically modified layer of silica gel 
can no longer be wetted by eluting agents and spray reagents containing a 
large amount of water. 
In order to ensure the required wettability with water, the hydrophobic 
character of the modified layer of silica gel must be reduced. Using less 
than the stoichiometric amount of halogenosilanes or mixing silica gel 
with a maximum degree of modification and unmodified silica gel before the 
coating operation sometimes gives rise to considerable disadvantages, as 
has been shown in practice. The method usually practiced in which the 
hydrophobic character of silica gel layers to be modified in situ is 
reduced by using alkoxy- or aralkoxy-silanes which are slow to react for 
the chemical modification, frequently has the disadvantage that the degree 
of covering is greatly reduced. The actual reversed phase effect therefore 
is frequently only inadequate. 
In the case of chemical modification of silica gel layers with organic 
molecules containing polar-hydrophilic groups, such as, for example, alkyl 
chains carrying epoxy or amino groups, it is known that, exclusively, the 
alkoxy- or aralkoxy-silanes which are slow to react can be employed for 
the modification since the corresponding halogenosilanes do not exist. 
Silica gel layers modified in this manner accordingly have degrees of 
covering which are in principle lower, and in some cases too low. A higher 
surface concentration would be advantageous with this type of 
modification, however, because, in contrast to the purely hydrophobically 
modified layers, the layer in any case has the desired wettability with 
water, even with maximum reaction, because of the groups which have been 
introduced, some of which are quite polar. 
SUMMARY OF THE INVENTION 
It is thus an object of this invention to develop a separation material for 
TLC based on silica gel as the carrier material, which, after modification 
of the silica gel layer with (hydrophobic) reversed phase materials, has a 
homogeneous degree of covering which is on the one hand low, and thus 
enables the layer to be wetted with water, but on the other hand is 
sufficiently high to enable the reversed phase effect to be effective to 
the desired degree, so that even quite hydrophobic substances can still be 
separated by chromatography in an eluting agent system containing water. 
It is another object of this invention to satisfy the need to be able 
suitably to control, by the modification reaction, the degree of covering 
of the silica get layer which can be wetted with water so that a wide 
range of applications becomes possible. 
It is furthermore an object of this invention to develop hydrophilically 
modified TLC separation materials, of which the degree of covering, which 
can likewise be controlled by the modification, is clearly higher than in 
the case of materials which have been prepared previously e.g., in 
accordance with German Patent No. 2,712,113 and German Patent No. 
2,809,137. 
Upon further study of the specification and appended claims, further 
objects and advantages of this invention will become apparent to those 
skilled in the art. 
It has now been found that pretreatment of the usual HPTLC finished 
products with solutions of catalysts before the actual in situ 
modification of the silica gel layer with alkoxy- or aralkoxy-silanes 
which are slow to react leads to extremely homogeneous degrees of covering 
of the layer. These are considerably higher than without pretreatment. 
Moreover, it is possible to carry out the entire process, including the 
pretreatment, without the exclusion of atmospheric humidity. 
It has furthermore been found, surprisingly, that due to the quantitative 
and, above all, the qualitative compositions of the catalyst solutions, 
the degree of covering can for the first time be adjusted to the most 
diverse values in a controllable manner. This effect is not limited only 
to pure (hydrophobic) reversed phase materials, but can also be utilized 
for hydrophilic materials, in which higher degrees of surface covering can 
now be achieved in a controllable manner. The invention thus provides 
separation materials sized and dimensioned for TLC which can be 
specifically adapted in an optimum manner to the particular separation 
problem. By the fine regulation which can be carried out of the proportion 
of hydrophobic and hydrophilic surface areas on the silica gel layer, 
together with the possibility of using water-containing eluting agent 
systems, so that the hydrophobic/hydrophilic interactions can in turn be 
influenced, outstanding separations by thin layer chromatography can be 
achieved. 
This technical solution, which opens up an abundance of new possibilities 
for TLC, was not obvious from the state of the art. A process for 
increasing the surface concentration of the modifying reagent by 
silanization of pulverulent solids carrying hydroxyl groups in the 
presence of catalysts, with the exclusion of moisture, is indeed described 
in German Patent Specification No. 2,426,306; however, the expert can 
neither see nor conclude from this publication the technical doctrine 
according to the invention, in particular the controllability of the 
degree of covering. 
This invention accordingly relates to a new separation material for thin 
layer chromatography which is based on carrier materials coated with 
adsorbents and comprises a silica gel layer, the surface of which has been 
modified by silanizing agents after it has been coated onto the carrier, 
wherein the silica gel surface can be wetted with water and has a uniform 
degree of covering of 0.15 to 0.8 .mu.mol/m.sup.2 in the case of reversed 
phase (RP) materials or 1.2 to 2.5 .mu.mol/m.sup.2 in the case of 
hydrophilic materials. Preferred such separation materials have a uniform 
covering of the water-wettable silica gel layer of 0.3 to 0.5 
.mu.mol/m.sup.2 in the case of reversed phase materials based on C 
18-alkyl chains (RP 18) and of 0.35 to 0.7 .mu.mol/m.sup.2 in the case of 
reversed phase materials based on C 8-alkyl chains (RP 8), and a 
separation material which has a uniform covering of 1.5 to 2.3 
.mu.mol/m.sup.2 in the case of hydrophilic materials. 
The invention furthermore relates to a process for the preparation of these 
separation materials, which comprises a procedure in which the silica gel 
surface which can be wetted with water and is to be modified is 
homogeneously doped, before treatment with the silanizing agent, by 
impregnation with a solution of catalysts which are capable of catalyzing 
silanization reactions of silica gels. A process in which the doping and 
modification are carried out without the exclusion of moisture is 
preferred. 
A process which comprises a procedure in which a catalyst solution suitable 
for the desired control of the surface modification has a concentration of 
preferably 0.01-20% by weight is preferred. Processes which comprise a 
procedure in which alkoxy- or aralkoxy-silanes are used as the silanizing 
agents for the preparation of the separation materials according to the 
invention are furthermore preferred. Moreover, the invention relates to a 
process for the preparation of separation materials according to the 
invention in which a mixture of acetyl chloride and glacial acetic acid is 
preferably used as the catalyst, and a process in which tri-, di- or 
mono-chloro- or -fluoro-acetic acid is employed as the catalyst. 
DETAILED DISCUSSION 
Because of their preparation, the separation materials according to the 
invention have an adjustable defined covering of hydrophobic, hydrophilic 
and partially hydrophobic/hydrophilic radicals, which is distinguished by 
high uniformity. 
The degree of covering varies from 0.15 to 0.8 .mu.mol/m.sup.2 in the case 
of reversed phase materials (RP), preferably 0.3 to 0.5 .mu.mol/m.sup.2 in 
the case of reversed phase materials based on C18-alkyl chains and 0.35 to 
0.7 .mu.mol/m.sup.2 in the case of reversed phase materials based on 
C8-alkyl chains, and 1.2 to 2.5 .mu.mol/m.sup.2, preferably 1.5 to 2.3 
.mu.mol/m.sup.2, in the case of hydrophilic materials. 
The degree of covering of the surface .tau. (.mu.mol/m.sup.2) is defined 
here in accordance with Kovats (Adv. in Colloid and Interface Science 6, 
(1976), 95-137). The separation materials according to the invention can 
also be characterized by their degree of reaction. This is given in % and 
relates to the maximum degree of covering which can be achieved, which is 
limited to about 4 .mu.mol/m.sup.2, above all because of steric 
influences. 
For reversed phase materials, any desired degrees of covering under the 
maximum degree of covering which can be achieved according to the state of 
the art can be obtained, the hydrophobic character of the modified silica 
gel surface being reduced. The separation materials according to the 
invention thus still have water-wettability in the defined ranges. For 
hydrophilically modified layers, in which the aliphatic or arylaliphatic 
chain is thus substituted by polar groups, for example epoxy or amino, 
separation materials with a degree of covering which can be adjusted to a 
significantly higher level than was hitherto possible for layers modified 
in this manner (according to German Patent No. 2,712,113 and German Patent 
No. 2,809,137) can be obtained. 
The range of separation materials for thin layer chromatography is 
therefore quite considerably increased by the modified silica gel layers 
according to the invention. 
The separation materials according to the invention moreover have the same 
advantages of the separation materials of German Patent No. 2,712,113 and 
German Patent No. 2,809,137 which are modified in situ, and are thus 
distinguished by an outstanding reproducibility, an insensitivity towards 
the water content of the layer and atmospheric humidity, a high purity of 
the layer, a homogeneous packing and layer surface structure and fewer 
problems in preparation, especially on a production scale. 
The HPTLC separation materials according to the invention can be prepared 
in a surprising and extremely simple manner. For this, the finished 
layers--in contrast to German Patent Specification 2,426,306--are 
homogeneously doped with catalyst solutions before the actual reaction 
with silanes. 
Suitable catalysts are in principle all those which are known to be capable 
of catalyzing silanization reactions of silica gels. A wide range is 
available to the expert from the relevant literature, and suitable 
examples are inorganic and organic acids, reactive derivatives thereof and 
inorganic and organic bases. Inorganic and organic acids and reactive 
derivatives thereof are preferably employed. Substituted organic acids are 
also most suitable. 
Specific examples which may be mentioned of the possible inorganic acids 
are: HCl, HBr, HI, HF, H.sub.2 SO.sub.4, HNO.sub.3, H.sub.3 PO.sub.4, 
H.sub.3 BO.sub.3, HClO.sub.4, HBrO.sub.4, HIO.sub.4 of mixtures of two or 
more individual components. All the hydrogen halides are particularly 
suitable. Examples of possible organic acids are carboxylic acids or 
substituted carboxylic acids, sulfonic acids or amino acids, but 
preferably carboxylic acids and their substitution derivatives, mixtures 
of various individual components also being possible. Preferred examples 
which may be mentioned of possible carboxylic acids and substituted 
carboxylic acids are: formic acid, acetic acid, propionic acid, butyric 
acid, valeric acid, caproic acid, mono-, di- or tri-chloroacetic acid and 
mono-, di- and tri-fluoroacetic acid. Acetic acid and the fluorinated and 
chlorinated acetic acids are particularly preferred. 
Particularly suitable reactive derivatives of the preferred carboxylic 
acids are the acid halides, preferably the chlorides and bromides, such as 
acetyl chloride or acetyl bromide, and furthermore the corresponding 
anhydrides, azides or esters. 
Mixtures of one or more carboxylic acids and/or one or more reactive acid 
derivatives, in particular acid halides, are furthermore outstandingly 
suitable. Specific examples which may be mentioned are catalyst systems 
consisting of acetyl chloride/acetic acid, acetyl chloride/propionic acid, 
propionyl chloride/acetic acid, propionyl chloride/propionic acid, acetyl 
chloride/formic acid, acetyl chloride/butyric acid, butyryl 
chloride/acetic acid, butyryl chloride/propionic acid, butyryl 
chloride/formic acid, acetyl chloride/valeric acid, valeryl 
chloride/valeric acid, propionyl chloride/butyric acid, propionyl 
chloride/valeric acid, formyl chloride formic acid, formyl chloride/acetic 
acid, acetyl chloride/acetic acid/propionic acid, acetyl chloride/acetic 
acid/formic acid, acetyl chloride/propionyl chloride/acetic acid, acetyl 
chloride/propionyl chloride/propionic acid and acetyl chloride/propionyl 
chloride/formic acid. 
In the mixtures mentioned, instead of the acids, it is also possible to use 
correspondingly substituted acids, preferably the mono-, di- or 
tri-fluoro- or -chloro-substituted acids. Catalyst mixtures comprising 
acetyl chloride and acetic acid are particularly preferred. 
The preferred suitable inorganic base is ammonia. Examples which may be 
mentioned of possible organic bases are pyridine, di- and tri-ethylamine, 
butylamine and ethylenediamine. 
The catalysts can be present in concentrated form, if appropriate in the 
gaseous or vaporous state, or in solutions, preferably in dilute 
solutions. Preferred suitable solvents are organic, optionally 
water-miscible solvents, in particular polar organic solvents, that is to 
say alcohols, such as, for example, methanol, ethanol, n-propanol, 
isopropanol, n-butanol and methyl-propyl alcohol, and also acetone, methyl 
ethyl ketone or less polar solvents, such as dioxane, methylene chloride 
and di- and tri-chloroethane, or, finally, non-polar solvents, such as 
benzene, nitrobenzene, toluene, xylene, n-hexane or n-heptane, provided 
that the catalysts or catalyst components have an adequate solubility in 
the corresponding solvents or can be adequately mixed with them. The 
solvents can be employed in the dried state or with certain water 
contents. 
The concentration of the catalyst or of the catalysts in the solvent can be 
varied between 0.01% to 20% by weight, based on the impregnating solution. 
The concentration is preferably 0.05 to 10%. In the case of strong acids 
or bases, a lower concentration is preferably chosen, while a higher 
concentration is preferably chosen in the case of weak acids or bases. In 
the case of catalyst mixtures, the ratio of the individual components in 
relation to one another can be varied within wide limits. Ratios of 
between 1:9 and 9:1, in particular 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, 
and 9:1, are preferably established in two-component systems. 
The time of doping with the catalyst solution is between 1 minute and 20 
minutes, preferably between 8 and 12 minutes. A silica gel plate is 
preferably doped in 0.8-1.0 liter of catalyst solution. The water contents 
established on the surface-active silica gel plates which have not yet 
been modified do not have an influence on the particular resulting degree 
of reaction during the modification. Predrying or activation of the plates 
is not necessary. Atmospheric humidity does not have to be excluded, in 
contrast to the process of German Patent Specification No. 2,426,306. 
After predoping of the plates with catalyst solution, either modification 
is carried out directly, or, preferably, one or more washing operations 
are carried out, to remove excess catalyst. This is not possible in the 
process described in German Patent Specification No. 2,426,306. The 
solvents mentioned are usually employed for the washing processes. The 
volume of solvent per washing and plate is preferably 0.7-1.0 liter. The 
plates are preferably exposed to the washing solution for 8-12 minutes per 
washing. Typically, the plate specific surface area is 500-600 m.sup.2 /g. 
The chemical modification of the silica gel layer which follows the doping 
with catalyst is carried out in a manner which is known per se (for 
example German Offenlegungsschrift No. 1,712,113). The modification here 
proceeds by a process in which the silica gel layer is impregnated or 
soaked with the silanizing agent. This can be effected, for example, by 
immersing the starting material in the solution of the silanizing agent or 
by spraying it with such a solution. A customary solvent which is inert 
toward the silanizing agent used is employed as the solvent. Solvents 
which are preferably used are organic solvents with boiling points between 
30.degree. and 180.degree. C., for example chlorinated hydrocarbons, such 
as methylene chloride, chloroform and/or di- and tri-chloroethane, or 
aromatic or aliphatic hydrocarbons. 
The silanizing agents used are alkoxy- or aralkoxysilanes of the 
R--SiX.sub.3 type which are slow to react, wherein R is an unsubstituted 
alkyl or aralkyl group in the case of (hydrophobic) reversed phase 
modification or an alkyl or aralkyl group substituted with polar groups in 
the case of hydrophilic modification. X can be alkoxy, aralkoxy or alkyl, 
but at least one X per silane molecule must be alkoxy or aralkoxy. 
R can contain 1-20 C atoms in the optionally branched alkyl chain, and 
alkyl chains of 8 or 18 C atoms are preferred. Typically, the aryl 
portions of R and X contain 6-10 C-atoms. The X alkyl portions contain 
1-20 C-atoms also. 
If R in the case of hydrophilic modification is substituted by polar 
groups, examples of possible substituents are hydroxyl, amino, epoxy, 
cyano, halogen, ammonium, sulfonium and carboxyl. Epoxy or amino groups 
are preferably employed as substituents. A large number of silanizing 
agents are known from the literature or can be prepared by methods 
analogous to known methods. They are suitable for the process according to 
the invention in the same way as they are suitable for the known 
modifications of surfaces of adsorbents. The amount of silanizing agent 
used for the surface modification depends, above all, on the thickness of 
the layer of silica gel and the specific surface area of the silica gel 
used for coating. In order to obtain complete covering of the silanol 
groups accessible on the untreated silica gel, the silanizing agent should 
be employed in an amount of at least 10 .mu.mol/m.sup.2 of silica gel 
surface. However, an excess of the silanizing agent is preferably used, 
for example 0.1 to 1 mmol/m.sup.2. A larger excess can also be 
advantageous in certain cases. After the impregnation with the silanizing 
agent, the separation materials are allowed to drip and are then passed 
through several cleaning baths in order to remove excess silanizing agent 
and to purify the modified layer. The required washing processes are 
essentially analogous to the process already described in Patent 
Specifications Nos. 2,712,113 and 2,809,137. 
Starting materials which can be used are all the usual separation materials 
with a TLC silica gel layer on carriers, that is to say also the high 
performance separation material such as is described, for example, in 
German Offenlegungsschrift No. 2,524,065. Carriers which can be used are 
all the customary materials, glass plates being preferred. However, foils, 
for example aluminium foil, or plastic films can also be used. The silica 
gel layer is applied to these carrier materials in the form of a usually 
aqueous suspension which can be brushed on, using customary brushing 
apparatuses or coating units. Binders, which increase the adhesion and the 
abrasion-resistance, and, if appropriate, indicators are also added to 
this suspension. Preferred binders are the organic binders mentioned in 
German Patent Specification No. 1,442,446 or in German Auslegeschrift No. 
1,517,929. The indicator most frequently used is a fluorescence indicator, 
preferably magnesium tungstate, which absorbs in the UV at 254 nm (German 
Patent No. 2,816,574). The binders are as a rule added in amounts of 0.1 
to about 10%, and the indicators in amounts of about 0.5 to 5% by weight. 
The layer thickness of the silica gel layer on the separation materials 
according to the invention is usually of the order of 100 to 300 .mu.m, as 
in the TLC separation materials hitherto customary. In exceptional cases 
or for particular applications, however, separation materials with thinner 
or thicker layers can also be prepared. The specific surface area of the 
silica gels is between about 1 and 1,000 m.sup.2 /g, and is in most cases 
between 200 and 800 m.sup.2 /g. 
The water-wettability of the modified silica gel layers according to the 
invention depends, inter alia, on the particular phase with which the 
layer has been modified. RP-18 materials (unsubstituted straight-chain 
alkyl with 18 C atoms) can as a rule still be wetted with water at a 
degree of covering of about 0.55 .mu.mol/m.sup.2, and RP-8 materials 
(unsubstituted straight-chain alkyl with 8 C atoms) can still be wetted 
with water at a degree of covering of about 0.7 .mu.mol/m.sup.2. 
The parameters for controlling the separation materials according to the 
invention which can be correspondingly adjusted are essentially the nature 
and composition of the catalyst solutions or catalyst mixtures. Depending 
on the desired end product, the expert can select the doping conditions or 
compose the most suitable solutions in each case by routine testing. Table 
1 shows the degrees of covering of the separation materials modified 
according to the invention as a function of the catalysts/solvents, used 
by way of example in their preparation, in silica gel layers modified in 
different ways. For comparison, the corresponding values are given for 
HPTLC separation materials which have been prepared according to German 
Patent Nos. 2,712,113 and 2,809,137. The conditions given are to be 
understood purely as examples, and are thus not intended as any 
limitations. The comparison examples are given as reference. 
From Table 1, it can be seen that separation materials with both lower 
(RP-18, RP-8) and higher degrees of covering (DIOL), in comparison with 
the state of the art, can be obtained. The very high degree of covering 
for the DIOL-modified separation material is particularly remarkable. 
Table 2 shows that the solvents required for the catalysts can also 
influence the degree of covering, under otherwise identical conditions. 
The solvents mentioned are to be taken purely as examples. 
Table 3 shows the degrees of covering or reaction of separation materials, 
during the preparation of which various catalysts, under otherwise 
identical conditions (Example 2), have been used for the modification. The 
choice of the catalysts and their concentration is also to be understood 
purely by way of example here. As can be seen from Table 3, the influence 
of the nature of the catalyst on the degree of covering of the separation 
materials according to the invention is of major importance. The degree of 
covering can thus be accordingly controlled, as is expressed particularly 
well in the example with chlorinated and fluorinated acetic acid. 
Surprisingly, catalyst systems consisting of two or more catalyst 
components result in a surprisingly wide variance in the controllability 
of the degree of covering, depending on the ratio with respect to one 
another in which the individual components are employed. As an example, 
Table 4 shows the correlation between the ratio of acetyl chloride to 
acetic acid, both of which can be used individually as catalysts, and the 
carbon content of an RP-18 HPTLC separation material, which is directly 
related to the degree of covering. Such catalyst systems frequently show 
synergistic effects in respect of the degree of covering when their action 
is compared with that of the individual components. 
Since the degree of covering and hence the hydrophobic character of the 
active silica gel surface can be varied, it is possible to separate a 
considerably larger number of hydrophobic/hydrophilic substances and 
substance mixtures by thin layer chromatography. Problem-specific 
separation materials are thus available. The range of applications can 
moreover be increased by the possibility of using water-containing eluting 
agent systems. This also results in an additional fine regulation of the 
separation properties. The range of applications of thin layer 
chromatography is thus decidedly increased by the separation materials 
according to the invention. 
Water wettability means under all indicated conditions that, using pure 
water or high water containing solvents, the hydrophobic repulsion forces 
of the surface area modified with partially hydrophilic groups are smaller 
than the capillary forces causing the solvent transport. 
The necessary control of the extent of surface coverage, i.e., silanization 
extent, can also be controlled by varying the time of impregnation for a 
given catalyst solution within the aforementioned range. The greater the 
degree of impregnation (the longer the time), of course, the greater the 
extent of surface coverage, all other conditions being equal. However, in 
general, it will be preferred to vary the extent of surface coverage by 
varying the nature of the catalyst solution as described above and than 
carrying out the impregnation step such that the silica gel becomes 
substantially saturated with the catalyst to the extent possible for a 
given solution. Furthermore the extent of silanization can be controlled 
by conventional modification of the silanization reaction conditions, 
e.g., the temperature and duration of the silanization reaction.

Without further elaboration, it is believed that one skilled in the art 
can, using the preceding description, utilize the present invention to its 
fullest extent. The following preferred specific embodiments are, 
therefore, to be construed as merely illustrative, and not limitative of 
the remainder of the disclosure in any way whatsoever. In the following 
examples, all temperatures are set forth uncorrected in degrees Celsius; 
unless otherwise indicated, all parts and percentages are by weight. 
EXAMPLES 
The examples given below differ only in the nature and composition of the 
catalyst used and the nature of the silanes employed. 
HPTLC silica get 60 F 254s pre-coated plates, 10.times.20 cm from E. Merck, 
Darmstadt, were used in all cases. Glass separation chambers from Desaga 
were used as immersion containers for all the preparation steps carried 
out. 
The generally applicable preparation plan is as follows: 
(a) Doping of the plates with the catalyst or catalyst mixture by immersion 
in a corresponding solution 
(b) Immersion of the plates in a corresponding organic solvent to remove 
excess amounts of catalyst 
(c) Modification of the plates by immersion in the corresponding silane 
solution 
(d) Several successive washing processes by immersion of the plates in 
corresponding solvents and/or solvent mixtures of different polarity. 
EXAMPLE 1 
Preparation of an HPTLC RP-18 pre-coated layer which can easily be wetted 
with water 
re (a) Doping of an HPTLC silica gel 60 F 254s precoated plate with a 
solution of 0.9 ml of concentrated HCL in 900 ml of methanol (=0.04% HCL) 
in the course of 10 minutes. 
re (b) Intermediate washing operations, each of 10 minutes duration, in 900 
ml of methanol and then in 900 ml of toluene. 
re (c) Silanisation in 900 ml of a 10% toluene solution of 
methyloctadecyldimethoxysilane in the course of 20 minutes. 
re (d) Washing operations on the plates, each of 10 minutes duration, with 
2 900 ml portions of toluene, 900 ml of methylene chloride/methanol (1/1), 
2 900 ml portions of acetone/water (1/1) and 900 ml of methanol. 
EXAMPLE 2 
Preparation of an HPTLC RP-18 pre-coated plate which can still just be 
wetted with water 
re (a) Doping of an HPTLC silica gel 60 plate with a solution consisting of 
63 ml of acetyl chloride and 27 ml of glacial acetic acid in 900 ml of 
toluene (ratio of 7:3, total concentration of 10%) in the course of 10 
minutes. 
re (b) Intermediate washing operations, of 10 minutes duration, with 900 ml 
of toluene. 
re (c) Analogously to Example 1. 
re (d) Analogously to Example 1. 
EXAMPLE 3 
Preparation of an HPTLC RP-18 pre-coated plate which can easily be wetted 
with water 
re (a) Doping of an HPTLC silica gel 60 plate with a solution consisting of 
81 ml of acetyl chloride and 9 ml of glacial acetic acid in 900 ml of 
toluene (ratio of 9:1, total concentration of 10%) in the course of 10 
minutes. 
re (b, c and d) Analogously to Example 2. 
EXAMPLE 4 
Preparation of an HPTLC RP-8 pre-coated plate which can still just be 
wetted with water 
re (a and b) Analogously to Example 2. 
re (c) Use of methyloctyldimethoxysilane, otherwise analogously to Example 
2. 
re (d) Analogously to Example 2. 
EXAMPLE 5 
Preparation of an HPTLC diol pre-coated plate 
re (a) Doping of an HPTLC silica gel 60 plate with a solution consisting of 
4.5 ml of trichloroacetic acid in 900 ml of toluene (total concentration 
of 0.5%) in the course of 10 minutes. 
re (b) No intermediate washing. 
re (c) Silanization with 900 ml of a 10% toluene solution of 
.gamma.-glycidyloxypropyltrimethoxysilane in the course of 20 minutes. 
re (d) Analogously to Example 2. 
TABLE 1 
__________________________________________________________________________ 
Separation Degree of covering .tau. 
Degree of 
material HPTLC 
Catalyst/Solvent (.mu.mol/m.sup.2) 
conversion (%) 
Reference 
__________________________________________________________________________ 
RP-18 -- 2.05 51.0 German Patent 
2,712,113 
German Patent 
2,809,137 
RP-18 0.04% HCl in CH.sub.3 OH 10% acetyl chloride/ 
0.36 9.0 Example 1 
glacial acetic acid (7:3) in toluene 
0.61 15.0 Example 2 
RP-8 -- 2.94 77.0 German Patent 
2,712,113 
German Patent 
2,809,137 
RP-8 10% acetyl chloride/ 0.74 19.0 Example 4 
glacial acetic acid (7:3) in toluene 
DIOL -- 0.64 16.3 German Patent 
2,712,113 
German Patent 
2,809,137 
DIOL 0.5% trichloroacetic acid in toluene 
1.81 46.5 Example 
__________________________________________________________________________ 
5 
TABLE 2 
______________________________________ 
Degree of cover- 
Degree of 
Solvent ing .tau. (.mu.mol/m.sup.2) 
conversion (%) 
______________________________________ 
n-Heptane 0.31 7.8 
Toluene 0.6 15.0 
Methylene chloride 
0.57 14.8 
______________________________________ 
TABLE 3 
______________________________________ 
Degree of 
covering .tau. 
Degree of 
Catalyst (.mu.mol/m.sup.2) 
conversion (%) 
______________________________________ 
0.04% HCl in methanol 
0.36 9.0 
10% acetyl chloride in toluene 
0.18 4.5 
10% glacial acetic acid in toluene 
0.25 6.2 
10% propionic acid in toluene 
0.18 4.5 
10% trifluoroacetic acid in toluene 
1.05 26.2 
10% trichloroacetic acid in toluene 
1.01 25.2 
10% dichloroacetic acid in toluene 
0.76 19.0 
100 g monochloroacetic acid in 
0.52 13.0 
1 l of toluene 
______________________________________ 
TABLE 4 
______________________________________ 
Acetyl chloride/glacial 
acetic acid 10% in toluene 
1:9 3:7 5:5 6:4 8:2 9:1 
______________________________________ 
% C 14.5 10.2 6.9 6.5 6.2 6.1 
______________________________________ 
The preceding examples can be repeated with similar success by substituting 
the generically or specifically described reactants and/or operating 
conditions of this invention for those used in the preceding examples. 
From the foregoing description, one skilled in the art can easily ascertain 
the essential characteristics of this invention, and without departing 
from the spirit and scope thereof, can make various changes and 
modifications of the invention to adapt it to various usages and 
conditions.