Electric conductivity detector and ion chromatograph

Abstract

An electric conductivity detector includes at least a cell part having a cell through which liquid flows therein and measurement electrodes measuring a current of liquid flowing through the liquid in the cell, a detection circuit electrically connected to the measurement electrodes and configured to detect a current value flowing between the measurement electrodes, and to output a signal based on the detected value, and a processing unit configured to take in a signal output from the detection circuit and perform signal processing, in which the cell part and the detection circuit are configured to be accommodated in a column oven regulating a temperature of an analytical column of an ion chromatograph.

Claims

1. An electric conductivity detector comprising at least: a cell part having a cell through which liquid flows therein and a pair of measurement electrodes measuring a current flowing through the liquid in the cell; a detection circuit electrically connected to the measurement electrodes and configured to detect a current value flowing between the measurement electrodes, and to output a signal based on the detected value; and a processing unit configured to take in a signal output from the detection circuit and perform signal processing, wherein the cell part and the detection circuit are accommodated in a common casing to form an integral detection device, and the common casing containing the cell part and the detection circuit is accommodated in a column oven regulating a temperature of an analytical column of an ion chromatograph, wherein the common casing is made of a thermally conductive material so that heat in the column oven can be sufficiently conducted to the cell part and the detection circuit, and the detection device further comprises a heat exchange block disposed in the common casing, a flow passage leading to an inlet of the cell is provided inside the heat exchange block with a heater and a temperature sensor are attached to the heat exchange block, and a temperature of liquid before being introduced into the cell is regulated in the heat exchange block.

2. The electric conductivity detector according to claim 1, wherein the detection circuit includes at least an analog circuit for detecting a magnitude of a current flowing between the measurement electrodes.

3. The electric conductivity detector according to claim 2, wherein the detection circuit includes an A/D conversion circuit configured to convert an analog signal output from the analog circuit into a digital signal and to output the digital signal to the processing unit.

4. An ion chromatograph comprising: an analysis flow passage; a liquid sending device for sending a mobile phase in the analysis flow passage; a sample injection part for injecting a sample into the analysis flow passage; an analytical column for separating the sample injected by the sample injection part into individual components on a downstream of the sample injection part on the analysis flow passage; the electric conductivity detector according to claim 1 for detecting ionic sample components separated by the analytical column by measuring the electric conductivity of an eluate from the analytical column on a downstream of the analytical column on the analysis flow passage; and the column oven accommodating the analytical column therein and configured to regulate the temperature of the analytical column to a set temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a partially exploded perspective view schematically illustrating an embodiment of an electric conductivity detector.

(2) FIG. 2 is a flow passage configuration diagram schematically illustrating an embodiment of an ion chromatograph.

DETAILED DESCRIPTION

(3) Hereinafter, embodiments of an electric conductivity detector and an ion chromatograph according to the present invention will be described with reference to the drawings.

(4) A configuration of the electric conductivity detector of an embodiment will be described with reference to FIG. 1. In addition, in FIG. 1, in order to illustrate an internal structure of a detection device 2, the detection device 2 is illustrated in a state that an upper surface cover of a casing 6 of the detection device 2 is removed.

(5) The electric conductivity detector 1 of this embodiment is constituted of the detection device 2 and a processing unit 4. The detection device 2 and the processing unit 4 are separately configured. The detection device 2 and the processing unit 4 are electrically connected to each other via a cable.

(6) The detection device 2 includes a cell part constituted of a cell 14 in which liquid flows through and measurement electrodes 16 for applying a voltage across the cell 14, and a detection circuit board 18 (detection circuit) on which at least an analog circuit is mounted to apply a voltage between the measurement electrodes 16 and detect a current flowing between the measurement electrodes 16, the cell 14 and the detection circuit board 18 being accommodated in a common casing 6. A heat exchange block 11 is also accommodated in the casing 6. A heater 12 and a temperature sensor 13 are attached to the heat exchange block 11. Inside the heat exchange block 11, a flow passage leading to an inlet of the cell 14 is provided, and temperature regulation of liquid before being introduced into the cell 14 is sufficiently performed in the heat exchange block 11. A detection signal of the temperature sensor 13 is taken into the processing unit 4 through a communication cable, and an output of the heater 12 is controlled so that a temperature detected by the temperature sensor 13 becomes a preset temperature.

(7) In addition, although the heater 12 and the temperature sensor 13 are electrically connected to the processing unit 4 through the detection circuit board 18 in this embodiment, the heater and the temperature sensor do not necessarily need to be connected through the detection circuit board 18.

(8) As will be described later, the detection device 2 of this embodiment is accommodated in a column oven 28 (see FIG. 2) of an ion chromatograph. Since an inside of the column oven 28 is thermostatically controlled, a temperature of the detection device 2 accommodated in the column oven 28 also becomes stable. For this reason, the detection device 2 does not necessarily need to have the heater 12 and the temperature sensor 13 for performing temperature control independently. However, since the detection device 2 having a small heat capacity compared to the column oven 2 is independently provided with the heater 12 and the temperature sensor 13, finer temperature control than by the column oven 28 is possible, and a temperature of liquid flowing through the cell 14 and a temperature of the detection circuit 18 can be controlled with higher accuracy.

(9) In addition, since the detection device 2 of this embodiment is independently provided with the heater 12 and the temperature sensor 13 and has a function of regulating an internal temperature independently, the detection device 2 does not necessarily need to be accommodated in the column oven 28.

(10) The casing 6 of the detection device 2 is made of, for example, a thermally conductive material such as aluminum. Thus, when this detection device 2 is accommodated in the column oven 28 (see FIG. 2), heat in the column oven 28 can be sufficiently conducted to the heat exchange block 11, the cell 14, and the detection circuit board 18. An inlet pipe 8 and an outlet pipe 10 are drawn to an outside of the casing 6 and are configured in such a way that liquid flowing in through the inlet pipe 8 passes through the heat exchange block 11 and is introduced into the cell 14, and liquid having passed through the cell 14 flows out through the outlet pipe 10. The inlet pipe 8 and the outlet pipe 10 may be provided in advance, or may be connected from the outside.

(11) The detection circuit board 18 accommodated in the detection device 2 is electrically connected to the processing unit 4 via communication cables. On the detection circuit board 18, there is mounted an analog circuit that applies a constant voltage between the measurement electrodes 16 and detects a current value flowing between the measurement electrodes 16. In a more preferred embodiment, an A/D conversion circuit that converts an analog signal from the analog circuit into a digital signal and outputs the digital signal to the processing unit 4 is also mounted on the detection circuit board 18.

(12) The processing unit 4 is configured to perform various types of signal processing, such as taking in a signal output from the detection circuit board 18 of the detection device 2 and determining electric conductivity of liquid flowing through the cell 14 based on the signal. The processing unit 4 is implemented by a dedicated computer or a general-purpose personal computer.

(13) In this embodiment, because the cell part constituted of the cell 14 and the measurement electrodes 16 and the detection circuit 18 are accommodated in the common casing 6 to form the integral detection device 2, the cell part and the detection circuit 18 can be handled as a single piece and can be easily disposed in the column oven 28 (see FIG. 2) of the ion chromatograph.

(14) Next, an embodiment of an ion chromatograph using the above-described electric conductivity detector 1 will be described with reference to FIG. 2.

(15) The ion chromatograph of this embodiment includes an analysis flow passage 20, a liquid sending device 22 that sends a mobile phase, a sample injection part 24 that injects a sample into the analysis flow passage 20, an analytical column 26 that is provided downstream of the sample injection part 24 on the analysis flow passage 20 and separates the sample by each component, a suppressor 30 that is provided downstream of the analytical column 26 on the analysis flow passage 20 and removes unnecessary ion components in the mobile phase having passed through the analytical column 26, and the above-described electric conductivity detector 1 that is provided downstream of the suppressor 30 on the analysis flow passage 20.

(16) The analytical column 26 is accommodated in the column oven 28. Although illustration is omitted, the column oven 28 is internally provided with a heater and a temperature sensor, and an output of the heater is regulated so that the internal temperature becomes a set temperature.

(17) The detection device 2 of the electric conductivity detector 1 is also accommodated in the column oven 28. Each of the inlet pipe 8 and the outlet pipe 10 of the detection device 2 of the electric conductivity detector 1 constitutes a part of the analysis flow passage 20 of this ion chromatograph. The inlet pipe 8 is drawn to an outside of the column oven 28 and connected to an outlet side of the suppressor 30. The outlet pipe 10 is drawn to the outside of the column oven 28 and connected to a drain.

(18) The processing unit 4 of the electric conductivity detector 1 is disposed outside the column oven 28, and the detection circuit 18 of the detection device 2 accommodated in the column oven 28 and the processing unit 4 disposed outside the column oven 28 are electrically connected by a communication cable.

(19) In the ion chromatograph of this embodiment, when a sample is injected by the sample injection part 24 into the analysis flow passage 20 through which the mobile phase from the liquid sending device 22 flows, the sample is guided to the analytical column 26 by the mobile phase. The sample introduced into the analytical column 26 is temporally separated by each component, and each component elutes from the analytical column 26 sequentially.

(20) The mobile phase containing the sample component eluted from the analytical column 26 is subjected to removal of unnecessary ion components in the suppressor 30, and thereafter introduced into the cell 14 in a state of being regulated to a predetermined temperature in the heat exchange unit 11 (see FIG. 1). A constant voltage is applied across the cell 14, and a current according to concentration of components in the mobile phase flowing through the cell 14 flows between the measurement electrodes 16. The detection circuit 18 detects a current value of the current and outputs a signal based on the detected value to the processing unit 4. In the processing unit 4, electric conductivity of the liquid in the cell 14 is determined based on the signal from the detection circuit 18.

(21) As described above, in the ion chromatograph of this embodiment, since the detection device 2 in which the cell part including the cell 14 and the measurement electrodes 16 and the detection circuit 18 are integrated is accommodated in the column oven 28, not only the temperature of the liquid flowing through the cell 14 but also the temperature of the detection circuit 18 can be maintained constant. Accordingly, even if fluctuations occur in the temperature of the surrounding environment (for example, room temperature), the liquid flowing through the cell 14 and the detection circuit 18 are not affected. Thus, the measurement of electric conductivity of the eluate from the analytical column 26 can be stably performed, and it is possible to suppress occurrence of drift of the detection signal due to temperature fluctuations.

(22) Furthermore, in this embodiment, since the detection device 2 of the electric conductivity detector 1 is independently provided with the heater 12 and the temperature sensor 13 and can control the internal temperature with higher accuracy, the temperature of the liquid flowing through the cell 14 and the temperature of the detection circuit 18 can be further stabilized.

(23) Furthermore, as a preferred embodiment, if an A/D conversion circuit that converts an analog signal from an analog circuit that measures the current value flowing between the measurement electrodes 16 into a digital signal is also mounted on the detection circuit 18, an output signal from the A/D conversion circuit is not affected by temperature fluctuations of the surrounding environment. Thus, occurrence of drift of the detection signal can be further suppressed, and reproducibility of measurement results can be further increased.

(24) Although not illustrated in FIGS. 1 and 2, the electric conductivity detector 1 may be electrically connected to another arithmetic control unit. Such an arithmetic control unit may have a function of controlling operation of each element constituting the ion chromatograph, such as the liquid sending device 22, the sample injection device 24, and the column oven 28. Then, such an arithmetic control unit can be implemented by a dedicated computer or a general-purpose personal computer.

(25) As already mentioned, a main object of the present invention is to stabilize a temperature of liquid flowing through the cell and a temperature of the detection circuit. Therefore, the present invention will suffice to include at least one of a configuration having the detection circuit accommodated in the column oven together with the cell part, and a configuration in which the detection device having the cell part and the detection circuit which are integrated independently includes a temperature control function. The above embodiments aim at synergetic effect that the accuracy of temperature control of the cell part and the detection circuit is further improved by providing both of these configurations, and the present invention is not limited to the aspects of the above embodiments.