Patent ID: 12198920

DESCRIPTION OF EMBODIMENTS

The ion analyzer according to the present invention includes mass spectrometers, ion mobility spectrometers, and ion mobility mass spectrometers which are combinations of the previously mentioned devices. The ion source in the ion analyzer according to the present invention is an ESI ion source. All elements of the configuration except for the ion source, such as the technique for the mass separation in the mass spectrometer or the presence/absence of an ion-dissociating operation and the type of dissociation technique, can be appropriately selected.

First Embodiment

A mass spectrometer as one embodiment of the ion analyzer according to the present invention is hereinafter described with reference to the attached drawings.

FIG.1is an overall configuration diagram of the mass spectrometer according to the present embodiment.FIG.2Ais a front view showing the configuration of the ESI ion source in the mass spectrometer, andFIG.2Bis a sectional view at line A-AA inFIG.2A.

The present mass spectrometer is a single-type atmospheric pressure ionization quadrupole mass spectrometer. For convenience of explanation, three axes of X, Y and Z which are orthogonal to each other are defined in the space, as shown inFIGS.1,2A and2B.

As shown inFIG.1, the chamber1in the mass spectrometer according to the present embodiment is divided into four sections: an ionization chamber11, first intermediate vacuum chamber12, second intermediate vacuum chamber13and analysis chamber14. The ionization chamber11is at substantially atmospheric pressure, while the analysis chamber14is maintained in a high-vacuum state by evacuation using a high-performance vacuum pump (not shown, which is normally a combination of a turbomolecular pump and a rotary pump). The first and second intermediate vacuum chambers12and13are also individually evacuated by vacuum pumps. Thus, a multi-pumping system in which the degree of vacuum increases from the ionization chamber11to the analysis chamber14in a stepwise manner is constructed.

Within the ionization chamber11, an ESI probe2for ionization is provided as the ion source. A liquid sample containing sample components is sprayed in the form of charged droplets from the ESI probe2in a roughly X-axis direction. The charged droplets sprayed from the ESI probe2come in contact with the gas in the ionization chamber11and are thereby atomized. Additionally, the droplets also shrink due to active vaporization of the solvent from the droplets. During that process, the sample components in the droplets are ejected in an electrically charged state and turned into ions.

The ionization chamber11communicates with the first intermediate vacuum chamber12through a thin desolvation tube3. The central axis of the ion intake3a, which is the opening of the desolvation tube3in the ionization chamber11extends substantially parallel to the Z axis. In other words, the direction of spray from the EST probe2is substantially orthogonal to the central axis of the ion intake3a(i.e., the direction in which ions are drawn). Due to the pressure difference between the two open ends of the desolvation tube3, a flow of gas from the ionization chamber11into the first intermediate vacuum chamber12through the desolvation tube3is formed. The ions generated from the sample components within the ionization chamber11are mainly carried by this flow of gas and drawn through the ion intake3ainto the desolvation tube3, to be ejected into the first intermediate chamber12along with the flow of gas.

The first intermediate vacuum chamber12contains a multipole ion guide4. A skimmer5having a small hole at its apex is provided in the partition wall which separates the first and second intermediate vacuum chambers12and13from each other. Due to the effect of the electric field created by the ion guide4, the ions are converged into the vicinity of the small hole in the skimmer5and sent into the second intermediate vacuum chamber13through that same hole.

The second intermediate vacuum chamber13also contains a multipole ion guide6. Due to the effect of the electric field created by this ion guide6, the ions are converged and sent into the analysis chamber14. The analysis chamber14contains a quadrupole mass filter7and an ion detector8. The ions are introduced along the ion beam axis C into the space extending the longitudinal direction of the quadrupole mass filter7. Due to the effect of the electric field created by voltages applied to the quadrupole mass filter, only an ion having a specific mass to charge ratio is allowed to pass through the quadrupole mass filter7and reach the ion detector8. The ion detector8produces a detection signal corresponding to the amount of ions which have reached the detector. This signal is sent to a data processing unit (not shown). In this mass spectrometer, the analysis sensitivity can be improved by increasing the amount of ions sent into the quadrupole mass filter7and subjected to the analysis.

Next, the configuration of the ESI probe2is described in detail with reference toFIGS.2A and2B.

FIG.2Ashows the ESI probe2as viewed from a front area in the direction of the spray flow of the charged droplets.FIG.2Bis a sectional view at line A-AA inFIG.2A.

As shown inFIG.2A, the ESI probe2includes eight electrically conductive capillaries211-218arranged on the same circle U at substantially regular intervals of angle (in the present example, at angles of 45 degrees) and extending parallel to the axis S of the circle. For each of the eight capillaries211-218, a cylindrical nebulizing-gas tube221-228is provided, with each tube forming a concentric double-tube structure with the corresponding capillary211-218. The ESI probe2further includes an auxiliary electrode23having a columnar shape located on, and extending parallel to, the axis S which corresponds to the center of the circle U on which the eight capillaries211-218are arranged. The end of the auxiliary electrode23protrudes from those of the capillaries211-218in the X-axis direction.

That is to say, the single auxiliary electrode23is arranged so as to be surrounded by the eight capillaries211-218in the ESI probe2. The eight capillaries211-218are at roughly equal distances from the auxiliary electrode23. The configuration of one capillary and one nebulizing-gas tube forming a double-cylinder structure with that capillary is equivalent to that of the capillary and the nebulizing-gas tube in a conventionally and commonly used ESI probe.

The auxiliary electrode23is grounded and has a fixed potential of zero. To each capillary211-218, a DC high voltage equal to or higher than several kV, for example, is applied from a DC high voltage source24. The polarity of this voltage is identical to that of the ion which is the measurement target; when the measurement target is a positive ion, a positive DC high voltage Vh is applied to the capillaries211-218(it should be noted that only the voltage application line connected to one capillary214is shown inFIG.2Ain order to prevent the drawing from being overly complex).

The ion-generating operation in the ESI probe2is hereinafter described. As an example, it is hereinafter assumed that the measurement target is a positive ion.

Though not shown, a liquid sample containing a compound isolated by a column in a liquid chromatograph, for example, is supplied to the ESI probe2. This liquid sample is distributed to the eight capillaries211-218in approximately equal quantities and reaches the tips of the capillaries211-218. Meanwhile, an appropriate kind of inert gas which acts as the nebulizing gas is supplied to the nebulizing-gas tube221-228.

When a positive high voltage is applied to the capillaries211-218, a strong electric field is created around the tip of each capillary211-218due to the potential difference between the auxiliary electrode23having a potential of zero and the capillaries211-218. In a common type of ESI ion source, the potential which serves as the reference for the capillary's potential (typically, the ground potential) is the potential at or near the entrance end of the desolvation tube3inFIG.1. By comparison, in the mass spectrometer according to the present embodiment, the auxiliary electrode23having the ground potential which serves as the reference is located close to the capillaries211-218. Therefore, the electric field created around the tip of each capillary211-218is strong, and this electric field produces a strong Coulomb repulsion force acting inside the charged droplets formed at the tip of each capillary211-218. This helps the atomization of the charged droplets. Consequently, with the help of the nebulizing gas, a large amount of charged droplets is sprayed from the capillaries211-218.

Since multiple capillaries are present and the auxiliary electrode having the reference potential is arranged close to those capillaries, a large amount of charged droplets is sprayed. However, since those charged droplets have the same polarity, a Coulomb repulsion force acts between the charged droplets. Therefore, if there were no influence from an external electric field, the spray flow of the charged droplets would spread in a direction orthogonal to the axis of the spray flow as the droplets move forward, so that it would be difficult to draw ions generated from the charged droplets into the desolvation tube3.

By comparison, in the mass spectrometer according to the present embodiment, since the potential of the auxiliary electrode23located on the axis S is lower than that of the surrounding capillaries211-218, a potential gradient directed from the surrounding area toward the axis S is formed in a plane orthogonal to the axis S (Y-Z plane). That is to say, a converging electric field in which positively charged particles (droplets and ions) are converged into an area around the axis S is formed within an area in front of the tips of the capillaries211-218. Due to this converging electric field, the charged droplets sprayed from the capillaries211-218and the ions generated from those droplets undergo a force which makes the droplets and ions move toward the axis S, as indicated by the thick arrows inFIG.2B. Thus, the spray flow containing the charged droplets and ions is prevented from spreading due to the Coulomb repulsion force, so that the ions generated from the spray flow are efficiently drawn into the desolvation tube3.

As described to this point, the auxiliary electrode23in the mass spectrometer according to the present embodiment produces the effect of strengthening the electric field around the tips of the capillaries211-218and the effect of converging the spray flow containing the charged droplets and ions into an area around the axis S. Thus, by using the ESI probe2, it is possible to improve the ionization efficiency and generate a greater amount ions, as well as improve the ion collection efficiency to more efficiently introduce the generated ions into the desolvation tube3and send them to the subsequent stage.

First Modified Example of First Embodiment

Each ofFIGS.3and4shows one modified example of the ESI probe2in the mass spectrometer according to the previously described embodiment. It should be noted that the capillaries211-218and the nebulizing-gas tubes221-228, which are only partially shown inFIGS.3and4, are identical in configuration to those shown inFIG.2.

The ESI probe2A shown inFIG.3includes a doughnut-shaped heating-gas supplier25arranged so as to surround the capillaries211-218. The heating-gas supplier25has a heating-gas spouting port251continuously extending along the entire circumference around the axis S, or heating-gas spouting ports251arranged at predetermined intervals of angle around the axis S. The heating-gas spouting port251is inclined inwards so that the spouted gas will travel toward the axis S. Therefore, the heating gas spouted from the heating-gas spouting port251surrounds the spray flow of the charged droplets and hits the outer circumferential portion of the same flow.

In the ESI probe the distribution of the droplets in the spray flow P will be such that a charged droplet having a lower mobility, i.e., a larger size, is located closer to the outer circumferential portion of the spray flow P due to the effects of both the previously described converging electric field created by the auxiliary electrode23and the nebulizing-gas flow spouted from the nebulizing-gas tubes221-228. In a large-sized charged droplet, the Coulomb repulsion force acts inside the droplet less effectively, so that the atomization progresses rather slowly, and the ionization efficiency is difficult to improve.

On the other hand, the heating gas spouted from the heating-gas spouting port251efficiently hits the large-sized charged droplets located in the outer circumferential portion of the spray flow P. This gas helps the vaporization of the solvent in those charged droplets and thereby promotes the atomization of the droplets and the generation of ions. Thus, the ESI probe2A according to the present modified example can further improve the ionization efficiency.

The ESI probe2B shown inFIG.4includes a heating-gas supplier26which spouts the heating gas across the spray flow P of the charged droplets coming from the capillaries211-218. This configuration also enables the heating gas to efficiently hit the large-sized charged droplets located in the outer circumferential portion of the spray flow P and promote the vaporization of the solvent from the charged droplets.

Second Modified Example of First Embodiment

In the ESI probes2,2A and2B in the mass spectrometer according to the previously described embodiment, the plurality of capillaries211-218are arranged at substantially regular intervals of angle on substantially the same circle U. Accordingly, the charged droplets are sprayed in roughly equal quantities in the circumferential direction around the auxiliary electrode23. However, the amounts of ions generated from the sprayed charged droplets and drawn into the desolvation tube3are less likely to be uniform in the circumferential direction around the auxiliary electrode23. One reason for this problem is that the partition wall separating the desolvation tube3and the ionization chamber11from the first intermediate vacuum chamber12has a potential equal or close to the ground potential (or a potential which is at least significantly closer to the ground potential than that of the capillaries211-218), so that the ion generation efficiency in a spray flow from a capillary located close to the desolvation tube3or the partition wall is relatively low. Another reason is that, although the electric field created by the auxiliary electrode23certainly has the converging effect, the charged droplets sprayed from the ESI probe2and the ions generated from those droplets are not converged into a beam-like form, so that the ions generated from a spray flow from a capillary located close to the desolvation tube3(inFIG.1, the capillary located in the positive direction of the Z axis) are less likely to be drawn into the desolvation tube3.

Another problem is that the charged droplets sprayed from a capillary located close to the desolvation tube3and the ions generated from those droplets are likely to cause contamination by adhering to the ion intake3aof the desolvation tube3and the outer surface of its duct line. A modified example of the mass spectrometer according to the previously described embodiment, which is shown inFIGS.5A and5B, can deal with these problems.FIG.5Ais a front view of the ESI probe2C according to the present modified example, andFIG.5Bis a sectional view at line A-AA inFIG.5A. InFIGS.5A and5B, the desolvation tube3, which is not shown inFIGS.2A and2B, is partially shown. InFIGS.5A and5B, the same components as shown inFIGS.2A and2Bare denoted by the same reference signs, and descriptions of those components will be omitted unless particularly necessary.

In this ESI probe2C, the eight capillaries211-218are arranged on the same circle U. Within a range from capillary211to capillary218extending counterclockwise inFIG.5A, the capillaries neighboring each other in the circumferential direction are arranged at regular intervals of angle. On the other hand, the interval of angle between the capillary218and the neighboring capillary211is larger than the other intervals. Specifically, the former angular interval is 40 degrees, while the latter is two times the former one, 80 degrees. The eight capillaries211-218in the ESI probe2C can be considered to have originally been prepared as nine capillaries arranged at regular intervals of angle on the same circle U, from which one capillary was removed, leaving the eight capillaries. The position of the single removed capillary is such that the desolvation tube3is present exactly on the extension of the central axis of that capillary.

Therefore, when the positional relationship between the desolvation tube3and the capillaries211-218is observed on the Y-Z plane as shown inFIG.5A, the duct line of the desolvation tube3is located within the space where none of the capillaries211-218is present, i.e., the section where the interval of angle between the two capillaries neighboring each other in the circumferential direction on the circle U is large. Additionally, an electrically conductive electrode holder28, which is substantially integrated with the auxiliary electrode23, is located at a position which overlaps the desolvation tube3on the Y-Z plane and yet is displaced in the negative direction of the X axis, in order to hold the auxiliary electrode23as well as give the ground potential to the same electrode23.

By the DC high voltage Vh applied to the capillaries211-218, a strong electric field is created around the tip of each capillary211-218. The liquid sample distributed to each capillary211-218is given electric charges from this electric field and sprayed in the form of charged droplets with the help of the nebulizing gas. This is similar to the case of the mass spectrometer according to the previously described embodiment. In the mass spectrometer according to the present modified example, all capillaries211-218are comparatively distant from the desolvation tube3, so that the electric field created around the tip of each capillary211-218is rather unlikely to be affected by the potential of the desolvation tube3or the partition wall. Therefore, the charged droplets can be satisfactorily formed at any of those capillaries211-218, and the ionization is efficiently performed. Furthermore, since the desolvation tube3is located so as to avoid the spray flow from any of the capillaries211-218, the charged droplets in the spray flow or the ions generated from the spray flow are likely to be drawn into the desolvation tube3without adhering to the ion intake3aor duct line of the desolvation tube3. Consequently, the ion collection efficiency is improved.

Thus, a greater amount of ions can be sent to the subsequent stage, and a high level of analysis sensitivity can be achieved. Contamination of the desolvation tube3due to the adhesion of the charged droplets and ions to the ion intake3aor duct line can also be reduced. This makes it possible to maintain the performance of the device for a long time and reduce the burden of the maintenance work for the device. Furthermore, since the electrode holder28which holds the auxiliary electrode23is located within the space where a large interval between the neighboring capillaries is secured, it is possible to hold the auxiliary electrode23in a stable manner while assuredly establishing the electric insulation of the electrode holder28from the capillaries211-218and the nebulizing-gas tubes221-228.

It is evident that the present modified example also allows for the addition of the heating-gas supplier25or26as shown inFIG.3or4.

It is not essential that the capillaries neighboring each other in the sections other than the section having the large space be arranged at regular intervals of angle in the previously described manner. The central axis of the ion intake3aof the desolvation tube3and the axis S of the ESI probe2C do not need to be orthogonal but may be oblique to each other.

Other Modifications

The configuration of the ESI probe2,2A,2B or2C according to the previously described embodiment or its modified examples may be changed or modified in various forms.

For example, the number of capillaries is not limited to the previously mentioned number; any number equal to or greater than two can be appropriately selected. Arranging the plurality of capillaries211-218on the same circle U is not essential; they may be arranged in any appropriate form. However, it should be noted that, if the distance from the auxiliary electrode23varies from one capillary to another, the strength of the electric field created around the tips of the capillaries will also vary, and the charged droplets sprayed from the capillaries will also significantly vary in size. Therefore, in order to maximally equalize the sizes of the charged droplets and improve the ionization efficiency, it is preferable for the plurality of capillaries211-218to be located at equal or close distances from the auxiliary electrode23.

The shape of the auxiliary electrode23is not limited to the columnar shape as described earlier. In particular, the shape of the end of the auxiliary electrode23does not need to be a flat shape parallel to the Y-Z plane. By giving the end a hemispherical shape or any other appropriate shape, the potential gradient of the converging electric field can be adjusted so as to improve the convergence of the spray flow.

The number of auxiliary electrodes23does not need to be one. A plurality of auxiliary electrodes may be provided.

FIG.6shows a modified example in which eight auxiliary electrodes231-238that respectively correspond to the eight capillaries211-218are provided. This figure is a front view of the ESI probe2as observed from the same viewpoint as inFIG.2A. The present configuration can also create a strong DC electric field around the tip of each capillary211-218, as well as an electric field in which the spray flows of the charged droplets ejected from the capillaries211-218are converged into an area around the axis S.

Second Embodiment

A mass spectrometer which is another embodiment of the ion analyzer according to the present invention is hereinafter described. The overall configuration of the present mass spectrometer is identical to that of the device according to the first embodiment, and therefore, will not be described.FIG.7Ais a front view showing the configuration of the ESI ion source in the mass spectrometer according to the present embodiment, andFIG.7Bis a sectional view at line A-AA inFIG.7A. InFIGS.7A and7B, the components which are essentially identical to those of the ESI ion source in the mass spectrometer according to the first embodiment are denoted by the same reference signs, and descriptions of those components will be omitted unless particularly necessary.

In the ESI probe2E in the present ESI ion source, the configuration and arrangement of the capillaries211-218and the nebulizing-gas tubes221-228are identical to those of the first embodiment, while the shape and arrangement of the auxiliary electrode as well as the applied voltage are different from those of the first embodiment.

That is to say, the auxiliary electrode27is an electrical conductor having a substantially cylindrical shape and arranged so as to surround the capillaries211-218. The axis of this auxiliary electrode27coincides with the axis S of the circle on which the eight capillaries211-218are arranged. Accordingly, as in the previously described embodiment, the capillaries211-218are at roughly equal distances from the auxiliary electrode27.

The eight capillaries211-218are all grounded (it should be noted that only the ground wire connected to one capillary215is shown inFIG.7Ain order to prevent the drawing from being overly complex). On the other hand, a DC high voltage equal to or higher than several kV, for example, is applied from the DC high voltage source24to the auxiliary electrode27. The polarity of this voltage is identical to that of the ion which is the measurement target; when the measurement target is a positive ion, the DC high voltage is a positive voltage.

When a liquid sample is introduced into each of the capillaries211-218, the positive DC high voltage is applied to the auxiliary electrode27. Due to the closeness of the capillaries211-218to the auxiliary electrode27, a strong electric field is created around the tip of each capillary211-218. Therefore, the charged droplets formed at the tips of the capillaries211-218are easily atomized. Consequently, with the help of the nebulizing gas, a large amount of charged droplets is sprayed from the capillaries211-218.

These charged droplets have positive charges. Since the voltage applied to the auxiliary electrode27surrounding the eight capillaries211-218is a positive high voltage, an electric field which acts on the positively charged droplets (and positive ions ejected from those droplets) so as to push thein inwards, i.e., toward the axis5, is created. Therefore, as in the first embodiment, although a Coulomb repulsion force acts between the charged droplets, the spray flow of the charged droplets does not easily spread but is converged into an area around the axis S. Consequently, the ions efficiently generated from the charged droplets are efficiently drawn into the desolvation tube3and transported to the subsequent stage.

The second embodiment also allows for various modifications similar to those of the first embodiment.

That is to say, similar to the configurations shown inFIGS.3and4, a doughnut-shaped heating-gas supplier25surrounding the auxiliary electrode27may be added, or a heating-gas supplier26configured to spout a heating gas across the spray flow P of the charged droplets coming from the capillaries211-218may be added.

The number and arrangement of the capillaries may be appropriately changed. The shape of the auxiliary electrode27is not limited to a cylindrical shape. The auxiliary electrode27may consist of an appropriate number of segments.

The first and second embodiments as well as their modified examples are mere examples of the present invention, and any change, modification or addition appropriately made within the gist of the present invention will naturally be included within the scope of claims of the present application.

For example, the previously described embodiments are concerned with a single-type quadrupole mass spectrometer. However, as noted earlier, it is possible to appropriately select the technique for the mass separation, the presence/absence of an ion-dissociating operation and the type of dissociation technique, as well as other related elements. Therefore, it is naturally possible to apply the present invention in various types of mass spectrometers, such as a time-of-flight mass spectrometer, ion trap mass spectrometer, triple quadrupole mass spectrometer, quadrupole time-of-flight mass spectrometer, or ion trap time-of-flight mass spectrometer.

The present invention is generally applicable in any type of ion analyzer in which an ESI ion source is used to ionize sample components. Accordingly, the device is not limited to mass spectrometers; for example, it may be an ion mobility spectrometer or an ion mobility mass spectrometer which is a combination of an ion mobility spectrometer and a mass spectrometer.

Various Modes

A person skilled in the art can understand that the previously described illustrative embodiments are specific examples of the following modes of the present invention.

(Clause 1) One mode of the ion analyzer according to the present invention is an ion analyzer equipped with an ion source employing an ESI method, where the ion source includes:a plurality of capillaries configured to spray a supplied liquid sample in the same direction;one or more auxiliary electrodes arranged so as to be surrounded by the plurality of capillaries; anda voltage supplier configured to apply, to the plurality of capillaries, a DC high voltage for which the potential of the one or more auxiliary electrodes is used as a reference.

(Clause 10) Another mode of the ion analyzer according to the present invention is an ion analyzer equipped with an ion source employing an ESI method, where the ion source includes:a plurality of capillaries configured to spray a supplied liquid sample in the same direction;one or more auxiliary electrodes arranged so as to surround the plurality of capillaries; anda voltage supplier configured to apply, to the one or more auxiliary electrodes, a DC high voltage for which the potential of the plurality of capillaries is used as a reference.

In the ion analyzers described in Clauses 1 and 10,

a liquid sample containing a component to be analyzed is distributed to a plurality of capillaries, and electrically charged droplets are sprayed from each capillary. Accordingly, the total amount of liquid sample to be introduced into the ion source can be increased, whereby the throughput of the analysis can be improved. Alternatively, the amount of liquid sample to be passed through one capillary can be decreased, whereby the sprayed droplets can be atomized, and the generation of the ions can be promoted.

In the ion analyzers described in Clauses 1 and 10, the electric field around the tip of the capillary is strengthened by arranging the auxiliary electrode close to the capillaries. Therefore, the charge-induced splitting of the liquid sample which has reached the tips of the capillaries is promoted, and the ionization efficiency is thereby improved. Simultaneously, due to the effect of the electric field created by the auxiliary electrode, the charged droplets sprayed from the capillaries and the ions generated from those droplets are prevented from spreading; conversely, they are converged as they move forward. Therefore, the generated ions are more likely to be introduced, for example, into a transport tube which transports ions into a vacuum chamber, so that the ion collection efficiency is improved. Consequently, the amount of ions subjected to the analysis increases, and a high level of analysis sensitivity is achieved.

(Clauses 2 and 11) In the ion analyzer described in Clause 1 or 10, the ion source may further include nebulizing-gas tubes provided so that each of the plurality of capillaries has one nebulizing-gas tube configured to spout a nebulizing gas in the same direction as the direction in which the liquid sample is sprayed from the capillaries.

The ion analyzers described in Clauses 2 and 11 can satisfactorily spray charged droplets from the tips of the capillaries.

(Clause 3) The ion analyzer described in Clause 1 or 2 may be configured as follows:the plurality of capillaries are arranged on substantially the same circle; andthe one or more auxiliary electrodes are a single electrode located at a substantially-central position of the circle on which the plurality of capillaries are arranged.

(Clause 12) Similarly, ion analyzer described in Clause 10 or 11 may be configured as follows:the plurality of capillaries are arranged on substantially the same circle; andthe one or more auxiliary electrodes are a single electrode having a cylindrical shape coaxial with the circle on which the plurality of capillaries are arranged.

In the ion analyzers described in Clauses 3 and 12, since the strength of the electric field around the tips of the capillaries are roughly equal, the charged droplets atomized to roughly equal extents can be sprayed from all capillaries. This improves the ionization efficiency. Additionally, in the ion analyzers described in Clauses 3 and 12, due to the potential of the capillaries and that of the auxiliary electrode, the potential gradient of the electric field within the area where the spray flow of the charged droplets is formed becomes roughly rotation-symmetrical with respect to the axis of the spray flow. Therefore, the spray flow of the charged droplets can be easily converged into an area around that axis, which improves the efficiency of the use of the ions generated from the charged droplets. Thus, a greater amount of ions can be subjected to the analysis, and the analysis sensitivity can be further improved.

(Clause 4) The ion analyzer described in Clause 3 may further include an ion transport tube configured to collect ions generated from the spray flow coming from the plurality of capillaries and transport the ions to a subsequent stage, the ion transport tube having an ion intake in front of the spray flow and including a duct line extending in a direction intersecting with the direction of spray from the capillaries, where the plurality of capillaries are arranged on substantially the same circle except for a position where the ion transport tube is located on the extension of the direction of spray.

(Clause 5) In the ion analyzer described in Clause 4, the duct line of the ion transport tube may extent a direction substantially orthogonal to the direction of spray from the capillaries.

In normal cases, the potential of the ion transport tube is set at the ground potential or a potential comparatively close to it. Due to the influence of this potential, the electric field created around the tip of a capillary located close to the ion transport tube is likely to be weakened. In addition, the charged droplets sprayed from a capillary located close to the ion transport tube, and the ions generated from those droplets, are less likely to be carried by the gas stream and taken into the ion transport tube. By comparison, in the ion analyzers described in Clauses 4 and 5, since all capillaries are comparatively distant from the ion transport tube, a strong electric field is created around the tip of each capillary, and the charged droplets can be satisfactorily produced. Furthermore, the charged droplets contained in the spray flow, and the ions generated from those droplets, are efficiently taken into the ion transport tube. Thus, a greater amount of ions can be sent to the subsequent stage, and the analysis sensitivity can be improved. Contamination of the ion transport tube and its ion intake due to the adhesion of the charged droplets and ions can also be reduced.

(Clause 6) The ion analyzer described in Clause 4 or 5 may be configured as follows:the plurality of capillaries are arranged so that the spacing of the capillaries neighboring each other in the circumferential direction on the circle is largest at a position where the ion transport tube is located on the extension of the direction of spray; anda holder which holds the auxiliary electrode and/or a wiring which gives a potential to the auxiliary electrode is located in a space where the spacing of the capillaries neighboring each other is largest.

In the ion analyzer described in Clause 6, the holder and/or wiring for the auxiliary electrode can be arranged in a sufficiently large space between the neighboring capillaries, so that the electric insulation between the holder or wiring and the capillaries can be satisfactorily ensured.

(Clauses 7 and 13) The ion analyzer described in one of Clauses 1-6 or one of Clauses 10-12 may further include a heating-gas supplier configured to blow a heating gas onto an outer circumferential portion of the spray flow coming from the plurality of capillaries, so as to wrap the spray flow.

In the ion analyzers described in Clauses 7 and 13, the heating gas spouted from the heating-gas supplier mainly hits the outer circumferential portion of the spray flow of the charged droplets ejected from the plurality of capillaries. In this portion of the spray flow, there are comparatively large-sized charged droplets. The heating gas promotes the vaporization of the solvent in these charged droplets and effectively improves the ionization efficiency. Since the flow of the heating gas is formed so as to wrap the spray flow of the charged droplets, the spread of the spray flow will be even more reduced, and the efficiency of the use of the ions will be further improved.

(Clauses 8 and 14) The ion analyzer described in one of Clauses 1-6 or one of Clauses 10-12 may further include a heating-gas supplier configured to blow a heating gas onto the spray flow coming from the plurality of capillaries so that the heating gas flows across the spray flow.

In the ion analyzers described in Clauses 8 and 14, the heating gas spouted from the heating-gas supplier mainly hits the outer circumferential portion of the spray flow of the charged droplets ejected from the plurality of capillaries. In this portion of the spray flow, there are comparatively large-sized charged droplets. The heating gas promotes the vaporization of the solvent in these charged droplets and effectively improves the ionization efficiency.

(Clauses 9 and 15) The ion analyzer described in one of Clauses 1-8 or one of Clauses 10-14 may be a single-type quadrupole mass spectrometer, triple quadrupole mass spectrometer, or quadrupole time-of-flight mass spectrometer including the ion source.

In these types of mass spectrometers, it is necessary to transport ions form the ion source, which is at atmospheric pressure, to the vacuum chamber in the subsequent stage through a desolvation tube, sampling cone or similar part. The ion analyzers described in Clauses 9 and 15 can efficiently collect ions generated in the ion source and transport them to the subsequent stage. Thus, the ion analyzers described in Clauses 9 and 15 can achieve a high level of analysis sensitivity.

REFERENCE SIGNS LIST

1. . . Chamber11. . . Ionization Chamber12. . . First Intermediate Vacuum Chamber13. . . Second intermediate Vacuum Chamber14. . . Analysis Chamber2,2A,2B,2C,2D,2E . . . Electrospray Ionization (ESI) Probe211-218. . . Capillary221-228. . . Nebulizing-Gas Tube23,231-238,27. . . Auxiliary Electrode24. . . DC High Voltage Source25,26. . . Heating-Gas Supplier251. . . Heating-Gas Spouting Port28. . . Electrode Holder3. . . Desolvation Tube4,6. . . Ion Guide5. . . Skimmer7. . . Quadrupole Mass Filter8. . . Ion Detector