JPH06310088A - Ion source for mass spectrograph - Google Patents

Abstract

PURPOSE:To analyze a high polarity high polymer substance by introducing a sample from a liquid chromatograph and mixed solution of a moving phase to a nozzle vibrating by an ultrasonic wave, heating this after it is transformed into a fine droplet by electrifying it, and imparting only an ion of the sample to a mass spectrometer white evaporating solution from the droplet. CONSTITUTION:A mass spectfograph is composed of an ultrasonic atomization part, a high voltage supply part, a gas blowing part and a mass spectrometry part. Here, important is the atomization part, and an electrostrictive element 1 to vibrate in a frequency of about 30kHz, an oscillator 2 and an amplifier 3 are arranged in this, and AC voltage is impressed on the element 1, and ultrasonic vibration is generated, and this is amplified by a stepped horn 4. Next, sample solution separated and eluted by a column 8 is made to reach a solution supply pipe 5 through a tube 9, and is flowed out through the supply pipe 5 and the horn 4, and this is atomized by the ultrasonic vibration. High voltage of (+3-+6)kV is given to the horn 4 from high voltage electric power supply 10 of a high voltage supply part, and nitrogen gas is flowed to a heated chamber 15 in the gas belowing part, and is transformed into a droplet containing no moving phase.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to means for ionizing a liquid sample eluted from a liquid chromatograph and introducing it into a mass spectrometer.

[0002]

2. Description of the Related Art A liquid sample eluted with a mobile phase from a liquid chromatograph (hereinafter abbreviated as LC) is introduced into an ion source of a mass spectrometer (hereinafter abbreviated as MS) and ionized. Since 1972, a liquid chromatograph direct coupling mass spectrometer (hereinafter abbreviated as LC / MS) that detects the mass / charge ratio of an ionized sample and its ionic strength by MS has been developed.

Since LC has excellent separation ability and qualitative ability even for polar compounds, heat labile compounds, etc., LC is a powerful analytical method for separating mixed samples. However, it does not give much information about the structure. MS, on the other hand, gives information about the molecular weight and structure of one component. Therefore, the LC / MS method in which LC and MS are combined is a powerful analytical method that enables separation and qualitative / quantitative determination of mixed samples. LC / MS equipment is LC
And an interface for introducing the liquid sample eluted from the LC into the ion source of the MS for ionization (hereinafter referred to as LC
/ MS interface) and MS. For this interface, more than 20 methods have been devised so far. These are properly used depending on the properties such as thermal stability, polarity and volatility of the sample to be analyzed. For example, particle beam method for non-polar substances, atmospheric pressure chemical ionization method or thermospray method (Thermosp
ray method), and for highly polar substances, the electrospray method can be used.

In the present invention, as one method of the LC / MS interface, about 200 μl / mi delivered from the LC is used.
As a method for introducing a high flow rate n 2 sample solution into the MS and ionizing it, the sample solution is miniaturized by ultrasonic vibration.

A liquid sample is atomized by ultrasonic vibration, and M
Regarding the method of introducing into an analytical instrument such as S, JP-A-56
There is an invention described in Japanese Patent Publication No. 126241. This publicly known example is LC
The liquid sample that has flowed out further is atomized by ultrasonic vibration, and at the same time, means for vaporizing the atomized sample by the heating means, and after the atomization and vaporization of the sample, the solvent molecules of small mass are removed by the jet separator, It includes means for extracting only relatively large sample molecules, i.e., means for concentrating the sample, and means for introducing the concentrated sample into the analytical instrument. According to this method, thermal instability, which was difficult with the conventional vaporization method that vaporizes the sample only with thermal energy,
Vaporization of hardly volatile compounds and highly polar compounds becomes easy. As a result, it can be said that this is an excellent invention in that these substances can be ionized and MS analysis can be performed. When using this method for MS analysis, the electron impact method (Electron Impact Method)
Impact method; EI method), chemical ionization method (Chemical Ioniza)
ionization method; CI method), field ionization method (Field Ionization)
Law; FI method) was considered. On the other hand, these ionization methods are not suitable for the ionization of highly polar high molecular weight substances such as peptides and proteins, so that the present invention has a limitation that they are not suitable for MS measurement of these substances.

[0006]

Ionization of high-polarity high molecular weight substances such as peptides and proteins, which has been difficult with the conventional method for introducing micronization of sample solutions by ultrasonic vibration,
Enables MS measurement.

[0007]

[Means for Solving the Problems]

(1) A step of introducing a mixed solution of a sample and a mobile phase sent from the LC into a nozzle to which a high voltage is applied and vibrating ultrasonically, and spraying the mixed solution as charged fine droplets And (2) a step of mixing the fine charged droplets with a heated gas to evaporate the mobile phase solution from the charged droplets to form ions only in the sample and lead them to the MS.

[0008]

The mixed solution of the sample and the mobile phase sent from the LC is atomized from the nozzle opening by ultrasonic vibration.
By applying a high voltage to this nozzle, a strong electric field is formed between the nozzle tip and the MS orifice facing it. If the nozzle has a positive potential with respect to the MS orifice, the droplet will be positively charged. Further, if the nozzle has a negative potential with respect to the MS orifice, the droplet is negatively charged. The charged droplets become finer due to electrostatic repulsion of homopolar charges. On the other hand, this droplet mixes with the heated gas (for example, nitrogen gas) sent from the gas blowing part. As a result, the mobile phase evaporates from the droplets, and further miniaturization due to electrostatic repulsion progresses. The sample ions are introduced into the MS orifice by the strong electric field between the nozzle and the MS orifice and the flow of the heated gas. The charged droplets are almost completely desolvated between the nozzle and the MS orifice, and between the orifice and the MS skimmer, and become ions of only the sample.

[0009]

1 is a sectional view of an apparatus according to an embodiment of the present invention.

The present invention includes an ultrasonic atomizing unit, a high voltage supplying unit,
It consists of a gas blower and a mass spectrometer. The function of each unit will be described below.

(1) Ultrasonic atomizing unit 1 is an electrostrictive element and vibrates at a frequency of about 30 kHz. 2 is an oscillator and 3 is an amplifier. Ultrasonic vibration is generated by supplying an AC voltage to the first electrostrictive element. A stepped horn 4 amplifies the vibration generated by the electrostrictive element 1. Reference numeral 4 includes an input horn 4a and an output horn (nozzle) 4b. A through hole is provided at the center of 4 so that liquid can pass therethrough. 4b serves as a nozzle for ejecting the liquid. The lengths of 4a and 4b are determined so that the vibration has the maximum amplitude at the tips thereof. 5 is a solution supply pipe. A through hole is provided at the center of 5. 6 is an insulator. The nuts 1 and 6 and 4 are tightened with a constant torque. The sample solution separated and eluted by the column 8 reaches the tube 5 through the tube 9. 4 and 5 are screwed together, and the sample solution passes through 5 and 4,
It flows out from the tip of b. When the solution is flowed while 1 is operated, the solution is subjected to ultrasonic vibration and atomized from the tip of 4b.

(2) High voltage supply section In order to positively charge the atomized droplets, a high voltage of +3 to +6 kV is supplied to the stepped horn 4. 10 is a high voltage power supply. 10 and the screw 18 are connected by a cable 11, and a high voltage is applied to 4. An insulator 6 insulates 1 and 4 so that the oscillator 3 is not destroyed by a leak current from 4. MS orifice 1 in front of 4b
Two are arranged. The power source 12 supplies a voltage of about +100 V to the power source 12. Therefore, a strong electric field is formed between 4b and 12. The strong electric field causes the atomized droplets to be positively charged and sprayed. Similarly, in order to charge the atomized droplet to-, the electrical polarities of 4 and 12 are-
To

(3) Gas blower unit The following device is provided for mixing the charged droplets and the heated gas. Reference numeral 14 is a blower pipe for sending nitrogen gas to the tip of the horn. The chamber 15 is heated by the heater 16. Heated chamber 1
Nitrogen gas of 3 to 4 l / min is passed through and heated to 60 to 70 ° C. The total amount of this heated nitrogen gas is stored in the tube 17
Through, into the space between 14 and 4. 4 and 14 are fastened with screws 18. 4 and 14 with gasket 19
Are in close contact with each other, and nitrogen gas does not leak from the joint portion of 4 and 14. Heated nitrogen gas is 4
It is ejected from around the tip of the tip b, mixed with the above-mentioned charged droplets, and ejected. The droplets are dried and finely divided by the nitrogen gas. The atomized droplets are further atomized by electrostatic repulsion of homopolar charges. Through this process, the charged droplets become ions of the sample only, containing almost no mobile phase.

(4) Mass Spectrometer On the MS side, a skimmer 20 is arranged after the 12 orifices, and the space between 12 and 20 is differentially exhausted. Also, 20
Is supplied from 21 to about + 50V. It is considered that the above-mentioned ionization of the sample proceeds even in the decompression section of 12 and 20. That is, the sample ions collide with neutral molecules several times in this depressurized portion, the mobile phase solution is completely desorbed, and at the same time, the ion aggregate is destroyed and becomes a single ion. The ions thus generated pass through 20 and then move to a higher vacuum portion for mass analysis. Also, 4, 12, 2
When the polarity of the voltage applied to 0 is set to −, − ions are generated and are detected by mass spectrometry.

FIG. 2 shows tuftsin (C ₂₁ H ₄₀ N ₈ O ₆ ; molecular weight 50), which is one of the peptides, measured by the apparatus shown in FIG.
It is the result of measuring 0.60). Using 100% methanol as the LC mobile phase, the solution was introduced into the MS orifice without branching at a flow rate of 200 μl / min and MS measurement was performed. The sample amount is 2 μg. Monovalent ion with one proton added at m / z 501, 2 protons at m / z 251
The divalent ions added individually are detected.

[0016]

The solution sent from the liquid supply section is atomized by the ultrasonic atomization section. When the solution flow rate is within 1 ml / min, the average particle size of the droplet at the position where it can be taken into the MS is about 50 μm. On the other hand, by applying a high voltage to the nozzle forming the ultrasonic atomizer, a strong electric field is formed between the MS orifice facing the nozzle tip. Due to this strong electric field, the atomized droplets are charged and finely divided by electrostatic repulsion. This droplet mixes with the heated nitrogen gas sent from the gas blower. As a result, the droplets are dried and further miniaturized. Solution flow rate is 200μl /
If it is less than min, the particle size of 50% or more of the droplets at the position where it can be taken into the MS can be 15 μm or less. Charged droplets
The mobile phase solution is almost completely desorbed between the nozzle and the orifice of the MS, and between the orifice and the MS skimmer, and the ions of the sample only become.

In this way, the ultrasonic atomization unit atomizes the solution having a high flow rate to improve the ionization efficiency. Also,
By combining ultrasonic atomization and heated nitrogen gas,
Further, the liquid can be made finer and the ionization can be promoted. In the present invention, from a low flow rate of 50 μl / min to 200 μl
LC / MS analysis is possible in which an LC solution with a high flow rate of 1 / min is directly introduced into the MS orifice without branching. As a result, the branching operation of the LC solution is unnecessary or simplified, and MS measurement of highly polar high molecular weight substances such as peptides and proteins has become possible.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of peptide measurement according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electrostrictive element, 2 ... Oscillator, 3 ... Amplifier, 4 ... Stepped horn, 5 ... Liquid supply pipe, 6 ... Insulator, 7 ... Nut, 8 ... Column, 9, 17 ... Tube, 10 ... High voltage power supply, 11 ... Cable, 12 ... Orifice, 13, 21 ... Power supply, 14 ...
Blower pipe, 15 ... Chamber, 16 ... Heater,
18 ... screw, 19 ... gasket, 20 ... skimmer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazumi Matsumura 882 Ichige, Katsuta City, Ibaraki Prefecture Hitachi Ltd., Measuring Instruments Division

Claims (2)

[Claims] 1. A sample solution sent from a liquid chromatograph is introduced into a nozzle to which a high voltage is applied and which is vibrating ultrasonically, and the sample solution is charged as a charged droplet from the tip of the nozzle. Means for spraying, mixing the sprayed droplets with a heated gas, ionizing the sample contained in the sprayed droplets, and introducing the sample into a mass spectrometer facing the nozzle. Characteristic mass spectrometer ion source. 2. A means for converting the sample solution into charged droplets by applying a high voltage to the ultrasonically vibrating nozzle to form a strong electric field between the nozzle and the mass spectrometer. The mass spectrometer ion source according to claim 1, wherein: