JPS6251424B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solvent mixing device for gradient elution in high performance liquid chromatography, and in particular to a solvent mixing device that can provide sufficient mixing concentration stability and accuracy with a small-capacity mixer. Regarding equipment.

Gradient elution in high-performance liquid chromatography is a very effective method for separating complex mixtures and considering analysis conditions. However, the conventional solvent mixing apparatus used in this case does not have sufficient stability and accuracy in determining the mixing concentration when mixing different solvents. For this reason, when a high-performance liquid chromatograph detector uses a mixed solvent as a mobile phase, it is affected by concentration fluctuations, resulting in large baseline changes, making it difficult to perform high-sensitivity analysis, and when setting the actual mobile phase concentration. There were problems in that the deviation from the concentration was large and the reproducibility of the concentration was insufficient.

The inventors of this invention conducted intensive research in view of the above situation and found that the cause of the instability of the solvent mixture concentration in the conventional device is (i) operation of the control valve;
The present invention was achieved by discovering that this problem mainly exists in (ii) the piping between the control valve and the liquid pump, and (iii) the arrangement of the mixer, and by improving these points.

According to the present invention, a plurality of solvent tanks for the mobile phase are connected to the suction port of the liquid feeding pump through respective control valves, and the control valves are sequentially operated during the suction stroke of the liquid feeding pump. In a solvent mixing device that sucks and mixes each solvent at a predetermined ratio into a liquid sending pump by opening and closing, the "open" state of one control valve and the "open" state of the next control valve during the suction stroke are different. “Fully closed” during which all of the control valves are “closed”
This is a high-speed liquid chromatograph in which the state can be adjusted in a very short time, the connecting piping between the control valve and the inlet of the liquid pump has a small pressure deformation and small capacity, and a mixer is placed on the discharge port side of the liquid pump. A solvent mixing device is provided.

In this invention, the "open" state refers to a state in which even a small amount of solvent can pass through the control valve, that is, a state in which the control valve is open even slightly. Moreover, the "closed" state refers to a state in which the control valve is completely closed.

As a specific example of configuring the "fully closed" state in the device of the present invention, the control valve has a small dead volume and a relatively fast operating speed, and the time it takes to change from the "open" state to the "closed" state is longer than the "closed" state. Use a solenoid valve that is shorter than the time it takes to change from the state to the "open" state, and adjust the timing of the drive signal so that there is no time for two control valves adjacent to each other to become "open" when the control valve operates. For example, controlling or selecting a drive circuit to drive each control valve.

In addition, as specific examples of configuring the connecting piping between the control valve and the liquid pump in the device of this invention to have a small pressure deformation and a small capacity, the piping can be made of stainless steel pipe, and the piping can be made of Teflon (registered trademark) pipe. When performing this, the Teflon pipe with an inner diameter of 1 mmφ x outer diameter of 2 mmφ should be at least 10 cm or less, and the piping should be directly connected to the outlet of each control valve and the inlet of the liquid pump, and no mixer etc. should be interposed in between. Can be mentioned.

No special explanation is required regarding the configuration in which the mixer is disposed on the discharge port side of the liquid feeding pump in the device of the present invention.

Next, the configuration of the solvent mixing apparatus of the present invention will be explained in further detail based on the embodiment shown in the drawings.

1 shown in FIG. 1 is an embodiment of the solvent mixing apparatus of the present invention. 2 is a dual small plunger pump, the suction port of which is directly connected to the outlet of a plurality of electromagnetic valves 4a, 4b through a connecting pipe 3 made of stainless steel pipe, and the inlet of these electromagnetic valves 4a, 4b are connected to Teflon tubes 5a, 5b, respectively. and is connected to the solvent tanks 6a and 6b. Solvent tanks 6a and 6b are filled with solvents A and B, respectively. 7 is a mixer, which is connected via a pressure sensor 8 to the discharge port of the pump 2, and via a damper 9 to a sample inlet of a high performance liquid chromatograph having a known configuration, and to a column and a detector 100. There is. The pump 2 and the solenoid valves 4a, 4b are controlled by a programmer 10.

FIG. 2 shows the valve structure of the solenoid valve 4a. When the valve stem 11 supported by the diaphragm 12 is at the lowest position (the position indicated by the broken line in the figure), it is in the "closed" state.
Other positions are in the "open" state. Even in the “open” state, the valve stem 11 is in the uppermost position (the position indicated by the solid line in the figure).
Hereinafter, the state when the opening is in the "fully open" state will be particularly referred to as the "fully open" state.

FIG. 3 shows a drive circuit for the solenoid valve 4a. If the coil 13 of the solenoid valve 4a is energized,
It goes to the "fully open" state, and when the power is turned off, it goes to the "closed" state. A series circuit of a Zener diode 14 and a diode 15 is connected in parallel with the coil 13 so that the response of the coil 13 is not delayed when the transistor 16 switches from conduction to cutoff.

FIG. 4 is a time chart of the operation of the solenoid valve 4a, in which A shows the drive signal applied to the transistor 16, and B shows the state of the solenoid valve 4a.
When the solenoid valve 4a changes from "closed" to "open",
After the drive signal turns from OFF to ON (t′ ₁ −
The valve stem 11 starts to rise after the ON delay time of time t′ ₀ ), and the “open” state begins, and the valve stem 11 starts to rise after the ON delay time of time _t ′ ₀ ), and the “open” state begins.
After the ON movement time, it becomes "fully open" state. In other words, the drive signal becomes "fully open" after an ON operation time of (t' ₂ - t' ₀ ) after the drive signal is turned from OFF to ON. On the other hand, when changing from "fully open" to "closed", the valve stem 11 is opened with a delay of the OFF delay time (t ₁ - t ₀ ) after the drive signal changes from ON to OFF.
begins to descend and reaches the "closed" state after an OFF movement time of (t ₂ - _{t 1} ). In other words, the drive signal
The state becomes "closed" after an OFF operation time of (t ₂ - t ₀ ) after switching from ON to OFF.

In the drive circuit shown in FIG. 3, a series circuit of a Zener diode 14 and a diode 15 is connected to a coil 13.
In other words, the OFF
This is to prevent the delay time from increasing.

Although solenoid valves have various characteristics, all the solenoid valves making up this device are selected to have characteristics that satisfy the following formula when comparing each two.

O＜Δt＜10mS () However, Δt=(t' ₁ - t' ₀ ) - (t ₂ - t ₀ ) () Here, (t' ₁ - t' ₀ ) is the ON delay time of one solenoid valve. (t ₂ −t ₀ ) is the OFF operation time of the other solenoid valve.

Also, this time of 10 mS can be set to a different value if the pump has a different capacity per stroke.

The programmer 10 issues a drive signal to drive the pump 2 and the solenoid valves 4a, 4b according to a time chart as shown in FIG. In other words, the fifth
In synchronization with the suction profile of the pump 2 shown in Figure A, the fifth solenoid valve 4a is connected to the
It emits the drive signal shown in Figure B, and also outputs the solenoid valve 4.
A drive signal shown in FIG. 5c is sent to b. The drive signals to the electromagnetic valves 4a and 4b are inverted at the same time during the suction stroke of the pump 2.

Since the solenoid valves 4a and 4b have the characteristics described above, they "open" and "close" a little later than when the drive signal is turned on and off. FIGS. 5D and 5E show the "open" and "close" timings of the electromagnetic valves 4a and 4b, respectively, and from the characteristics of the above equation (), there is always a "fully closed" state for a time Δt.

Since the solvent mixing device of the present invention is configured as described above, it has the following excellent effects.

(i) Conventional equipment was not configured to go through a "fully closed" state when switching control valves, so if the drive signals of two control valves were reversed at the same time, the OFF operation time of the control valves would be reduced to ON operation. If the time is longer than that, the two control valves may be in the "open" state at the same time, and as a result, the solvent on the control valve side that is moving from "open" to "closed" is pushed out by the movement of the valve stem of the control valve and "closed". A part of the flow flows backward from the outlet of the control valve 4a through 3'a and 3'b, and from the outlet of the control valve 4b through 3'b in Fig. 1. When a control valve operates from "closed" to "open", other control valves are in the "open" state, so the valve stem moves from "closed" to "open". The solvent sucked into the control valve is not only sucked in from the inlet of the valve, but also partially through the other control valve that is in the "open" state, causing the phenomenon of solvent backflow, and the extent of these phenomena varies. This changes due to differences in the viscosity of the solvents, changes in the liquid level in the solvent tank, differences in piping resistance, etc., and the actual mixing ratio of the solvents fluctuates, resulting in instability of the solvent mixture concentration and inaccurate mixture concentration. It had become the cause of

In contrast, in the apparatus of the present invention, the control valve is always switched through the "fully closed" state, so there is no room for the above phenomenon to occur, and the stability and accuracy of the solvent mixture concentration are accordingly improved.

However, if the time in the "fully closed" state is long, it will affect the suction operation of the pump, so in consideration of variations in the characteristics of the control valve, the time during which the "fully closed" state occurs is set to 10 mS or less in this device. . If this is the case, the effect can be ignored because the pump suction time is within the range of 12 seconds to 2 seconds at a normal analysis flow rate of 0.5 to 3 ml/min.

(ii) In conventional devices, the control valve and the inlet of the liquid pump were usually connected with a Teflon pipe, so even if the OFF operation time of the control valve was shorter than the ON operation time and the control valve reached a "fully closed" state, Since the movement speed of the valve stem of the control valve from "open" to "close" is extremely fast (usually 1 to 3 mS), the solvent (usually 5 to 6μ) that is pushed out from inside the valve as the valve stem operates ) flows back into the solvent tank, but some of it is not sucked into the pump and expands the Teflon pipe, causing the next control valve to change from "closed" to "open".
When this happens, the expanded volume of solvent flows back into the control valve as it moves from "closed" to "open," causing instability in the solvent mixture concentration, similar to the phenomenon described above.

On the other hand, in the device of the present invention, the connecting pipe between the control valve and the liquid pump is hardly expanded, so there is no cause for instability as described above, and the stability of the solvent mixture concentration is improved accordingly.

(iii) In conventional equipment, the mixer was often installed on the suction side of the liquid pump, that is, in the connecting pipe between the control valve and the liquid pump, but the mixer was often installed on the suction side of the liquid pump on the low pressure side. In addition, since the capacity of the mixer needs to be relatively large, depending on the type of solvent, bubbles may easily occur in the mixer during mixing, even if the solvent has been degassed to some extent in advance.
This was one of the causes of fluctuations in the mixing ratio of the solvents.

In contrast, in the device of the present invention, the mixer is provided on the high-pressure side, which is the discharge port side of the liquid pump, so that bubbles are less likely to occur.

In the apparatus of this invention, since the mixer is located after the liquid pump, substantial mixing of the solvents is performed after the solvent is discharged from the liquid pump.

As mentioned above, the solvent mixing device of the present invention has extremely good stability and accuracy of the solvent mixture concentration, and therefore not only enables high-sensitivity analysis in high-performance liquid chromatography, but also enables the difference between the actual concentration and the set concentration. It can be made extremely small. In fact, in the high-performance liquid chromatograph of the above example, when water and methanol were mixed as solvents, the wavelength of the detector was short (210 nm), but it was stable even at extremely high sensitivity (0.01 AμFS). It was possible to conduct an analysis using this method.

Furthermore, since the main cause of instability in the solvent mixture concentration has been removed, even small-capacity mixers can be used stably, allowing for precision and precision with little time lag.
Gradient elution with good reproducibility is now possible.

It goes without saying that the present invention can be easily applied to cases where three or more types of solvents are used.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the configuration of one embodiment of the solvent mixing device of the present invention, FIG. 2 is a partial sectional view of the valve part of the solenoid valve used in the solvent mixing device shown in FIG. 1, and FIG. 3 is the same as that shown in FIG. Figure 4 is a time chart of the operating characteristics of the solenoid valve, and Figure 5 is a diagram of the operating characteristics of the dual small plunger pump and the solenoid valve in the solvent mixing apparatus shown in Figure 1. It is a time chart. 1... Solvent mixing device, 2... Dual small plunger pump, 3... Connection piping, 4a, 4b... Solenoid valve, 6a, 6b... Solvent tank, 7... Mixer,
10...programmer, 100...sample inlet of high performance liquid chromatograph, column, detector.

Claims (1)

[Scope of Claims] 1. A plurality of solvent tanks for the mobile phase are connected to the suction port of the liquid feeding pump through respective control valves, and the control valves are sequentially opened and closed during the suction stroke of the liquid feeding pump. In a solvent mixing device that sucks each solvent into a liquid feeding pump at a predetermined ratio and mixes them, the "open" state of one control valve and the "open" state of the next control valve during the suction stroke are In addition to creating a "fully closed" state in which all of the control valves are "closed" in a very short time, the connecting piping between the control valve and the liquid pump inlet is configured to have small pressure deformation and small capacity. A solvent mixing device for a high performance liquid chromatograph, characterized in that a mixer is arranged on the discharge port side of a liquid sending pump.