Polymeric sorbent with raised polarity for gas chromatography and method of preparing same

BACKGROUND OF THE INVENTION The present invention relates to polymeric sorbents with enhanced polarity for gas chromatography and to a process for its preparation which has significantly better properties than the materials previously known.

Polymeric sorbents for gas ehromatography have reached their maximum development in the period of expansion of macroporous crosslinked polymers. Unlike conventional sorbents referred to as carriers, mainly inorganic porous substances, it is not necessary to treat the polymeric sorbents by coating the surface with a so-called anchored phase as a rule liquid before use. Their application is therefore mainly in the gas-solid mode (as opposed to the conventional arrangement, where gas-liquid predominates).

Among the best known polymeric sorbents for gas chromatography are chemically very non-polar copolymers of styrene with divinylbenzene. Only some types are ethylene dimethacrylate polymer. Polar sorbents include porous polyphenylene oxide to concentrate gaseous components.

The degree of polarity is an important parameter describing the ability of a system to divide different groups of substances. In the case of gas ehromatography, it is customary to use Rohrschneider constants in the literature to express the polarity (J. Chromatogr. 22, 1966), ie 0.01 times the difference in the retention indexes of benzene (x), ethanol (y), methyl ethyl ketone (z), nitromethane (s) and pyridine (s) on squalan (linear isoprene trimmer) as the anchored phase and on the anchored phase tested. Because this method is not completely correct for gas-solid phase chromatography, modified indices are used below when graphite coal sorbents at 150 ° are used as standard instead of squalane. Modified indexes are indicated by a comma.

As mentioned above, one of the most polar sorbents is polyethylene dimethacrylate characterized by modified constants: x '= 1.30, y' = 2.90, z '= 2.21, u' = 3.44, Ts' not determined. Even subsequent modification of some polymeric sorbents does not significantly increase polarity. They are mainly used for separating nonpolar substances,

Significant improvement can be achieved with sorbents based on hydroxyl alkyl acrylates or methacrylates (cf. and 159,990), or with their modifications, whereby the values ​​are: x '= 2.29, y' - 3.53, z '= 2.75, u '= 4.09, s' not determined. An increase in polarity can also be achieved by ternary copolymerization according to CS. and 175 156.

A further substantial increase is achieved by the application of sorbents based on glycidyl esters of acrylic or raethecrylic acid copolymerized with alkylene dimethacrylate and acrylonitrile, respectively. A. 0. 188 619. The modified Rohrschneider constants of the best sample were:

x '= 3.62, y' = 4.64, z '= 4.43, u' = 7.00, s' = 5.97. These sorbents are characterized by relatively short retention times with good sorption properties documented by peak symmetry and linearity of the sorption isotherm.

According to the invention, it has been found that even these properties are not definitive and can be further improved significantly.

The essence of the increased polarity polymer sorbents for gas chromatography according to the invention consists in that it consists of copolymers of glycidyl methacrylate and ethylene dimethacrylate containing 20 to 60% by weight of the first component in macroporous form with a measurable inner surface and in the form of regular spherical particles subjected to heating. to a temperature of 250 to 300 ° C for less than 4 hours in an oxygen-free atmosphere.

The process of preparing the polymeric sorbents according to the invention is characterized in that the copolymer of glycidyl methacrylate with ethylene dimethacrylate is heated in a stream of inert gas at 250 to 300 ° C for 10 min to 4 hours and extracted after cooling with a nonpolar solvent selected from benzene, toluene. , xylene and a polar solvent selected from the group of alcohols or acetone and dried.

Heating of the macroporous copolymers of glycidyl methacrylate with ethylene dimethacrylate at temperatures of 250 to 300 ° C in an inert, oxygen-free atmosphere results in both weight loss due to effluent pyrolytic process, consisting of monomers and other substances, and restructuring of the internal structure resulting from conformational changes. These can only be described indirectly, for example, by chromatographic data because they are carried out at the molecular level. Excretion of oxygen is necessary, in particular, to avoid oxidative degradation of the sorbent, its coloration and loss of desired properties. Properly prepared sorbent has a white color, remains in the form of strictly spherical, individual particles.

The actual processing takes place in a tube, for example glass, metal, which, however, can withstand temperatures of up to 300 ° C without changes. In order to accommodate the polymer, it must be provided with a partition at the bottom to prevent sorbent leakage but to allow gas flow. Suitable are, for example, sintered glass frits, metal sieves, glass or metal wool rolls, mineral wool and others. Below this partition, the gas inlet is represented as a rule by narrowing the tube to a diameter corresponding to the inner diameter of the hoses used. The upper part is also closed, for example, with a ground-glass stopper, screwing or the like, allowing gas evacuation and temperature measurement within the sorbent bed to be treated. The entire cylinder should be as small as possible as small as possible to avoid undesired radial temperature gradients.

The filled cylinder is embedded in a tube furnace allowing heating to a temperature of up to about 500 ° C heated by a resistance wire, microwave or otherwise. Before starting heating, an inert gas, such as nitrogen, argon, helium, is introduced from below into the tubes at a rate such that the column is not lifted and the material is not lost by drift. At the same time, the gas also acts as a temperature equalizing medium in the column. The effluent gas is then discharged to a volatile disposal device, such as a furnace, a freeze separator, or any other device eliminating environmental pollution.

After the modification time has elapsed, the heating is switched off and the sorbent is allowed to cool at a constant gas flow. After reaching a temperature of about 20 to 50 ° C, the product can be removed from the tube and subjected to extraction with an aromatic solvent and then with alcohol. Suitable are, for example, benzene, toluene, ethanol, methanol. The extraction efficiency in the Soxhlet apparatus has the greatest efficiency. After the solvent has been aspirated, the sorbent is dried either in air under constant safety conditions or under reduced pressure in a corresponding oven to constant weight. The sorbent thus obtained is then directly usable as a gas chromatography column.

The whole procedure is documented by the following examples.

He did

Macroporous copolymer of glycidyl methacrylate with ethylene dimethacrylate (60:40% by weight), fraction 100 to 250 (µm with specific surface area (Sg) 64 m2g^-1, characterized by the polarity expressed by the modified Rohrschneider constants x '2.27, y' 3.86, z '3.09, u' 4.87, s' 4.02, was filled into a glass tube with a diameter of 12 mm and a length of 200 mm fitted with a glass frit on one side. The tube was placed in a tube furnace at a rate of 100 ml min^-1 injected nitrogen. The tube contents were heated to 250 ° C for 60 minutes. Then, the sorbent was extracted with benzene and alcohol, dried and used as a pack in a gas chromatography column. The following constants were found: x '= 3.03, y' = 4.85, z '= 3.92, u' = 6.40.

Example 1

The sorbent treatment was carried out in the same manner as in Example 1 except that the fraction 150-200 µm was heated to 260 ° C for 2 hours. The resulting sorbent had the constants: x '= 3.43, y' = 5.39, z = 4.26, u '= 7.15. The acetic acid ester mixture was then separated on a column packed with this sorbent. Using a 100 cm x 0.3 cm column, nitrogen flow 25 ml min^-1 retention times (in parentheses for the starting copolymer at 170 ° C): methyl acetate 1.40 (1.50), ethyl acetate 1.9 (2.2), propyl acetate 3 (3.4), butyl acetate 4 , 8 (6.4), pentyl acetate 7.7 (11.4), hexyl acetate 11.7. On the same column, a mixture of 1-chlorobutane (boiling point 77.9 ° C), ethyl acetate (bv 77.1) and methyl ethyl ketone (bv) was virtually completely separated. 79.6), while on the polyethylene dimethacrylate all three substances appear as one peak and on the starting sorbent the separation factor is 0.80 and 0.65, respectively.

Example 3-8

Macroporous copolymer of glycidyl acrylate and ethylenedimethacrylate (45:65% by weight) with a specific surface area (sg) of 109 m²G^_1The fraction 150-180 µm was modified by heat treatment at different temperatures for different times. The table gives an overview of the results:

<td rowspan="2">Example</td><td colspan="2">Modifications</td><td rowspan="2">X</td><td colspan="4">Rohrschneider constants</td>

<td>Temperature Deň: 32 ° C</td><td>Time, h</td><td>y</td><td>of</td><td>at</td><td>with</td>

<td> 3⁺</td><td> -</td><td> -</td><td> 1 ,44</td><td> 2,66</td><td> 2,23</td><td> 3,48</td><td> 2,67</td>

<td> 4</td><td> 250</td><td> 1</td><td> 1 ,86</td><td> 2,85</td><td> 2,67</td><td> 4,76</td><td> -</td>

<td> 5</td><td> 250</td><td> 2</td><td> 2,49</td><td> 4,01</td><td> 3,39</td><td> 5,47</td><td> -</td>

<td> 6</td><td> 250</td><td> 4</td><td> 2,50</td><td> 3,97</td><td> 3,38</td><td> 5,48</td><td> -</td>

<td> 7</td><td> 260</td><td> 2</td><td> 2,09</td><td> 3,64</td><td> 2,87</td><td> 4,69</td><td> -</td>

<td> 8</td><td> 280</td><td> 1</td><td> 3,15</td><td> 4,85</td><td> 4,02</td><td> 6,55</td><td> -</td>

<td>⁺ default</td><td>copolymer</td><td></td><td></td><td></td><td></td><td></td><td></td>

<td>Example 1</td><td>ad 9</td><td></td><td></td><td></td><td></td><td></td><td></td>

The sorbent obtained according to Example 8 was packed into a 100 x 0.3 cm column, and at a flow rate of 25 ml min-1 a separation of the hydrocarbon mixture was carried out, which could be characterized by retention times at 150 ° C. 175 ° C), hexane 1,2 (1,5), heptane 2 (2,6), octane 3,1 (5,2), nona 5,4 (10), dean 9 (19,2), undecane 15.3 min.

Example 10

Copolymer of glycidyl methacrylate with ethylenedimethacrylate (20:80% by weight) in macroporous form with a specific surface area of ​​212 m²G^-1characterized by modified Rohrschneider constants: x '1.05, y' 2.37, z '1.89, u' 2.92, was in a metal tube provided with a metal silo partition with a mesh size of 50 µm below which it was gas inlet and sealed with a drain pipe and thermowell, heated for 30 min to 300 ° C in an argon stream. After cooling, it was extracted with toluene and methanol, dried and packed into a chromatography column. The sorbent thus treated exhibited constants: x '= 2.12, y' = 4.56; z '= 3.71, u' = 5.89.