JP2982189B2 - High frequency inductively coupled plasma mass spectrometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial application field> The present invention supplies high-frequency energy to a high-frequency induction coil to form a high-frequency magnetic field to generate high-frequency inductively coupled plasma, and to excite a sample using the plasma. The present invention relates to a high-frequency inductively coupled plasma mass spectrometer for analyzing an element to be measured in the sample by generating ions through the interface consisting of a nozzle and a skimmer and guiding the ions to a mass spectrometer for detection.

<Prior Art> FIG. 3 is a diagram illustrating a general configuration of an analyzer using high frequency inductively coupled plasma. In this figure, an outer chamber 1b and an outermost chamber 1c of a plasma torch 1 are supplied with argon gas from an argon gas supply source 3 via a gas controller 2, and an inner chamber 1a is provided with a solid sample in a sample introduction device 4. Is vaporized by the laser light emitted from the laser light source 5 and then carried in by an argon gas as a carrier gas. When the sample is a liquid, the sample introduction device 4 and the laser light source 5 shown in FIG. 3 are removed, and a nebulizer for atomizing the liquid sample to be introduced and supplying the atomized liquid sample to the inner chamber 1a of the plasma torch 1 is mounted. Also, the sample is often liquid rather than solid.

On the other hand, a high-frequency current flows through a high-frequency power supply 10 through a high-frequency induction coil 6 wound around the plasma torch 1, and a high-frequency magnetic field (not shown) is formed around the coil 6. When electrons or ions are implanted in the argon gas in the vicinity of the high-frequency magnetic field in this state, the high-frequency inductively coupled plasma 7 is instantaneously generated by the action of the high-frequency magnetic field.

Further, the inside of the fore-chamber main body 11 sandwiched between the nozzle 8 and the skimmer 9 is sucked by a vacuum pump 12 at, for example, 1 Torr. Further, ion lenses 14a and 14b are provided in the center chamber 13, and the inside of the center chamber 13 is controlled by a first oil diffusion pump 15, for example.
10 ^-4 Torr. Sucked into, the rear chamber 17 housing the mass filter (e.g. quadrupole mass filter) 16 is sucked by the second oil diffusion pump 18, for example, in 10 ^-5 Torr..

In this state, the sample vaporized as described above is introduced into the high frequency inductively coupled plasma, and ionization and light emission are performed. The ions in the plasma 7 are divided into a nozzle 8, a skimmer 9,
And after passing through the extraction electrode 9 ', the ion lens 14a,
The light is converged by passing between 14b (or a doublet quadrupole lens), and then guided to the secondary electron multiplier 19 through the mass filter 16 and detected. This detection signal is sent to the signal processing unit.
The data is sent to 20 and is calculated and processed, whereby the measured value of the element to be measured in the sample is obtained.

On the other hand, a high frequency inductively coupled plasma mass spectrometer has a very wide dynamic range of signal strength (for example, 10 ⁸ or more).
Therefore, when a signal is strong in one secondary electron multiplier, the signal is used in the analog mode when the signal is weak, and when the signal is weak, the mode is switched to the pulse count mode to detect ions. In this case, in the pulse count mode, the concept of the integration time for counting pulses is important, and the longer the integration time, the higher the S / N
The ratio was improving. That is, FIG. 4 is a block circuit diagram showing a specific configuration of the signal processing unit 20, which is incident on a dual mode secondary electron multiplier 21 (corresponding to the secondary electron multiplier 19 in FIG. 3). When the intensity of the ion to be applied is high, the analog output of the dual mode secondary electron multiplier 21 is amplified by the current / voltage conversion amplifier 22 and then sampled and held by the sample and hold circuit 23 for a certain period of time.
Central processing unit (CPU) 3 after A / D conversion by A / D converter 24
It is sent to 0 for arithmetic processing. When the intensity of ions incident on the dual mode secondary electron multiplier 21 is low, the pulse output of the dual mode secondary electron multiplier 21 is amplified by the pulse amplifier 26 for pulse counting and then shaped. The waveform is shaped by the discriminator 27, then counted by the counter 28, and the counter output signal is sent to the central processing unit (CPU) 30 to be processed. The sample and hold circuit 23 and the A / D converter 24 are controlled by a sampling timing generation circuit 25 instructed by the CPU 30, and the counter 28 is adjusted in timing by a counter gate timing generation circuit 29 instructed by the CPU 30. It has become.

<Problems to be Solved by the Invention> However, in the above conventional example, when measuring ions in the analog mode, if a general A / D converter is used as the A / D converter 24, the A / D conversion Since the device is not easily adapted to the concept of integration time, there is a disadvantage in that data must be measured and sampled several times to perform data manipulation.

The present invention has been made in view of such circumstances,
The challenge is to provide a high-frequency inductively coupled plasma mass spectrometer that can introduce the same concept of integration time as pulse mode in analog mode and does not require oversampling or averaging circuits to measure analog mode. Is to do.

<Means for Solving the Problems> The present invention supplies high-frequency energy to a high-frequency induction coil to form a high-frequency magnetic field to generate high-frequency inductively coupled plasma, and to excite a sample using the plasma to generate ions. A high-frequency induction plasma mass spectrometer that analyzes the element to be measured in the sample by guiding the ions to a mass spectrometer through an interface including a nozzle and a skimmer to detect the ions, and the detector of the mass spectrometer. Means for outputting the output of the secondary electron multiplier in both the pulse mode and the analog mode, a pulse counter for counting the pulse mode output signal, and converting the analog mode output signal into a frequency signal, The analog mode counter that counts the frequency signal and the two counters are the same based on the command of the CPU. Characterized in that a gate time generation circuit for counting by preparative timing.

The present invention also provides a high-frequency induction coil which supplies high-frequency energy to form a high-frequency magnetic field to generate a high-frequency inductively coupled plasma, and excites a sample using the plasma to generate ions. In a high-frequency inductively coupled plasma mass spectrometer that analyzes an element to be measured in the sample by conducting the detection to a mass spectrometer through an interface consisting of: a secondary electron multiplier that is a detector of the mass spectrometer. Means for outputting the output of the tube in both the pulse mode and the analog mode, a multiplexer for inputting the output signal of the pulse mode and the output signal obtained by converting the output signal of the analog mode into a frequency signal, and a command of the CPU. A counter for a pulse counter that counts pulse signals output from the multiplexer and a command of the CPU. In which characterized in that a gate time generation circuit for controlling the timing of the counting of the counter Zui.

<Operation> The present invention operates as follows. That is, the output of the dual mode secondary electron multiplier, which is the detector of the mass spectrometer, is measured in both the pulse count mode and the analog mode, and a V / F converter is provided in the signal processing section in the analog mode to provide the V / F converter. The output of the / F converter is counted by an analog mode counter operating at the same gate timing as that of the pulse counting counter, or the output of the V / F converter is counted by a pulse counting counter via a multiplexer. For this reason, the same concept of the integration time as in the pulse count mode can be introduced into the analog mode, and no oversampling or averaging circuit for measuring the analog mode is required.

<Example> Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a main part of an embodiment of the present invention. In FIG. 1, the same symbols as those in FIG. 31 is a V / F converter that converts voltage to frequency, 32 is an analog counter, 3
Reference numeral 3 denotes a gate time generation circuit that controls the analog counter 32 and the analog mode counter 28 in response to a command from the CPU 30. In the embodiment of the present invention having the block circuit having such a main configuration, the current (analog) output of the dual mode secondary electron multiplier 21 is supplied to the current / voltage amplifier 22.
And then V / F converted by V / F converter 31, then
The count is performed by the analog counter 32, and the output signal of the counter is processed by the CPU 30. Further, the pulse output of the dual mode secondary electron multiplier 21 is amplified by a pulse counting pulse amplifier 26, and then shaped by a waveform shaping discriminator 27, and then counted by an analog mode counter 28. Counter output signal is CPU30
Is calculated. The analog counter 32 and the analog mode counter 28 are controlled by a gate time generation circuit 33 instructed by the CPU 30.

As described above, when the output of the dual mode secondary electron multiplier 21 is measured in both the pulse count mode and the analog mode, the V / F converter 31 is added to the analog mode signal processor.
Since the output of the V / F converter is counted by the counter 32 operating at the same gate timing as the gate timing of the pulse counting counter 28, the concept of the integration time similar to the pulse count mode is also used in the analog mode. It is a high-frequency inductively coupled plasma mass spectrometer that can be introduced and does not require oversampling or averaging circuits for measuring analog modes.

On the other hand, FIG. 2 is a block diagram showing a main part of another embodiment of the present invention. In the drawing, the same symbols as those in FIGS. 1 and 3 are used with the same meanings, and will be described repeatedly here. Is omitted. 34 is a multiplexer. In another embodiment of the present invention having a block circuit having such a main configuration, the output of the dual mode secondary electron multiplier 21 is amplified by the current / voltage conversion amplifier 22 and then by the V / F converter 31. V / F conversion is performed. The output of the dual mode secondary electron multiplier 21 is amplified by a pulse counting pulse amplifier 26 and then shaped by a waveform shaping discriminator 27. The outputs of the V / F converter 31 and the waveform shaping discriminator 27 are sent to a multiplexer 34, which in turn sends the outputs to a counter 28. The counter 28 counts the pulses sent from the multiplexer 34, and the output signal is sent to a central processing unit (CPU) 30 for arithmetic processing.
The counter 28 is controlled by a gate time generation circuit 33 instructed by the CPU 30.
It is now controlled directly by the U30 commander.

As described above, when the output of the dual mode secondary electron multiplier 21 is measured in both the pulse count mode and the analog mode, the V / F converter 31 is added to the analog mode signal processor.
Since the output of the V / F converter is counted by the counter 28 via the multiplexer 34, the same concept of the integration time as in the pulse count mode can be introduced in the analog mode, and an over-range for measuring the analog mode can be introduced. A high-frequency inductively coupled plasma mass spectrometer that does not require a sampling or averaging circuit.

<Effects of the Invention> According to the present invention as described in detail above, in a high frequency inductively coupled plasma mass spectrometer, the output of a dual mode secondary electron multiplier, which is a detector of a mass spectrometer, is output in a pulse count mode and an analog mode. Measurement in both modes, a V / F converter is provided in the signal processing unit of the analog mode, and the output of the V / F converter is an analog mode counter that operates at the same gate timing as the gate timing of the pulse counting counter. Either counting or the output of the V / F converter is counted by a counter shared with the pulse counting counter via a multiplexer. For this reason,
The same concept of the integration time as in the pulse count mode can be introduced into the analog mode, and a high-frequency inductively coupled plasma mass spectrometer that does not require oversampling or an averaging circuit for measuring the analog mode is realized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a main part of an embodiment of the present invention, FIG. 2 is a block diagram showing a main part of another embodiment of the present invention, and FIG. 3 is a general view of a high frequency inductively coupled plasma mass spectrometer. FIG. 4 is a block diagram showing a main part of a conventional example. DESCRIPTION OF SYMBOLS 1 ... Plasma torch, 2 ... Flow control part, 3 ... Argon gas supply source, 4 ... Sample cell, 6 ... High frequency induction coil, 7 ... High frequency induction coupling plasma, 8 ... Nozzle, 9 ... Skimmer, 16: Mass filter, 17: Rear chamber, 20: Signal processing unit, 21: Dual mode secondary electron multiplier 22: Current / voltage conversion amplifier 23: Sample / hold circuit 24: A / D converter 26 Pulse amplifier for pulse counting 27 Waveform shaping discriminator 28 32 Counter 30 Central processing unit (CPU) 31 V / F converter 33 Gate time generation Circuit, 34 …… multiplexer

Claims (2)

(57) [Claims] A high-frequency induction coil is supplied with high-frequency energy to form a high-frequency magnetic field to generate a high-frequency inductively coupled plasma, and the plasma is used to excite a sample to generate ions, and the ions are transmitted from a nozzle and a skimmer. In the high-frequency induction plasma mass spectrometer that analyzes the element to be measured in the sample by conducting the detection to the mass spectrometer through an interface, the secondary electron multiplier, which is the detector of the mass spectrometer, Means for outputting an output in both a pulse mode and an analog mode, a counter for a pulse counter for counting the output signal in the pulse mode, and an analog for converting the output signal in the analog mode to a frequency signal and counting the frequency signal A mode counter and both counters are counted at the same gate timing based on a command of the CPU. Inductively coupled plasma mass spectrometer, characterized in that a gate time generation circuit because 2. A high-frequency induction coil is supplied with high-frequency energy to form a high-frequency magnetic field to generate a high-frequency inductively coupled plasma, and the plasma is used to excite a sample to generate ions. In a high-frequency inductively coupled plasma mass spectrometer that analyzes an element to be measured in the sample by guiding the mass spectrometer through an interface and detecting the secondary electron multiplier, a secondary electron multiplier that is a detector of the mass spectrometer Means for outputting the output of both the pulse mode and the analog mode, a multiplexer for inputting the output signal of the pulse mode and the output signal obtained by converting the output signal of the analog mode into a frequency signal, and based on a command of the CPU. A pulse counter for counting pulse signals output from the multiplexer and a command from the CPU, Inductively coupled plasma mass spectrometer, characterized in that a gate time generation circuit for controlling the timing of the counting of said counter Te.