Control device and method for pulse direct current spray ion source

Abstract

The invention provides a control device and method of a pulse direct current spray ion source, the control device comprises a first power supply, the first power supply applies voltage to an electrode of the ion source; the current detection unit is used for detecting the current on the mass spectrum cone opening and sending the current to the controller; the controller sends a voltage adjusting instruction according to the received current, the high-voltage power supply dynamically adjusts the applied voltage of the electrode in the spraying stage according to the adjusting instruction, and the ion source outputs stable spray; and when the applied voltage of the electrode reaches a first threshold value, the ion source enters a spraying stage. The device has the advantages of simple structure and the like.

Description

Technical Field

[0001] The present invention relates to an ion source, and particularly to a control device and method for a pulsed direct current electrospray ion source. Background Art

[0002] The pulsed direct current electrospray ion source (PDESI) is an open atmospheric pressure ionization technique that enables in-situ and rapid mass spectrometry detection of samples. The PDESI ion source consists of a glass capillary, a high-voltage electrode, and a fixing member. The front end of the glass capillary has a fine opening, and liquid sampling can be achieved by means of siphon action. During the ionization process of the PDESI ion source, the sample does not make direct electrical contact with the high-voltage electrode, so it can be used for picoliter sample mass spectrometry analysis.

[0003] In the PDESI ion source, the high-voltage electrode in the capillary is non-contact with the liquid sample. The high-voltage current needs to be conducted to the liquid sample through gaseous conductive ions and the conductive molecular film on the capillary wall (mainly water molecules). Therefore, the electric field at the tip of the PDESI ion source is affected by the resistivity of the sample, gaseous conductive ions, and the conductive molecular film on the capillary wall, and the latter two are affected by the ambient temperature and humidity.

[0004] Compared with the conventional electrospray ion source, the spray speed of the PDESI ion source is affected by the spray high voltage, sample characteristics, capillary tip morphology, and ambient temperature and humidity due to the absence of an injection pump, which in turn affects the stability of the mass spectrometry detection signal and the spray duration. Although the spray speed can be adjusted by manually adjusting the spray high voltage, the spray of the PDESI ion source is a highly dynamic process, and it is difficult to achieve real-time and accurate control.

[0005] Currently, the methods for stable spraying are as follows: 1. Analyze the TIC (Total Ion Current) of the mass spectrometer to indirectly measure the spray speed. However, since the ratio between the number of ions reaching the detector and the spray current is affected by various factors, the control accuracy based on this method will be limited. Analyzing the TIC of the mass spectrometer will also affect the detection efficiency, especially for mass spectrometers with slower analysis speeds such as ion traps.

[0006] 2. Use multiple PDESI probes for sampling and calculate the average value to improve stability, but the detection efficiency will be reduced and the cost will increase exponentially. Summary of the Invention

[0007] To solve the deficiencies in the above-mentioned prior art solutions, the present invention provides a control device for a pulsed direct current electrospray ion source.

[0008] The object of the present invention is achieved by the following technical solutions: A control device for a pulsed direct current electrospray ionization source, comprising a first power supply, and the first power supply applies a voltage to the electrode of the ionization source; the control device further comprises: A current detection unit, which is used to detect the current on the mass spectrometry cone orifice and send it to the controller; A controller, the controller issues a voltage adjustment instruction according to the received current, the first power supply dynamically adjusts the applied voltage of the electrode during the spraying stage according to the adjustment instruction, and the ionization source outputs a stable spray; when the applied voltage of the electrode reaches the first threshold, the ionization source enters the spraying stage.

[0009] Another object of the present invention is to provide a control method for a pulsed direct current electrospray ionization source, and this object of the invention is achieved through the following technical solutions: A control method for a pulsed direct current electrospray ionization source, the control method comprising the steps of: Step 1, the first power supply applies a voltage to the electrode of the ionization source and gradually increases the voltage value; When the voltage value reaches the first threshold, the sample in the ionization source is ionized, and the ionization source enters the spraying stage; Step 2, during the spraying stage, the current detection unit detects the current of the mass spectrometry cone orifice and sends it to the controller; the controller issues a voltage adjustment instruction according to the received current, the first power supply dynamically adjusts the applied voltage of the electrode during the spraying stage according to the adjustment instruction, and the ionization source outputs a stable spray.

[0010] Compared with the prior art, the beneficial effects of the present invention are: 1. Simple structure; The mass spectrometer has few modifications and has no impact on the mass spectrometry analysis speed and performance; 2. Detect the current of the mass spectrometry cone orifice, directly measure the spraying current, with high accuracy and fast response speed; 3. With an intelligent control algorithm, online learning can be realized, the controller parameters can be dynamically adjusted, closed-loop real-time control is achieved, and the control accuracy is high; The stability of the mass spectrometry analysis result is improved, and the spraying duration can also be controlled to increase the number of target substances detected; 4. Wide application range, can solve the impacts brought by inconsistent spray needle sizes, environmental changes and sample characteristics; 5. Detect situations such as spraying completion, broken needle and needle head blockage through the state parameter detection probe.. Description of the Drawings

[0011] Referring to the accompanying drawings, the disclosure of the present invention will become easier to understand. It is easy for those skilled in the art to understand that: these drawings are only used to illustrate the technical solutions of the present invention and are not intended to limit the protection scope of the present invention. In the drawings: Figure 1 is a schematic structural diagram of a control device according to an embodiment of the present invention; Figure 2 is a schematic diagram of the high - voltage and spray current changes according to an embodiment of the present invention; Figure 3 is a schematic diagram of a controller according to an embodiment of the present invention; Figure 4 is a schematic diagram of the voltage and current changes when spray is abnormal according to an embodiment of the present invention. Detailed implementation manners

[0012] Figures 1 - 4 The following description and the following illustrate alternative specific embodiments of the present invention to teach those skilled in the art how to implement and reproduce the present invention. To teach the technical solution of the present invention, some conventional aspects have been simplified or omitted. Those skilled in the art should understand that variations or substitutions derived from these specific embodiments will fall within the scope of the present invention. Those skilled in the art should understand that the following features can be combined in various ways to form multiple variations of the present invention. Thus, the present invention is not limited to the following alternative specific embodiments, but is defined only by the claims and their equivalents.

[0013] Embodiment 1.

[0014] The control device of the pulsed direct - current spray ionization source according to Embodiment 1 of the present invention, as Figure 1 shown, includes: The first power supply 42 applies a voltage to the electrode 111 of the ion source 11.

[0015] The current detection unit 31 is used to detect the current on the mass spectrometry cone orifice 21 and send it to the controller 51.

[0016] The controller 51 issues a voltage adjustment instruction according to the received current. The first power supply 42 dynamically adjusts the applied voltage of the electrode 111 during the spray stage according to the adjustment instruction, and the ion source 11 outputs a stable spray. When the applied voltage of the electrode 111 reaches the first threshold, the ion source 11 enters the spray stage.

[0017] For automated operation, further, the control device further includes: The position sensor 61 is used to detect whether the ion source 11 is in place, and the detection result is sent to the controller 51.

[0018] To reduce the influence of the current detection unit 31 on the mass spectrometry cone orifice 21, further, the current detection unit 31 uses an isolation - type ammeter, and the second power supply 41 applies a bias voltage to the mass spectrometry cone orifice 21 through the isolation - type ammeter.

[0019] Control method for pulsed direct current electrospray ionization source according to an embodiment of the present invention, the control method comprising steps.

[0020] Step 1, as Figure 2 shown, the first power supply 42 applies a voltage to the electrode 111 of the ion source 11 and gradually increases the voltage value.

[0021] When the voltage value reaches the first threshold, the sample in the ion source 11 is ionized and the ion source 11 enters the spraying stage.

[0022] Step 2, during the spraying stage, the current detection unit 31 detects the current at the mass spectrometry cone orifice 21 and sends it to the controller 51; the controller 51 issues a voltage adjustment instruction according to the received current, and the first power supply 42 dynamically adjusts the applied voltage of the electrode 111 during the spraying stage according to the adjustment instruction, and the ion source 11 outputs a stable spray.

[0023] In order to achieve closed-loop control, further, the working mode of the controller 51 is: The controller 51 dynamically adjusts the applied voltage of the electrode 111 according to the deviation value between the current at the mass spectrometry cone orifice 21 and the target value, and the preset PID parameters to obtain a stable spray.

[0024] In order to improve the spraying stability, further, as Figure 3 shown, the SCN network is used as the state observer of the ion source 11 to approximate the effect of the controlled ion source 11.

[0025] The input voltage and output current at the start of the controlled ion source 11 are input into the SCN observer for online training, and the ion source hysteresis effect model is quickly approximated through the incremental learning method to complete the online learning of the network.

[0026] At the initial stage of the control system, the SCN is a single-node L (the value of L is set in advance) -layer feedforward network, and the output of each layer of this network can be expressed as;

[0027] w j and are b j the weights and biases of each node in the hidden layer (the generation intervals of and are set in advance, such as [- λ , λ ), is the output of the previous hidden layer, g j is the sigmoid activation function, β j is the output weight of each node in the L-th layer.

[0028] Before controlling the ion source, first set the maximum number of nodes that the SCN can generate NAnd the maximum number of layers L (to avoid overfitting of the network). Input the difference between the system output current and the ideal current and the controller output voltage into the SCN, and calculate the difference sequence between the neural network layers . Then, determine whether the square of the inner product of e and the activation function g for each layer is less than the set threshold. If it is less, no new w j and b j will be generated for this layer. If it is greater, new network nodes w j and b j (taking values in [- λ , λ ) will be generated for this layer, and the hidden layer weights β j will be updated using the least squares method. The model training ends until the difference between the output current and the ideal current is less than the set threshold, and the fitting of the effect model is completed (the training will also terminate when the number of SCN nodes is greater than N or the maximum number of layers L).

[0029] The trained SCN observer outputs the state variables of the ion source; The trained SCN observer outputs the state variables of the ion source.

[0030] Use the output system state variables for fuzzy inference, adaptively adjust the PID control parameters, and obtain a stable spray current.

[0031] To improve efficiency, further, the control method includes the steps of: Step 3: As the sample is depleted, the spray current gradually deviates from the target value, the applied voltage climbs and reaches the second threshold, and the controller 51 turns off the high-voltage output of the first power supply 42, and the spraying ends.

[0032] To implement the diagnostic function, further, in step 1, when the voltage value reaches the first threshold, the current output by the current detection unit 31 is 0; In step 2, under the adjustment instruction output by the controller 51, the applied voltage continues to increase, the current detection unit 31 outputs current pulses, and then the current drops, and the current remains below the normal value; The applied voltage is gradually increased to the second threshold, the current drops, and it is diagnosed that the needle of the ion source 11 is broken.

[0033] To implement the diagnostic function, further, in step 1, when the voltage value reaches the first threshold, the current output by the current detection unit 31 is below the normal value; In step 2, under the adjustment instruction output by the controller 51, the applied voltage is increased to the second threshold, the current remains below the normal value, and the position time is greater than normal, and it is diagnosed that the needle of the ion source 11 is blocked.

[0034] Embodiment 2.

[0035] Application example of the control device and method according to Embodiment 1 of the present invention.

[0036] In this application example, as Figure 1 shown, the current detection unit 31 uses an isolation-type ammeter, which can measure currents in the range of picoamperes to microamperes, and its internal resistance is about in the order of ohms. The second power supply 41 applies a certain bias voltage to the mass spectrometry cone orifice 21 through the isolation-type ammeter, so that the influence of the existence of the isolation-type ammeter on the bias voltage of the mass spectrometry cone orifice 21 is extremely low and will not affect the ion transmission of the mass spectrometer.

[0037] The position sensor uses an optoelectronic module to detect whether the ion source is in place.

[0038] The control method of the pulsed direct current electrospray ion source according to the embodiment of the present invention, the control method includes steps.

[0039] Step 1, as Figure 2 shown, the first power supply 42 applies a voltage to the electrode 111 of the ion source 11 and gradually increases the voltage value.

[0040] When the voltage value reaches the first threshold, the sample in the ion source 11 is ionized and the ion source 11 enters the spraying stage.

[0041] Step 2, in the spraying stage, the current detection unit 31 detects the current of the mass spectrometry cone orifice 21 and sends it to the controller 51; the controller 51 issues a voltage adjustment instruction according to the received current. The formation method of the adjustment instruction is: as Figure 3 shown, use the SCN network as the state observer of the ion source 11 to approximate the effect-controlled ion source 11.

[0042] Input the input voltage and output current at the start of the controlled ion source 11 into the SCN observer for online training, and quickly approximate the ion source hysteresis effect model through the incremental learning method to complete the online learning of the network.

[0043] At the initial stage of the control system, the SCN is a single-node L (the value of L is set in advance) -layer feedforward network, and the output of each layer of this network can be expressed as;

[0044] w j and are b j the weights and biases of each node in the hidden layer (and the generation intervals are set in advance, such as [- λ , λ ), is the output of the previous hidden layer, g j is the sigmoid activation function, β jis the output weight of each node in the L-th layer.

[0045] Before controlling the ion source, first set the maximum number of nodes that the SCN can generate N and the maximum number of layers L (to avoid overfitting of the network). Input the difference between the system output current and the ideal current and the controller output voltage into the SCN, and calculate the difference sequence between each layer of the neural network . Then determine whether the square of the inner product of e and the activation function g in each layer is less than the set threshold. If it is less, no new w j and b j will be generated in this layer. If it is greater, new network nodes w j and b j (take values in [- λ , λ ) will be generated in this layer, and the hidden layer weight β will be updated using the least squares method j . The model training ends until the difference between the output current and the ideal current is less than the set threshold, and the fitting of the effect model is completed (the training will also terminate when the number of SCN nodes is greater than N or the maximum number of layers L).

[0046] The trained SCN observer outputs the state variables of the ion source.

[0047] Fuzzy inference is performed using the output system state variables to adaptively adjust the PID control parameters. The controller 51 outputs a voltage adjustment value and sends it to the first power supply 42.

[0048] Figure 3 Among them, u is the control voltage output by the controller, If is the actual electrospray current value, It represents the desired electrospray current value, e represents the difference between the desired current and the actual current, x is the system state variable observed by the SCN, and KP, KI, and KD are the parameters of the proportional, integral, and differential links of the PID controller.

[0049] The first power supply 42 dynamically adjusts the applied voltage of the electrode 111 during the spraying stage according to the adjustment instruction, and the ion source 11 outputs a stable spray.

[0050] Step 3: As the sample is depleted, the spray current gradually deviates from the target value, the applied voltage climbs and reaches the second threshold, and the controller 51 turns off the high-voltage output of the first power supply 42, and the spraying ends.

[0051] In step 1, as shown in Figure 4 (a) and Figure 4 (b), when the voltage value reaches the first threshold, the current output by the current detection unit 31 is 0; Under the action of the closed-loop controller, the voltage U rapidly increases and exceeds the PDESI probe spray threshold voltage, and a pulse appears instantaneously in I. As the voltage U rises again and reaches the preset maximum voltage U3, the weak spray current I slowly decreases. If the spray state parameters change as described above, it can be judged that there is a micro fracture in the needle tip.

[0052] In step 2, under the adjustment instruction output by the controller 51, the applied voltage rapidly increases, and the current detection unit 31 instantaneously outputs a current pulse, and most of the samples are ejected. The callback of the applied voltage can only maintain a weak spray current (below the normal value).

[0053] The applied voltage is gradually increased to the second threshold, and the weak spray current slowly decreases, diagnosing that there is a micro fracture in the needle tip of the ion source 11.

[0054] In step 1, as Figure 4 (c) and Figure 4 (d) shows, when the voltage value reaches the first threshold, the current detection unit 31 outputs a weak spray current (below the normal value).

[0055] In step 2, under the adjustment instruction output by the controller 51, the applied voltage rapidly increases to the second threshold, the current still remains below the normal value, and the position time is greater than normal, diagnosing that the needle tip of the ion source 11 is blocked.

Claims

1. A control device for a pulsed direct current electrospray ionization source, comprising a first power supply, the first power supply applying a voltage to an electrode of the ionization source; characterized in that, The control device further includes: A current detection unit, which is used to detect the current on the mass spectrometry cone orifice and send it to the controller; A controller, which issues a voltage adjustment instruction according to the received current. The first power supply dynamically adjusts the applied voltage of the electrode during the spraying stage according to the adjustment instruction, and the ion source outputs a stable spray; when the applied voltage of the electrode reaches the first threshold, the ion source enters the spraying stage.

2. The control device according to claim 1, characterized in that The control device further includes: A position sensor, which is used to detect whether the ion source is in place and send the detection result to the controller.

3. The control device according to claim 1, characterized in that The current detection unit adopts an isolated ammeter, and the second power supply applies a bias voltage to the mass spectrometry cone orifice through the isolated ammeter.

4. The control device according to claim 1, characterized in that, The controller adopts a PID controller.

5. A control method for a pulsed direct current electrospray ion source, the control method including the steps of: Step 1: The first power supply applies a voltage to the electrode of the ion source and gradually increases the voltage value; When the voltage value reaches the first threshold, the sample in the ion source is ionized, and the ion source enters the spraying stage; Step 2: During the spraying stage, the current detection unit detects the current on the mass spectrometry cone orifice and sends it to the controller; the controller issues a voltage adjustment instruction according to the received current, and the first power supply dynamically adjusts the applied voltage of the electrode during the spraying stage according to the adjustment instruction, and the ion source outputs a stable spray.

6. The control method according to claim 5, wherein The working mode of the controller is: The controller dynamically adjusts the applied voltage of the electrode according to the deviation value between the current on the mass spectrometry cone orifice and the target value, and the preset PID parameters to obtain a stable spray.

7. The control method according to claim 6, wherein Use the SCN network as the state observer of the ion source to approximate the effect of the controlled ion source; Input the input voltage and output current at the start of the controlled ion source into the SCN observer for online training, and approximate the ion source hysteresis effect model through the incremental learning method to complete the online learning of the network; The trained SCN observer outputs the state variables of the ion source; Use the output system state variables for fuzzy reasoning to adaptively adjust the PID control parameters to obtain a stable spray current.

8. The control method according to claim 5, characterized in that The control method includes the steps of: Step 3: As the sample is depleted, the spray current gradually deviates from the target value, the voltage climbs and reaches the second threshold, and the controller shuts off the high-voltage output of the first power supply, and the spraying ends.

9. The control method according to claim 5, wherein In step 1, when the voltage value reaches the first threshold, the current output by the current detection unit is 0; In step 2, under the adjustment instruction output by the controller, the applied voltage continues to increase, the current detection unit outputs current pulses, and then the current drops, and the current is maintained below the normal value; The applied voltage is gradually increased to the second threshold, the current drops, and it is diagnosed that the needle of the ion source is broken.

10. The control method according to claim 5, wherein In step 1, when the voltage value reaches the first threshold, the current output by the current detection unit is below the normal value; In step 2, under the adjustment instruction output by the controller, the applied voltage is increased to the second threshold, the current is maintained below the normal value, and the position time is greater than the normal value, and it is diagnosed that the needle of the ion source is blocked.

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