Patent Abstract:
A gas chromatograph set of the present invention comprises a plurality of gas chromatographs and a flow passage assembly. Each of the gas chromatographs includes a column for separating sample-components, a carrier gas supply unit for supplying a carrier gas to the column and a detector for detecting eluted components from the column. The carrier gas supply unit comprises a carrier gas passage, and a flow controller unit for controlling a flow-rate that is connected to the carrier gas passage. The flow passage assembly comprises a metal plate inside which the carrier gas passages of the gas chromatographs are formed.

Full Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a gas chromatograph used for measuring component concentrations in various samples. 
   2. Description of the Related Art 
   A gas chromatograph is provided with a column for separating sample components, a carrier gas supply unit for supplying carrier gas to the column and a detector for detecting eluted components from the column, and also has an injector for injecting a sample into the carrier gas, which is placed on the upstream side of the column. 
   A flow controller unit for controlling a flow rate, which includes a valve and a flow-rate sensor, is installed in the carrier gas supply unit so that a carrier gas, supplied from a carrier gas inlet, is supplied to a column from the valve through the flow-rate sensor. 
   With respect to the carrier gas supply unit, a structure in which a carrier gas passage is formed inside a metal substrate has been proposed (see Japanese Patent Application Laid-Open No. 11-218528). In this metal substrate, only one carrier gas passage is formed. 
   In the case of using a packed column in which a filler has been filled up as the column, since a bleeding component from the packed column is large, upon a temperature-rise analysis (that is, a method in which the temperature of the packed column raises during analysis), a base line on the chromatogram fluctuates largely, affecting adversely on a quantitative analysis. For this reason, generally, two of the same packed columns are installed, and these are connected to respective detectors. Then, the fluctuations in the base line are cancelled by obtaining a difference between detection outputs of these detectors. 
   The carrier gas has been supplied to each of the packed columns from each of the corresponding carrier gas supply units. 
   However, generally, a gas chromatograph has a column oven having a temperature ranging from room temperature to about 400° C. and a sample vaporization chamber having a temperature of about 250° C., together with heat-generating parts, such as a detector. Hence, there is a temperature difference of 2 to 3° C. between the carrier gas passages of the two carrier gas supply units. 
   It has generally been known that, even if the volume flow rate of gas is constant, there is a change of 0.6% in the mass flow rate when the surrounding temperature changes by 1° C. Moreover, the temperature coefficient of the flow-rate sensor is about 0.4%/° C. For this reason, a difference in a level of 2 to 3% occurs between the carrier-gas flow rates of the two carrier gas passages due to the above-mentioned temperature difference of 2 to 3° C. Consequently, base-line fluctuations occur in the chromatogram, resulting in adverse effect on the quantitative analysis. 
   There are differences among the flow rates of carrier gases, supplied from carrier gas passages made of a plurality of flow-passage assemblies to supply gases to a plurality of packed columns due to the above-mentioned temperature difference in the passage assemblies, resulting in a base-line shift of chromatogram that affects adversely on the quantitative analysis. 
   There have been demands for a constant carrier-gas flow rate not only in an attempt to cancel base-line fluctuations by obtaining a difference between a pair of detectors, but also in an attempt to use a plurality of gas chromatographs under the same conditions. 
   Moreover, there have been the same demands in capillary columns as in packed columns. 
   SUMMARY OF THE INVENTION 
   The objective of the present invention is to make carrier gas flow rates constant in a plurality of gas chromatographs. 
   A gas chromatograph set of the present invention comprises a plurality of gas chromatographs and a flow passage assembly. Each of the gas chromatographs includes a column for separating sample-components, a carrier gas supply unit for supplying a carrier gas to the column, and a detector for detecting eluted components from the column. Each carrier gas supply unit comprises a carrier gas passage and a flow controller unit for controlling a flow-rate that is connected to the carrier gas passage. The flow passage assembly comprises a metal plate inside where the carrier gas passages of the gas chromatographs are formed. 
   In the present invention, since a plurality of carrier gas passages are formed inside the commonly-used metal plate, it is possible to eliminate a temperature difference among the carrier gas passages, and consequently to eliminate a difference in the carrier gas flow rates among the gas chromatographs. 
   Since the flow passage assembly is shared, it becomes possible to cut costs. 
   With respect to the kinds of gas chromatograph to which the present invention is suitably applied, those which use a packed column in which the filler is filled up are proposed. 
   Moreover, with respect to the usage method of a gas chromatograph to which the present invention is suitably applied, a system in which two sets of gas chromatographs are installed to make a pair, with a sample is injected into one of the gas chromatographs so that a difference of detection signals between the two detectors can be obtained, is proposed. With this system, since a difference between detection signals from the detectors of the two gas chromatographs is obtained, it becomes possible to obtain a stable base line, and consequently to carry out an accurate quantitative analysis. 
   The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTIONS OF THE DRAWINGS 
       FIG. 1  is a flow passage drawing that schematically shows one embodiment; 
       FIG. 2  is a plan view that shows a carrier gas supply unit in the embodiment; 
       FIG. 3  is a plan view that shows a positional relationship between elements such as valves and flow passages inside a substrate in the carrier gas supply unit; and 
       FIG. 4 , consisting of  FIGS. 4(A) to 4(C) , is a plan view that shows a metal plate that forms a flow passage assembly in the carrier gas supply unit. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  schematically shows one embodiment. Two sets of gas chromatographs are provided. In one of the gas chromatographs, a carrier gas supply unit, which supplies a carrier gas to a column  10 - 1  through an injection port  8 - 1 , is provided with a valve  2 - 1  that is connected to a carrier gas inlet, a flow-rate sensor  4 - 1  placed on the downstream side of the valve  2 - 1  and a pressure sensor  6 - 1 . The valve  2 - 1  is feed-back controlled based upon a detection signal from the flow-rate sensor  4 - 1  so as to fix the flow rate to a predetermined value. 
   The other gas chromatograph also has the same structure, and a carrier gas supply unit, which supplies a carrier gas to a column  10 - 2  through an injection port  8 - 2 , is provided with a valve  2 - 2  that is connected to a carrier gas inlet, a flow-rate sensor  4 - 2  placed on the downstream side of the valve  2 - 2  and a pressure sensor  6 - 2 . The valve  2 - 2  is also feed-back controlled based upon a detection signal from the flow-rate sensor  4 - 2  so as to fix the flow rate to a predetermined value. 
   Carrier gas passages of the two carrier gas supply units constitute a flow passage assembly  14  in which the respective carrier gas passages are formed inside of a common single substrate made of metal having superior heat conductivity. The valves  2 - 1  and  2 - 2 , the flow-rate sensors  4 - 1  and  4 - 2  and the pressure sensors  6 - 1  and  6 - 2  are attached to the metal substrate of the flow passage assembly  14 , and are respectively connected to the respective carrier gas passages. 
   Detectors  12 - 1  and  12 - 2 , which respectively detect eluted components, are connected to the columns  10 - 1  and  10 - 2  on the downstream side. 
   A flow controller unit is constituted by valves  2 - 1  and  2 - 2  and flow-rate sensors  4 - 1  and  4 - 2 . 
   In this gas chromatograph set, the two gas chromatographs may be used as independent gas chromatographs, respectively. Moreover, in the case of one of them being used as a reference system in an attempt to suppress fluctuations in the base line, a sample is injected into only one of the injection ports  8 - 1  and  8 - 2  so that a difference in the detection signals from the two detectors can be obtained. 
     FIGS. 2 to 4  specifically show a carrier gas supply unit in this embodiment. 
     FIG. 2  is a plan view in which carrier gas inlet connectors  16 - 1  and  16 - 2 , valves  2 - 1  and  2 - 2 , flow-rate sensors  4 - 1  and  4 - 2  and pressure sensors  6 - 1  and  6 - 2  are placed and secured onto a metal substrate of the flow passage assembly  14 . Reference numerals,  18 - 1   a  and  18 - 2   a,  respectively represent carrier gas outlets of the respective carrier gas supply units. Two holes  38 , formed on both sides of each of alignments of the carrier gas outlets  18 - 1   a  and  18 - 2   a,  are used for securing a block (not shown) that introduces a carrier gas toward the downstream side. 
   As indicated by broken lines in  FIG. 3 , the carrier gas passages are formed inside the metal substrate of the flow passage assembly  14 , and are connected to carrier gas inlet connectors  16 - 1  and  16 - 2 , valves  2 - 1  and  2 - 2 , flow-rate sensors  4 - 1  and  4 - 2  and pressure sensors  6 - 1  and  6 - 2  that are secured to the substrate, through inlet/outlet holes formed on the substrate surface. One of the carrier gas passages is connected to the carrier gas outlet  18 - 1  from the carrier gas inlet connector  16 - 1  through the flow-rate sensor  4 - 1  via the valve  2 - 1 , and the pressure sensor  6 - 1  is connected to the carrier gas passage in the middle of the passage. In the same manner, the other carrier gas passage is connected to the carrier gas outlet  18 - 2  from the carrier gas inlet connector  16 - 2  passing through the flow-rate sensor  4 - 2  via the valve  2 - 2 , and the pressure sensor  6 - 2  is connected to the carrier gas passage in the middle of the passage. 
   Referring to  FIG. 4 , the flow passage assembly  14  is explained. 
   The flow passage assembly is constituted by three metal plates, that is, an upper plate  14   a,  a middle plate  14   b  and a lower plate  14   c,  and is arranged so that the upper plate  14   a  is placed on the upper side and the lower plate  14   c  is placed on the lower side, with the middle plate  14   b  being placed in between; thus, these plates are integrally joined to one another. 
   The two carrier gas passages are formed in the middle plate  14   b  as grooves that penetrate the plate in the thickness direction. One of the carrier gas passages is provided with three flow passage grooves  22 - 1 ,  28 - 1  and  36 - 1 . One end of the flow passage groove  22 - 1  forms an inlet hole  20 - 1   b . The other end  24 - 1   b  of the flow passage groove  22 - 1  is adjacent to one end  26 - 1   b  of the flow passage groove  28 - 1 , and the valve  2 - 1  is connected between the two ends  24 - 1   b  and  26 - 1   b . The other end  30 - 1   b  of the flow passage groove  28 - 1  and an end  34 - 1   b  of a flow passage branched from the middle of the flow passage groove  28 - 1  are adjacent to one end  32 - 1   b  of the flow passage groove  36 - 1  so that the flow-rate sensor  4 - 1  is connected among the three ends  30 - 1   b ,  32 - 1   b  and  34 - 1   b . The other end of the flow passage groove  36 - 1  serves as a carrier gas outlet  18 - 1   b . The pressure sensor  6 - 1  is connected to a groove end  29 - 1   b  of a branched flow passage groove from the flow passage groove  28 - 1 . 
   In the same manner, the other carrier gas passage is provided with three flow passage grooves  22 - 2 ,  28 - 2  and  36 - 2 . One end of the flow passage groove  22 - 2  forms an inlet hole  20 - 2   b.  The other end  24 - 2   b  of the flow passage groove  22 - 2  is adjacent to one end  26 - 2   b  of the flow passage groove  28 - 2 , and the valve  2 - 2  is connected to the two ends  24 - 2   b  and  26 - 2   b  in between. The other end  30 - 2   b  of the flow passage groove  28 - 2  and an end  34 - 2   b  of a flow passage branched from the middle of the flow passage groove  28 - 2  are adjacent to one end  32 - 2   b  of the flow passage groove  36 - 2  so that the flow-rate sensor  4 - 2  is connected among the three ends  30 - 2   b,    32 - 2   b  and  34 - 2   b.  The other end of the flow passage groove  36 - 2  serves as a carrier gas outlet  18 - 2   b.  The pressure sensor  6 - 2  is connected to a groove end  29 - 2   b  of a branched flow passage groove from the flow passage groove  28 - 2 . 
   The upper plate  14   a  to be superposed on the upper face of the middle plate  14   b  is provided with through holes  20 - 1   a,    20 - 2   a,    24 - 1   a,    24 - 2   a,    30 - 1   a,    30 - 2   a,    32 - 1   a,    32 - 2   a,    18 - 1   a,    18 - 2   a,    29 - 1   a,    29 - 2   a,    34 - 1   a  and  34 - 2   a  formed therein at positions that respectively correspond to the respective ends of the flow passage grooves in the middle plate  14   b,  that is,  20 - 1   b,    20 - 2   b,    24 - 1   b,    24 - 2   b,    30 - 1   b,    30 - 2   b,    32 - 1   b,    32 - 2   b,    18 - 1   b,    18 - 2   b,    29 - 1   b,    29 - 2   b,    34 - 1   b  and  34 - 2   b,  when the upper plate  14   a  is positioned on the middle plate  14   b  so as to be superposed thereon. 
   The lower plate  14   c  to be superposed on the lower face of the middle plate  14   b  is provided with no through holes at positions corresponding to the flow passage grooves of the middle plate  14   b  in a manner so as to close the lower face side of the flow passage grooves of the middle plate  14   b.    
   The upper plate  14   a , middle plate  14   b  and lower plate  14   c  are respectively provided with through holes  38   a ,  38   b  and  38   c  for attaching the inlet connectors  16 - 1  and  16 - 2 , the valves  2 - 1  and  2 - 2 , the flow-rate sensors  4 - 1  and  4 - 2 , the pressure sensors  6 - 1  and  6 - 2 , and a block used for directing carrier gases toward the downstream side (not shown in the Figure), and these through holes  38   a ,  38   b  and  38   c  are formed at positions that are made corresponding with one another when the upper plate  14   a , the middle plate  14   b  and the lower plate  14   c  are positioned and respectively superposed. 
   The upper plate  14   a,  the middle plate  14   b  and the lower plate  14   c,  shown in  FIG. 4 , are positioned and superposed on one another, and joined to each other to form an integral substrate serving as the flow passage assembly  14  with flow passages formed therein, and the inlet connectors  16 - 1  and  16 - 2 , the valves  2 - 1  and  2 - 2 , the flow-rate sensors  4 - 1  and  4 - 2 , and the pressure sensors  6 - 1  and  6 - 2  are then attached onto the upper plate  14   a;  thus, the carrier gas supply unit is formed. 
   In accordance with this carrier gas supply unit of the present embodiment, in the first carrier gas passage, carrier gas, directed through the carrier gas inlet  16 - 1 , is directed to the valve  2 - 1  through the flow passage  22 - 1  inside the substrate of the flow passage assembly  14 , and from the valve  2 - 1 , the gas is again directed to the flow-rate sensor  4 - 1  through the flow passage  28 - 1  inside the substrate. The carrier gas that has passed through the flow-rate sensor  4 - 1  is again directed to the carrier gas outlet  18 - 1  through the flow passage  36 - 1  inside the substrate, and supplied to the injection port  8 - 1  therefrom. Moreover, the gas is also directed to the pressure sensor  6 - 1  from the middle point of the flow passage  28 - 1  so as to detect the pressure. 
   The second carrier gas passage also has the same structure, and carrier gas directed through the carrier gas inlet  16 - 2  is directed to the valve  2 - 2  through the flow passage  22 - 2  inside the substrate, and from the valve  2 - 2 , the gas is again directed to the flow-rate sensor  4 - 2  through the flow passage  28 - 2  inside the substrate. The carrier gas that has passed through the flow-rate sensor  4 - 2  is again directed to the carrier gas outlet  18 - 2  through the flow passage  36 - 2  inside the substrate, and supplied to the injection port  8 - 2  therefrom. Moreover, the gas is also directed to the pressure sensor  6 - 2  from the middle point of the flow passage  28 - 2  so as to detect the pressure. 
   In the respective carrier gas passages, the flow rates are measured by the respective flow-rate sensors  4 - 1  and  4 - 2  so that the valves  2 - 1  and  2 - 2  are feed-back controlled so as to set predetermined flow rates. 
   Since the first and second carrier gas passages are formed inside the common metal substrate of the flow passage assembly  14 , the two carrier gas passages are always maintained at the same temperature. Consequently, a sample is injected into the injection port of one of the gas chromatographs with the other chromatograph having no sample injected therein, and an analysis is carried out in this state so as to obtain a difference between the detectors of the two gas chromatographs; thus, it becomes possible to suppress fluctuations in the base line. 
   A method of manufacturing the flow passage assembly  14  will be described. 
   The metal plates  14   a,    14   b  and  14   c  are made of metal having high thermal conductivity, and preferable material examples include stainless steel and iron, with a preferable thickness in a range of 0.2 to 1 mm. 
   Onto the metal plates  14   a,    14   b  and  14   c,  the passage grooves and the through holes are formed through etching or stamping processes. The metal plates  14   a,    14   b  and  14   c  are joined to one another through pressure welding. Specifically, the pressure welding refers to a process in which metal plates are pressed so as to be integrally welded by applying a pressure of about 10 MPa in a high-temperature atmosphere of no less than 800° C. 
   Although the embodiments have exemplified a structure in which carrier gas flow passages of two gas chromatographs are formed by a common flow passage assembly, carrier gas flow passages of three or more gas chromatographs may be formed by a common flow passage assembly. 
   The gas chromatograph of the present invention can be utilized to quantity-measure component concentrations in a sample in various fields, such as chemical, biochemical, environmental and medical fields. 
   Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.

Technology Classification (CPC): 6