Method for manufacturing a gas phase chromatography column and column obtained using such a method

Abstract

The present invention relates to a method for manufacturing a chromatography column, in particular for a gas phase chromatography, comprising a stationary phase made from a sol. This method comprises the following steps: (a) introducing this sol at the first end of the column, (b) moving said sol towards the second end of the column, so that a sol layer is formed on the internal wall of the column, this layer being able to form a gel on said internal wall, and (c) drying of the gel. The present invention also relates to a capillary column as well as to a microcolumn which may be manufactured according to this method.

Claims

1. A method for manufacturing a chromatography column comprising a stationary phase made from a sol comprising a pore-forming agent, comprising: (a) introducing a sol comprising a pore-forming agent at a first end of the column, (b) moving said sol towards a second end of the column, so that a thin sol layer is formed on the internal wall of the column wherein said sol layer forms a gel on the internal wall of the column, (c) drying the gel, and (d) removing the pore-forming agent from the dried layer, so as to form a microporous, mesoporous layer or other porous layer, the size and/or the density of the pores being controlled, said porous layer forming the stationary phase.

2. The method according to claim 1, wherein the sol forms a plug, extending from the first end of the column and over a length of less than two-thirds of the total length of the column, the plug being moved along the column under the effect of a pressure.

3. The method according to claim 1, wherein (c) is carried out by circulating a gas inside the column and, if required, during (a).

4. The method according to claim 3, wherein the gas is air or helium, nitrogen or another inert gas.

5. The method according to claim 1, wherein the pore-forming agent comprises cetyltrimethylammonium bromide (CTAB), diblock copolymers of ethylene oxide and of propylene oxide, triblock copolymers of ethylene oxide and of propylene oxide, or another surfactant.

6. The method according to claim 1, wherein (d) is carried out after (c) with a treatment selected from the group consisting of calcination, washing with an organic solvent of the alcohol or acetone type, and UV insolation.

7. The method according to claim 6, wherein the calcination is carried out by circulating dry oxygen, dry helium, dry nitrogen or another dry gas inside the column, the temperature of this gas being comprised between 100 C. and 500 C.

8. The method according to claim 1, wherein (a) to (c) are reproduced at least once before applying (d).

9. The method according to claim 1, wherein further comprising subjecting the internal wall of the column to a preparation treatment prior to (a) to reinforce the adhesion of the sol on the internal wall, wherein said treatment increases the hydrophilicity of the internal wall.

10. The method according to claim 1, further comprising subjecting the internal wall of the column to an activation treatment prior to (a) to reinforce adhesion of the stationary phase, wherein the activation treatment promotes covalent grafting between the gel and the internal wall during the condensation of the gel.

11. The method according to claim 10, wherein the activation treatment of the internal wall of the column is carried out by oxidation of said internal wall, this oxidation being carried out by plasma, via a gas route or via a liquid route.

12. The method according to claim 1, wherein the internal wall of the column is in silicon, in silica, in molten silica, in polymer or in metal.

13. The method according to claim 1, wherein the stationary phase has a thickness of less than or equal to 3 m.

14. The method according to claim 1, wherein the chromatography column is a capillary column with an internal diameter of less than or equal to 2 mm.

15. The method according to claim 1, wherein the chromatography column is a microcolumn for which at least one of the internal transverse lengths is less than or equal to 500 m.

16. The method according to claim 1, wherein: the sol forms a plug, and (b) comprises moving the plug along the column.

17. The method according to claim 16, wherein moving the plug forms the thin layer of the sol on the internal wall of the column.

18. The method according to claim 16, comprising moving the plug under the effect of pressure.

19. The method according to claim 16, comprising forming the plug to have a length of 20 to 50 cm in the column.

20. The method according to claim 16, comprising selecting a moving speed of the plug to leave the thin layer of the sol having a desired thickness on the internal wall of the column.

21. The method according to claim 16, comprising selecting a solvent concentration of the sol to leave the thin layer of the sol having a desired thickness on the internal wall of the column.

22. The method according to claim 16, comprising selecting a volume of the sol to form the plug to leave the thin layer of the sol having a desired thickness on the internal wall of the column.

23. The method according to claim 16, comprising forming the plug to extend over a length less than two thirds of a length of the column.

24. The method according to claim 16, comprising forming the plug to extend over a length less than half of a length of the column.

25. The method according to claim 16, comprising forming the plug to extend over a length less than one third of a length of the column.

26. The method according to claim 16, comprising forming the plug to extend over a length less than one tenth of a length of the column.

27. The method according to claim 16, comprising forming the plug to extend from the first end over a length less than a length of the column.

28. The method according to claim 1, wherein: the sol forms a plug at the first end, and (b) comprises moving the plug from the first end to the second end.

29. The method according to claim 28, comprising moving the plug under the effect of pressure.

30. The method according to claim 1, comprising: moving said sol towards a second end of the column to form the thin sol layer on the internal wall of the column and a passage from the first end to the second end.

31. The method according to claim 30, comprising: flowing a gas through the passage to dry to sol layer.

32. The method according to claim 2, comprising moving the plug under the effect of pressure of a gas or of a supercritical fluid.

33. The method according to claim 32, wherein the gas is the same as a gas applied in (c).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1A and 1B schematically illustrate a device allowing application of the method for manufacturing a chromatography column according to the invention, this column being a capillary column.

(2) FIG. 2 is a chromatogram obtained with the application of a capillary column comprising a stationary phase in silica and manufactured according to the method of the invention.

(3) FIG. 3 is a chromatogram obtained with the application of a microcolumn comprising a stationary phase in silica and manufactured according to the method of the invention.

DETAILED DISCLOSURE OF THE INVENTION AND OF PARTICULAR EMBODIMENTS

(4) As illustrated in FIG. 1A, the device 1 giving the possibility of applying the method for manufacturing a chromatography column according to the invention, comprises a flask 2 which is partly filled with a sol 3.

(5) The sol 3 is a colloidal suspension which comprises a solid phase with a grain size of less than 0.2 m, dispersed in a liquid phase. The solid phase is prepared from the tetraethoxysilane (TEOS) precursor of formula Si(OC.sub.2H.sub.5).sub.4.

(6) The liquid phase is an aqueous solution which comprises an alcohol (ethanol) and a surfactant.

(7) The surfactant plays the role of a pore-forming agent since it allows formation in the sol of spherical micelles of the same size, these micelles delimiting spaces or pores. The surfactant therefore gives the possibility of obtaining a network of ordered mesopores and of controlling the developed surface of the obtained stationary phase. Indeed, by means of a surfactant, the porosity of the stationary phase is under control. The size and the distribution of the pores are controlled.

(8) From among the surfactants which may be used in the sol, mention may be made of cationic surfactants such as cetyltrimethylammonium bromide (acronym CTAB) or amphiphilic diblock or triblock copolymers such as the triblock copolymer marketed by Aldrich under the trade name of Pluronic F127.

(9) In an alternative of the invention, the surfactant is present in the sol in a surfactant/Si molar ratio comprised between 0.08 and 0.2, and advantageously of the order of 0.1. Such a surfactant/Si ratio gives the possibility of obtaining a three-dimensional pore-forming lattice, for example cubic or hexagonal. Indeed, with a surfactant/Si ratio being greater than 0.2, the pore-forming lattice is lamellar and has great likelihood of collapsing during the calcination step aiming at removing the surfactant.

(10) This flask 2 is provided, at its neck 4, with a septum 5. This septum 5 is sealably crossed by a tube 6 for injecting a gas into the flask 2, on the one hand, and by a capillary column 7 intended to form a chromatography column according to the invention, on the other hand.

(11) In the place of the capillary column 7, it would be quite possible to arrange a microcolumn.

(12) Prior to putting a first end of the column in contact with the sol-gel solution, the internal wall of the column is subject to a treatment by oxidation, so as to increase the density of OH groups present at the surface. This has the consequences: the increase in the hydrophilicity of the internal wall, which promotes deposition of sol on the internal wall during sweeping of the column with the sol plug, the generation of sites for grafting the material forming the stationary phase with the internal wall.

(13) This treatment by oxidation is carried out via a liquid route by having a solution formed with ethanol, water and soda pass through the inside of the column, followed by rinsing with deionized water and then drying.

(14) The injection tube 6 is connected to a gas supply source (not shown) and opens into the upper portion 2 of the flask 2, above the level of the sol 3.

(15) The gas is advantageously an inert gas, such as helium or nitrogen. But this gas may also be air. In this case, the humidity level of the air is controlled so as not to interfere with the conditions for applying the sol-gel deposition.

(16) The applied gas pressure is adapted according to the dimensions of the capillary column 7. This applied gas pressure is advantageously less than or equal to 10 bars and, preferentially comprised between 0.2 and 4 bars. A gas pressure of the order of 2 bars is particularly preferred for a capillary column with a diameter of 100 m and with a length of 2 m.

(17) The capillary column 7, as for it, plunges into the sol 3 at its first end 7a, its second end 7b, located outside the flask 2, being left at atmospheric pressure.

(18) Although there is no limitation as to its both transverse and longitudinal dimensions, the capillary column 7 has an internal diameter which is less than or equal to 2 mm, advantageously less than or equal to 1 mm. Preferably, this internal diameter is comprised between 50 m and 500 m and, still more preferentially, between 50 m and 250 m. It also has a length which is advantageously comprised between 10 cm and 100 m, advantageously between 50 cm and 50 m and, still more preferentially, between 1 m and 30 m.

(19) This device 1, in its configuration illustrated in FIG. 1A, gives the possibility of carrying out the step for sampling a determined amount of sol 3. To do this, gas is injected through the injection tube 6 into the inside of the flask 2. Under the effect of the overpressure generated by the injection of gas into the flask 2, the sol 3 is pushed into the internal cavity of the capillary column 7.

(20) When the introduced amount of sol 3 is sufficient, for example when the sol forms a plug with a length comprised between 20 and 50 cm inside the column, the capillary column 7 is then slightly pulled in order to position it so that its first end 7a opens into the upper portion 2 of the flask 2 and no longer plunges into the sol 3. This configuration of the device 1 is illustrated in FIG. 1B.

(21) This step which has just been described gives the possibility of forming a plug of sol in the cavity of the capillary column 7, from its first end 7a. The amount of plug sampled from the sol 3 is very clearly greater than the required amount for coating the whole internal wall of the capillary column 7, as this will be seen hereafter.

(22) Under the effect of maintaining the overpressure inside the flask 2, this plug is then pushed into the internal cavity of the capillary column 7. During the gradual displacement of the plug inside and along the capillary column 7, a thin sol layer is deposited on the internal wall of this capillary column 7. Consequently, the plug loses a portion of its volume gradually during this displacement of the plug inside and along the capillary column 7. However, the initially sampled amount of sol is adapted so that this loss is negligible. This thin sol layer adheres to this internal wall because of its hydrophilicity related to the presence, in the sol, of silane groups which will form covalent bonds with this internal wall.

(23) The thickness of this thin sol layer deposited on the internal wall of the capillary column 7 may be adjusted by the concentration of solvent in the sol. The higher this concentration, the more the thickness of this thin sol layer decreases during the drying step which will be described below. The thickness of this thin sol layer may also be adjusted by the displacement speed of the plug of sol inside and along the capillary column 7. This displacement speed of the plug of sol as for it depends on the overpressure of applied gas but also on the amount of sampled sol plug and on the viscosity of the sol, the latter parameter in turn depending on the composition of the sol.

(24) When the sol plug has attained the second end 7b of the capillary column 7, the injected gas escapes through this second end 7b left clear. The circulation of gas sustained in this capillary column 7 allows the thin sol layer 3 deposited on the internal wall of the capillary column 7 to dry.

(25) Therefore it should be noted that the gas allows the displacement of the plug inside and along the capillary column 7 as well as the drying of the thin sol layer deposited on the internal wall of the capillary column 7. This drying of the thin sol layer will moreover begin immediately after deposition of this thin layer on the internal wall of the capillary column 7.

(26) Under the effect of this drying, the sol gels and the alcohol and then the water evaporate. Evaporation of the alcohol allows the surfactant to be organized in micelles, these micelles in turn being organized as a network, a so called pore-forming network, which is compact. The evaporation of the water, as for it, promotes the condensation of the gel around these micelles: the silanol groups of the gel not having formed any covalent bonds during gelling react with each other, on the one hand, for generating siloxane bridges which form the bases of the silica matrix and with OH groups of the internal wall of the capillary column 7, on the other hand, which reinforces at the end of the method according to the invention, the covalent anchoring of the stationary phase on this internal wall.

(27) After drying, the surfactant is removed in order to release the mesopores and thus make available the whole surface of the mesoporous silica. This removal of the surfactant may for example be accomplished by calcination or by washing with a solvent. This solvent may be an alcohol, such as ethanol or isopropanol, or further a ketone, for example acetone.

(28) The calcination may be accomplished under a gas flow, by means of a gas, in particular of an inert gas as those mentioned above (helium or nitrogen) and at a temperature comprised between 100 C. and 500 C., this temperature is of course to be adapted depending on the surfactant present in the sol. This gas should be dry and is advantageously introduced into the capillary column through the tube. It is also possible to use oxygen gas which has the advantage of lowering the temperature of this calcination step by about 100 C.

(29) Making a Capillary Column According to the Method of the Invention

(30) The method was applied on a capillary column in molten silica with a length of 1 m and an internal diameter of 100 m.

(31) Activation of the Internal Wall of the Column

(32) A Brown's mixture made by dissolving 140 mg of NaOH in a mixture comprising 15 ml of water and 20 ml of ethanol, was introduced into the capillary column, with a pressure gradient of 1 bar for 30 minutes, i.e. at a flow rate of the order of 0.2 l/s. The capillary column was then washed with distilled water with a 1 bar pressure gradient until a neutral pH is attained at the outlet of the capillary column. The capillary column was then dried by nitrogen flow, with a pressure gradient of 1 bar.

(33) Preparation of the Sol

(34) The sol produced is formed from tetraethylorthosilicate (TEOS), ethanol and water in TEOS/EtOH/H.sub.2O molar ratios of 1/3.8/5.

(35) 4.4 ml of ethanol and 4.4 ml of TEOS were added to 1.8 ml of a solution of water and hydrochloric acid with a pH=1.25. This first solution was refluxed at 60 C. for 60 min. 102 mg of hexadecyltrimethylammonium bromide (CTAB) were dissolved in 0.5 ml of ethanol, with ultrasound, by slightly heating (30 C.).

(36) It was then proceeded with mixing, by means of a vortex, 1.5 ml of the first solution in the solution containing CTAB. The obtained final solution was filtered on a polytetrafluoroethylene (PTFE) membrane with a porosity of 0.2 m.

(37) This final solution has a TEOS/CTAB molar ratio of 1/0.1.

(38) Deposition of the Sol into the Column

(39) About 2 l of the sol prepared in the previous step were introduced into the column with a pressure gradient of 1 bar, for 10 seconds. Next, the drying step was conducted by having nitrogen flow with a pressure gradient of 1 bar for 15 minutes at a temperature of 20 C. The temperature of the nitrogen was then raised at a rate of 1 C./minute, until a temperature of 120 C. is attained, a temperature at which the nitrogen flow was maintained for 7 hours.

(40) Calcination and Removal of CTAB

(41) Helium was then introduced into the column with a 0.4 bar gradient for 20 minutes at a temperature of 120 C., Next, the temperature of the helium was raised at a rate of 4 C./minute until a first temperature of 230 C. was attained, this first temperature being then maintained for 90 minutes, and then the temperature of the helium was raised at a rate of 1 C./minute until a second temperature of 250 C. was attained, this second temperature being then maintained for 60 minutes.

(42) Separation of the n-Alkanes

(43) The thereby obtained capillary column after the four steps detailed above was used for achieving separation of a mixture of C1-C5 n-alkanes.

(44) The obtained chromatogram with this capillary column after injecting 0.5 l of a mixture above (methane, ethane, propane, butane and pentane) is reproduced in FIG. 2. This chromatogram was obtained by connecting the thereby formed column to a commercial analysis device with reference Agilent GC6850 series 2, with a detector of the Flame Ionization Detector type. The injection conditions were the following: the temperature of the capillary column was 30 C., and the carrier gas used was helium under a pressure of 82.74 kPa (12 psi).

(45) The chromatogram reproduced in FIG. 2 shows that all the compounds were well separated and this with very good separation efficiency, for example with 4,100 theoretical plates per meter for ethane.

(46) Making a Microcolumn According to the Method of the Invention

(47) The method was applied on a microcolumn in silicon with a length of 1.33 m and a rectangular section of 40 m160 m.

(48) Activation of the Internal Wall of the Column

(49) A Brown's mixture made by dissolving 140 mg of NaOH in a mixture comprising 15 ml of water and 20 ml of ethanol, was introduced into the microcolumn, with a pressure gradient of 3 bars for 120 minutes, i.e. at a flow rate of the order of 0.3 l/s. The microcolumn was then washed with distilled water with a 3 bar pressure gradient until a neutral pH is attained at the outlet of the microcolumn. The microcolumn was then dried by nitrogen flow, with a pressure gradient of 3 bars.

(50) Preparation of the Sol

(51) The sol produced is formed from tetraethylorthosilicate (TEOS), ethanol and water in TEOS/EtOH/H.sub.2O molar ratios of 1/3.8/5.

(52) 4.4 ml of ethanol and 4.4 ml of TEOS were added to 1.8 ml of a solution of water and hydrochloric acid with a pH=1.25. This first solution was refluxed at 60 C. for 60 min. 102 mg of hexadecyltrimethylammonium bromide (CTAB) were dissolved in 0.5 ml of ethanol, with ultrasound, by slightly heating (30 C.).

(53) By means of a vortex, 1.5 ml of the first solution was mixed in the solution containing CTAB. The obtained final solution was filtered on a polytetrafluoroethylene (PTFE) membrane with a porosity of 0.2 m.

(54) This final solution has a TEOS/CTAB molar ratio of 1/0.1.

(55) Deposition of the Sol into the Column

(56) About 1.2 l of the sol prepared in the previous step were introduced into the microcolumn with a pressure gradient of 4 bars, for 30 seconds. A drying step followed by having nitrogen flow with a pressure gradient of 4 bar for 20 minutes at a temperature of 20 C. The temperature of the nitrogen was then raised at a rate of 1 C./minute, until a temperature of 120 C. is attained, a temperature at which the nitrogen flow was maintained for 7 hours.

(57) Calcination and Removal of CTAB

(58) Helium was then introduced into the column with a 1.7 bar gradient for 20 minutes at a temperature of 120 C. Next, the temperature of the helium was raised at a rate of 4 C./minute until a first temperature of 230 C. was attained, this first temperature being then maintained for 120 minutes, and then the temperature of the helium was raised at a rate of 1 C./minute until a second temperature of 250 C. was attained, this second temperature being then maintained for 90 minutes.

(59) Separation of the n-Alkanes

(60) The thereby obtained microcolumn after the four steps detailed above was used for achieving separation of a mixture of C.sub.1-C.sub.5 n-alkanes.

(61) The obtained chromatogram with this microcolumn after injecting 500 ppm of a mixture above (methane, ethane, propane, butane and pentane) is reproduced in FIG. 3. This chromatogram was obtained by connecting the thereby formed column to a commercial analysis device with reference Agilent GC6850 series 2, with a detector of the Flame Ionization Detector type.

(62) The injection conditions were the following: the temperature of the microcolumn was 30 C., the carrier gas used was helium under a pressure of 82.74 kPa (12 psi).

(63) The chromatogram reproduced in FIG. 3 shows that all the compounds were well separated and this with very good separation efficiency, for example with 6,600 theoretical plates per meter for ethane.

BIBLIOGRAPHY

(64) [1] J. Vial et al., Journal of Chromatography A, 1218, 2011, pages 3262-3266 [2] Rouqudrol et al., Pure & Applied Chemistry, 66(8), 1994, pages 1739-1758