Heating device for a chromatography column

Abstract

The present invention relates to a heating device for a gas chromatography column, comprising a support including a strip of a thermally conductive material, said strip being wound around an axis with two non-contiguous opposite ends to form a cylinder having an axial slot, and a heating wire wound on said cylinder so as to form a track adapted to receive a chromatography column wound in one or more layers. The support is capable of absorbing the difference between the thermal expansions of the column, the heating wire, and the strip wound on the support. Figure for the abstract: Fig 1

Description

Title of the invention: Heating device for a chromatography column technical field

[0001] The present invention relates to a heating device for a gas chromatography column. State of the art

[0002] A measurement chain for gas chromatography analysis includes an injector, at least one separation column, and at least one detector.

[0003] For the purposes of the analysis, it is necessary to control the temperature of the measurement chain at all points. A commonly accepted sizing rule is to maintain the injector temperature at a constant value above the boiling point of the gaseous sample to be analyzed.

[0004] With regard to the column, its temperature must be adjusted to ensure good separation of the different gas peaks constituting the sample to be analyzed, while also favoring a good analysis speed. It is preferable to work at a column temperature between the dew point and the boiling point of the sample.

[0005] Depending on the nature of the sample to be analyzed, two types of analysis are typically implemented: isothermal analysis, during which the column is maintained at a constant temperature, and analysis using linear ramp temperature programming, which consists of gradually raising the column temperature in steps. This latter method is particularly well-suited to complex samples composed of a mixture of substances with a significant difference in boiling points.

[0006] The temperature ramps are adjusted according to the nature of the sample and the required separation capacity or analysis time. These ramps also allow control of the absorption / desorption phenomena between the stationary phase on the column and the mobile phase (gas) in the column. This interaction between the stationary and mobile phases determines the transit rate of a given analyte and thus allows the separation of two different analytes present in a sample.

[0007] Therefore, temperature control must be precise and homogeneous over the entire circumference of the column.

[0008] The chromatography column is in the form of a fused silica capillary tube, which is typically wound on a coil core.

[0009] During the analysis, the column and said coil core are placed in an enclosure thermal including heating means allowing precise temperature control, for example isothermally or by programming ramps.

[0010] This thermal chamber takes up a significant amount of space in commonly used chromatography devices. Furthermore, due to the thermal inertia of such a chamber, energy consumption is high and cooling is often slow, imposing a delay between consecutive analyses. In addition, such a thermal chamber is an expensive component in a chromatography device.

[0011] Direct heating of the column and its coil core, for example by a heating wire, can minimize the size and thermal inertia of the device. However, such direct heating is difficult to control precisely and uniformly. In particular, it requires careful control of the heat transfer ratio between the column and the heating wire on the one hand, and between the column and a cooling device on the other.

[0012] Document EP962767A1 illustrates a system in which a thermally insulated tube comprises a column, a heating wire, and a temperature sensor. Such a device requires insulation that is flexible and resistant to high temperatures. Such insulation is expensive to manufacture and bulky. Furthermore, cooling is slow due to the thermal inertia of the assembly.

[0013] In patent US7513936 A1, another system for directly heating the column is proposed. This system comprises two discs with heating elements, allowing the heating of a column wound in a planar spiral shape arranged between the discs. The mechanical tension of such spirals is difficult to control, and such a device is difficult to manufacture in an automated manner.

[0014] US20170370888 illustrates a column support comprising three concentric support rings. An inner ring has a heating wire and is inserted into an intermediate ring around which the column is wound in a single layer. The two rings containing the heating wire and the column are inserted into an outer ring. In this system, homogeneous heating of the column is difficult to achieve and does not favor winding the column in multiple layers. Description of the invention

[0015] One object of the invention is to design a compact heating device for a capillary column allowing direct heating (for example, resistive heating) with precise and homogeneous temperature control along the length of the column. This device must allow for the programming of consecutive temperature ramps between 20°C and 300°C, and alternatively, for the heating of the column isothermally.

[0016] To this end, the invention proposes a heating device for a chromium column. gas-phase matography, including

[0017] • a support comprising a strip of a thermally conductive material, said strip being wound around an axis with two opposite, non-contiguous ends to form a cylinder having an axial slot, • and a heating wire, wound around said cylinder so as to form a track suitable for receiving a chromatography column wound in one or more layers.

[0018] The support is capable of absorbing the difference between the thermal expansions of the column, the heating wire and the wound strip of the support.

[0019] The present invention allows for a more compact geometry and the use of longer columns, by using a single heating element wound on a support capable of compensating for mechanical expansion between the different parts of the system. The invention makes it possible to maintain good thermal contact between the column and the heating element during the heating and cooling cycle.

[0020] The heating device according to the invention is designed by minimizing the amount of material used to make the support, and by choosing a lightweight material with a high coefficient of thermal conductivity.

[0021] Such a heating device minimizes the energy required to heat and cool the column and saves time by facilitating rapid heating and cooling. Thus, each thermal chromatography cycle results in energy and analysis time savings.

[0022] Advantageously, the heating wire is wound in a single layer of tightly packed turns around the cylinder. Preferably, the strip has one end folded inward toward the cylinder on one side of the axial slot. The heating device may include a temperature sensor inserted into the fold on one side of the cylinder slot.

[0023] Preferably, the support comprises two flanges made of a thermally conductive material attached to the cylinder and extending radially outwards from each end of the cylinder. In some embodiments, at least one flange has a foldable tab between a mounting position where the tab extends radially outwards from the flange so as to allow the chromatography column to be wound onto the track, and a holding position where the tab extends substantially parallel to the axis of the cylinder so as to hold the chromatography column wound onto the track.

[0024] The invention also relates to an assembly comprising a heating device as described above and a capillary chromatography column wound on the track formed by the heating wire. Advantageously, the chromatography column is wound in the form of contiguous turns forming at least one layer extending continuously from one flask to the other, the column being held rolled up by each tab.

[0025] Another object of the invention relates to a method for manufacturing a heating device for a gas chromatography column, comprising:

[0026] • the supply of a strip of a thermally conductive material; • the winding of said strip around an axis with two opposite ends not joined so as to form a cylinder having an axial slot; • the winding of the heating wire on said cylinder to form a track suitable for receiving a chromatography column wound in one or more layers.

[0027] Preferably, said method further comprises the provision of two flanges made of a thermally conductive material, and the assembly of each flange to a respective end of the cylinder.

[0028] Advantageously, the said method further comprises winding a chromatography column onto the track formed by the heating wire.

[0029] In certain embodiments, said at least one flange comprises a tab extending radially outwards, the method further comprising, after winding the chromatography column onto the track, a step of folding each tab substantially parallel to an axis of the cylinder.

[0030] Preferably, at least one of the parts of a thermally conductive material is made of sheet metal.

[0031] The invention also relates to a method for heating a chromatography column, comprising:

[0032] • the supply of an assembly as described above, • connecting the heating wire to an electrical source to bring said wire to a temperature determined,

[0033] the chromatography column being heated by conduction from the support and the heating wire.

[0034] In some embodiments, heating generates a difference in thermal expansion of the upper support and the chromatography column, the cylinder deforming by displacement of the edges of the slit to absorb said difference in thermal expansion. Brief description of the figures

[0035] Other features and advantages of the invention will become apparent from the detailed description that follows, with reference to the accompanying drawings, in which:

[0036] Fig. 1 is a perspective view of a heating device according to the invention, comprising a chromatography column.

[0037] Fig. 2 is a side view of the heating device comprising a chromatography column.

[0038] Fig. 3 is a cross-sectional view of the heating device comprising a chromatography column.

[0039] Fig. 4 is a cross-sectional view from below in a plane perpendicular to the axis of a detail of an embodiment of an axial slot.

[0040] Fig. 5 is a view of a flask.

[0041] Figure 6 is a cross-sectional view illustrating the arrangement of the heating wire and the chromatography column.

[0042] Fig. 7 is a detailed top view of two foldable tabs.

[0043] Fig. 8 is a detail view of a foldable tab. Detailed description of implementation methods

[0044] Figures 1-3 illustrate a heating device for a chromatography column 4 according to the invention.

[0045] Such a device comprises a chromatography column support in the form of a band 1 made of a thermally conductive material. Advantageously, said band 1 consists of a lightweight material with a high coefficient of thermal conductivity, for example aluminum or magnesium.

[0046] In the present text, "light" means a material with a density of less than 3.

[0047] In this text, "high thermal conductivity coefficient" means a thermal conductivity coefficient greater than or equal to 220 W / mK

[0048] In some embodiments, said strip 1 is made of sheet metal. In other embodiments, the strip can be obtained by machining.

[0049] Said strip 1 is wound around an axis X to form a cylinder. Said cylinder may have a circular, oval, elliptical, or any other suitable curved base.

[0050] The ends 12, 13 of the strip are arranged non-contiguously to form an axial slot 16, i.e. parallel to the X-axis, suitable for absorbing thermal expansions of the device. The width of said slot is typically less than 1 mm.

[0051] In certain embodiments, the ends 12, 13 of the strip 1 are folded into the area of ​​the axial slot 16. Such an embodiment of an axial slot 16 is illustrated in [Fig. 4], which shows a cross-section in a plane P perpendicular to the X-axis, as indicated in [Fig. 2]. Preferably, the folded portions are arranged so as to stabilize the assembled heating device.

[0052] Advantageously, one end 12 of the strip is folded to form a cavity suitable for retaining a temperature sensor 11 by the elasticity of the material. Alternatively, the temperature sensor 11 can be fixed in the cavity to by means of glue or cement.

[0053] The heating device further comprises two flanges 2 arranged coaxially at the two parallel ends of the cylinder. With reference to [Fig. 5], said flanges 2 are typically in the form of flat rings perpendicular to the X-axis. The flanges 2 consist of a lightweight material with a high coefficient of thermal conductivity, for example, aluminum or magnesium. Advantageously, the flanges 2 are made of sheet metal, and particularly advantageously of aluminum sheet metal.

[0054] The flanges 2 comprise a set of tabs 21, 22 and 23 bent towards the cylinder and the other respective flange, the function of which will be described later.

[0055] The use of sheet metal, allowing shaping by cutting and folding of the strip and flanges, is particularly suitable for minimizing the manufacturing cost of the device.

[0056] The heating device comprises a heating wire 3 wound around the outside of the cylinder formed by the strip 1 so as to form a heating track. The heating wire 3 preferably has an enamel coating and a varnish, or a ceramic coating. The diameter of the heating wire 3 can be adapted according to the desired resistance and resulting heating, and according to the diameter of the cylinder. In some embodiments, said heating wire 3 is wound around the surface of the cylinder in close turns. By way of illustration and not limitation, the heating wire 3 can be wound in a single layer as illustrated in [Fig. 6]. In other embodiments, the heating wire 3 can be wound in several layers. The turns are delimited laterally by the flanges 2. The ends of the heating wire 3 are connected to an electrical source for heating the heating wire 3 by Joule heating.

[0057] The column 4 is wound in one or more layers on the track formed by the heating wire 3. Preferably, the column 4 is wound in close-set turns that are laterally limited by the flanges 2 and radially limited by the tabs 21 folded over the outer face of the cylinder. Advantageously, the wound column 4 has an outer diameter substantially identical to the outer diameter of the flanges 2.

[0058] We will now describe the assembly steps of the heating device and the column 4. A first step consists of rolling the strip 1 into a cylinder and folding the ends 12, 13 to form an axial slot 16. Optionally, a temperature sensor 11 can be inserted into the fold of the edge 12 of the strip 1. The flanges 2 are then assembled onto the two ends of the cylinder. With reference to Figures 5-8, the flanges have several tabs 21, 23, one end of which is connected to the circumference of the flange and the other end extends radially outwards or inwards from the flange. Other tabs 22 can be arranged on the flange in a tangential direction.

[0059] The next step consists of winding the heating wire 3 onto the cylinder in one or more layers of close-wound turns, such that at least one layer extends continuously from one flange to the other. The heating wire 3 can be held onto the cylinder by using a lug welded to one end of the heating wire 3 and screwing said lug onto the band 1 or the flanges 2, or by winding the heating wire in one or more turns around an unfolded tab 21, 22, 23. The column 4 is then wound in close-wound turns in one or more layers onto the track formed by the heating wire 3, forming at least one layer extending continuously from one flange to the other, and leaving the ends 41, 42 of the column protruding.

[0060] In some embodiments, the temperature sensor 11 is inserted after the column is wound by means of a hole in one of the flanges near the tab 23. Advantageously, said temperature sensor 11 is covered on its entire periphery by the band 1 in order to optimize the response of the temperature sensor 11. The temperature sensor typically includes an electrical power cable 24 which passes through an opening drilled in one of the flanges.

[0061] Finally, the tabs 21, 22, and 23 are folded around the column 4, their position after assembly being substantially parallel to an axis of the cylinder, in order to radially delimit the wound column. We begin, by way of illustration and without limitation, with tab 22, which is arranged tangentially to prevent the rotation of the flanges 2 relative to the band 1. Next, tab 23 is folded; it can be used to hold a cable 24 supplying power to the temperature sensor, or folded so as not to cover said cable 24. Tab 23 closes the opening containing the temperature sensor 11, thus preventing said temperature sensor 11 from translating in the direction of the cylinder axis. In some embodiments, tab 23 is folded back to close the cavity containing the temperature sensor 11 before filling said cavity with glue or cement to fix the temperature sensor 11.

[0062] The tabs 21 are then successively folded around the column. Each tab can be folded either to the outside or to the inside of the strip 1.

[0063] The elasticity of the tabs 21,22,23 allows them to be manipulated several times in order to optimize the arrangement of the flanges and the column, and, for example, to insert the temperature sensor at a later stage of the assembly or to change the temperature sensor between different chromatography analyses.

[0064] The ends 41 of column 4 can then be fluidly connected respectively to an injector and a detector in a chromatography device.

[0065] We will now describe the heating and cooling steps during a gas chromatography analysis.

[0066] The device is at ambient temperature, which is typically between 15°C and 25°C. The heating wire 3 is connected to and supplied with an electric current, in order to heat said heating wire 3 by Joule heating. Said wire 3 heats the column by conduction to a temperature intended for chromatographic analysis. The temperature intended for chromatographic analysis is higher than the ambient temperature and can reach up to 350°C or more. The temperature rise can typically reach values ​​of up to 120°C per minute. The strip 1, the flanges 2, and the column 4 are heated simultaneously by the heating wire 3. Because the thermal inertia of said components is low, heating is rapid, and stabilization can be achieved within an interval that is, by way of illustration and not limitation, between 1 and 10 seconds.Given the homogeneity of the heating, a single temperature sensor 11 is sufficient to know the temperature of the column.

[0067] After the power supply is disconnected, the column and the support return to ambient temperature. The shape of the device promotes convection cooling of the support and the column. Cooling can be accelerated by forced convection using a suitable device, for example, a fan or a cold gas source.

[0068] Given the difference in the coefficients of thermal expansion of the materials used, a difference in thermal expansion between the support and the chromatography column may occur during temperature variations. The axial slit 16 formed by the ends 12 and 13 of the strip has a variable width, adapted to mechanically absorb said difference in expansion, so as to prevent breakage of the column.

[0069] A vaporized liquid to be analyzed is then injected into column 4 and the analysis is started. The analysis can be carried out at a constant temperature, or, alternatively, using a temperature ramp, consisting of gradually and / or incrementally raising the temperature of column 4. The power supply to the heating wire 3 is then switched off and the device cools to ambient temperature.

[0070] If a difference in thermal expansion between the support and the chromatography column 4 had occurred during the temperature rise, the device will return to its initial geometry during cooling, and the deformation of the axial slit 16 formed by the ends 12 and 13 will be reversed.

[0071] An analysis cycle can then be repeated on the same sample or on another liquid to be analyzed.

Claims

Demands

1. Heating device for a gas chromatography column (4), comprising • a support including a strip (1) of a thermally conductive material, said strip (1) being wound around an axis with two opposite ends not contiguous to form a cylinder having an axial slot (16), • and a heating wire (3), wound on said cylinder so as to form a track adapted to receive a chromatography column (4) wound in one or more layers.

2. Device according to claim 1, wherein the heating wire (3) is wound in the form of contiguous turns in a single layer around the cylinder.

3. Device according to any one of the preceding claims, wherein the strip (1) has one end folded inwards towards the inside of the cylinder on one side of the axial slot (16).

4. Device according to claim 3, comprising a temperature sensor (11), inserted in the fold on one side of the cylinder slot.

5. Device according to any one of claims 1 to 4, wherein the support comprises two flanges made of a thermally conductive material attached to the cylinder extending radially outwards from each end of the cylinder.

6. Device according to any one of claims 4 or 5, wherein at least one flange has a tab (21) that is foldable between a mounting position where the tab (21) extends radially outwards from the flange so as to allow winding of the chromatography column (4) onto the track and a holding position where the tab (21) extends substantially parallel to the axis of the cylinder so as to hold the chromatography column (4) wound onto the track.

7. Assembly comprising the device according to any one of the preceding claims and a capillary chromatography column (4) wound on the track formed by the heating wire (3).

8. Assembly according to claim 7 in its dependent relationship with claim 6, wherein the chromatography column (4) is wound in the form of contiguous turns forming at least a layer extending continuously from one flask to the other, the column (4) being held rolled up by each tab (21).

9. Method of manufacturing a heating device for a gas chromatography column (4), comprising: • supplying a strip (1) of a thermally conductive material; • winding said strip (1) around an axis with two opposite ends not contiguous so as to form a cylinder having an axial slot (16); • winding the heating wire (3) on said cylinder to form a track adapted to receive a chromatography column (4) wound in one or more layers.

10. A method according to claim 9, further comprising supplying two flanges made of a thermally conductive material, and assembling each flange to a respective end of the cylinder.

11. Method according to claim 9 or claim 10, further comprising winding a chromatography column (4) onto the track formed by the heating wire (3).

12. A method according to claim 10 in combination with claim 11, wherein at least one flange comprises a tab (21) extending radially outwards, the method further comprising, after winding the chromatography column (4) onto the track, a step of folding each tab (21) substantially parallel to an axis of the cylinder.

13. A method according to any one of claims 9-12 wherein at least one of the parts of a thermally conductive material is made of sheet metal.

14. Method of heating a chromatography column (4), comprising: • supplying an assembly according to claim 8, • connecting the heating wire (3) to an electrical source to bring said wire to a determined temperature, the chromatography column (4) being heated by conduction from the support and the heating wire (3).

15. The method according to claim 14, wherein the heating generates a difference in thermal expansion of the upper support and the chromatography column (4), the cylinder deforming by displacement of the edges (12,13) ​​of the slit to absorb said difference in thermal expansion.

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