JP4228963B2 - Gas analyzer - Google Patents

Description

  The present invention relates to a gas analyzer such as a gas chromatograph, and more particularly to a sample concentrator installed in a stage preceding an analysis unit in such a gas analyzer.

  Conventionally, in gas chromatographs, a sample concentrator for increasing the concentration of a sample component is installed as a pretreatment device in front of a capillary column for separating a sample component (see Patent Document 1, etc.), or the selectivity of a sample component is increased. There is a case where a focusing unit for increasing the height is installed (see Patent Document 2 or the like). In general, when such sample concentration or focusing (clario focusing) is performed, a so-called heat desorption method (thermal desorption) is often used. In the thermal desorption method, when the sample gas is allowed to flow through the collection part for collecting the sample component, the sample part is condensed by cooling the collection part and trapped in the collection part, and then the carrier gas is supplied to the collection part. The sample components trapped in the collecting part are vaporized at a stretch by performing rapid heating while flowing the gas, and the sample components are put on a carrier gas and sent to the subsequent stage. Hereinafter, a sample concentrating device and a focusing device using such a heat desorption method will be collectively referred to as a sample concentrating device.

  By providing the sample concentrator as described above at the front stage of the chromatographic column, even if the sample component contained in the original sample gas is very small, it can be concentrated to increase the concentration and send it to the column. Therefore, the effect that the detection sensitivity is improved can be obtained.

Japanese Patent No. 3006488 Japanese Patent Laid-Open No. 5-126817

  In a gas chromatograph, various sample components are temporally separated when passing through a column, and the sample components coming out of the column are sequentially detected by a detector. Therefore, the separation performance of the components is a very important factor for the gas chromatograph. Although the separation performance depends on the type of column, etc., in a gas chromatograph equipped with a sample concentrator as described above, if various sample components are preliminarily separated in the sample concentrator, Separation of components becomes easier, and improvement in analysis accuracy can be expected.

  The present invention has been made in view of these points, and an object of the present invention is to satisfactorily separate a plurality of sample components having close polarities and boiling points in the process of adsorption / desorption of sample components. An object of the present invention is to provide a gas analyzer equipped with a sample concentrating device that can be fed into a gas.

The present invention, which has been made to solve the above problems, uses adsorption / desorption of sample components by cooling / heating before the analysis unit for analyzing the components in the sample gas to be analyzed. In the gas analyzer provided with the sample concentration unit for increasing the component concentration, the sample concentration unit includes:
a) collection means provided to extend in the flow direction of the sample gas in order to collect the sample components contained in the flowing sample gas;
b) a cooling means for cooling the collection means so as to produce a temperature distribution in the flow direction of the sample gas when the sample component is adsorbed on the collection means;
c) When the sample component adsorbed on the collection means is heated and desorbed and sent to the analysis unit, the temperature increase rate with respect to the portion that is relatively low temperature by the cooling means is relatively high. Heating means for heating the collecting means so as to produce a gradient of the temperature rise rate that is greater than the temperature rise rate for the part being present;
The cooling means is cooled so that a temperature distribution is generated such that the temperature decreases as it goes from the upstream side to the downstream side of the collection means, and the heating means is upstream of the collection means on the upstream side. It is characterized by heating so that the temperature rise is faster than that .

While flowing the sample gas to the collecting means, said by cooling means, when the cooling from the upstream side so that the temperature distribution where the temperature is lowered toward the downstream side results in collecting means, contained in the sample gas Among various components, the component with the lower boiling point is adsorbed at the downstream side, that is, the position near the outlet end of the collecting means, and the component with the higher boiling point is adsorbed at the upstream side, that is, near the inlet end of the collecting means. Will be. That is, components having different boiling points are adsorbed at different sites along the extending direction of the collecting means.

  Next, at the time of heat desorption, the carrier means such as an inert gas is allowed to flow through the collection means in which the sample components are adsorbed in this way, while the heating means causes the temperature downstream from the collection means to be higher than the upstream side. Heating is done so that the rise is faster. Assuming that the temperature of the entire collecting means is uniform, the lower boiling point component desorbs from the collecting means faster in time. Here, however, the low boiling point component is not adsorbed. Since the temperature rise is faster at the portion closer to the outlet end of the collecting means, the time lag between the vaporization of the low-boiling component and the vaporization of the high-boiling component is further increased. In addition to this, since the low boiling point component is close to the outlet end of the collecting means, the time difference between the low boiling point component and the high boiling point component is as follows. It gets even bigger. In other words, low-boiling components reach the analysis section in a short time after the start of heating, and high-boiling components reach the analysis section with a considerable delay, and the components are separated well due to differences in boiling points. Can do.

  As described above, according to the gas analyzer of the present invention, a plurality of sample components can be appropriately separated in the sample concentrating unit according to the difference in boiling points and then introduced into the analyzing unit. In addition, when the sample component is further separated and detected by the analyzer, the overall separation characteristics can be greatly improved, and sample components that have been difficult to separate in the past can be clearly separated. Can do. This improves the accuracy of the analysis. In addition to a gas chromatograph, for example, a gas analyzer that uses a gas sensor or the like can further improve the gas identification by separating sample components in advance and introducing them into the gas sensor.

  Hereinafter, a gas chromatograph which is an embodiment of a gas analyzer according to the present invention will be described with reference to the drawings. FIG. 1 is an overall configuration diagram centering on the gas flow path of the gas chromatograph of this embodiment, and FIG. 2 is a configuration diagram (a), (b) of the main part of the sample concentration section of the gas chromatograph in this embodiment, and its operation. It is explanatory drawing (c), (d), (e) which shows this.

  As shown in FIG. 1, the gas chromatograph of the present embodiment is roughly divided into a sample introduction unit 10, a sample concentration unit 20, and an analysis unit 30, and the sample introduction unit 10 includes a hexagonal valve 11 and a measuring tube 12. The sample concentration unit 20 includes a collection unit 21, valves 26 and 29, and a heating current supply unit 27, and the analysis unit 30 includes a column oven 31, a capillary column 32, and a detector 33. Further, a control unit 40 is provided to control the whole.

  First, the overall operation of this gas chromatograph will be described. In the sample introduction unit 10, the hexagonal valve 11 is connected under the control of the control unit 40 in a connection state indicated by a solid line in FIG. 1 (hereinafter referred to as a state S 1) or a connection state indicated by a dotted line (hereinafter referred to as a state S 2). Or alternatively. In the state S 1, the carrier gas flows through the hexagonal valve 11 to the sample concentration unit 20, while the sample gas passes through the measuring tube 12 by the hexagonal valve 11. As a result, a predetermined amount of sample gas is held in the measuring tube 12. When the hexagonal valve 11 is switched from the state S1 to the state S2, the carrier gas flows through the measuring tube 12 to the sample concentrating unit 20 by the hexagonal valve 11. Therefore, the sample gas previously held in the measuring tube 12 is pushed by the carrier gas and sent to the sample concentrating unit 20. When the sample gas is sent from the sample introduction unit 10, the collection unit 21 traps various components in the sample gas in the sample concentration unit 20. At this time, the valve 29 is switched to the discharge side, and the sample gas after the component is adsorbed is discharged. At this time, the carrier gas is caused to flow through the column 32 by the valve 29.

  When introducing a sample gas (a gas containing a concentrated sample component) into the column 32, the collection unit 21 is connected to the column 32 by the valve 29, and the collection unit 21 vaporizes the sample component and places it on the carrier gas. The sample components are fed into the column 32. In the column 32, the sample components are separated while the sample gas passes through, and the sample components emitted from the column 32 are sequentially detected by the detector 33.

  Next, the configuration and operation of the sample concentrating unit 20 which is a feature of the present embodiment will be described in detail with reference to FIG. 2A is a schematic configuration diagram of the collection unit 21, and FIG. 2B is a cross-sectional view taken along the line a-a 'in FIG. The collection unit 21 includes a collection tube 22 as a collection means in the present invention, a refrigerant conduit 23 that extends in parallel with the outer surface of the collection tube 22 in a range indicated by A in FIG. Similarly, the heater 24 wound around the refrigerant conduit 23 and the collection tube 22 in the range A is included. As the collection tube 22, various forms such as, for example, a hollow tube coated with an adsorbent and a hollow tube filled with an appropriate adsorbent are conceivable, and sample components to be analyzed are included. It is preferable to select an appropriate one according to the type of the material. A refrigerant such as liquid nitrogen is introduced into the refrigerant conduit 23 from the right side, that is, from the downstream side of the sample gas. Further, the heater 24 is a uniform heating element, and the winding interval is narrowed in the right direction in FIG. 2A, that is, from the upstream side to the downstream side of the sample gas. Although not shown, a temperature sensor for detecting the temperature is installed at an appropriate position.

  When adsorbing the sample component to the collection tube 22, the sample gas is flowed from the left to the right in the collection tube 22, the valve 26 is opened, and the refrigerant is flowed to the refrigerant conduit 23 to collect the sample tube. Cool 22. The collection tube 22 exchanges heat with the refrigerant through the refrigerant conduit 23, and the temperature of the refrigerant gradually increases according to the flow. Therefore, the temperature of the collection tube 22 is higher on the upstream side of the refrigerant flow, that is, on the downstream side of the sample gas flow. A temperature gradient is formed such that the temperature is low and the temperature increases toward the upstream side of the sample gas. That is, as shown in FIG. 2 (c), since a temperature gradient exists in the collection tube 22 in the direction in which the sample gas passes, among the various components contained in the sample gas, the lower boiling point compound advances to the front and is collected. The relatively high boiling point compound adsorbed by the collecting tube 22 is adsorbed by the collecting tube 22 on the near side. In this way, as shown in FIG. 2D, the lower boiling point compound is adsorbed to the right side of the collection tube 22, that is, closer to the outlet end.

  After the sample components are sufficiently adsorbed to the collection tube 22 as described above, a carrier gas is passed through the collection tube 22, and the collection tube 22 is heated at a predetermined timing to collect the sample components. Remove from. At this time, a heating current is supplied from the heating current supply unit 27 to the heater 24. As described above, since the winding interval of the heater 24 is narrower toward the downstream side of the sample gas, the unit area of the collection tube 22 is closer to the downstream side. The amount of heat supplied per hit is large and heating is fast. That is, the temperature increase rate of the collecting tube 22 during heating has a gradient as shown in FIG. Therefore, even if the initial temperature before heating of the collection tube 22 is uniform, the time required to reach the target heating temperature is shorter on the downstream side of the sample gas, and the target heating is delayed on the upstream side from the downstream side. Reach temperature. As described above, since the sample components originally adsorbed on the downstream side have a low boiling point, even if the entire collection tube 22 has the same temperature rise, the sample components located on the downstream side are collected in the collection tube 22. It should be removed quickly. In addition, since the temperature rises rapidly on the downstream side in this configuration, the difference in desorption time between the low boiling point sample component located on the downstream side and the high boiling point sample component located on the upstream side is further widened. .

  The sample component thus desorbed from the collection tube 22 is introduced into the column 32 along with the carrier gas flow, but the time difference between the low boiling point component and the high boiling point component is further increased in view of the time to reach the column 32. Further spread. This is because the lower boiling point component is adsorbed at a position closer to the outlet end of the collection tube 22 and the moving distance to the column 32 is short. As described above, in the sample concentrating portion of this embodiment, the difference in the adsorption position in the collection tube 22 due to the temperature non-uniformity during cooling and the difference in the desorption time due to the non-uniform temperature rise rate during heating. Are appropriately combined, a low boiling point compound and a high boiling point compound can be introduced into the column 32 with a large time difference.

  The configuration for forming the gradient of the cooling temperature in the direction of the flow of the sample gas in the collection tube 22 and the gradient of the temperature increase rate during heating are not limited to those described above, and various configurations are possible. I can think. Examples are given below.

  FIG. 3 shows an example of a configuration in which a Peltier element is used as the cooling means. FIG. 3A is a cross-sectional view taken along the line b-b ′ in FIG. In this configuration, the heater 23 is wound directly around the collection tube 22 and disposed in a groove 53 formed in a heat transfer block 52 provided in contact with the Peltier element 51. The distance d between the inner surface of the groove 53 and the collection tube 22 becomes shorter as it goes to the downstream side (right side in the drawing) of the sample gas. Since the cooling effect of the collection tube 22 is higher as the distance d is shorter, a gradient of the cooling temperature can be formed as in the above embodiment.

  Further, in order to increase the temperature stability of the collection tube 22, it is preferable to provide a metal block such as the heat transfer block. However, if the thermal conductivity of the metal block is too good, the gradient of the temperature gradient becomes small. Therefore, in such a case, as shown in FIG. 4, a heat shield 62 made of a material having poor thermal conductivity is appropriately inserted in the metal block 61 so as to prevent thermal conduction in the direction of the sample gas flow. Or forming a gap (slit).

  On the other hand, in order to give a gradient to the temperature rise rate with the heater, for example, the resistance value of the heater itself changes continuously or stepwise in the longitudinal direction, or the wire diameter of the heater changes sequentially. The same effect can be obtained.

  Of course, other than the above description, it is obvious that any change, correction or addition made within the spirit of the present invention is included in the claims of the present application. For example, although the above embodiment has been described with respect to a gas chromatograph as a gas analyzer, it is obvious that the present invention can be applied to other gas analyzers such as a gas analyzer using a gas sensor.

The whole block diagram centering on the gas flow path of the gas chromatograph by one Example of this invention. The block diagram (a), (b) of the principal part of the collection unit of the gas chromatograph in a present Example, and explanatory drawing (c), (d), (e) which shows the operation | movement. The block diagram of the principal part of the collection unit by the other Example of this invention. The block diagram of the principal part of the collection unit by the other Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Sample introduction part 20 ... Sample concentration part 21 ... Collection unit 22 ... Collection pipe 23 ... Refrigerant conduit 24 ... Heater 26 ... Valve 27 ... Heating current supply part 29 ... Valve 30 ... Analysis part 32 ... Column 33 ... Detector 40 ... Control part 51 ... Peltier element 52 ... Heat transfer block 53 ... Groove part 61 ... Metal block 62 ... Thermal insulation part

Claims (1)

In a gas analyzer equipped with a sample concentrator that increases the component concentration in the sample gas using adsorption / desorption of the sample component by cooling / heating before the analyzer that analyzes the component in the sample gas that is the object of analysis The sample concentration unit
a) collection means provided to extend in the flow direction of the sample gas in order to collect the sample components contained in the flowing sample gas;
b) a cooling means for cooling the collection means so as to produce a temperature distribution in the flow direction of the sample gas when the sample component is adsorbed on the collection means;
c) When the sample component adsorbed on the collection means is heated and desorbed and sent to the analysis unit, the temperature increase rate with respect to the portion that is relatively low temperature by the cooling means is relatively high. Heating means for heating the collecting means so as to produce a gradient of the temperature rise rate that is greater than the temperature rise rate for the part being present;
The cooling means is cooled so that a temperature distribution is generated such that the temperature decreases as it goes from the upstream side to the downstream side of the collection means, and the heating means is upstream of the collection means on the upstream side. A gas analyzer characterized in that heating is performed so that the temperature rise is faster than that .

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