Multi-element low-pressure gradient mixing control method for liquid chromatography
By controlling the alternating suction and discharge processes of the parallel screw pumps and adjusting the piston movement speed and time, the accuracy and repeatability issues of low-pressure gradient mixing are solved, uniform mixing of multi-element mobile phases is achieved, and costs are reduced.
Patent Information
- Application Number
- CN202510997678.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-19
- Publication Date
- 2025-10-10
AI Technical Summary
In the prior art, parallel screw pumps have insufficient mixing accuracy and repeatability when performing low-pressure gradient mixing, and are relatively expensive, making it difficult to achieve uniform mixing of multiple mobile phases.
By controlling the alternating suction and discharge processes of the first and second screw pumps in parallel, combined with the adjustment of the piston movement speed and time, and using the screw gap and solenoid valve delay for compensation, precise mixing of multi-element mobile phases can be achieved.
The accuracy and repeatability of low-pressure gradient mixing are improved, meeting the requirements of preparative liquid chromatography, reducing costs, and achieving uniform mixing of multi-element mobile phases.
Smart Images
Figure CN120761557A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of liquid chromatography control, and in particular to a liquid chromatography multivariate low-pressure gradient mixing control method. Background Art
[0002] Flash preparative liquid chromatography instruments typically use two or more mobile phases for gradient or isocratic elution of the column. In dual-pump systems, high-pressure gradient mixing can be achieved by using two pumps, A and B, to deliver different mobile phases. This approach comes with a cost disadvantage and is primarily used for binary mobile phase mixing. For a more cost-effective gradient or isocratic solution, a single pump plus a proportional valve can achieve low-pressure gradient mixing. Because parallel lead screw pumps deliver liquid continuously, but their aspiration is not, mobile phase mixing cannot be simply achieved by switching the pump on and off. Low-pressure gradient or isocratic mixing must be coordinated with the aspiration process. The mixing period for the multi-phase mobile phase is measured from the moment the piston switches from push to aspiration (screw motor drive direction reversal) until the piston completes aspiration (full travel distance L). The solenoid valve inlet for the corresponding mobile phase is opened and closed based on the piston's travel distance. However, mixing accuracy can be reduced due to lead screw backlash and the time delay between the solenoid valve opening and closing. Summary of the Invention
[0003] The purpose of the present invention is to provide a liquid chromatography multivariate low-pressure gradient mixing control method to address the deficiencies in the prior art. The method enables a parallel screw pump to perform the function of low-pressure gradient mixing while ensuring uniform mixing and mixing accuracy and repeatability that meet the requirements of preparative liquid chromatography.
[0004] The present invention provides a liquid chromatography multivariate low-pressure gradient mixing control method, which comprises the following steps: Controlling a first screw pump and a second screw pump connected in parallel to alternately suck and discharge liquid; wherein, when the first screw pump alternates between sucking and discharging liquid, the piston of the first screw pump stops moving for a set time; when the second screw pump alternates between sucking and discharging liquid, the piston of the second screw pump stops moving for a set time; When the first screw pump and the second screw pump discharge liquid at the same time, the sum of the piston movement speeds of the first screw pump and the second screw pump is the set speed value; When only the first screw pump is discharging liquid, the moving speed of the first screw pump is the set speed value; when only the second screw pump is discharging liquid, the moving speed of the second screw pump is the set speed value.
[0005] The liquid chromatography multivariate low-pressure gradient mixing control method as described above, wherein, optionally, before the parallel first screw pump and the second screw pump cyclically alternately aspirate and discharge liquid, an initialization process is further included: The initialization process includes: moving the pistons of the first screw pump and the second screw pump in the direction of discharging liquid until both pistons move to the photoelectric origin at the front end of the corresponding cavity; Control the piston of the first screw pump to move and start sucking liquid, and keep the piston of the second screw pump stationary; until the first screw pump starts to discharge liquid at a set speed value.
[0006] As described above, in the liquid chromatography multivariate low-pressure gradient mixing control method, optionally, during the initialization process, when the pistons of the first screw pump and the second screw pump are moved to the corresponding photoelectric origin positions, the movement speed of the pistons of the first screw pump and the second screw pump is not greater than half of the set speed value.
[0007] As described above, in the liquid chromatography multivariate low-pressure gradient mixing control method, optionally, during the process of the first screw pump or the second screw pump aspirating liquid, the proportional valve is controlled according to the moving distance of the piston, and the piston stroke is corrected using the correction value.
[0008] The liquid chromatography multivariate low-pressure gradient mixing control method as described above, wherein, optionally, when the mobile phase requires a mixture of at least two liquids; The closing time of the proportional valve corresponding to each liquid corresponds to the distance between the piston of the first screw pump or the second screw pump and the photoelectric origin: in, is the distance between the position corresponding to the photoelectric origin when the i-th liquid is aspirated; L is the distance between the first screw pump or the second screw pump and the photoelectric origin after a single aspiration is completed; L0 is the compensation distance between the first liquid aspiration and the photoelectric zero point; P i is the proportion of the i-th liquid in the mobile phase.
[0009] In the liquid chromatography multivariate low-pressure gradient mixing control method as described above, optionally, the number of the proportional valves is 2-4.
[0010] As described above, in the liquid chromatography multivariate low-pressure gradient mixing control method, optionally, when the first screw pump is aspirating liquid, the maximum movement speed of the piston of the first screw pump is greater than the set speed value; when the second screw pump is aspirating liquid, the maximum movement speed of the piston of the first screw pump is greater than the set speed value.
[0011] In the liquid chromatography multivariate low-pressure gradient mixing control method as described above, optionally, the first screw pump and the second screw pump have the same shape and size.
[0012] Compared to the prior art, the present invention rationally controls the alternating time of the first and second screw pumps connected in parallel. When the first screw pump alternates between suctioning and discharging liquid, the piston of the first screw pump stops moving for a set time; when the second screw pump alternates between suctioning and discharging liquid, the piston of the second screw pump stops moving for a set time. When the first and second screw pumps are discharging liquid simultaneously, the sum of the piston movement speeds of the first and second screw pumps is the set speed value. Furthermore, when only the first screw pump is discharging liquid, the piston movement speed of the first screw pump is the set speed value, and when only the second screw pump is discharging liquid, the piston movement speed of the second screw pump is the set speed value. In this way, the screw gap and the delay in the opening and closing time of the solenoid valve can be taken into account, and the accuracy and repeatability requirements under different proportional distribution can be achieved by adjusting the compensation parameters. BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Figure 1 It is a structural schematic diagram of the screw pump proposed in the present invention.
[0014] Figure 2 This is a timing diagram of the screw pump operation proposed by the present invention.
[0015] Figure 3 It is a schematic diagram of the proportion distribution when the mobile phase proposed by the present invention is a mixture of two liquids.
[0016] Figure 4 It is a flowchart of the steps of the method proposed by the present invention.
[0017] Description of the accompanying drawings: 1-first screw pump, 2-second screw pump. DETAILED DESCRIPTION
[0018] The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and are not to be construed as limiting the present invention.
[0019] In response to the problems raised in the background technology, the present invention proposes the following embodiments to solve them.
[0020] Please refer to Figures 1 to 4 This embodiment proposes a liquid chromatography multivariate low-pressure gradient mixing control method, which includes the following steps: The first screw pump 1 and the second screw pump 2 are controlled to alternately suck and discharge liquid in cycles; when the first screw pump 1 alternates between sucking and discharging, the piston of the first screw pump 1 stops moving for a set time; when the second screw pump 2 alternates between sucking and discharging, the piston of the second screw pump 2 stops moving for a set time. In the embodiment, the first screw pump 1 and the second screw pump 2 operate alternately, that is, when the first screw pump 1 sucks liquid, the second screw pump 2 discharges liquid; when the first screw pump 1 discharges liquid, the second screw pump 2 sucks liquid; only in alternation, the first screw pump 1 and the second screw pump 2 exist in the case of discharging liquid at the same time. In the alternation of the sucking process and the discharging process of the first screw pump 1, the piston is temporarily stopped moving to give the screw rod of the first screw pump 1 enough time to adjust and eliminate the influence of the screw rod gap. In the alternation of the sucking process and the discharging process of the second screw pump 2, the piston of the second screw pump 2 stops moving for a set time to give the screw rod of the first screw pump 1 enough time to adjust and eliminate the influence of the screw rod gap. During the stop of the piston of the first screw pump 1 or the piston of the second screw pump 2, the corresponding screw rod is adjusted to prepare for turning, and the screw rod gap is eliminated at the same time.
[0021] In order to ensure that the liquid can be stably and uniformly discharged, and in order to ensure that the liquid is discharged at a constant speed, in the embodiment, when the first screw pump 1 and the second screw pump 2 discharge liquid at the same time, the sum of the moving speeds of the pistons of the first screw pump 1 and the second screw pump 2 is a set speed value; when only the first screw pump 1 discharges liquid, the moving speed of the first screw pump 1 is the set speed value; when only the second screw pump 2 discharges liquid, the moving speed of the second screw pump 2 is the set speed value. In specific implementation, the determination method of the set speed value is the ratio of the determined flow phase flow to the cross-sectional area of the cavity of the first screw pump 1 or the second screw pump 2. In this way, the flow phase can be stably flowed to ensure accuracy.
[0022] In the embodiment, during the process of alternately sucking and discharging liquid in cycles of the first screw pump 1 and the second screw pump 2, the flow phase can be stably and uniformly discharged. In actual application, in order to ensure that the first screw pump 1 and the second screw pump 2 alternately suck and discharge liquid at appropriate time, initialization processing is also needed before the first screw pump 1 and the second screw pump 2 alternately suck and discharge liquid in cycles. Specifically, before the first screw pump 1 and the second screw pump 2 alternately suck and discharge liquid in cycles, the initialization process also includes: The initialization process includes: moving the pistons of the first screw pump 1 and the second screw pump 2 to the direction of discharging liquid until both pistons move to the optical origin at the front end of the corresponding cavity; that is, moving the pistons of the first screw pump 1 and the second screw pump 2 to the corresponding optical origin, that is, moving the pistons of the first screw pump 1 and the second screw pump 2 to the position of the corresponding optical origin.
[0023] Then, the piston of the first screw pump 1 is controlled to move and start sucking liquid, while the piston of the second screw pump 2 is kept stationary until the first screw pump 1 starts to discharge liquid at a set speed value. The process of the first screw pump 1 from the photoelectric origin to the uniform speed discharge specifically includes: stopping for a set time to allow the screw of the first screw pump 1 to adjust the screw gap, then accelerating the suction, sucking liquid at a uniform speed, decelerating the suction, stopping for a set time, then accelerating the discharge, and then starting the uniform speed discharge; at the same time, the piston of the second screw pump 2 remains stationary; when the piston of the first screw pump 1 starts to discharge liquid at a uniform speed, the piston of the second screw pump 2 continues to remain stationary for a set time, and then starts to accelerate the suction, suck liquid at a uniform speed, decelerate the suction, and remains stationary for a set time; the first screw pump 1 starts to decelerate the discharge, and the second screw pump starts to accelerate the discharge, and then begins to cycle alternately sucking and discharging liquid.
[0024] During initialization, the pistons of the first and second screw pumps 1 and 2 are moved to their corresponding photoelectric origins at a speed no greater than half the set speed. Reducing the piston speed helps improve the accuracy of the piston stop position and prevent stalling.
[0025] During specific implementation, in order to achieve mixing between different liquids and correct the stroke of the piston, in this embodiment, during the process of the first screw pump 1 or the second screw pump 2 sucking liquid, the proportional valve is controlled according to the moving distance of the piston, and the piston stroke is corrected using the correction value. During specific implementation, the proportional valve is arranged upstream of the first screw pump 1 and the second screw pump 2, and the proportional valve has at least two solenoid valves, each of which corresponds to a liquid. By turning on and off different solenoid valves, different liquids are mixed in proportion to achieve the effect of mixing multiple liquids to form a mobile phase. It should be pointed out that in order to ensure the accuracy of liquid mixing, when controlling the proportional valve, at the same time point, only the solenoid valve corresponding to one liquid is opened, that is, only the same liquid is sucked in at the same time. The accuracy of sucking in various liquids can be controlled by the conduction time of the solenoid valve on the proportional valve.
[0026] Please refer to Figure 3 For example, when the mobile phase requires a mixture of at least two liquids, the closing time of the proportional valve corresponding to each liquid corresponds to the distance between the piston of the first screw pump 1 or the second screw pump 2 and the photoelectric origin: in, is the distance between the position corresponding to the photoelectric origin when the i-th liquid is aspirated; L is the distance between the first screw pump 1 or the second screw pump 2 and the photoelectric origin after a single aspiration is completed; L0 is the compensation distance between the first liquid aspiration and the photoelectric zero point; P i is the proportion of the i-th liquid in the mobile phase.
[0027] Specifically, when two liquids are mixed, the values of i in the above formula are 1 and 2; that is, when the two liquids are mixed, the time for the proportional valve corresponding to the first liquid to close corresponds to the length of the piston of the first screw pump 1 or the second screw pump 2 from the photoelectric origin: The time for closing the proportional valve corresponding to the second liquid corresponds to the length of the piston of the first screw pump 1 or the second screw pump 2 from the photoelectric origin: Among them, due to Substituting this into the above formula, we can obtain that the time it takes for the proportional valve corresponding to the second liquid to close corresponds to the distance between the piston of the first screw pump 1 or the second screw pump 2 and the photoelectric origin, L. Therefore, in practical applications, the time it takes for the proportional valve corresponding to the second liquid to close corresponds to the distance between the piston of the first screw pump 1 or the second screw pump 2 and the photoelectric origin, L, without using the above formula.
[0028] When the three liquids are mixed, The values of i in are 1, 2, and 3; that is, the time for the proportional valve corresponding to the first liquid to close corresponds to the distance between the piston of the first screw pump 1 or the second screw pump 2 and the photoelectric origin: The time for closing the proportional valve corresponding to the second liquid corresponds to the length of the piston of the first screw pump 1 or the second screw pump 2 from the photoelectric origin: The time for closing the proportional valve corresponding to the third liquid corresponds to the length of the piston of the first screw pump 1 or the second screw pump 2 from the photoelectric origin: ; In the above formula, P1 is the proportion of the first liquid in the mobile phase, P2 is the proportion of the second liquid in the mobile phase, and P3 is the proportion of the third liquid in the mobile phase.
[0029] The length of the piston of the first screw pump 1 or the second screw pump 2 from the photoelectric origin corresponding to the time when the proportional valve corresponding to each liquid is opened is the length of the piston of the first screw pump 1 or the second screw pump 2 from the photoelectric origin corresponding to the time when the proportional valve corresponding to the previous liquid is closed. In practical applications, the sum of the proportions of all types of liquids should be 1. For example, when the mobile phase is a mixture of two liquids, and the proportion of the first liquid is 40%, the proportion of the other liquid should be 60%. In this case, the length of the piston of the first screw pump 1 or the second screw pump 2 from the photoelectric origin corresponding to the time when the proportional valve corresponding to the first liquid is closed is ; is the content of the second liquid in the mobile phase.
[0030] In a specific implementation, the number of proportional valves is 2-4, and each valve corresponds to a liquid. Thus, when the number of valves is 4, 2-4 liquids can be mixed in proportion.
[0031] While the second screw pump 2 is discharging liquid at a constant speed, the first screw pump 1 must complete aspiration and pause twice before and after aspiration. Therefore, to ensure synchronization between the second and first screw pumps 2, the maximum speed of the piston of the first screw pump 1 must be greater than the set speed value during aspiration; and the maximum speed of the piston of the second screw pump 2 must be greater than the set speed value during aspiration. Furthermore, the cross-section of the cavity of the first screw pump 1 and the receptor of the second screw pump 2 must be equal. In phase, during the first screw pump 1's constant speed discharging, the second screw pump 2 must complete aspiration and pause twice before and after aspiration. Therefore, to ensure synchronization between the first and second screw pumps 1 and 2, the maximum speed of the piston of the first screw pump 1 must be greater than the set speed value during aspiration. In a specific implementation, the first and second screw pumps 1 and 2 have the same shape and dimensions. This facilitates the alternating control of the first and second screw pumps 1 and 2. To achieve uniform discharge.
[0032] To facilitate understanding of this solution, the following example uses a low-pressure quaternary pump and liquids S1-S4 as an example. The mobile phase of each channel corresponds to a solenoid valve, which controls the suction of each mobile phase to achieve uniform suction and discharge of each liquid at a uniform speed. In this example, for a binary gradient, the proportion of S1 is 40% and the proportion of S2 is 60%. Please refer to Figure 4 , this method is specifically performed as follows: Step 1: Start the operation, and initialize the first screw pump 1 and the second screw pump 2 respectively, that is, move the pistons of the first screw pump 1 and the second screw pump 2 to the corresponding photoelectric origin.
[0033] Step 2: Move the first screw pump 1 to suck liquid, and keep the second screw pump 2 stationary; Step three: After the first screw pump 1 completes the suction, it starts to discharge the liquid. When the first screw pump 1 starts to decelerate and discharge the liquid, the second screw pump 2 starts to accelerate and discharge the liquid. When the speed of the first screw pump 1 drops to 0, the speed of the second screw pump 2 increases to the set speed value.
[0034] Step 4: The second screw pump 2 maintains the set speed value for discharging. During this process, the first screw pump 1 changes from a discharge speed of 0 to a delay of a period of time, such as 50ms, and then switches from discharging to absorbing liquid. During the absorbing process, the first screw pump 1 first accelerates the absorbing liquid, then maintains a uniform absorbing speed, and then decelerates the absorbing liquid. After the absorbing speed drops to 0, there is a delay for a period of time. At this time, the uniform discharge process of the second screw pump 2 ends.
[0035] Step 5: The second screw pump 2 starts to decelerate the discharge, and the first screw pump 1 starts to accelerate the discharge until the discharge speed of the second screw pump 2 drops to 0. At the same time, the discharge speed of the first screw pump 1 increases to the set speed value.
[0036] Step six, the first screw pump 1 maintains the set speed value to discharge the liquid; at the same time, the second screw pump 2 starts to accelerate the liquid suction, maintains a constant speed of liquid suction, and decelerates the liquid suction after a delay of 50ms. After the liquid suction speed drops to 0, there is a delay of 50ms. At this time, the first screw pump 1 starts to decelerate the discharge, and the second screw pump 2 starts to accelerate the discharge; while the speed of the first screw pump 1 drops to 0, the speed of the second screw pump 2 increases to the set speed value.
[0037] Step 7: Repeat steps 4 to 6 until the control stops running.
[0038] In this embodiment, regardless of the first screw pump 1 or the second screw pump 2, the total stroke of sucking and discharging liquid is L, and the completion of suction and discharge is based on the corresponding piston movement distance driven by the motor; the mobile phase can be selected from a variety of mobile phases.
[0039] If both S1 and S2 mobile phases are selected, then when the motor drives the piston to start aspirating the mobile phase, it is at position 0, that is, the photoelectric origin. At this time, the mobile phase S1 solenoid valve A is opened. When the movement distance L1 = P1 * (L-L0) + L0, the mobile phase S1 solenoid valve A is closed and the S2 mobile phase solenoid valve B is opened. When the total stroke L is reached, all liquid inlet solenoid valves are closed and the motor stops the aspiration process.
[0040] Before the motor drives the piston to push the liquid, it first pushes the liquid at a set speed, L0, to eliminate screw gaps and prevent flow interruptions and pressure fluctuations when the two screw pumps alternate. When the first screw pump 1 and the second screw pump 2 alternate, after one screw pump's cavity has pushed the remaining set distance, each pump pushes the mobile phase at half the set speed, ensuring smooth alternating movement of the mobile phase between the two screw pumps.
[0041] For extreme gradient ratios below 8% or above 92%, the solenoid valve switches during the motor's acceleration or deceleration. A transient voltage suppressor (TVS) diode quickly discharges the solenoid valve coil energy, shortening the demagnetization time and reducing the solenoid valve closing time Δt, typically from 20-50 milliseconds to 5-10 milliseconds. This delayed closing time Δt affects gradient ratio accuracy. At the maximum speed Vmax, the delay error is Vmax * Δt, which is the distance the valve needs to be switched in advance. During acceleration or deceleration, the delayed closing time Δt remains constant; what changes is Vx, the constant speed from the initial speed V0 to Vmax. Since Vx does not change much during Δt during acceleration or deceleration, Vx is used as the approximate step compensation for the early valve switching. That is, the compensation value for gradient ratio conversion during acceleration or deceleration is approximately Vx * Δt.
[0042] The basic principles of the present invention have been described above in conjunction with specific embodiments. However, it should be noted that the advantages, strengths, and effects mentioned in the present invention are merely illustrative and non-limiting, and should not be construed as necessarily possessed by each embodiment of the present invention. Furthermore, the specific details disclosed above are provided for illustrative purposes and to facilitate understanding, and are not intended to be limiting. These details do not necessarily limit the present invention to being implemented using these specific details.
[0043] The block diagrams of the devices, apparatuses, equipment, and systems involved in the present invention are intended to be illustrative examples only and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the block diagrams. As will be appreciated by those skilled in the art, these devices, apparatuses, equipment, and systems may be connected, arranged, or configured in any manner. Words such as "include," "comprise," "have," and the like are open-ended words, meaning "including but not limited to," and may be used interchangeably therewith. The words "or" and "and" used herein refer to the words "and / or" and may be used interchangeably therewith, unless the context clearly indicates otherwise. The word "such as" used herein refers to the phrase "such as but not limited to," and may be used interchangeably therewith.
[0044] Additionally, as used herein, "or" used in a list of items beginning with "at least one" indicates a separate list, so that, for example, a list of "at least one of A, B, or C" means A or B or C, or AB or AC or BC, or ABC (i.e., A and B and C). Furthermore, the word "exemplary" does not mean that the example described is preferred or better than other examples.
[0045] It should also be noted that in the system and method of the present invention, each component or each step can be decomposed and / or recombined, and such decomposition and / or recombination should be regarded as equivalent solutions of the present invention.
[0046] Various changes, substitutions, and modifications may be made to the technology described herein without departing from the teachings as defined by the appended claims. Moreover, the scope of the claims is not limited to the specific aspects of the processes, machines, manufacture, compositions of things, means, methods, and actions described above. Currently existing or later developed processes, machines, manufacture, compositions of things, means, methods, or actions that perform substantially the same function or achieve substantially the same results as the corresponding aspects described herein may be utilized. Accordingly, the appended claims include within their scope such processes, machines, manufacture, compositions of things, means, methods, or actions.
[0047] The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects without departing from the scope of the present invention. Therefore, the present invention is not intended to be limited to the aspects shown herein, but rather to be accorded the widest scope consistent with the principles and novel features disclosed herein.
[0048] The above description has been provided for the purpose of illustration and description. Furthermore, this description is not intended to limit the embodiments of the present invention to the forms disclosed herein. Although a number of example aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations thereof.
Claims
1. A liquid chromatography multivariate low-pressure gradient mixing control method, characterized in that: The steps include: Controlling a first screw pump (1) and a second screw pump (2) connected in parallel to cyclically alternately suck and discharge liquid; wherein, when the first screw pump (1) alternates between sucking and discharging liquid, the piston of the first screw pump (1) stops moving for a set time; and when the second screw pump (2) alternates between sucking and discharging liquid, the piston of the second screw pump (2) stops moving for a set time; When the first screw pump (1) and the second screw pump (2) discharge liquid at the same time, the sum of the piston movement speeds of the first screw pump (1) and the second screw pump (2) is the set speed value; When only the first screw pump (1) discharges liquid, the moving speed of the first screw pump (1) is the set speed value; when only the second screw pump (2) discharges liquid, the moving speed of the second screw pump (2) is the set speed value.
2. The liquid chromatography multivariate low-pressure gradient mixing control method according to claim 1, characterized in that: Before the parallel first screw pump (1) and the second screw pump (2) cyclically alternately suck and discharge liquid, an initialization process is also included: The initialization process includes: moving the pistons of the first screw pump (1) and the second screw pump (2) in the direction of discharging liquid until both pistons move to the photoelectric origin at the front end of the corresponding cavity; The piston of the first screw pump (1) is controlled to move and start sucking liquid, and the piston of the second screw pump (2) is kept stationary; until the first screw pump (1) starts to discharge liquid at a set speed value.
3. The liquid chromatography multivariate low-pressure gradient mixing control method according to claim 2, characterized in that: During the initialization process, when the pistons of the first screw pump (1) and the second screw pump (2) are moved to the corresponding photoelectric origin positions, the moving speed of the pistons of the first screw pump (1) and the second screw pump is not greater than half of the set speed value.
4. The liquid chromatography multivariate low-pressure gradient mixing control method according to claim 1, characterized in that: During the process of the first screw pump (1) or the second screw pump (2) sucking liquid, the proportional valve is controlled according to the moving distance of the piston, and the piston stroke is corrected using the correction value.
5. The liquid chromatography multivariate low-pressure gradient mixing control method according to claim 2, characterized in that: When the mobile phase requires a mixture of at least two liquids; The time for the proportional valve corresponding to each liquid to be closed corresponds to the length of the piston of the first screw pump (1) or the second screw pump (2) from the photoelectric origin: in, is the distance between the position corresponding to the photoelectric origin when the i-th liquid is aspirated; L is the distance between the first screw pump (1) or the second screw pump (2) and the photoelectric origin after a single aspiration is completed; L0 is the compensation distance between the first liquid aspiration and the photoelectric zero point when the first liquid is aspirated; P i is the proportion of the i-th liquid in the mobile phase.
6. The liquid chromatography multivariate low-pressure gradient mixing control method according to claim 5, characterized in that: The number of the proportional valves is 2-4.
7. The liquid chromatography multivariate low-pressure gradient mixing control method according to any one of claims 2 to 6, characterized in that: When the first screw pump (1) is sucking liquid, the maximum moving speed of the piston of the first screw pump (1) is greater than the set speed value; when the second screw pump (2) is sucking liquid, the maximum moving speed of the piston of the first screw pump (1) is greater than the set speed value.
8. The liquid chromatography multivariate low-pressure gradient mixing control method according to any one of claims 2 to 6, characterized in that: The first screw pump (1) and the second screw pump (2) have the same shape and size.