JPS633154B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid chromatograph, and more particularly to a liquid chromatograph that enables non-pulsating and constant flow of liquid without being affected by the value of back pressure.

In liquid chromatography, one of the most important conditions is to supply the mobile phase liquid to the column in a non-pulsating flow and at a predetermined constant flow rate. Pulsating flow causes noise in the detector, and fluctuations in flow rate due to pulsating flow change the retention time of the liquid, making identification of sample components difficult and causing errors in quantitative values.

Conventionally, the most widely used pulseless flow, constant flow pump used in liquid chromatographs is a positive displacement pump having dual pistons.
This type of pump can perform ideal liquid delivery when the back pressure is low, but as the back pressure increases, pulsation appears due to seal compression, liquid compression, etc., and the flow rate decreases. Come. This is because at the turning point of the piston, a portion of the piston stroke is eaten up by seals and liquid compression, and the higher the back pressure, the greater the proportion. In order to overcome this difficulty, liquid feeding control has conventionally been performed using a flow feedback method or a pressure feedback method. In other words, in the former method, a capillary reach tube is installed in the flow path, and the rotational speed of the piston drive motor is fed back so that the pressure drop (differential pressure) within the capillary reach tube is maintained at a predetermined value near the turn of the piston. The latter is a method in which the rotational speed of the motor is feedback-controlled so that the back pressure is maintained at a predetermined value near the piston turning point. However, both methods always compare the feedback signal with a reference value and change the motor rotation speed in the control section, that is, near the piston turn-around, so within this control section, the liquid is sent at a constant pressure rather than at a constant flow. It has the disadvantage of becoming a liquid. In addition, when performing gradient elution by controlling the opening and closing time of the valve on the suction side, since suction is performed intermittently, control must be performed within the suction stroke, but there are sections where the motor rotation speed is constantly fluctuating. Therefore, there is a drawback that the inhalation stroke cannot be detected accurately, and therefore it is difficult to obtain an accurate solvent concentration.

The purpose of the present invention is to effectively compensate for the drop in flow rate due to compression of the liquid and seals, thereby enabling non-pulsating flow and constant flow of liquid, as well as enabling accurate control of solvent concentration in gradient elution methods. Our goal is to provide chromatographs.

In order to achieve the above object, the present invention supplies a solvent from two or more solvent reservoirs to a mixing tank through respective on-off valves, and further supplies the mixed solvent to a column by a liquid feeding pump, The liquid feeding pump is at least a plunger pump that is driven reciprocally via a cam, and the cam is formed such that a composite pattern of suction and discharge of the plunger pump provides an intermittent flow on the suction side and a continuous flow on the discharge side. In a liquid chromatograph, the pressure drop start point and pressure rise start point of the plunger pump discharge pressure are respectively detected, and the rotational speed of the motor that drives the cam is increased by a certain number of times from the drop start point to reach the rise start point. It is characterized in that the motor rotation speed is returned to the original speed at the point when the motor rotation speed reaches its original speed.

In the present invention, when performing gradient elution, the two on-off valves are alternately opened and closed in a time period corresponding to the actual suction stroke of the pair of plunger pumps, and their opening time ratio is set as above. It is preferable to match the mixing ratio of the mixed solvent.

Hereinafter, the present invention will be explained in more detail with reference to Examples. FIG. 1 is an apparatus configuration diagram of a column chromatograph of the present invention. Solvents A and B in solvent reservoirs 1 and 2 are led to a mixing tank 5 via valves 3 and 4, respectively. Valve 3 and valve 4 are on-off valves that allow passage of the solvent only when they are open. The solvent coming out of the mixing tank 5 is sucked into a pump 6 and discharged, and then enters a pressure detector 7. The pressure sensor 7 is a transducer that converts pressure into an electrical signal. The solvent that has passed through the pressure detector 7 is pumped through a sample introduction device 8 to a column 9, and after passing through the column, it is drained through a detector 10. The opening/closing of the valves 3 and 4, the rotational speed of the motor of the pump 6, etc. are controlled by a microcomputer 11 or the like as a control device.

Next, FIG. 2 is an explanatory diagram of a pump used in the present invention. The pair of plungers 14 face each other at 180 degrees with the cam 12 as the center, and are reciprocated via the cam follower 13 as the cam 12 rotates.
The pump interior chamber 24 is sealed by a seal 16, which prevents the reciprocating movement of the plunger 14 and the check valve 15.
The inhalation and ejection of the solvent is repeated by the cooperative action of the two. The cam 12 is rotated by a motor 18, and by controlling its rotational speed, the plunger 14
The reciprocating speed, that is, the discharge flow rate of the solvent can be set arbitrarily. FIG. 3 shows the relationship between the rotation angle θ of the cam 12 that drives the plunger 14 and the distance L of the cam follower 13 from the center of the cam 12. Furthermore, the cam 12 satisfies the following conditions.

0゜〜θ ₁ dL／dθ＝m ₀ (1) θ ₁ 〜180゜ dL／dθ＝m ₁ (2) 180゜＋θ ₁ 〜360゜ dL／dθ＝m ₂ (3) m ₀ ＝m ₁ ＋m ₂ (4) Below, to simplify the explanation, m ₁ = m ₂ = m ₀ /
The operation of the plunger pump in case 2 will be explained. In this case, the motion of the plunger 14 when the cam 12 is rotated at a constant speed is as shown in FIG. 4. FIG. 4A shows the movement of one plunger, and FIG. 4B shows the movement of the other plunger, simultaneously showing the suction and discharge patterns of the solvent. The suction pattern for suction from the suction tube 21 and the discharge pattern for discharge from the discharge tube 22 shown in FIG. 2 are a combination of the suction and discharge patterns from the two plungers. That is, this composite pattern is as shown in FIG. 5 when the pump back pressure is normal pressure. In other words, suction is an intermittent flow, but discharge is a continuous flow. However, as the back pressure becomes higher than normal pressure, deviation from the pattern shown in FIG. 5 occurs, making quantitative inhalation and ejection difficult. In other words, the discharge stroke starts from point A in FIG. 4, but the discharge does not start until the pressure in the pump interior chamber 24 in FIG. . The higher the back pressure, the longer the compression strokes A to B become. Similarly, when moving from discharge to suction, the pump internal chamber 24 in FIG.
Inhalation begins after the back pressure returns to normal pressure, that is, inhalation begins at point C in Figure 4, but if the back pressure is high, inhalation begins after reaching point II. In this way, the combined suction and discharge pattern when the back pressure is high is as shown in FIG. 6, resulting in discharge accompanied by a decrease in flow rate and pulsating flow. This is because when the back pressure increases, the displacement volume of the plunger cannot contribute 100% to the discharge due to seal compression, liquid compression, etc.

In the present invention, when the pump back pressure is high and pulsating flow occurs as described above, this problem is solved by doubling the rotational speed of the cam 12 only in the sections A and B in FIG. 6. In other words, in this section, the cam 12
If the rotation speed is doubled, the flow rate will be doubled, and as is clear from FIG. 6, pulsating flow can be prevented. In this case, it is necessary to detect points A and B, and point A is the point where the flow rate starts to decrease, that is, the pressure P
This is the point at which the cam rotation speed starts to decrease, and the cam rotational speed can be doubled from this point.

In other words, the back pressure (pump discharge pressure) is mainly determined by the fluid resistance (pressure loss) of the column 9, and is therefore proportional to the flow rate (flow rate) of the liquid flowing through the column 9. In the process of moving from point H to points A and B in FIG. 4, due to compression of the fluid, liquid is not discharged from the pump chamber of the plunger in question, but only from the pump chamber of the other plunger.
Originally, between A and B, the total amount discharged from the pump inner chambers of both plungers is a predetermined amount, and this determines the back pressure. However, as mentioned above,
Since only one side of the liquid is discharged between B and B, liquid is supplied to the column 9 at a flow rate smaller than the predetermined flow rate (1/2 in the examples shown in FIGS. 4 and 6). Therefore, as soon as the column moves to point A, the pressure loss in the column 9 becomes small and the back pressure starts to decrease. Point A can be detected by detecting this decrease in back pressure using the pressure detector 7.

The pressure P is constantly detected by the pressure detector 7 and its value is sent to the microcomputer 11, and it is easy to know when dP/dt<0.
Next, regarding the detection of the point B, if the rotation speed is twice as high as the point B, the flow rate will be twice as much as the point L. In other words, when it reaches point B, dP/dt>0, so
Similarly, it can be easily detected by the pressure detector 7, and at this point the rotational speed can be returned to the original speed. The above is the case where m ₁ = m ₂ = m ₀ /2, but in the general case, dP/dt<0 point and dP/dt>
It can be seen that it is sufficient to control the rotational speed between zero points to be m ₀ /m ₁ times.

FIG. 7 shows the fluctuation of back pressure in the conventional case where the rotational speed is not controlled. The pressure or flow rate decreases periodically due to seals and liquid compression, and the pulsating flow is also large. On the other hand, FIG. 8 shows back pressure fluctuations in the case of the present invention in which the rotational speed is controlled as described above, and it can be seen that smooth liquid feeding without pulsation is possible.

On the other hand, in the present invention, solvent suction is performed intermittently as shown in FIG. 5, but when performing gradient elution, simply controlling the opening times of valves 3 and 4 in FIG. It may not be possible to obtain a concentration proportional to For this reason, in the present invention, the opening times of valves 3 and 4 are mixed in the time period when suction is actually performed, that is, in the actual suction stroke of each plunger pump (between points N and H in FIG. 4). Accurate solvent concentration can be obtained by alternately switching and controlling according to the ratio. In other words, by opening the valve 3 and closing the valve 4 for a certain period of time from point 2, and then closing the valve 3 and opening the valve 4 between the points 2 and 4, the flow is sucked by the pump 6 and flows into the mixing tank 5. The mixing ratio of the two liquids matches the opening time ratio of valves 3 and 4. In addition, ni~
Since the suction operation is not performed except between the hot points, the valves 3 and 4 may be in either open or closed state.

By the way, as is clear from FIGS. 4 and 6, the suction end point E is both the suction end point and the discharge start point A. As mentioned above, point A is the point at which the pressure begins to decrease, that is, the point where dP/dt<0, and therefore, the end point of suction E can be easily detected. Next, the point C where the plunger moves to the suction stroke is the point at which the cam has rotated by a certain angle (180-θ ₁ ) from the suction end point E. That is, when looking at one plunger, the point at which it moves to the next suction stroke is at a constant angle (360-θ ₁ ), but in this example, since the other plunger faces each other with a phase difference of 180°, When considering a pair of plungers, the point C at which the next suction stroke begins is a certain angle {(360−θ ₁ )−180} = (180
−θ ₁ ). Therefore, since the rotational speed between E and D, that is, the rotational speed between A and B and the rotational speed between B and D are known, the time t ₁ required for the journey between E and C can be easily known. Next, the point at which suction actually begins is when the plunger enters the suction stroke and the pump interior chamber 2
4 (Fig. 2) is the point at which the pressure returns from back pressure to normal pressure. The displacement volume of the plunger required to return from this back pressure to normal pressure is the same as the volume required to reach back pressure from normal pressure in the discharge stroke. This volume is the volume of the compression stroke between A and B, and is known. Therefore, the time t ₂ required for the strokes between C and D can be easily determined from the speed of the plunger in the suction stroke. From the above, the inhalation start point D is t ₁ +t ₂ hours after the inhalation end point E, and thus E,
Two points can be detected accurately. By controlling the opening times of the valves 3 and 4 during the suction process as described above, it is possible to obtain a solvent concentration that is accurately proportional to the opening times.

Although the above embodiment uses one cam to drive the pair of plungers, the same operation can be performed using two cams.

As described above, according to the present invention, it is possible to transfer liquid with high precision in a pulseless flow, and moreover, it is possible to perform accurate gradient elution.

[Brief explanation of the drawing]

FIG. 1 is an apparatus configuration diagram of a liquid chromatograph of the present invention, FIG. 2 is an explanatory diagram showing an embodiment of a plunger pump used in the present invention, FIG. 3 is an explanatory diagram of a pump drive cam, and FIG. A, B, FIG. 5, and FIG. 6 are diagrams showing suction and discharge patterns to explain the principle of the present invention, and FIGS. 7 and 8 are pressure curves to compare the effects of the conventional method and the present invention, respectively. be. 1, 2...Solvent reservoir, 3, 4...Valve, 5...Mixing tank, 6
...Pump, 7...Pressure detector, 11...Microcomputer, 12...Cam, 14...Plunger, 15
...Check valve, 16...Seal, 18...Motor, 2
4...Inner chamber of the pump.

Claims (1)

[Scope of Claims] 1. The solvent is supplied from two or more solvent reservoirs to the mixing chamber through respective on-off valves, and the mixed solvent is further supplied to the column by a liquid feeding pump,
The liquid pump is at least a pair of plunger pumps that are reciprocated via a cam, and the cam is
In a liquid chromatograph in which the composite pattern of suction and discharge of a plunger pump is formed to give an intermittent flow on the suction side and a continuous flow on the discharge side, the pressure drop start point and pressure rise start point of the plunger pump discharge pressure are determined. A liquid characterized in that it is equipped with a control device that detects each of them, increases the rotational speed of a motor that drives the cam by a certain number from the starting point of decrease, and returns the rotational speed of the motor to the original rotational speed when the rotational speed of the motor that drives the cam reaches the starting point of increasing. Chromatograph. 2. In claim 1, the two on-off valves are alternately opened and closed in a time period corresponding to the actual suction stroke of the pair of plunger pumps, and the ratio of their opening times is determined based on the mixed solvent. A liquid chromatograph characterized by matching the mixing ratio of