Gas chromatograph/mass spectrometer systems

0001The present invention relates to gas chromatograph/mass spectrometer systems.

0002A detector of a gas chromatograph (GC) continuously measures a specific physical property of the gas effluent from the column and draws a chromatogram representing the change in the specific physical property. A thermal conductivity detector (TCD) or a hydrogen flame ionization detector (FID) is typically used as a detector of a gas chromatograph system. Constituents of a sample are measured qualitatively based on the time (retention time) and quantitatively based on the height (or area) of each peak in the chromatogram.

0003A gas chromatograph/mass spectrometer (GC/MS), on the other hand, carries out a mass spectrometric analysis for each constituent of the sample separated by the column with a mass spectrometer (MS) and thus enables highly sensitive and accurate identification of each constituent.

0004Since, in many cases, a gas chromatograph requires temperature control of the column, the column is placed in an oven. Thus the casing of a gas chromatograph unit is generally large enough to accommodate an oven. In a conventional gas chromatograph system that uses a normal detector such as the TCD or FID, the detector is typically mounted on the top of the casing of the gas chromatograph unit, and therefore, as shown in Fig. 5, a sample inlet 62 and a sample outlet 63 (which is to be connected to the detector) are arranged on the top of the casing 61.

0005A mass spectrometer unit, on the other hand, occupies a larger space than the normal detectors do. Thus, in a conventional gas chromatograph/mass spectrometer system, as shown in Fig. 3, a mass spectrometer unit 52 is placed at a side of the casing of the gas chromatograph unit 51. This requires a modification to the normal configuration of the column and the sample outlet in the casing of a gas chromatograph unit 51, which prevents standardization of gas chromatograph units and increases the cost. In usage also, an additional plan area (table-top or floor space) is necessary for the mass spectrometer unit 52 besides that for the casing of the gas chromatograph unit 51, whereas a normal detector does not require such an additional area because it is mounted on the top of the casing as described above. The irregular configuration of a conventional gas chromatograph system with a mass spectrometer unit thus prevents consistent arrangement of gas chromatograph units and lowers the efficiency of space utility in normally narrow laboratories or the like.

0006According to the invention there is provided a gas chromatograph/mass spectrometer system which is characterized by a configuration in which a mass spectrometer unit is mounted on the top of a casing of a gas chromatograph unit.

0007A preferred embodiment of the invention described hereinbelow enables a standardization of the structure of a gas chromatograph unit whether it is coupled with a normal detector or it is coupled with a mass spectrometer unit. The standardization provides simplified manufacturing and handling and considerably reduces the manufacturing cost. The preferred embodiment also provides a gas chromatograph/mass spectrometer system that requires a smaller plan area (table-top or floor space) when it is installed or when it is used.

0008In the system of the preferred embodiment, a sample gas outlet of the gas chromatograph unit is disposed in the top of the casing of the gas chromatograph unit, whereas a sample gas inlet of the mass spectrometer unit is disposed in the bottom of the mass spectrometer unit. When the mass spectrometer unit is mounted on the top of the casing of the gas chromatograph unit, the sample gas outlet is connected to the sample gas inlet of the mass spectrometer unit, forming a minimum path between a column in the gas chromatograph unit and the mass spectrometer unit. When a gas chromatograph analysis is conducted, a constituent of the sample gas separated by the column placed in an oven (which is housed in the casing of the gas chromatograph unit) flows through the minimized path and comes into the mass spectrometer unit for a mass spectrometric analysis, which prevents dispersion of the constituent in the carrier gas and maintains the sharp peaks of the chromatogram.

0009Since, in the gas chromatograph/mass spectrometer system of the preferred embodiment, the mass spectrometer unit is mounted on the top of the gas chromatograph unit, the configuration of the sample gas outlet, the column and other components of the gas chromatograph unit inside of the casing can be set in common with that of a conventional gas chromatograph unit coupled with a normal detector. This enables the structure of the gas chromatograph unit to be substantially identical with that of the conventional gas chromatograph system with a normal detector, which simplifies the manufacturing and handling lines and reduces the manufacturing cost considerably. Since the plan area (table-top or floor space) needed to install the mass spectrometer unit is mostly comprised in the installation area of the gas chromatograph unit, the preferred gas chromatograph/mass spectrometer system can be installed even in narrow laboratories. The small installation area allows other analytical apparatuses being installed as close neighbors, which enables a prompt analysis of a rapidly degradable sample in various aspects.

0010In the preferred embodiment of the invention, terminals for a power line, control and detection signal lines, and other necessary electrical lines of both the gas chromatograph unit and the mass spectrometer unit may be arranged at corresponding positions of the upper and the lower units. These terminals are respectively connected with each other, manually or automatically, when the mass spectrometer unit is mounted on the top of the casing of the gas chromatograph unit. This structure allows a single power source unit and a single operation panel (which usually includes a keyboard and a display) to be disposed in either one of the units. The user can control the whole system including both the gas chromatograph unit and the mass spectrometer unit and can analyze data through the operation of the control panel provided to either one of the units.

0011The foregoing configuration of the gas chromatograph unit and the mass spectrometer unit allows the following structure of the mass spectrometer unit. The casing of the mass spectrometer unit is composed of a flat base plate and an air-tight enclosing concave cover. All the openings of the mass spectrometer unit, such as the sample gas inlet, electricity conduit, etc., necessary to connect to the gas chromatograph unit are made in the base plate, and there is no opening in the enclosing cover. Thus, the enclosing cover is easy to manufacture and the manufacturing cost is reduced. Another advantage of the structure is that maintenance of the components inside of the mass spectrometer unit is facilitated because they stand open on the base plate and are easily accessible when the enclosing cover is removed. The casing of conventional gas chromatographs, on the other hand, is composed of a box housing having several openings and a flat cover. In this case, the box housing is difficult to manufacture and the maintenance of the inside of the mass spectrometer unit is troublesome because the components are surrounded by the walls of the box housing.

0012The invention will now be further described, by way of illustrative and nonlimiting example, with reference to the accompanying drawings, in which: <ul id="ul0001" list-style="none" compact="compact"><li>Figs. 1A and 1B are a side view and a cross-sectional view, respectively, of a gas chromatograph/mass spectrometer system embodying the present invention;</li><li>Fig. 2 is a perspective view of a mass spectrometer unit of the gas chromatograph/mass spectrometer system of the embodiment with an enclosing cover raised;</li><li>Fig. 3 is a side view of a conventional gas chromatograph/mass spectrometer with an inside view of a mass spectrometer unit;</li><li>Fig. 4 is a perspective view of a mass spectrometer unit of a conventional gas chromatograph/mass spectrometer system with a flat cover raised; and</li><li>Fig. 5 is a perspective view of a casing of gas chromatograph unit.</li></ul>

0013A gas chromatograph/mass spectrometer embodying the present invention is described with reference to Figs. 1A, 1B and 2. A gas chromatograph/mass spectrometer system 10 of the present embodiment includes a gas chromatograph unit 11 and a mass spectrometer unit 12. As shown in Fig. 1B, the gas chromatograph unit 11 includes a capillary column 20 (or sometimes a plurality of columns), a heater 22 and a fan 23 for heating the capillary column 20, and a thermal insulation member 24 surrounding the heater 22, fan 23 and column 20. Thus the inner space of the casing of the gas chromatograph unit 11 is mostly occupied by an oven surrounded by the thermal insulation member 24. A small electric circuit rack 25 including a power source unit and a control unit for the gas chromatograph unit 11 and the mass spectrometer unit 12 is also provided in the casing of the gas chromatograph unit 11.

0014Referring to Fig. 1A, the mass spectrometer unit 12 includes an ion source 39, a quadrupole unit 40, and an ion detector 41 (hereinafter collectively referred to as mass spectrometer members). The mass spectrometer unit 12 is mounted on the top of the gas chromatograph unit 11, and they are connected to each other via a sample flow conduit 13 passing through the top of the casing of the gas chromatograph unit 11 and the bottom of the mass spectrometer unit 12. A vacuum pump (a turbo-molecular pump, for example) 15 is fixed via an exhaust pipe 16 to the bottom of the mass spectrometer unit 12 at the end opposite to the sample flow conduit 13. A sample inlet 18 for providing a sample gas to the chromatographic column 20 is placed in the top face of the gas chromatograph unit 11, and an operation panel 17 is provided in a side face of the gas chromatograph unit 11. Detailed structure of the mass spectrometer unit 12 will be described later.

0015In a conventional gas chromatograph/mass spectrometer system with the mass spectrometer unit 52 attached at the side (see Fig. 3), the sample gas outlet should be disposed in the side face of the casing in order to minimize the travel distance of the gas effluent from the column to the mass spectrometer unit and to avoid dispersion in the travel. This necessitates a different design of the gas chromatograph unit 51 from that of a conventional gas chromatograph unit coupled with a normal detector. In the gas chromatograph/mass spectrometer system 10 of the present embodiment having the structure described above, however, a gas chromatograph unit designed for a conventional gas chromatograph system can be used.

0016Since the mass spectrometer unit 12 is mounted on the top of the gas chromatograph unit 11, no additional table-top or floor space is substantially needed besides that for the gas chromatograph unit 11. This provides an efficient use of a narrow table-top or laboratory floor, and enables other analytical apparatuses placed in close neighbors.

0017Another feature of the gas chromatograph/mass spectrometer system of the present embodiment is that the casing of the mass spectrometer unit 12 is composed of a planar base plate 31 and a bathtub-shaped enclosing cover 38, as shown in Fig. 2. The mass spectrometer members (the ion source 39, the quadrupole unit 40, the ion detector 41, etc.) are fixed on the base plate 31 and all the openings are formed in the base plate 31. In particular, the sample gas inlet 32 is formed in the base plate 31 immediately below the ion source 39. The vacuum port 34 is formed in a vacant space of the base plate 31. The sample gas inlet 32 connects with the sample flow conduit 13, and the vacuum port 34 with the exhaust pipe 16. Electricity conduits 36 and 37 are formed in the vicinity of the quadrupole unit 40 and the ion detector 41, wherein a feed-through unit with multiple conducting pins is fixed air-tightly in every electricity conduit 36 and 37. Driving voltages to the ion source 39, an ion lens, the quadrupole unit 40, etc. are applied via the feed-through unit in the electricity conduit 36, whereas detection signal from the ion detector 41 is sent to the control unit in the gas chromatograph unit 11 via the feed-through unit of the other electricity conduit 37. Thus the operation of the whole gas chromatograph/mass spectrometer system 10 including the gas chromatograph unit 11 and the mass spectrometer unit 12 can be done solely on the operation panel 17.

0018The control unit (and/or the power source unit) for the mass spectrometer unit 12 may be provided separately from that for the gas chromatograph unit 11: it may be placed near the top of the casing of the gas chromatograph unit or it can be attached to the casing of the mass spectrometer unit 12.

0019A groove 42 is formed along the ends of the base plate 31, and an O-ring 43 is fitted in the groove 42, whereby the enclosing cover 38 is air-tightly sealed to the base plate 31.

0020In a mass spectrometer unit of a conventional gas chromatograph/mass spectrometer system as shown in Fig. 4, mass spectrometer members are placed in a casing composed of a box housing 54 and a flat cover 55. The openings such as a sample gas inlet 56, an electricity conduit 57, and a vacuum port (not shown in the drawing but provided in the bottom face of the box housing 54) are arranged in several faces of the box housing 54. Thus the box housing is rather complicated and it requires time- and labor-consuming process to manufacture it, which naturally caused a high manufacturing cost. Another problem about the conventional mass spectrometer casing is the difficulty in the maintenance of the mass spectrometer members 53 because they are accommodated in the narrow box housing 54.

0021In the mass spectrometer unit 12 of the present embodiment, on the other hand, the spectrometer members are placed on the flat base plate, and all the openings such as the electricity conduits 36 and 37, the vacuum port 34, etc. are formed in the base plate 31. Thus the enclosing cover 38 needs no openings, which thereby can be easily manufactured. When the enclosing cover 38 is removed, the mass spectrometer members stand open and are accessible freely from any direction, which facilitates the maintenance.