JPS6226757A - Inductive coupling plasma mass spectrograph - Google Patents

Abstract

PURPOSE:To automate operation of an inductive coupling plasma mass spectrograph by controlling starting and suspension of the operation of the mass spectrograph by comparing the variation in the amount of light from inductive coupling plasma, which results from sample introduction and is detected by a photodetector which is installed in the mass spectrograph, with a predetermined level. CONSTITUTION:Ions produced in an inductive coupling plasma torch 2 are collected by a sampling nozzle 8, converged by a convergent lens system 12 and then introduced into a tetrode rod 16 to separate the ions according to mass. Then, the separated ion groups are introduced into a secondary electron duplicator tube 18 and subjected to mass spectrography. A photodiode 20 used as the photodetector is installed on the central axis of the tetrode rod 16 in order to monitor the light of inductive coupling plasma. Variation in the optical amount of the inductive coupling plasma resulting from sample introduction is detected by the photodiode 20 and the detection result is delivered to a scanning control circuit 26. Operation of this mass spectrograph is started when the detection result is the same or higher than a predetermined level and stopped when the detection result is lower than the set level. Due to the above structure, it is possible to automate measurement by positively utilizing the light from the plasma.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an apparatus for extracting ions from inductively coupled plasma (CP) and measuring a mass spectrum.

(Prior Art) In recent years, attempts have been made to use inductively coupled plasma, which is used as a light source for optical emission spectrometry, as an ion source for a mass spectrometer to perform elemental analysis using ions in a solution (for example, in Analyst magazine). , Volume 106, No. 125
(See pages 5-1267 (19'81)).

In this inductively coupled plasma mass spectrometer, light generated from plasma is detected as background noise, which deteriorates the analytical S/N ratio and limits the detection limit. Therefore, various efforts have been made to suppress background noise caused by light.

(Problems to be Solved by the Invention) In the operation of such an inductively coupled plasma mass spectrometer, after a sample is introduced into the plasma, the operator starts the operation of the mass spectrometer. As a result, there are problems in that it is a burden on the operator and it is difficult to carry out measurements quickly because a time margin is required between the introduction of the sample and the start of measurement.

On the other hand, it is known that when a sample is introduced into plasma, the intensity of light changes.

Therefore, an object of the present invention is to automate measurements by a mass spectrometer by actively utilizing light from plasma, which would normally be an interfering component in analysis.

(Means for Solving the Problems) In the inductively coupled plasma mass spectrometer of the present invention, a photodetector is provided at a position within the device that can receive light from the plasma, and the detection intensity of this photodetector is set to a set value. When this happens, the mass spectrometer starts operating.

A control circuit is provided that stops the operation of the mass spectrometer when the detection intensity of this photodetector becomes less than a set value.

(Embodiment) The figure schematically represents an embodiment of the inductively coupled plasma mass spectrometer of the present invention.

2 is a torch that generates inductively coupled plasma; a mist sample is supplied to the central nozzle along with carrier gas (Ar), plasma gas (Ar) is supplied to the outside of the nozzle, and cooling gas (Ar) is supplied to the outside of that. be done. The torch 2 is provided with a high frequency coil 4.

6 is a sample collection section that collects a part of the inductively coupled plasma;
The tip end surface becomes a cooling jacket 7, and a sampling nozzle 8 is opened in the cooling jacket 7. Since the sampling nozzle 8 becomes hot, the cooling jacket 7 is cooled by the cooling water 9.

Inductively coupled plasma is generated at atmospheric pressure, and a sample is collected through a sampling nozzle 8 due to the pressure difference between the inductively coupled plasma and the sample collecting section 6. 10 is a lens system section that adjusts the traveling direction of the ion beam in the collected sample. An ion focusing lens system 12 is provided. Reference numeral 14 denotes an analysis section which has a quadrupole rondo 16 and selects ions having a specific m/Z (mass to charge ratio) from the ion beam guided from the lens system 12. The quadrupole rods 16 are made to face each other, and a direct current voltage and a high frequency voltage are applied in a superimposed manner to each of the two sets of opposing rods. 18 is a secondary electron multiplier tube as a detector.

Inductively coupled plasma is at atmospheric pressure, but the analysis section needs to be in a high vacuum, so the sample collection section 6 and the lens system section 1 are
0. A vacuum evacuation system is provided in each of the analysis sections 14 and 14, and differential evacuation is performed by communicating between each section through small holes in the partition walls.

As a result, for example, the sample collection section 6 has a pressure of about I Torr, the lens system section IO has a pressure of 10-' to 10-3 Torr, and the analysis section 1
4 is maintained at a vacuum level of 10-' to 10-' Torr.

20 is a photodiode as a photodetector arranged on the central axis between the quadrupole rods 16 to monitor the light of the inductively coupled plasma.

22 is an amplifier that amplifies the detection signal of the photodiode 20, and 24 is a differentiation circuit that differentiates the detection signal amplified by the amplifier 22.

26 is a scan control circuit that performs scanning by controlling the voltage applied to the quadrupole rod 16, and 28 is a circuit that applies DC voltage and high frequency voltage to the quadrupole rod 16 under the control of this scan control circuit 26. R-F (high frequency) 1! It is the source. Although the above functions of scan control circuit 26 and R-F power supply 28 are the same as those provided in conventional quadrupole mass spectrometers.

In this embodiment, the scan control circuit 26 inputs the output signal of the differentiating circuit 24, and when the input signal exceeds a certain positive value, the signal is used as a trigger to start scanning by the R/F power supply 28, and the input It also has a function of stopping scanning by the RF power supply 28 using the signal as a trigger when the signal becomes less than a certain negative value.

The differentiating circuit 24 and the scanning control circuit 26 form a control circuit in the present invention that starts or stops the operation of the mass spectrometer depending on changes in light from the inductively coupled plasma.

Next, the operation of this embodiment will be described. After the ions in the inductively coupled plasma are collected by the sampling nozzle 8, they are converged by the converging lens system 12 and guided between the quadrupole rods 16. After being mass separated by the heavy pole rod 16, it is deflected by the deflector 19 and reaches the secondary electron multiplier tube 18.

On the other hand, light from the inductively coupled plasma travels straight and reaches the photodiode 20, where it is converted into an electrical signal. In order to detect changes in light intensity, the output signal of the photodiode 20 is amplified by an amplifier 22, passes through a differentiating circuit 24, and then is guided to a scanning control circuit 26. The scan control circuit 26 uses the output signal obtained from the differentiating circuit 24 as a trigger to start or stop scanning of the RF power supply 28 .

In this embodiment, since the photodetector 20 is provided on the central axis between the quadrupole rondos 16, changes in the amount of plasma light can be detected most effectively. However, the photodetector 20 can also be provided, for example, in the lens system section 10 or the sample collection section 6 at a position where it receives the emission 3 of light from the plasma.

(Effects of the Invention) The inductively coupled plasma mass spectrometer of the present invention monitors the amount of light from the plasma using a photodetector provided within the mass spectrometer immediately after generating plasma of only carrier gas. Since the light intensity changes as the sample is introduced, this change in light intensity is used as a scanning start signal for the JR quantity analyzer to automatically start mass spectrum measurement, and the sample can be introduced while the mass spectrum is being measured. When it stops, the monitored light intensity change is used as a scan stop signal for the mass spectrometer,
It is configured to complete mass spectrum measurements.

As a result, the following effects can be achieved.

(1) Measurement operations can be automated.

(2) Measurement is made faster.

(3) The burden placed on the operator during measurement can be reduced.

[Brief explanation of the drawing]

The figure is a schematic end view showing one embodiment of the present invention. 2... Torch for inductively coupled plasma, 6...
...Sample collection section, lO...Lens system section, 14...Analysis section, 18...Secondary electron multiplier, 20...Photodiode , 22...Amplifier, 24...Differential circuit, 26...Scan control circuit, 28...R-F power supply.

Claims (1)

[Claims] (1) In an apparatus that uses inductively coupled plasma as an ion source and detects ions in the inductively coupled plasma with a mass spectrometer, a photodetector is provided in the apparatus at a position where it can receive light from the inductively coupled plasma, and A control circuit is provided that starts the operation of the mass spectrometer when the detection intensity of the photodetector exceeds a set value, and stops the operation of the mass spectrometer when the detection intensity of the photodetector becomes less than the set value. An inductively coupled plasma mass spectrometer characterized by: