WO1994004915A1

WO1994004915A1 - Gas chromatograph with a separating column, preferably in the form of a capillary tube, and a device for heating the column

Info

Publication number: WO1994004915A1
Application number: PCT/EP1993/002169
Authority: WO
Inventors: Gerhard Krebs
Original assignee: Gerhard Krebs
Priority date: 1992-08-20
Filing date: 1993-08-16
Publication date: 1994-03-03
Also published as: DE4227509C1

Abstract

A gas chromatograph with a separating column, preferably in the form of a capillary tube, and a device for heating the column, in which the separating column (1) or a bearer (2) accepting the column (1) is arranged at a radial distance around the core (11) of a transformer (10) to form a secondary circuit.

Description

Gas chromatograph with a separation column - preferably designed as a capillary - and a device for heating the column.

DESCRIPTION

The invention relates to a gas chromatograph with a separation column - preferably designed as a capillary - and a device for heating the column.

A gas chromatograph is a laboratory device for performing gas chromatography. This gas chromatography is a method for the chemical analysis of complex mixtures. The sample mixture is evaporated and transported by means of a carrier gas stream through a thin capillary - the so-called column. Due to physico-chemical differences between the components of the mixture, the rate of migration through the column is different. This causes the mixture to separate during the passage of the column. At the column exit, the individual components can then be detected qualitatively by determining the residence time in the column and quantitatively by determining the size of a detector signal.

The rate of migration of the components through the column is significantly affected by the column temperature. In order to shorten the analysis time or to make slowly migrating components accessible to gas chromatography in the first place, the column is usually heated.

In the prior art, gas chromatographs are known in which the column is heated by a thermostatted air bath in an insulated housing. The

REPLACEMENT LEAF Like a hair dryer, hot air is generated with a heating coil by electrical resistance heating and is evenly distributed and kept in circulation by means of a fan in the housing. However, temporal and spatial fluctuations in the column temperature cannot be completely avoided. A reduction in the separation efficiency of the column and a deterioration in the reproducibility of the chromatograms are disadvantageous consequences. This makes automatic evaluation more difficult and requires reworking or repetition of the analysis process. Attempts have also been made to form the column with an electrically conductive coating and to heat it by means of electrical resistance heating. Difficulties arise with the coating, however, if it is not applied to the outer wall of the column with the required uniformity. The heating can have considerable differences in places. This also gives rise to the aforementioned difficulties and disadvantages.

The invention is based on the object of specifying a gas chromatograph with a separating column designed as a capillary and a device for heating the column, which has been improved and developed so extensively with respect to the heating device that the disadvantages, difficulties and technical limits mentioned above are overcome become.

The problem is solved in a gas chromatograph of the type mentioned in the preamble of claim 1 with the invention in that the separating column or a support receiving the separating column is arranged at a radial distance around the core of a transformer to form a secondary circuit.

In this embodiment, the separation column or a support receiving the separation column simultaneously represents the secondary

REPLACEMENT LEAF circuit of the transformer and is heated inductively when the primary circuit is excited. Advantageously, the inductive heating can be set and controlled sensitively, it is also uncomplicated and can be implemented with very economical means.

One embodiment provides that the column made of electrically non-conductive material such as e.g. Quartz exists and is wound in turns around a metal tube that forms the carrier and has a small, constant material thickness. This metal tube represents the secondary circuit of the transformer in the manner of a short-circuit winding and is inductively heated to a greater or lesser extent in accordance with the input power in the primary circuit of the transformer. Due to the high thermal conductivity of the metal, it is heated uniformly over its entire surface and evenly releases the temperature through thermal contact and radiation to the column laid around in turns. At least one temperature sensor is arranged on the metal pipe for sensitive monitoring of the temperature. An advantageous heat transfer between the metal tube and the column arises from the fact that the turns of the column are wrapped around the metal tube to form mutual contact surfaces.

One embodiment of the invention provides that the column consists of electrically conductive material or is coated accordingly and is arranged around the transformer core to form a secondary winding. The required heat is generated by induction directly inside the column. It is provided that the column forming the secondary winding of the transformer is placed around it in a regular arrangement with a constant radial distance from the transformer core.

REPLACEMENT LEAF In this embodiment, too, it is provided that at least one temperature sensor is arranged on the secondary winding.

One embodiment provides that the metal tube is designed with a double shell and the column is arranged between an inner tube shell and an outer tube shell. A particularly good and uniform heat transfer from the tube shells to the column is achieved here.

One embodiment provides that the winding formed by the column is covered with insulation. This insulation ensures uniform heat distribution over the cross section of the column, which ensures a particularly good analysis result. Both the inside of the metal tube and the outside of the winding on the metal tube can be covered with insulation.

Further details, features and advantages of the invention result from the following explanation of an exemplary embodiment shown schematically in the drawing. The drawings show in detail:

Figure 1: A side view of the chromatograph; FIG. 2 shows a section of the chromatograph along section line II-II in FIG. 1.

The chromatograph shown in FIG. 1 has a column 1 designed as a capillary. Its input 4 has an injector (not shown) and its output 5 has a detector (also not shown). In order to carry out gas chromatography, which is known to be a method for the chemical analysis of complex mixtures, a sample mixture is evaporated and passed through the capillary 1 by means of a carrier gas stream 15 - the so-called

REPLACEMENT LEAF Pillar - transported. During the passage of the column, the mixture is separated in accordance with different migration speeds of the individual mixture components. At the column exit 5, the individual components can then be detected qualitatively by determining the residence time in column 1 and quantitatively by determining the size of the signal from the detector at the exit 5. The rate of migration of the components depends to a considerable extent on the column temperature. In order to shorten the analysis time or to make slowly moving components accessible to gas chromatography in the first place, it is known that the column 1 must be heated. The design of the heating device of the chromatograph according to the invention consists in that the separation column 1 or a support 2 receiving the separation column 1 is arranged at a radial distance around the core 11 of a transformer 10 to form a secondary circuit.

In the embodiment chosen as an example in FIG. 1, the column 1 consists of electrically non-conductive material such as Quartz and is wound in windings 20 around a metal tube 2 which forms the carrier and has a comparatively small, constant material thickness. A metal tube 2, at least one temperature sensor 3 is arranged. A plurality of temperature sensors 3 can preferably be arranged and connected in series, for example, from which a very exact indication of the inductively generated temperature of the carrier tube 2 can then be determined.

For the function of the device according to the invention for heating the separation column 1, it is necessary that the windings 20 of the capillary 1 are wrapped around the metal tube 2 with the formation of mutual contact surfaces. A good heat transfer is created by the body contact between the windings 20 and the metal tube 2, whereby also

REPLACEMENT LEAF additional heat is transmitted by radiation from the metal tube 2 to the windings 20 of the column 1.

In the example shown in FIGS. 1 and 2, it is assumed that the separating column 1 consists of electrically non-conductive material, for example quartz, and consequently it cannot itself be heated inductively. Therefore, a metallic carrier in the form of the tube 2 is required, which is the secondary circuit of the transformer 10. Its primary circuit or primary winding 12 is connected in a known manner to an alternating current source. However, it may also be the case that the column 1 consists of electrically conductive or appropriately coated material. In this case, the column 1 can be arranged directly, even with the formation of a secondary winding, in windings 20 around the transformer core 11, with the omission of a metallic carrier 2. When an induction field was generated, heat would then be generated directly in the winding 20, the control of which could be carried out by at least one temperature sensor 3 and preferably several temperature sensors. In the case of such an arrangement, which likewise falls under the invention, with an electrically conductive column, it is necessary for the column 1 forming the secondary winding 20 of the transformer 10 to be arranged in a regular arrangement with a constant radial distance from the transformer core 11 around it is wrapped around. To achieve a short-circuit current, the injector side 4 must be electrically conductively connected to the detector side 5.

FIG. 2 shows the gas chromatograph with the heating device according to the invention in the section of the plane II-II in FIG. 1. The separating column 1, which in the assumed example consists of a non-conductive material such as quartz, is wound in windings 20 around the carrier 2, which is formed by a metal tube made of brass, aluminum or the like, for example. The transformer 10 shown in section

REPLACEMENT LEAF with the core 11 has the primary winding 12 and as a secondary short-circuit winding the metal tube 2. According to one embodiment of the invention, the metal tube 2 can be double-shelled and the column 1a can be arranged between an inner tube shell 2a and an outer tube shell 2b. This configuration creates a particularly intimate thermal contact between the carrier 2 and the windings 20 of the column 1.

In another embodiment, use can advantageously be made of the measure that the winding 20a formed by the separation column 1 is covered with insulation 8. This insulation 8 both prevents heat loss and ensures a uniform heat distribution over the circumference and the width of the winding 20a. It is particularly advantageous if both the inside 2a of the metal tube 2 and the outside 20b of the winding 20a are covered with insulation 8a, 8b. Both the double-shell design of the metal tube 2a, 2b on the left-hand side of FIG. 2 and the implementation of a double insulating layer 8a, 8b on the right-hand side of FIG. 2 show how these configurations can be implemented on a case-by-case basis.

By using the heating according to the invention, the energy consumption for the column heating, which is estimated at about 2000 watts in the prior art, can be reduced to 10% or less of this power if the system is dimensioned accordingly. As a result, air conditioning of the measuring rooms can also be omitted. This is particularly the case if, in accordance with the last-mentioned proposals, the metal tube is constructed with two shells and is covered with an inner or outer insulating layer 8a, 8b. In addition, the invention allows a smaller and lighter structure of the gas chromatograph, so that the mobile use of such a device is made considerably easier.

REPLACEMENT LEAF With the help of the concept of a device for direct heating of the separation column 1 proposed by the invention, extremely thin capillaries, for example with an inner diameter of <0.2 mm, can be used as separation columns. Such extremely thin columns have correspondingly high separation capacities and in this way not only enable very fast but also meaningful analyzes. What is essential for this is a high-precision, low-inertia temperature control of the gas chromatograph, as is not possible with conventional devices when equipped with indirect heating, for example through heated air. The separation performance of the column, which is improved with the invention, and better reproducibility of the results result in an advantageous reduction in the costs for gas chromatographic analyzes, since the average time for recording and evaluating a chromatogram is considerably shortened. The automatic evaluation also plays a significant role in this. A lowering of the detection limits in trace analysis is also made possible by an improved signal / noise ratio.

The advantages achieved with the invention improve the analysis quality in environmental technology and - due to the energy savings and the improved results in trace analysis - make a direct contribution to environmental protection.

In this respect, the invention results in an ideal solution to the problem set forth above.

REPLACEMENT LEAF

Claims

PATENT CLAIMS

1. Gas chromatograph with a separation column - preferably designed as a capillary - and a device for heating the column, characterized in that the separation column (1) or a support (2) receiving the separation column (1) at radial distance around the core ( 11) a transformer (10) is arranged around to form a secondary circuit.

2. Gas chromatograph according to claim 1, characterized gekennzeich¬ net that the column (1) made of electrically non-conductive material such as e.g. Quartz exists and is wound in windings (20) around a metal tube (2) forming the carrier and having a small, constant material thickness.

3. Gas chromatograph according to claims 1 and 2, characterized in that at least one temperature sensor (3) is arranged on the metal tube (2).

4. Gas chromatograph according to one of claims 1 to 3, characterized in that the windings (20) of the column (1) are placed around the metal tube (2) to form mutual contact surfaces.

5. Gas chromatograph according to claim 1, characterized gekennzeich¬ net that the column (1) consists of electrically conductive material or is coated with it, and is arranged to form a secondary winding around the transformer core (11) around.

REPLACEMENT LEAF

6. Gas chromatograph according to claim 5, characterized gekennzeich¬ net that the secondary winding (20) of the transformer

(10) forming column (1) in a regular arrangement with a constant radial distance from the transformer core

(11) is arranged around it.

7. Gas chromatograph according to claims 5 and 6, characterized in that at least one temperature sensor is arranged on the secondary winding (20).

8. Gas chromatograph according to one of claims 1 to 7, characterized in that the metal tube (2) is double-shelled and the column (la) is arranged between an inner tube shell (2a) and an outer tube shell (2b).

9. Gas chromatograph according to one of claims 1 to 8, characterized in that the winding (20a) formed by the column (1) is covered with thermal insulation (8).

10. Gas chromatograph according to one of claims 1 to 8, characterized in that both the inside (2a) of the metal tube (2) and the outside (20b) of the Säulen¬ winding (20) with thermal insulation (8a), ( 8b) are covered.

REPLACEMENT LEAF