FILLER FOR HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY AND METHOD OF MANUFACTURING THE SAME

Abstract: A method of producing a filler, for high-performance liquid chromatography for preparing optical isomers separately, inexpensively and easily. The method contributes to improvement of the quality of the product prepared separately, maintains the separation power of the chromatography and minimizes the quantity of eluate. A material filler prepared by coating a supporter with a polysaccharide derivative is rinsed with a solvent to produce the title filler which produces little eluate derived from the polysaccharide derivative.

Description: The present invention relates to a packing material for high-performance liquid chromatography and a process for producing same. Moreover, the present invention relates to the use of said packing material for the separation of an optical isomer by high-performance liquid chromatography. The packing material for high-performance liquid chromatography of the present invention contributes to an improvement in the quality of a separated optical isomer in the field of separation of optical isomers. The present invention provides also a process for easily producing a packing material for high-performance liquid chromatography, which produces only a small amount of a dissolved matter, without reducing the separating capacity at a low cost by coating a carrier with a polysaccharide derivative and removing a dissolved matter derived from the polysaccharide derivative with a solvent. Packing materials for high-performance liquid chromatography can be roughly classified into those of chemical bond type and those of coating type. In the packing materials of the chemical bond type, the amount of the dissolved matter from a substance having the separating capacity is usually small, since this substance is chemically bonded to a carrier. On the other hand, a solvent in which the substance having the separating capacity is soluble cannot be used for the packing materials of the coating type, since this substance is physically absorbed on a carrier and, in addition, there is a high possibility of the peeling and dissolution of this substance depending on the using conditions. The formation of the dissolved matter should be avoided, since it causes a drift phenomenon on the base line in a chromatogram in the analysis, and it causes contamination of the separated product in the separation. The packing material for high-performance liquid chromatography, which comprises a polysaccharide derivative coated on a carrier, is suitable for the separation of an optical isomer, and it is known that the separation capacity thereof is very high (see Japanese Patent Laid-Open Nos. 082,858/1985, 108,751/1985, 142,930/1985, etc.). However, the packing material for high-performance liquid chromatography, which comprises a polysaccharide derivative coated on a carrier, has defects that a polymer of a relatively low molecular weight part of the polysaccharide derivative is dissolved to make the base line of the chromatogram unstable, depending on the mobile phase used, that the dissolved matter contaminates the separated product in the course of the separation and that the separation capacity is deteriorated in the course of the use for a long period of time. Under these circumstances, there is a demand for the development of a packing material for high-performance liquid chromatography, which a polysaccharide derivative coated on a carrier which forms only a greatly reduced amount of the dissolved matter. JP-A-5-148163 discloses a method of separating a chemical substance from a mixture containing said substance, which comprises the step of treating said mixture with a carbamate derivative of a specific polysaccharide. This publication specifically relates to the optical resolution of a mixture of optical isomers. JP-B-4-75893 discloses a composite structure useful as a filler for chromatography, said structure comprising a polysaccharide supported on a porous carrier. After intensive investigations made for the purpose of solving the above-mentioned problems, the inventors have found that the intended packing material can be obtained without reducing the separating capacity by coating a carrier with a polysaccharide derivative and then washing the obtained product with a specified solvent to remove a dissolved matter derived from the polysaccharide derivative. The present invention has been completed on the basis of this finding. The present invention provides a packing material for high-performance liquid chromatography, which comprises .a polysaccharide derivative coated on a carrier, wherein 80 to 100% of the hydroxyl groups of the polysaccharide of the polysaccharide derivative are substituted with a substituent, and which is characterized in that the amount of dissolved low-molecular weight polysaccharide derivative having a degree of polymerization of from 50 to 100 contained in said polysaccharide derivative is not more than 0.1 mg as determined by passing a mixed solution of n-hexane/2-propanol in a volume ratio of 9/1 through a column having an inner diameter of 1 cm and a length of 25 cm at a flow rate of 4.7 ml/min and at a temperature of 40°C, taking 564 ml of the solution and concentrating the solution to dryness. The present invention further provides a process for producing the above packing material for high-performance liquid chromatography, which comprises coating a carrier with a polysaccharide derivative, wherein 80 to 100% of the hydroxyl groups of the polysaccharide of the polysaccharide derivative are substituted with a substituent, and then washing it with a solvent being an aliphatic hydrocarbon, a lower alcohol or a mixture thereof at a temperature of from 50 to 70°C for at least 3 hours. The present invention is also directed to the use of the above packing material for the separation of an optical isomer by high-performance liquid chromatography. Preferred embodiments of the invention are set forth in the sub-claims. The polysaccharide used in the present invention may be any of natural and synthetic polysaccharides so far as it is optically active. The polysaccharide is preferably that having a high regularity in the bonding manner or a polysaccharide having a high purity which can be easily obtained. Examples of the polysaccharides include celluloses, amylose, β-1,4-chitosan, chitin, β-1,4-mannan and β-1,4-xylan. Among them, celluloses are particularly preferred. The term "polysaccharide derivatives" herein indicates compounds in which 80 to 100 % of hydroxyl groups of polysaccharide are substituted with a substituent. The polysaccharide derivatives are, for example, carbamate derivatives having a urethane bond formed therein, ester derivatives having an ester bond formed therein, and ether derivatives having an ether bond formed therein. In the present invention, the carbamate derivatives are particularly suitably used. Celluloses (β-1,4-glucans) which are natural polysaccharides contained in pulps, and those having various molecular weight distributions are available on the market. Celluloses having a uniform molecular weight cannot be easily obtained except synthetic celluloses produced by using a bacterium. However, it is said that a microcrystalline cellulose obtained by acid hydrolysis of a pulp usually has a narrow molecular weight distribution and a high degree of crystallization due to the removal of an amorphous part therefrom, and contains only a small amount of impurities such as mannan and xylan (see U. S. Patent Nos. 2,978,446 and 3,141,875). However, even the cellulose thus obtained can not have a monodisperse molecular weight distribution and, therefore, a derivative obtained from the cellulose has no monodisperse molecular weight distribution. A main cause for the formation of the dissolved matter in question is a relatively low-molecular weight cellulose derivative having a degree of polymerization of around 50 to 100. It is, therefore, ideal to use cellulose derivatives comprising only a small proportion of the low-molecular weight cellulose derivatives in this range and a large proportion of high-molecular ones, even though they are not the monodisperse one. The carriers usable in the present invention are porous organic carriers or porous inorganic carriers, the latter being preferred. Suitable porous organic carriers include polymers such as polystyrenes, polyacrylamides and polyacrylates. Suitable porous inorganic carriers include synthetic and natural substances such as silica, alumina, magnesia, titanium oxide, glass, silicates and kaolin. They may be surface-treated so as to improve the affinity for the polysaccharide derivative. The surface treatment is conducted by, for example, silane treatment with an organic silane compound or surface treatment by plasma polymerization. In the present invention, the carrier is coated with the polysaccharide derivative by, for example, dissolving the polysaccharide derivative in an organic solvent, mixing the resultant solution with the carrier by thorough stirring and distilling the organic solvent. The viscosity of the solution of the polysaccharide derivative is preferably as low as possible, since the carrier used in the present invention is porous and the polysaccharide derivative must be deposited even in the inner part of the pores. Therefore, the degree of polymerization of the polysaccharide derivative used is preferably 500 or below. Thus, the polysaccharide derivatives contain those having a degree of polymerization of around 50 to 100, which are the main cause of the formation of the above-described dissolved matter. The polysaccharide derivative of the packing material, coated on the carrier as above descrived, is in the form of a very thin film (having a thickness of several ten Å). The solvent used for washing the coating layer without serious disturbance of the layer is preferably that used as a mobile phase when the packing material is used for the high-performance liquid chromatography. Since a mixture of an aliphatic hydrocarbon such as n-hexane and a lower alcohol such as ethanol or 2-propanol is used as the mobile phase when the packing material of the present invention is usually used for the high-performance liquid chromatography, such a solvent is preferably used as the washing liquid for the packing material of the present invention. Namely, an aliphatic hydrocarbon, a lower alcohol or a mixture of them is used as the washing solvent in the present invention. Among the aliphatic hydrocarbons, n-hexane is preferred from the viewpoints of the boiling point, viscosity and influence on the coating layer and, further n-heptane and isooctane are also usable. Among the lower alcohols, 2-propanol is preferred from these viewpoints and, further ethanol, 1-propanol and 1-butanol are also usable. The amount of the washing liquid which varies depending on the packing material to be handled is usually 30 to 50 ml per gram of the packing material. The higher the washing temperature, the higher the washing capacity. However, taking the thermal stability of the polysaccharide derivative into consideration, the washing temperature is usually 50 to 70°C. The washing time is at least 3h under the above-described conditions. The amount of the dissolved matter formed from the packing material for the high-performance liquid chromatography of the present invention is extremely small. The guideline of the amount thereof is not more than 0.1 mg as determined by passing a mixed solution of n-hexane / 2-propanol in a volume ratio of 9/1 through a column having an inner diameter of 1 cm and a length of 25 cm at a flow rate of 4.7 ml/min and at a temperature of 40°C, taking 564 ml of the solution and then concentrating the solution to dryness. The amount of the dissolved matter formed from the packing material of the polysaccharide derivative coating type of the present invention is far smaller than that formed from an ordinary packing material of the polysaccharide derivative coating type which is not washed with a solvent. Therefore, an optical isomer can be separated without contamination thereof with the dissolved matter to obtain the intended product having a high quality. In the analysis, the base line of the chromatogram is not drifted and only a short time is taken for the stabilization to shorten the analysis time and also to reduce the amount of the solvent for the mobile phase. The following Examples will further illustrate the present invention. Synthesis Example 1 3.5 kg of cellulose (degree of polymerization: about 300) was added to 56 ℓ of pyridine in nitrogen atmosphere. 23.1 kg (a large excess for the cellulose) of 3,5-dimethylphenylisocyanic acid was added to the resultant mixture at 100°C, and the reaction was conducted under stirring at 105°C for 12h. Then the reaction liquid was cooled. 3 ℓ of methanol was added to the reaction liquid, and the resultant mixture was thrown into 160 ℓ of methanol. A precipitate thus formed was recovered by filtration and dried to obtain 11.8 kg (yield: 88 %) of cellulose tris(3,5-dimethylphenylcarbamate). IR (cm -1 ): 1728.7 Elementary analysis value: C %; 64.83. H %; 6.16, N %: 6.90 Molecular weight (in terms of polystyrene): number average molecular weight (MN) 71,000 weight average molecular weight (MW) 204,000 MW/MN 2.88 Synthesis Example 2 10 kg of cellulose tris (3,5-dimethylphenylcarbamate) obtained in Synthesis Example 1 was dissolved in 40 ℓ of acetone. The solution was thrown into 400 ℓ of ethanol. A precipitate thus formed was recovered by filtration and dried to obtain 8.5 kg of cellulose tris (3,5-dimethylphenylcarbamate). Elementary analysis value: C %; 64.35, H %; 6.13, N %; 6.77 Molecular weight (in terms of polystyrene): number average molecular weight (MN) 100,000 weight average molecular weight (MW) 240,000 MW/MN 2.40 Example 1 720 g of cellulose tris (3,5-dimethylphenylcarbamate) obtained in Synthesis Example 1 was dissolved in 4.7 ℓ of acetone. The solution was dropped into 2,880 g of silica gel (particle diameter: 20 µm, pore diameter : 100 nm (1,000 Å)) treated with 3-amino-propylsilane, under stirring. After thorough mixing, the solvent was distilled off to obtain 3,580 g of a packing material (hereinafter referred to as "packing material A'"). 800 g of the packing material A' was suspended in 32 ℓ of 2-propanol, and the resultant suspension was stirred at 60°C for 3 hour to wash it. The packing material was taken by filtration, then immersed in 10 ℓ of n-hexane, taken by filtration and dried. The obtained product was suspended in 40 ℓ of n-hexane/2-propanol (volume ratio: 1/1). The suspension was stirred at 60°C for 3 hour to wash the product. The packing material thus obtained was taken by filtration, immersed in 10 ℓ of n-hexane, taken by filtration and dried to obtain the washed packing material (hereinafter referred to as "packing material A"). The elementary analysis of the starting silica gel, and packing material A' and packing material A was conducted to obtain the results given in Table 1. The packing material A was fed into a stainless steel column having an inner diameter of 1 cm and length of 25 cm to prepare the column packed with the packing material A (hereinafter referred to as "column A"). Then 4.7 ml/min of an n-hexane/2-propanol (volume ratio: 9/1) mixture was passed through the column immediately after the preparation at 40°C. 564 ml of the solution was taken and concentrated to dryness, and the quantity of the dissolved matter was determined. The results are given in Table 2. It is understood from Table 2 that the amount of the dissolved matter in the present invention was far smaller than that formed when the unwashed packing material was used (Comparative Example 1). The optical resolution experiments of racemic modification given in Table 3 were conducted with the column A under the conditions described below. The results are given in Table 3. It is understood from Table 3 that the separation capacity was not lower than that obtained when the unwashed packing material was used (Comparative Example 1). mobile phase n-hexane/2-propanol (volume ratio: 9/1) flow rate 4.7 ml/min detection wave length 254 nm temperature 40 C. Comparative Example 1 A column packed with the unwashed packing material A' as described above (hereinafter referred to as "column A'") was prepared in the same manner as that of Example 1. The quantity of the dissolved matter in the column A' immediately after the preparation was determined in the same manner as that of Example 1. The results are given in Table 2. Then the optical resolution experiments were conducted in the column A' in the same manner as that of Example 1. The results are given in Table 3. Example 2 A packing material (hereinafter referred to as "packing material B'" was prepared in the same manner as that of Example 1 except that cellulose tris (3,5-dimethylphenylcarbamate) obtained in Synthesis Example 2 was used. The packing material B' was washed with the solvent in the same manner as that of Example 1 to prepare a washed packing material (hereinafter referred to as "packing material B"). The results of the elementary analysis of the packing material B' and material B were as given in Table 1. A column (hereinafter referred to as "column B") packed with the packing material B was prepared in the same manner as that of Example 1 except that the packing material B was used. The quantity of the dissolved matter in the column B immediately after the preparation was determined in the same manner as that of Example 1. The results are given in Table 2. It is understood from Table 2 that the quantity of the dissolved matter was far smaller than that formed when the unwashed packing material was used (Comparative Example 2). Then the optical resolution experiments were conducted with the column B in the same manner as that of Example 1. The results are given in Table 3. It is understood from Table 3 that the separation capacity was not lower than that obtained when the unwashed packing material was used (Comparative Example 2). Comparative Example 2 A column (hereinafter referred to as "column B'") packed with the unwashed packing material B' was prepared in the same manner as that of Example 2. Next, the quantity of the dissolved matter in the column B' immediately after the preparation was determined in the same manner as that of Example 2. The results are given in Table 2. Then the optical resolution experiments were conducted with the column B' in the same manner as that of Example 2. The results are given in Table 3. Results of elementary analysis C % H % N % Ash % Silica gel 0.56 0.27 0.16 97.2 Packing material A 13.6 1.50 1.54 77.2 Packing material A' 13.9 1.46 1.56 77.2 Packing material B 13.3 1.48 1.54 77.5 Packing material B' 13.4 1.48 1.54 77.5 Results of quantitative determination of dissolved matter Kind of packing material Low-molecular-weight polymer (mg) 3,5-Xylidine (mg) Methyl 3,5-xylylcarbamate (mg) Ex. 1 packing material A 0.015 undetected undetected Comp. Ex. 1 packing material A' 2.16 0.034 0.03 Ex. 2 packing material B 0.039 undetected undetected Comp. Ex. 2 packing material B' 0.49 0.025 undetected

Claims: A packing material for high-performance liquid chromatography, which comprises a polysaccharide derivative coated on a carrier, wherein 80 to 100% of the hydroxyl groups of the polysaccharide of the polysaccharide derivative are substituted with a substituent, and which is characterized in that the amount of dissolved low-molecular weight polysaccharide derivative having a degree of polymerization of from 50 to 100 contained in said polysaccharide derivative is not more than 0.1 mg as determined by passing a mixed solution of n-hexane/2-propanol in a volume ratio of 9/1 through a column having an inner diameter of 1 cm and a length of 25 cm at a flow rate of 4.7 ml/min and at a temperature of 40°C,taking 564 ml of the solution and concentrating the solution to dryness. The packing material of claim 1, wherein the polysaccharide derivative is a cellulose derivative. The packing material of claim 1, wherein the polysaccharide derivative is selected from the group consisting of cellulose, amylose, β-1,4-chitosan, chitin, β-1,4-mannan and β-1,4-xylan. The packing material of claim 1, wherein the polysaccharide derivative is a carbamate derivative having a urethane bond formed therein, an ester derivative having an ester bond formed therein or an ether derivative having an ether bond formed therein. The packing material of claim 1, wherein the polysaccharide derivative has a degree of polymerization of not higher than 500. A process for producing the packing material for high-performance liquid chromatography of any of claims 1 to 5, which comprises coating a carrier with a polysaccharide derivative, wherein 80 to 100% of the hydroxyl groups of the polysaccharide of the polysaccharide derivative are substituted with a substituent, and then washing it with a solvent being an aliphatic hydrocarbon, a lower alcohol or a mixture thereof at a temperature of from 50 to 70°C for at least 3 hours. The process of claim 6, wherein the solvent is an aliphatic hydrocarbon having 1 to 8 carbon atoms, a lower alcohol having 1 to 4 carbon atoms or a mixture thereof. The use of the packing material of any of claims 1 to 5 for the separation of an optical isomer by high-performance liquid chromatography.

Inventors: MURATA KIYOKAZU, ODA HIROSHI, MURATA, KIYOKAZU, ODA, HIROSHI
Applicants: DAICEL CHEM, DAICEL CHEMICAL INDUSTRIES, LTD.
Application year: 1995
Main classification: G01N30
IPC codes: B01J20, G01N30