JP4403807B2 - Liquid chromatograph apparatus equipped with a differential refractometer - Google Patents

Description

  The present invention relates to a liquid chromatograph apparatus, and more particularly to a liquid chromatograph apparatus provided with a differential refractometer.

  A differential refractometer in a liquid chromatograph is a highly versatile detector that can detect a wide range of samples. The differential refractometer responds sensitively to the condition of the solvent being delivered, and the baseline tends to fluctuate. For this reason, a sample cell for feeding a sample solution and a reference cell for feeding a solvent as a reference solution are provided in the photometric detection unit, and the sample or A so-called double flow type method is known in which a detector output signal is stabilized by feeding a solvent. The general apparatus configuration is shown in FIG. One of the solutions in the solvent bottle 1 is fed by a liquid feed pump 2 as a mobile phase solvent on the sample solution side, and the other by a liquid feed pump 3 as a reference solution. The sample solution is injected by the injection valve 4 and then introduced into the sample cell S in the differential refractometer 7 through the analysis column 5. On the other hand, the reference solution is introduced into the reference cell R through the reference column 6. Usually, the analysis column 5 and the reference column 6 are arranged in a column thermostat. Sample injection is often performed using an autosampler.

  When a differential refractometer is used as a detector, the refractive index depends on the density of the liquid, so that it is necessary to reduce the change in density of the liquid in order to suppress detector noise. The cause of the density change is mainly derived from the pulsation of the liquid feeding pump. Therefore, suppressing the pulsation of the liquid feeding pump leads to reducing the noise of the differential refractometer. When the solvent is sent independently to the differential refractometer sample cell and reference cell using two liquid feed pumps, the pulsation can be reduced by independent control in order to suppress the pulsation width of each pump alone. It is common. On the other hand, there are cases where two liquid feed pumps are driven by a single motor.

  A method for removing periodic noise caused by pulsation of a liquid feeding pump from a chromatogram is described in many patent documents as follows. These are all methods for electrically processing data after obtaining a detection signal containing noise, and there is a possibility that the original measurement peak may be distorted by data processing, and a method for directly obtaining a measurement value with less noise. is not.

  Patent Documents 1 and 2 disclose a method of periodically cutting a pulsation noise pulse by a differentiation circuit and a holding circuit. Patent Document 3 discloses a method of reducing pulsation noise by electrically superimposing a signal pattern from a pressure sensor installed downstream of a liquid feed pump with a chromatogram to cancel out. Patent Document 4 discloses a method of reducing pulsation noise by adding a baseline pulsation pattern to a chromatogram in reverse phase, although not limited to a differential refractometer. Patent Document 5 describes that the pulsation is removed by inverting / non-inverting, amplifying / attenuating, adding / subtracting the pressure sensor output and the detector output. Patent Document 6 discloses a technique of selectively removing a pulsation frequency by installing a band cut filter downstream of a detector. Patent Document 7 discloses a technique for cutting a pulsation frequency using a spectrum analyzer and a digital filter.

Japanese Utility Model Publication No. 52-93589

Japanese Patent Laid-Open No. 52-115294 JP-A-60-113151 JP 60-205362 A Japanese Patent Laid-Open No. 1-126545 JP-A-5-215738 JP-A-5-333016

  When attempting to reduce the pulsation of the two liquid pumps independently, the pulsation width of each independent pump is reduced, but the noise level of the differential refractometer is not necessarily reduced. This is because if there is a phase difference between the reciprocating motions of the plungers of the two pumps, pressure fluctuations are transmitted unbalanced to the liquid in the sample cell and the reference cell, and the noise level changes even under the same measurement conditions. Further, when the two pumps are driven by one motor, the flow rates of the sample solution and the reference solution cannot be arbitrarily changed.

  An object of the present invention is to directly obtain a measurement value with less noise due to pulsation of a liquid feeding pump in a liquid chromatograph apparatus using a double flow type differential refractometer.

  As a result of intensive studies to solve the above-mentioned problems, it is possible to cancel the change in the density of the solvent derived from the pulsation of the liquid feeding pump between the sample cell and the reference cell by synchronizing the phases of the two liquid feeding pumps. As a result, the present invention has been completed.

  That is, the present invention is a differential refractometer having a sample cell and a reference cell, and a liquid feeding pump for feeding a solvent independently to the sample cell and the reference cell, and sucking and discharging the solvent by reciprocating movement of a plunger. The phase of the reciprocating motion of the two plungers is determined by two liquid feeding pumps, a phase detecting means for detecting the phase of the reciprocating motion of the plunger, and a signal derived from the phase from the phase detecting means. There is provided a liquid chromatograph apparatus comprising a control means for synchronizing with a frequency ratio of an integral multiple.

  A representative embodiment of the present invention is shown in FIG. Information about the phases of the two pumps is sent from the phase detection means 23 and 33 to the control means 8. The control means 8 controls the operations of the motors 21 and 31 based on the information about the phases of the two pumps, that is, the both phases are synchronized by a signal derived from the phases. The pump to be used may be a plunger reciprocating pump, and examples of the power transmission means 22 and 32 from the motors 21 and 31 to the plungers 24 and 34 include a cam type and a screw type. A stepping motor suitable for control is suitable as the motor. As the phase detection means 23 and 33, it is only necessary to detect the reciprocating motion of the plunger or the rotational motion of the motor and to transmit information on the phase to the control means 8. Any known method may be employed.

  For example, in the case of the cam type pump shown in FIG. 3, each pump is provided with a mechanism for detecting the cam angle. That is, the rotation monitoring disk 13 with a slit that rotates together with the cam as the power transmission means 22 (32) is attached to the shaft of the motor 21 (31) so that the cam angle matches the phase position of the pump, etc. By detecting the position of the slit 17 with the photosensor 14, information regarding a specific angle of the cam, that is, the phase can be detected. You may measure a rotation angle with a rotary encoder.

  For example, FIG. 4 shows a schematic diagram of a pump having a function of detecting a plunger position with a screw-type pump. That is, the screw 18 is connected to a reversible stepping motor 21 (31), and the plunger 24 (34) is reciprocated. A protrusion 15 is provided on a part of the plunger, and a mechanism for detecting the position of the plunger by the photo sensor 14 is provided. Alternatively, the linear movement of the plunger may be measured by a potentiometer.

  Next, the operation method and operation of the present invention will be described. When liquid feeding is started with two pumps, for example, the pump is moved at a low speed, the control means is operated, and both pumps are temporarily stopped at the same phase. After that, when the flow rates of both pumps are equal, the phase of the plunger, that is, the discharge timing is completely synchronized with the same frequency ratio by operating the sample feeding pump and the reference solution pump with the same control signal. Since the change in the density of the solvent in all the channels is synchronized with the discharge period of the pump, as a result, the change in the density of the sample side and the reference side solvent in the differential refractometer cell is completely offset. Therefore, since the refractive index change resulting from the liquid density change is always minimized, the pulsation-derived noise level can always be kept at the minimum.

  When the flow rates of the sample solution and the reference solution are different, the phases are synchronized by controlling with a signal that is an integral multiple of the reference solution at the set flow rate. In this case, noise is not always minimized, but the noise width does not change due to a phase shift.

  In addition to such an operation mode, for example, one instruction for starting / stopping liquid feeding may be used, and the phase of the pump may be detected to always stop / start at a constant phase position. In addition, when the other pump (B) starts feeding while only one of the two pumps (A) is moving, the phase position of the pump (A) is detected and synchronized. At this timing, the pump (B) may start feeding at a low speed, and the pump (B) may always be raised to the set flow rate while being controlled by a signal that is an integral multiple of the phase frequency ratio. Further, when the two pumps reach the set flow rate, the position of one pump (A) is detected, and the motor rotation speed of the pump (B) until the position detection timing of the other pump (B) is synchronized. May be fine-tuned for synchronization.

  In the conventional apparatus, as schematically shown in FIG. 5, the phase 42 of the pulsation of the liquid pump for the sample solution and the phase 43 of the pulsation of the liquid pump for the reference solution are not synchronized, and the signal 44 of the differential refractometer is used. Produces noise that is a combination of two pulsations. However, in the pump equipped with the plunger phase synchronization function according to the present invention, as schematically shown in FIG. 6, the phase 45 of the pulsation of the liquid pump for the sample solution and the phase 46 of the pulsation of the liquid pump for the reference solution are used. Can be completely synchronized, and noise derived from pulsation in the signal 47 of the differential refractometer can be more reliably minimized.

  Therefore, according to the present invention, in the liquid chromatograph apparatus using the double flow type differential refractometer, it is possible to directly obtain a measurement value with less noise due to the pulsation of the liquid feeding pump.

  In the liquid chromatograph according to the present invention using the cam type pump shown in FIG. 3 and having the configuration shown in FIG. 2, the control was performed with and without controlling the phase on the sample side and the reference solution side. The baselines of the differential refractometer output are shown in FIGS. 7B and 7A, respectively. The baseline was obtained by observing the output of the differential refractometer for 10 minutes with water flowing on the sample side and the reference side, both at a flow rate of 0.6 mL / min. It can be seen that the amplitude (b) of the noise when the synchronous control is performed is suppressed to half or less than that (a) when the synchronous control is not performed. FIG. 7 shows (a) and (b) in the same chart for comparison of noise amplitude, and the drift direction of noise (mV) is meaningless.

It is a figure which shows the general apparatus structure of the double flow type liquid chromatograph which uses a differential refractometer for a detector. It is a figure which shows the apparatus structure of the liquid chromatograph concerning this invention. It is a figure which shows the relationship between an example of the detection system of a cam angle in a cam type liquid feeding pump, and a control means. Since the configuration of the liquid feeding pump may be the same on the sample side and the reference solution side, only one side is shown. It is a figure which shows the relationship between an example of a plunger position detection system with a screw system pump, and a control means. Since the configuration of the liquid feeding pump may be the same on the sample side and the reference solution side, only one side is shown. It is a schematic diagram which shows the relationship between two pump pulsation phases and a differential refractometer signal when not mounting the liquid chromatograph which concerns on this invention. It is a schematic diagram which shows the relationship between two pump pulsation phases and a differential refractometer signal when the liquid chromatograph according to the present invention is mounted. It is the figure which compared the baseline noise of the differential refractometer output when (b) when not implementing this invention, and (a) when not implementing, in which a horizontal axis is time (minutes) and a vertical axis is Voltage (mV) is shown.

Explanation of symbols

1: solvent bottle 2: liquid pump for sample solution 3: liquid pump for reference solution 4: injection valve 5: analysis column 6: reference column 7: differential refractometer; S = sample side, R = reference side 8: control Means 13: Rotation monitoring disk 14: Photo sensor 15: Plunger position detection projection 17: Cam angle detection slit 18: Screw 21: Motor (sample side)
22: Power transmission means (sample side)
23: Phase detection means (sample side)
24: Plunger (sample side)
31: Motor (reference solution side)
32: Power transmission means (reference solution side)
33: Phase detection means (reference solution side)
34: Plunger (reference solution side)
42: Phase of liquid pump pulsation for sample solution 43: Phase of liquid pump pulsation for reference solution 44: Differential refractometer signal 45: Phase of liquid pump pulsation for sample solution 46: Phase of liquid pump pulsation for reference solution 47: Differential refractometer signal

Claims (5)

A differential refractometer having a sample cell and a reference cell, and a liquid feed pump for independently feeding a solvent to the sample cell and the reference cell at different flow rates , wherein the solvent is sucked and discharged by a reciprocating motion of a plunger. Two liquid pumps, phase detection means for detecting the phase of the reciprocation of the plunger, and a signal derived from the phase from the phase detection means, the phase of the reciprocation of the two plungers is an integral multiple. And a control means for synchronizing with a frequency ratio of 2. The liquid chromatograph according to claim 1 , wherein the liquid feed pump is a cam type and / or screw type pump. 3. The liquid chromatograph according to claim 2 , wherein the phase detection means detects the position of the slit that rotates together with the movement of the power transmission means of the cam type liquid feed pump. 3. A liquid chromatograph according to claim 2 , wherein a stepping motor is used as a motor for the liquid feed pump. Phase detection means, a screw type liquid chromatographic apparatus according to claim 2 or claim 4, wherein the detects a position of the projection portion provided in a portion of the plunger of the liquid supply pump.

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