阅读说明：本技术 拓宽质谱仪质量检测范围的分段四极杆装置及方法 (Segmented quadrupole rod device and method for widening mass detection range of mass spectrometer ) 是由 刘思雨 刘学 张丽平 于 2020-06-03 设计创作，主要内容包括：本发明提供一种拓宽质谱仪质量检测范围的分段四极杆装置及方法,该装置包括：中控电路、射频放大模块、分段四极杆；所述分段四极杆是把传统四极杆分为两段以上；所述射频放大模块数量与所述分段四极杆的段数相同,分别为对应的一段四极杆组提供射频电信号；所述射频放大模块由所述中控电路控制,所述中控电路发出的信号分成多路传递给所述射频放大模块,经所述射频放大模块放大后输出给每段杆组。本发明通过把四极杆分段,降低每段杆的电容,能够在相同的射频线圈条件下输出更高的电压,从而实现更宽的质量检测范围。(The invention provides a segmented quadrupole rod device and a method for widening the mass detection range of a mass spectrometer, wherein the device comprises the following components: the radio frequency amplifier comprises a central control circuit, a radio frequency amplification module and a segmented quadrupole rod; the segmented quadrupole rod divides the traditional quadrupole rod into more than two segments; the number of the radio frequency amplification modules is the same as that of the sections of the segmented quadrupole rods, and radio frequency electric signals are respectively provided for the corresponding sections of quadrupole rod groups; the radio frequency amplification module is controlled by the central control circuit, signals sent by the central control circuit are divided into multiple paths and transmitted to the radio frequency amplification module, and the signals are amplified by the radio frequency amplification module and then output to each rod group. The quadrupole rod is segmented, so that the capacitance of each segment of rod is reduced, higher voltage can be output under the same radio frequency coil condition, and wider quality detection range is realized.)

1. The utility model provides a widen segmentation quadrupole rod device of mass spectrometric quality detection range which characterized in that includes: the radio frequency amplification module is connected with the central control circuit;

the segmented quadrupole rod set comprises more than two groups of quadrupole rods, each group of quadrupole rods comprises four rod-shaped electrodes, and the rod-shaped electrodes are arranged in parallel; corresponding rod-shaped electrodes in the adjacent quadrupole rod sets are coaxial;

the radio frequency amplification modules are the same as the segmented quadrupole rod groups in number, provide radio frequency electric signals for the corresponding quadrupole rods respectively, and comprise direct current signals and high-voltage alternating current signals, wherein the high-voltage alternating current signals are two signals with the same amplitude and opposite phases;

the central control circuit controls the radio frequency amplification module, signals sent by the central control circuit are divided into multiple paths and transmitted to the radio frequency amplification module, and the signals are amplified by the radio frequency amplification module and then output to each group of quadrupole rods.

2. The segmented quadrupole rod set of claim 1, wherein: and each four-pole rod group has the same length.

3. The segmented quadrupole rod set of claim 1, wherein: the segmented quadrupole rods are hyperboloid electrode quadrupole rods or cylindrical electrode quadrupole rods.

4. The segmented quadrupole rod set of claim 1, wherein: and connecting parts are arranged between the segmented quadrupole rod sets or are not arranged, and the connecting parts are insulating parts made of non-conductive materials.

5. A method for widening mass detection range of a mass spectrometer is characterized in that: the method is used in an apparatus according to any of claims 1-4, comprising the steps of:

emitting ions to be detected to the segmented quadrupole rod device;

the radio frequency amplification module is adjusted to apply direct current signals and inverted high-voltage alternating current signals to the segmented quadrupole rod sets, the direct current signals between the adjacent quadrupole rod sets are the same, the high-voltage alternating current signals have the same amplitude, and the segmented quadrupole rods jointly form a group of long quadrupole rods;

qualified ions pass through the segmented quadrupole rod set.

6. A method for widening mass detection range of a mass spectrometer is characterized in that: the method is used in an apparatus according to any of claims 1-4, comprising the steps of:

emitting ions to be detected to the segmented quadrupole rod device;

the radio frequency amplification module is adjusted to apply direct current signals to one group or adjacent groups of quadrupole rods in the segmented quadrupole rod group, and ions to be detected are accelerated or decelerated;

the radio frequency amplification module is adjusted to apply direct current signals and reversed-phase high-voltage alternating current signals to quadrupole rod groups outside the quadrupole rod group applying the direct current signals in the segmented quadrupole rod group, the direct current signals between the adjacent quadrupole rod groups are the same, and the amplitude of the high-voltage alternating current signals is the same;

qualified ions pass through the segmented quadrupole rod set.

7. A method for widening mass detection range of a mass spectrometer is characterized in that: the method is used in an apparatus according to any of claims 1-4, comprising the steps of:

emitting ions to be detected to the segmented quadrupole rod device;

the radio frequency amplification module applies a direct current signal and an inverted high-voltage alternating current signal to the segmented quadrupole rod group, the amplitudes of the high-voltage alternating current signals are the same, and the amplitudes of the direct current signals are different;

qualified ions pass through the segmented quadrupole rod set.

Technical Field

The invention relates to the technical field of mass spectrometry, in particular to a segmented quadrupole rod device and a segmented quadrupole rod method for widening the mass detection range of a mass spectrometer.

Background

Mass spectrometry is a benchmark in the field of analysis, relying on high sensitivity, high resolution and high specificity detection of mass spectrometers. The mass spectrometry technology carries out qualitative and quantitative analysis of substances by detecting the mass-to-charge ratio of the substances, has the advantages of high detection sensitivity, strong specificity, high analysis speed and the like, and is widely applied to the research fields of chemistry, environmental science, life science and the like. The mass spectrometer consists of an ion source, an ion transmission part, a mass analyzer, a detector, a measurement and control and data processing system, a vacuum system and the like, wherein the mass analyzer is the most core part of the mass spectrometer and completes the mass analysis function of substances, and the mass analyzer can be divided into a plurality of types according to different analysis principles. Among them, the quadrupole mass analyzer is the earliest commercial mass spectrometer mass analyzer and is also a type of mass analyzer which is widely used at present.

The quadrupole rod mass analyzer is composed of four parallel electrode rods, and the same electric signals are applied to the four electrodesWhere U is a DC voltage, V is the amplitude of the RF,the high-voltage radio frequency signals of two adjacent electrodes have the same amplitude and 180-degree phase difference. During operation, the direct current voltage U is synchronously changed by scanning the radio frequency voltage or the radio frequency, so that the scanning and the detection of different m/z ions can be realized.

The quadrupole is a very precise device, and if the resolution of the quadrupole needs to reach 1000, the precision (including roundness, linearity and cylindricity), the positioning precision and the precision of the radio frequency power supply of the quadrupole need to reach 1000 times according to the simplest linear transfer model. If calculated according to a quadrupole rod with a diameter of 8mm and a 5-parameter system, the roundness of the quadrupole rod needs to be at least better than 2 μm. The overall accuracy of the quadrupole rods was measured to be between about 0.6 and 1.5 μm. The length and the radius of the quadrupole electrode are related to the resolution, the sensitivity and the detection quality range of the quadrupole mass analyzer, the radius of the quadrupole electrode commonly used at present is more than 2-16 mm, the length is usually 100-300 mm, and the longer the length is, the better the resolution of the analyzer is.

The longer the quadrupole rod is, the greater the processing difficulty is, the larger the capacitance is, the higher the requirement on the output signal of the radio frequency amplification circuit is, and the output high voltage can cause overlarge power consumption and difficult coil manufacturing. To improve the resolution of the instrument, a relatively long quadrupole needs to be manufactured, the length of the quadrupole is increased, the capacitance of the quadrupole is also increased, and accordingly, the radio frequency power supply is required to have high voltage matched with the quadrupole, so that the problem between the mass spectrometer detection resolution and the matching of the length of the quadrupole and the high voltage of the radio frequency circuit is caused.

Disclosure of Invention

The invention aims to solve the technical problems that the mass detection range of a mass spectrometer is enlarged, the resolution and the sensitivity are improved, the length of a quadrupole rod is too long, and a radio frequency coil cannot output high voltage matched with the quadrupole rod, and provides a segmented quadrupole rod device and a segmented quadrupole rod method for enlarging the mass detection range of the mass spectrometer.

The invention provides a segmented quadrupole rod device for widening the mass detection range of a mass spectrometer, which comprises: the radio frequency amplification module is connected with the central control circuit;

the segmented quadrupole rod set comprises more than two groups of quadrupole rods, each group of quadrupole rods comprises four rod-shaped electrodes, and the rod-shaped electrodes are arranged in parallel; corresponding rod-shaped electrodes in the adjacent quadrupole rod sets are coaxial;

the radio frequency amplification modules are the same as the segmented quadrupole rod groups in number, provide radio frequency electric signals for the corresponding quadrupole rods respectively, and comprise direct current signals and high-voltage alternating current signals, wherein the high-voltage alternating current signals are two signals with the same amplitude and opposite phases;

the central control circuit controls the radio frequency amplification module, signals sent by the central control circuit are divided into multiple paths and transmitted to the radio frequency amplification module, and the signals are amplified by the radio frequency amplification module and then output to each group of four-pole rod groups.

In an alternative embodiment, the segmented quadrupole rod sets, each quadrupole rod set, are the same length.

In an alternative embodiment, the segmented quadrupole rods are hyperboloid electrode quadrupole rods or cylindrical electrode quadrupole rods.

In an alternative embodiment, the segmented quadrupole rod sets are provided with or without connecting members therebetween, and the connecting members are insulating members of a non-conductive material.

The invention also provides a method for widening the mass detection range of a mass spectrometer, which is used in the device in any item, and comprises the following steps:

emitting ions to be detected to the segmented quadrupole rod device;

the radio frequency amplification module is adjusted to apply direct current signals and inverted high-voltage alternating current signals to the segmented quadrupole rod sets, the direct current signals between the adjacent quadrupole rod sets are the same, the high-voltage alternating current signals have the same amplitude, and the segmented quadrupole rods jointly form a group of long quadrupole rods;

qualified ions pass through the segmented quadrupole rod set.

The invention also provides a method for widening the mass detection range of a mass spectrometer, which is used in the device in any item, and comprises the following steps:

emitting ions to be detected to the segmented quadrupole rod device;

the radio frequency amplification module is adjusted to apply direct current signals to one group or adjacent groups of quadrupole rods in the segmented quadrupole rod group, and ions to be detected are accelerated or decelerated;

the radio frequency amplification module is adjusted to apply direct current signals and reversed-phase high-voltage alternating current signals to quadrupole rod groups outside the quadrupole rod group applying the direct current signals in the segmented quadrupole rod group, the direct current signals between the adjacent quadrupole rod groups are the same, and the amplitude of the high-voltage alternating current signals is the same.

Qualified ions pass through the segmented quadrupole rod set.

The invention also provides a method for widening the mass detection range of a mass spectrometer, which is used in the device in any item, and comprises the following steps:

emitting ions to be detected to the segmented quadrupole rod device;

the radio frequency amplification module applies a direct current signal and an inverted high-voltage alternating current signal to the segmented quadrupole rod group, the amplitudes of the high-voltage alternating current signals are the same, and the amplitudes of the direct current signals are different;

qualified ions pass through the segmented quadrupole rod set.

The invention has the following advantages and beneficial effects: by segmenting the conventional quadrupole rods, the processing difficulty of the quadrupole rods is reduced, the capacitance of each segment of the quadrupole rod is reduced, and the voltage requirement on the radio frequency amplification module is also reduced under the same voltage requirement; the working modes of the multi-section quadrupole rod set are respectively driven by the plurality of radio frequency amplification modules, so that the radio frequency voltage of each section of quadrupole rod is improved, and the quality detection range of the mass spectrometer can be widened. In addition, the segmented quadrupole rod device and the control mode of the multi-radio-frequency amplification module can realize multiple operation modes by using one set of device, and meet different analysis and detection requirements.

Drawings

It should be noted that the drawings described below only schematically illustrate some embodiments and do not include all possible embodiments.

FIG. 1 is a schematic diagram of a conventional quadrupole rod set-up in terms of construction and power-up;

FIG. 2 is a schematic diagram of the structure and power-up mode of a segmented quadrupole rod set provided in an embodiment of the present invention;

FIG. 3A is a schematic diagram of a conventional quadrupole control circuit;

FIG. 3B is a schematic diagram of a control circuit in an embodiment of a segmented quadrupole rod according to the present invention;

FIG. 4A is a graph showing the relationship between the scan curve and the stable region of the first segment of the rod set in the third power-up mode according to the embodiment of the present invention;

FIG. 4B is a graph showing the relationship between the scan curve and the stable region of the second rod set in the third power-up mode according to the embodiment of the present invention;

FIG. 4C is a diagram illustrating a relationship between a scan curve and a stable region of a third rod set in a third power-up mode according to an embodiment of the present invention;

FIG. 5A is a graph showing the simulation effect of ion passage rate in a conventional quadrupole scanning mode;

fig. 5B is a graph showing the simulation effect of the target ion throughput under the action of the third energization mode according to the embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention clearer, technical solutions of embodiments of the present invention are described below with reference to the accompanying drawings. It is to be understood that the described embodiments are merely a subset of the embodiments of the invention and not all embodiments. The described embodiments are to be considered in all respects only as illustrative and not restrictive. It should be noted that the figures and description omit representation and description of components or processes that are not relevant to the present invention and that are known to those of ordinary skill in the art for the sake of clarity.

The structure and voltage applying mode of a traditional quadrupole rod device in a mass spectrometer quadrupole rod mass analyzer are shown in figure 1, the device consists of four cylindrical electrodes with the length of L, a radio frequency amplification module provides electric signals of a rod group, the electric signals comprise direct current signals and high-voltage alternating current signals, the high-voltage alternating current signals comprise RF < + > and RF < - >, the amplitudes of the two signals are the same, the phases of the two signals are opposite, for the four electrodes in the quadrupole rod group, the alternating current signals applied to adjacent electrodes are opposite, and the electric signals applied to the two opposite electrodes are completely the same. As shown in fig. 1, the high voltage alternating current signals applied to the two adjacent electrodes 01 and 02 (or 03 and 04) have the same amplitude and are 180 degrees out of phase, and the electrical signals applied to the two opposite electrodes 02 and 03 (or 01 and 04) are identical. The two radio frequency signals RF + and RF-are both provided by the same radio frequency amplification module 0. Because the quadrupole rod is long and has large capacitance, the radio frequency amplification module has large load, so that the output voltage is low, and the quality detection range is limited.

The segmented quadrupole rod device for widening the mass detection range of the mass spectrometer comprises a central control circuit, a radio frequency amplification module and a segmented quadrupole rod set. The segmented quadrupole rod group divides a traditional quadrupole rod with the length of L into N (N is more than or equal to 2) segments, and N radio frequency amplification modules are used for respectively controlling each segment of quadrupole rod and are controlled by the same central control circuit. Through the quadrupole rod segmentation, reduce the load capacitance of each radio frequency amplification module, high-pressure alternating current signal amplifies through the same radio frequency amplification module, can amplify to higher voltage range to widen mass spectrum detection quality range, promote the resolution ratio and the sensitivity of detection.

In a specific implementation, the rod lengths of each group of the segmented quadrupole rod sets can be the same or different. For example, if N is 2, the segmented quadrupole rod set is composed of two groups of quadrupole rods, and under the condition that the rod lengths of each group are the same, the rod lengths of the first group and the second group of quadrupole rods are both L/2 of the original rod length, that is, the lengths of eight rods are both L/2; the quadrupole rods in each group may also have different lengths, for example, the length of the first group of quadrupole rods may be L/3, and the length of the second group of quadrupole rods may be 2L/3, although other lengths are also possible.

For segmented quadrupole electrodes, the electrodes may be hyperboloid electrodes or may be conventional cylindrical electrodes. Connection members may or may not be provided between the segmented quadrupole rod sets, and if provided, the connection members are insulating members of a non-conductive material. The length of the segmented quadrupole rod set and the distance between the adjacent electrode rod sets are both larger than zero and meet the set technical requirement parameters of the mass spectrometer.

Examples

For convenience of illustration, N =3 is selected in this embodiment for illustration, and each segment of the segmented quadrupole rods is equal in length, and each group of quadrupole rods is cylindrical without a connecting part therebetween, and fig. 2 is a schematic diagram of a structure and an energizing manner of the segmented quadrupole rod device in this case. The electrode is formed by combining 12 electrodes of 3 groups of segment quadrupole rod groups, and each segment of rod group is L/3 long. The four electrodes of each group of quadrupole rods are guaranteed to be horizontally and vertically level with the four electrodes of the front group of quadrupole rods (electrode 21 and electrode 11 are horizontally and vertically level, i.e. electrode 21 is directly behind electrode 11). Each group of quadrupole rods is independently controlled by a radio frequency amplification module, the radio frequency amplification module 1 controls a quadrupole rod group 1 consisting of four electrodes 11, 12, 13 and 14, wherein input signals on two electrodes 11 and 14 opposite to each other are RF +, and input signals on two electrodes 12 and 13 adjacent to the electrodes are RF-; the radio frequency amplification module 2 controls a quadrupole rod group 2 consisting of four electrodes 21, 22, 23 and 24, wherein the electrodes 21, 22, 23 and 24 are respectively coaxially aligned with the electrodes 11, 12, 13 and 14 in the horizontal and vertical directions, and the electric signals applied to the electrodes are opposite to the coaxial electrodes of the front segment rod group, namely, the electrodes 21 and 24 are RF-, and the electrodes 22 and 23 are RF +; similarly, the rf amplifying module 3 controls the quadrupole rod set 3 consisting of four electrodes 31, 32, 33, 34, which are aligned coaxially with the electrodes of the front segment rod set, and applies a reverse high voltage ac.

Fig. 3A is a schematic diagram of a conventional quadrupole control circuit, and fig. 3B is a schematic diagram of a segmented quadrupole control circuit in this embodiment.

In the traditional four-level-rod control circuit shown in fig. 3A, a central control 0 outputs a signal to a radio frequency amplification module 0, the radio frequency amplification module 0 performs secondary amplification on an alternating current signal in the signal and transmits the signal to a four-level-rod group with the length of L, and the larger the length L of the four-level rod is, a capacitor isThe higher the corresponding AC signal voltageThe lower the detection mass range.

In the embodiment of fig. 3B, the quadrupole is divided into three segments, the signal output by the central controller 0 is respectively output to the rf amplification modules 1, 2, and 3, each rf amplification module outputs a signal to a segment of quadrupole group, and since the length of each segment of quadrupole group is 1/3 of the original quadrupole group and the capacitance is 1/3, a higher ac voltage can be output under the amplification effect of the same rf amplification module。

According to the principle of action of the quadrupole mass analyzer,whereinThe magnitude of the amplitude of the radio frequency electric field,is a radio frequency (rf),in order to be the mass of the ions,for field radius, for the same operating q-point, the ion mass can be scannedAnd an alternating voltageIs in direct proportion. The multi-section quadrupole rods are driven in parallel in a segmented mode through the radio frequency amplification modules, the high-frequency alternating voltage of each section of rod is increased, and the mass scanning range can be enlarged.

Due to the limitation of processing conditions and circuit power consumption, the processing difficulty of the quadrupole rods is high for longer quadrupole rods, and the processing and manufacturing of the radio frequency amplification module are also difficult for the same voltage requirement. The multi-section rod is designed to be controlled by the plurality of radio frequency amplification modules respectively, so that the load of a radio frequency circuit is reduced, the processing is convenient, the radio frequency voltage of each section of quadrupole rod is convenient to promote, the quality detection range of a mass spectrometer is widened, and the resolution and the sensitivity of detection are improved.

The invention can correspond to different voltage application modes and different methods for widening the detection range of the mass spectrometer, and is described by taking the embodiment with N being 3 as an example, and the situation that N is 2 or other positive integers larger than 3 can be analogized, and the description in the embodiment is omitted.

The first method for widening the detection range of the mass spectrometer is to emit ions to be detected to a segmented quadrupole device, a conventional quadrupole charging mode is adopted corresponding to a first voltage application mode, a radio frequency amplification module is adjusted to enable three sections of rod sets to normally apply a direct current signal U and a high-voltage alternating current signal V, the direct current voltage U of each section of rod set is controlled to be the same, and the amplitude and the frequency of the high-voltage alternating current signal V are controlled to be the same. The three-segment quadrupole rod set jointly forms a long rod set with the length of L. Eligible selected ions pass through the segmented quadrupole rod set. Compared with the traditional four-pole rod with the length of L, the segmented four-pole rod can apply higher radio-frequency voltage under the same radio-frequency voltage, and the corresponding quality detection range is larger.

The second method for widening the detection range of the mass spectrometer is to emit ions to be detected to a segmented quadrupole rod device, the radio frequency amplification module is adjusted to be one group or a plurality of adjacent groups of quadrupole rods by corresponding to a second voltage application mode, only direct current voltage is applied but alternating current voltage is not applied, direct current signals and reversed-phase high-voltage alternating current signals are applied to other quadrupole rod groups, the direct current signals between the adjacent quadrupole rod groups are the same, the amplitude of the high-voltage alternating current signals is the same, namely, a conventional quadrupole rod group power-up mode is applied to other quadrupole rod groups, and selected ions meeting the conditions pass through the segmented quadrupole rod device. Taking the embodiment in which N is 3 as an example, the first rod group composed of the electrodes 11, 12, 13, 14 in fig. 2 is applied with only the dc voltage U, the ac voltage amplitude V is 0, at this time, both the RF + and RF-signals are equal to the dc voltage U, the first rod group can be regarded as a dc electric field at this time, and performs acceleration or deceleration action on ions uniformly, the second and third rod groups normally apply the dc voltage U and the ac high voltage V, perform a mass filtering function, and selected ions meeting the conditions pass through the segmented quadrupole rod device.

The third method for widening the detection range of the mass spectrometer is to emit ions to be detected to a segmented quadrupole rod device, the segmented operation is performed corresponding to the third voltage application mode, each segment of quadrupole rod set is controlled to apply the same radio frequency voltage and different direct current voltages U, and equivalently, each segment of rod adopts different U/V scanning so as to improve the passing rate of target ions. Taking the present embodiment with N being 3 as an example, setting RF1+ = RF2+ = RF3+, RF1- = RF2- = RF3-, the dc voltage of the first rod set U1=18.9, the dc voltage of the second rod set U2=18.7875, and the dc voltage of the third rod set U3=18.675 are respectively 0.168, 0.167, and 0.166 for each rod set, and the corresponding relationship diagram of the scan curve and the stable region for each rod is shown in fig. 4A to 4C. In the mode, the scanning lines of the three rods are all wiped near the top point of the first stable area, the direct-current voltage applied by the three rods is gradually reduced, the width of the scanning lines which are wiped near the top point of the stable area is gradually increased, the loss of target ions can be reduced, and selected ions meeting the conditions can pass through the segmented quadrupole rod device.

Through the sectional control, the passing rate of the quadrupole rod system to the target ions can be improved. And testing the ion filtering resolution effect of the parallel driving segmented four-level rod under the voltage condition, namely a third voltage application mode by using a Matlab program, wherein the target ions m/z 609 are provided with 100 ion simulation numbers, the simulation air pressure is 1mTorr, and a radio frequency scanning mode is adopted, the scanning range is 280 kHz-250 kHz, and the scanning speed is 6 k/ms. Fig. 5A is a simulation effect of a conventional long rod scan curve U/V =0.168, fig. 5B is a simulation effect of a segmented quadrupole rod device with scan curves U/V of each segment of rod set being 0.168, 0.167, and 0.166, respectively, in fig. 5A and 5B, the dotted lines are scan lines, and the solid lines constitute a stable region. In fig. 5A, the conventional long rod operates at a scan curve of U/V =0.168, with a q-point of 0.706 and an ion passage rate of about 0.22. In the sectional quadrupole device mode shown in fig. 5B, the three-section rod scanning curves correspond to 0.168, 0.167 and 0.166 respectively, the ion throughput at the same q point is 0.3, and the throughput is improved by about 1.33 times compared with the operation of the conventional long rod with the same scanning curve. Meanwhile, in fig. 5A, the half-peak width of a conventional long-rod scanning ion is 0.0106, and in fig. 5B, the half-peak width of the segmented quadrupole rod device in the scanning mode is 0.0097, and the half-peak width is reduced by 1.09 times. Simulation effect prompts that the segmented quadrupole rods adopt different scanning curves for segmented operation, the passing rate of target ions can be improved, the half-peak width is reduced, and the detection range and the resolution of the quadrupole rods are improved.

The above description of the embodiments of the present invention is only for illustrating the technical solutions of the present invention, and not for limiting the scope of the present invention, and the present invention is not limited to the disclosed embodiments, and those skilled in the art can modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some technical features, and these modifications or substitutions should fall into the protection scope of the present invention.