JPH1010109A - Method and instrument for mass spectrometric analysis directly coupled to liquid chromatograph - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a cell of a detector from being broken as a result of clogging of a flow path, by branching a to-be-eluted component into two, and guiding one to an ion source of a mass analyzer and the other to the detector with controlling a flow rate. SOLUTION: A mobile phase 1 is sent out by a pump 2, introduced from a sample injection opening 3 and separated to every component by an analyzing column 4. The separated component is divided half by a tee. One enters a UV (ultraviolet ray) detector 5 through a resistance column 9, where a component of a UV absorption characteristics is detected, so that a UV chromatograph shows a peak. The other component is sent to an ion source part through a capillary pipe 6. When the ion source is impressed to an electrospray ionization(ESI) probe with high pressure, a sample solution is emitted in the air as minutely charged liquid drops and eventually turned to an ion 11. The ion is sampled through a fine hole 10, analyzed at a mass spectrometric analysis part 12, and output in the form of a chromatograph from a data-processing device 15 through a detector 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct mass spectrometry for liquid chromatography and an apparatus therefor.

[0002]

2. Description of the Related Art Liquid chromatographic direct mass spectrometry has been widely used in recent years as a powerful analytical method for organic compounds that are hardly volatile or organic compounds that are thermally unstable.

[0003] In liquid chromatography, a sample dissolved in a liquid is introduced into an analytical column filled with a packing material, and a solvent serving as a mobile phase is caused to flow through the sample. The sample component is separated and detected from other components by the interaction of There are various methods for detecting the separated components, and among them, a detector using an ultraviolet absorption spectrum (UV detector) is widely used. UV
The signal from the detector 5 is further processed by a data processor and
It is displayed as a liquid chromatogram on RT and charts. Although the UV detector is a highly sensitive detector, the UV spectrum obtained from the UV detector does not always have sufficient structural information on the measurement component. Therefore, a mass spectrometer was directly connected to the liquid chromatograph to obtain more advanced structural information of the eluted components. The mass spectrometer first ionizes the introduced components and gives a mass spectrum. From this mass spectrum, molecular weight, structural information and the like can be obtained. In addition, a new chromatogram different from the liquid chromatogram can be obtained by integrating the amounts of ions in a specific mass range. This is the total ion chromatogram (TIC Total
Ion Chromatogram). The TIC is a chromatogram having information on components that can be ionized and detected. Therefore, a one-to-one correspondence with the mass spectrum can be obtained. In LC / MS, TIC has been widely used because it directly corresponds to a mass spectrum. Recent LC / M
With the spread of S, it has been required to perform analysis in comparison with a normal liquid chromatogram. for that reason,
It has become common practice to simultaneously measure the TIC signal from the UV detector, which is the most widely used LC detector, and the TIC signal from the mass spectrometer, and display and compare these two chromatograms on the same screen. Have been. This is disclosed in detail in Japanese Patent Application Laid-Open No. 4-132153.

[0004]

Various methods have been proposed for directly connecting a liquid chromatograph to a mass spectrometer. The prior art will be described with reference to FIG. There are various types of ion sources for a liquid chromatograph direct mass spectrometer (hereinafter abbreviated as LC / MS). FIG. 6 shows an electrospray method (ES) which is one of atmospheric pressure ionizations.
1 is a schematic diagram of LC / MS using I Electrospray).

[0005] The mobile phase 1 is sent to the analytical column 4 via the sample inlet 3 by the pump 2. The mobile phase leaving the analytical column enters the UV detector 5, and is further introduced into the ESI ion source through the connecting capillary pipe 6. The solution is discharged as charged droplets into the atmosphere from the tip 7 of the ESI probe to which a high voltage is applied. The droplet repeatedly collides with molecules in the atmosphere, evaporating, and the droplet is made finer. Finally, ions of the sample are released from the droplet into the atmosphere. Mass spectrometer 1 in which ion flow 11 is kept in vacuum from pores 10
2, mass analyzed, and detected by the detector 14. The data is then processed by the data processor 15 and output on the CRT 16 as a mass spectrum or TIC.

Here, the mobile phase and the sample components are guided to the ion source through the capillary pipe 6 via the UV detector 5 as described above. Here, since the UV detector 5 is arranged in series with the mass spectrometer, a big problem of cell destruction of the detector 5 occurs.

The flow rate of the mobile phase is about 1 ml / min when the inner diameter of the analytical column is 3 mm or more.

The sample is dissolved in the mobile phase, separated by the column 4, passed through the detector 5, and sent to the ion source through the capillary pipe 6. There are various types of atmospheric pressure ion sources. In many cases, the ion source is sprayed into the atmosphere from the tip of a capillary having an inner diameter of about 0.1 mm. LC / MS
The analysis often deals with thermally and chemically unstable compounds. These compounds may decompose, polymerize, or the like at the tip of the capillary, thereby filling the capillary pipe. Since the LC pump is a constant flow pump,
When it gets clogged, it increases the pressure and tries to secure the specified flow rate. Therefore, the liquid sending pressure may exceed 200 kg / cm ^2, and the cell of the UV detector 5 is easily broken.

As shown in FIG. 3, quartz cells 23 and 23 'are attached to both sides of a metal tube 20 having a liquid inlet 21 and a liquid outlet 22, as shown in FIG. . UV enters the cell through a quartz plate and passes through the central axis of the cell to measure the absorption of the sample. If the pressure rises due to clogging of the ESI probe and the like, and the pressure inside the cell exceeds the bonding force (generally, about 100 kg / cm ² ), the cell is easily broken. If an expensive UV cell is frequently destroyed due to clogging, it imposes a lot of economic burden on a measurer and makes it impossible to continue measurement stably.

[0010] The rise in the pressure of the LC / MS flow path at the time of an abnormality can be easily analyzed by replacing the flow path with an electric circuit. That is, the pump is replaced with a power supply, the flow rate is replaced with a current, the pressure is replaced with a voltage, and the resistance of a column or a capillary pipe is replaced with a resistance R.

The conventional LC / MS channel system shown in FIG. 6 is replaced by the electric circuit shown in FIG.

The resistance of the analysis column is R1, and the resistance of the capillary pipe 6 and the ESI probe 7 is R2. The location of the UV cell is point B, and the pressure (voltage) here is V2.

The voltage and current values at point A are V and I.

[0014]

I = V / (R1 + R2) (Equation 1) The voltage V2 at the point B is

[0015]

V2 = (R2) / (R1 + R2) (Expression 2)

Since R1≫R2 in the normal state,
Is approximated as follows:

[0017]

V2 = (R2 / R1) / (1 + R2 / R1) ≒ 0∵R2 / R1 ≒ 0 (Formula 3) When the tip of the ESI probe 7 is clogged, R2 ≒ ∞≫R1
Equation 2 is approximated as follows.

[0018]

V1 = V / (R1 / R2 + 1) ≒ V ∵R1 / R2 ≒ 0 (Equation 4) Also, the pressure V itself is also obtained from Equation 1.

[0019]

V = (R1 + R2) I = ∞ {R2 = ∞ (Equation 5) That is, V2 rises to the maximum pressure that the pump can deliver.

Therefore, the UV cell 5 is easily destroyed.

[0021]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an analysis method and apparatus in which a detector cell is not destroyed due to clogging of a flow path.

The eluate from the analytical column is split into two, one to the LC / MS ion source and the other to the detector through a resistor. A needle valve, a column, a capillary pipe, or the like can be used for the resistance. Accordingly, even if the ion source is clogged, the pressure does not increase at the detector and the cell of the detector is not destroyed.

[0023]

FIG. 1 is a block diagram according to one embodiment of the present invention. The mobile phase 1 is pumped out by the pump 2 and is fed into the analysis column 4 via the sample inlet 3.
The sample solution is introduced from the sample inlet 3 and separated by the analysis column 4 for each component. The separated components are eluted from the analytical column 4 together with the mobile phase, where they are divided into two by a tee 8.
One of the two flow paths enters the UV detector 5 through the resistance column 9. Here, the component exhibiting UV absorption is detected and gives a peak on the UV chromatogram. The solution leaving the UV detector 5 is discharged outside. The other part divided by the tee 5 is sent to the ion source through the capillary pipe 8. Ion source is electrospray ionization (ESI)
In this case, a high voltage is applied to the ESI probe 7 of the capillary pipe 6. As a result, the sample solution is released into the atmosphere as finely charged droplets. The fine droplets repeatedly collide with atmospheric molecules, and the solvent molecules are vaporized. As a result, the droplets are further miniaturized, and the ions are finally released into the atmosphere. The ions 11 are sampled from the pores 10, mass analysis of the ions is performed by the mass analyzer 12, and detected by the detector 14. Further, the data is stored in the data processing device 15.
To give a mass spectrum. The UV chromatogram and the TIC are collected by the data processor 15,
It is output on the CRT 16 as a chromatogram.

As in the prior art, the configuration of FIG. 1 is replaced by an electrical circuit as shown in FIG.

Here, the resistance of the column is R1, the resistance of the capillary pipe (including the ESI probe) is R2,
The resistor installed in parallel with 2 is R3. Since the ESI probe and the UV cell are open to the atmospheric pressure, they are expressed as ground in the electric circuit. That is, the resistance R4 of the UV cell
Can be approximated to zero.

[0026]

I = V / [R1 + {1 / (1 / R3 + 1 / R2)}] (Equation 6) Under normal analysis conditions, R1≫R3>R2> R4 ≒ 0. Here, assuming that the voltage at point A is V1 and the voltage at point B of the UV cell is V2

[0027]

V1 = (R5 · V) / (R1 + R5) (Expression 7) where R5 = 1 / (1 / R3 + 1 / R2)

[0028]

V2 = (R4 · V1) / (R3 + R4) ≒ 0∵4 ≒ 0 (Equation 8) Equation 8 indicates that no pressure is applied to the UV cell in actual LC / MS.

If the tip of the ESI probe is clogged, R
From 2 = ∞, from Equation 7

[0030]

V1 = (R3.V) / (R1 + R3) (Equation 9) Since Equation 8 is not changed, V2 ≒ 0.

As described above, even if the ESI probe is clogged,
No pressure is applied to the cell. Also, the pressure rise at the outlet of the column 4 can be reduced as compared with the conventional example. in this way,
The eluate from the analytical column is divided into 2 minutes, one of which is directed to an LC / MS ion source and the other is directed to a UV cell. Thereby, the pressure increase of the UV cell can be avoided, and the destruction of the cell can be prevented.

The distribution ratio of the liquid to the ESI probe and the UV cell is determined by the ratio of R2 and R3. Increasing R2 / R3 can increase the flow rate to the UV cell. On the other hand, R2 / R3
By reducing the ratio, the flow rate to the ESI probe 7 can be increased.

As shown in FIG. 4, the resistance of R3 can be used as a needle valve 91 to control the flow rate freely. In addition, as shown in FIG.
The flow rate can be controlled by adjusting the resistance by adjusting the diameter and length of the second.

In the embodiment shown in FIGS. 1, 4 and 5,
A resistance column, a needle valve, a capillary pipe, and the like are arranged upstream of the detector 5. Even if this is arranged downstream, the distribution of the ESI probe and the UV detector 5 does not change. However, when the ESI probe is clogged, the pressure of the UV detector increases. Therefore, in order to protect the cell, it is preferable that the resistor is arranged on the upstream side of the cell.

[0035]

According to the present invention, even if the ion source of the mass spectrometer is clogged or clogged, the pressure of the UV detector does not increase and the cell can be prevented from being destroyed. Thus, measurement can be performed for a long time with peace of mind, and the economic effect is enormous.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of the present invention.

FIG. 3 is an explanatory diagram of a cell of a UV detector.

FIG. 4 is a block diagram of a second embodiment of the present invention.

FIG. 5 is a block diagram of a third embodiment of the present invention.

FIG. 6 is an explanatory view of a fourth embodiment of the present invention.

FIG. 7 is an explanatory view of a fifth embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Mobile phase, 2 ... Pump, 3 ... Sample inlet, 4 ... Analysis column, 3 ... Standard sample inlet, 5 ... UV detector, 6 ... Capillary pipe, 8 ... Tei, 9 ... Resistance column, 10 ... Micropore, 11: ion flow, 12: mass spectrometer, 14: detector, 15: data processor, 16: CRT.

Claims (8)

[Claims] 1. A mass spectrometer which is directly connected to a liquid chromatograph having a detector and ionizes and detects components eluted from the liquid chromatograph. A liquid chromatograph direct mass spectrometer characterized in that the mass spectrometer is connected to the detector through a means for restricting the flow rate to the ion source of the other instrument. 2. The method according to claim 1, wherein the means for restricting the flow rate is a needle valve. 3. The method according to claim 1, wherein the means for restricting the flow rate is a column filled with a packing material. 4. The mass spectrometry of claim 1, wherein the means for restricting the flow rate is a capillary pipe. 5. A mass spectrometer which is directly connected to a liquid chromatograph having a detector and ionizes and detects components eluted from the liquid chromatograph. A liquid chromatograph direct mass spectrometer connected to the detector through a means for restricting the flow to the ion source of the meter and the other. 6. The mass spectrometer according to claim 5, wherein the means for restricting the flow rate is a needle valve. 7. The mass spectrometer according to claim 5, wherein the means for restricting the flow rate is a column filled with a packing material. 8. The mass spectrometer according to claim 5, wherein the means for restricting the flow rate is a capillary pipe.