GASCHROMATOGRAPHIC DEVICE COMPRISING AN INLET SYSTEM, A COLUMN AND A PRESSURE REDUCING MEANS

Abstract: The invention relates to a gas chromatographic device comprising at least an inlet system, a column and a pressure reducing means, said pressure reducing means being capable of reducing the pressure prevailing at the inlet of said pressure reducing means to a column outlet pressure which is essentially vacuum. Preferably, the inlet pressure of the device is 10 to 1000 kPa and the pressure prevailing at the outlet of said pressure reducing means is 0.00001 to 50 kPa (absolute pressure).

Description: Gaschromatographic device comprising an inlet system, a column and a pressure reducing means The present invention relates to a gaschromatographic device comprising an inlet system, a column and a pressure reducing means. More particularly, the present invention relates to a column for a gaschromatographic device comprising a pressure reducing means, said pressure reducing means being capable of reducing the pressure prevailing at the inlet of the column to a column outlet pressure which is essentially vacuum and said pressure reducing means being an integral part of the column. The market for routine analysis requires columns which have a long life time, have low bleed, have sufficient capacity and must also do the analysis in a short period of time. In particular the demand for systems comprising a gas chromatographic device coupled to a mass spectrometer (GC/MS) which are used for various analyses is continuously growing, in particular because these systems get more user friendly, their dimensions get smaller and their purchasing costs keep decreasing. For GC/MS the separation capacity of the column is no longer that important. Although some separation is required, long columns are generally not necessary. As the inlet pressure of the column is above atmospheric and the outlet pressure of the column is essentially vacuum because the column ends in the ionization chamber of the mass spectrometer, the columns in GC/MS systems are often very long as to provide the necessary pressure drop between the inlet and the outlet of the column. Consequently, long times are often required to perform the analyses. Although smaller bore columns having a reduced length could be used to provide the pressure drop, these columns have the disadvantage that they have a limited sample capability as well as practical problems with regard to installation, operation and elute peaks which are to fast to quantify using mass spectrometric systems. The present invention provides a solution for the problems described above. The present invention relates to a gas chromatographic device comprising at least an inlet system, a column and a pressure reducing means, said pressure reducing means being capable of reducing the pressure prevailing at the inlet of said pressure reducing means to a column outlet pressure which is essentially vacuum. The columns to be used in the gas chromatographic device according to the invention are relatively short which enables short analysis times. The eluting peaks have sufficient peak width(in seconds) to be properly integrated by todays mass spectrometric-systems. Further advantages are that under vacuum the optimal linear gas velocity increases about tenfold and that components elute from the column at lower temperatures, especially important for thermolabile and high boiling components. Additionally, the life time of the column is generally longer than that of conventional columns due to lower bleed. It is also not necessary to couple the column via a restriction to the ionization chamber of the mass spectrometer so that no leaks occur. Also favourable is that a fixed or standard inlet pressure can be used which is preferably 10 to 1000 kPa, more preferably 10 to 250 kPa. According to the present invention the pressure reducing means is such that the pressure prevailing at the outlet of said pressure reducing means is 0.00001 to 50 kPa (absolute pressure), preferably 0.01 to 20 kPa (absolute pressure). The pressure reducing means according to the invention is an integral part of the inlet system. Alternatively, it may be positioned between the inlet system and the column. It is also possible that the pressure reducing means is an integral part of the column. Integration with the column is to be realized by coupling the pressure reducing means to the column using coupling devices made of silica, quartz, glass, metal, polyimide or other organic or inorganic polymer or a bombination thereof. Alternatively, connectors can be used containing graphite, vespel, graphitized vespel type ferrules. According to the invention, the pressure reducing means is preferably an integral part of the column so that such a column can easily be installed in systems already in use. The pressure reducing means can also be positioned inside the inlet of the column as a frit, packing or by reducing the diameter of the column. The pressure reducing means has preferably a coiled tubular shape and is preferably made of silica, glass, metal, an organic polymer, an inorganic polymer or a combination thereof. More preferably, the pressure reducing means is made from silica or an organic or inorganic polymer. According to the invention, the column is also made of these materials, wherein the column has length of 0.25 to 100 m, preferably 0.5 to 25 m, an average internal diameter of 0.05 to 1.0 mm, preferably 0.25 to 0.75 and an average outer diameter of 0.2 to 1.0 mm. preferably 0.4 to 0.8 mm. According to an embodiment of the invention the pressure reducing means which is preferably an integral part of the column has the following dimensions: average internal diameter of 0.001 to 0.2 mm, preferably of 0.01 to 0.1 mm; average outer diameter of 0.2 to 0.8 mm, preferably of 0.3 to 0.6 mm; length of 1 mm to 2500 mm, preferably 10 to 1000 mm. According to another embodiment of the invention the pressure reducing means which is preferably an integral part of the column is comprised by an opening or hole having a cross section of 0.0001 to 0.1 mm, preferably 0.0005 to 0.01 mm, and a length of 0.25 to 100 mm, preferably 0.5 to 10 mm. The pressure reducing means may also be formed by a capillary having an average internal diameter of 0.1 to 5.0 mm, preferably 0.2 to 2 mm, a length of 5 to 500 mm, preferably 20 to 100 mm, wherein the capillary is preferably packed with deactivated or non-deactivated particles having an average size of 0.5 to 500 μm (micrometer), preferably 5 to 50 μm. The pressure reducing means according to the invention may be manufactured by employing micromachining technology using silicon etching/wafer technology. The pressure reducing means may be coated with chemically bonded or cross-linked liquid or solid stationary phases with an average film thickness of 0.001 to 50 micrometer, preferably 0.01 to 0.1 micrometer. The invention further relates to a column for a gas chromatographic device comprising a pressure reducing means, said pressure reducing means being capable of reducing the pressure prevailing at the inlet of the column to a column outlet pressure which is essentially vacuum and said pressure reducing means being an integral part of the column. The column has preferably a length of 0.25 to 100 m, more preferably 0.5 to 25 m, an average internal diameter of 0.05 to 1.0 mm, preferably 0.25 to 0.75 mm and an average outer diameter of 0.2 to 1.0 mm, preferably 0.4 to 0.8 mm. The column and/or the pressure reducing means are preferably made of silica, glass, metal, an organic polymer, an inorganic polymer or a combination thereof. The columns comprising the pressure restriction means or the columns comprised by the gas chromatographic devices comprising an inlet system and a pressure reducing means may have a internal surface which is deactivated with a chemical and/or physical deactivation agent. Examples of suitable deactivation agents are octamethyl tetrasiloxane, hydrosilane or of the polyethylene glycol type. These columns may additionally be coated, i.e. the internal surface thereof, with bonded and/or cross linked liquid or solid stationary phases, but also with non-bonded and/or non-crosslinked stationary phases having an average film thickness of 0.05 to 10 μm. If the columns are coated with a solid stationary phase, the average film thickness thereof is 1 to 100 μm, preferably 2 to 50 μm. The columns comprising the pressure restriction means or the columns comprised by the gas chromatographic devices comprising an inlet system and a pressure reducing means may be coated on the outside thereof with a single layer or with multiple layers of a organic polymer, e.g. polyimide, metal, salt or another polymeric or ceramic material. The invention further relates to columns comprising the pressure restriction means or the columns comprised by the gas chromatographic devices comprising an inlet system and a pressure reducing means which are winded on a cage, bunch or which are mounted on a flat disc. These columns may further comprise a silicone chip. The invention will now be illustrated by Figure 1. Figure 1 shows pressure reducing means (1), column (2) and a coupling device (4) for connecting and integrating the pressure reducing means with the column whereas arrow (3) indicates the connection to a MS-detector. Figure 1 illustrates two possible positions for the pressure reducing means (1), i.e. before or after the column (2). The column is a short wide-bore open tubular capillary column. Figure 2 shows two GC/MS-chromatograms of Polywax 655 obtained with the embodiments shown in Figure 1 (conditions: column: 10 m x 0.53 mm; stationary phase: CP-SIMDIST, film thickness: 0.17 micrometer; injection temperature: 350°C; interface temperature: 350°C; inlet pressure: 150 kPa; temperature profile: 150°C (1 min.), 20°C/min. to 400°C). Figure 2(A) shows that the C80-fraction elutes of the column at shorter retention times when compared with Figure 2(B) without a decreased resolution. Consequently, according to the invention the pressure reducing means is preferably positioned in front of the inlet of a column.

Claims: Claims 1. Gas chromatographic device comprising at least an inlet system, a column and a pressure reducing means, said pressure reducing means being capable of reducing the pressure prevailing at the inlet of said pressure reducing means to a column outlet pressure which is essentially vacuum. 2. Device according to claim 1, wherein the inlet pressure is 10 to 1000 kPa. 3. Device according to claim 1 or claim 2, wherein the pressure prevailing at the outlet of said pressure reducing means is 0.00001 to 50 kPa (absolute pressure). 4. Device according to any of claims 1 - 3, wherein the pressure reducing means is an integral part of the inlet system. 5. Device according to any of claims 1 - 3. wherein the pressure reducing means is positioned between the inlet system and the column. 6. Device according to any of claims 1 - 3. wherein the pressure reducing means is an integral part of the column. 7. Device according to any of claims 1 - 3, wherein the pressure reducing means is positioned inside the inlet of the column as a frit, packing or by reducing the diameter of the column. 8. Device according to any of claims 1 - 6, wherein the pressure reducing means is made of silica, glass, metal, an organic polymer, an inorganic polymer or a combination thereof. 9. Device according to any of claims 1 - 7. wherein the pressure reducing means has an average internal diameter of 0.001 to 0.2 mm. 10. Device according to any of claims 1 - 8, wherein the pressure reducing means has a length of 1 to 2500 mm. 1 1. Device according to any of claims 1 - 9, wherein in the pressure reducing means is packed with a packing of particles. 12. Column for a gas chromatographic device comprising a pressure reducing means, said pressure reducing means being capable of reducing the pressure prevailing at the inlet of the column to a column outlet pressure which is essentially vacuum and said pressure reducing means being an integral part of the column. 13. Column according to claim 1 1 , wherein the column has a length of 0.25 to 100 m. 14. Column according to claim 1 1 or claim 12, wherein the column has a internal diameter of 0.05 to 1.0 mm. 15. Column according to any of claims 1 1 - 13, wherein column and/or the pressure reducing means are made of silica, glass, metal, an organic polymer, an inorganic polymer or a combination thereof.

Inventors: DE NIJS RENE CORNELID MARIA, DE ZEEUW JAAP, PEENE JAN ADRIAAN, DE NIJS, RENE, CORNELID, MARIA, DE ZEEUW, JAAP, PEENE, JAN, ADRIAAN
Applicants: NIJS RENE CORNELID MARIA DE, PEENE JAN ADRIAAN, VARIAN CHROMPACK INTERNATIONAL, ZEEUW JAAP DE, DE NIJS, RENE, CORNELID, MARIA, DE ZEEUW, JAAP, PEENE, JAN, ADRIAAN, VARIAN CHROMPACK INTERNATIONAL BV
Application year: 1999
Main classification: G01N30
IPC codes: G01N30