JP2001249112A - Data collecting method and apparatus for time-of-flight mass spectrometer, and data processing method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To collect data using smaller amount of memory and a smaller circuit scale at lower cost than with a simple ADC method by enabling a TOFMS to handle a wider dynamic range than a simple TDC type device. SOLUTION: TOF spectrum signals are classified into a plurality of levels by means of a discriminator apparatus 2, with the classified signals inputted to a data collection apparatus 6 having serial in and parallel out shift registers. On condition that there is a classified signal input to any of the shift registers every time a shift clock from an oscillator 5 is divided by a dividing circuit 4 to make a shift for a certain number of bits, the time elapsed since the start of the clock and shift data are read and stored in the memory of the data collection apparatus 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a time-of-flight mass spectrometer (Time-of-flight mass spectrometer) for accelerating an ionized sample, measuring a difference in arrival time at a detector based on a difference in mass, and analyzing the sample.
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for collecting and processing data for Of Flight Mass Spectrometer (TOFMS).

[0002]

2. Description of the Related Art Conventionally, TOF data is collected in TOFMS by a method of (1) starting from a time at which an ionized sample is accelerated and arriving at a detector by a stopwatch method. Time to Di to record
gital (TDC) method, (2) Analyze to Diode
There is a method of A / D conversion with gital Converter (ADC).
Both have their advantages and disadvantages.

[0003]

The TDC method can be set so as not to count pulses below a certain threshold (threshold level), so that it is resistant to noise and records only the time when ions arrive at the detector. The advantage is that less memory is required, but the stopwatch operation cannot be performed in time when pulses come in succession, and counts down (dead time) .Therefore, the amount of ions that can be measured is small, and the amount of sample introduced is small. There is a disadvantage that must be kept.

In the ADC system, since the A / D conversion can be performed in a wide operation range from a pulse region to a current region of a secondary electron multiplier used as an ion detector, the amount of ions that can be handled is large, but the output of the detector is large. When the pulse width is narrow, if the A / D conversion speed is low, the pulse cannot be A / D converted, so that high-speed AD
It is necessary to operate C with a high-speed clock, which requires a large amount of memory. Also, since the memory speed is low for the high-speed ADC, it is necessary to operate a plurality of (normally eight or more) control circuits for connecting the ADC and the memory in parallel.
The circuit scale becomes large. High-speed ADCs are also expensive. In addition, they are more susceptible to noise than the TDC method.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem. When collecting TOF data, the dynamic range of a sample that can be handled by TOFMS is made larger than that of a mere TDC method, and the memory and the circuit scale are smaller than those of a simple ADC method. Another object of the present invention is to enable data collection at low cost.

Another object of the present invention is to provide a processing method and apparatus for creating time data based on data collected in this manner.

[0007]

SUMMARY OF THE INVENTION A data collection method for a time-of-flight mass spectrometer according to the present invention discriminates a spectrum signal into a plurality of levels and serializes each of the discriminated signals.
Input to each shift register of the parallel-out, and every time a certain number of bits are shifted by the shift clock, read and record the time from the clock start and the shift data on condition that there is a discriminated signal input to the shift register. It is characterized by doing so.

Further, in the data processing method for a time-of-flight mass spectrometer according to the present invention, the spectrum signal is discriminated by a plurality of levels, each discriminated signal is input to each serial-in / parallel-out shift register, and the shift is performed. Each time the clock shifts by a certain number of bits, the time from the clock start and the shift data are read out and recorded, on condition that there is a discriminated signal input to the shift register, and the time data is based on the recorded shift data. And recording the created time data in combination with the time from the clock start recorded corresponding to the shift data.

Further, in the data acquisition device for a time-of-flight mass spectrometer of the present invention, a plurality of comparators set to different threshold levels to which spectrum signals are inputted, and signals discriminated by each of the comparators are inputted. A plurality of serial-in / parallel-out shift registers; a frequency dividing circuit for dividing the shift clock to generate an output for each fixed number of shift clocks; a counter for counting the output of the frequency dividing circuit; A read signal generating means for generating a read signal by an AND signal of the output and the shift data, and a memory in which the shift data is written by the read signal and the contents of the counter are written.

Further, in the data processing apparatus for a time-of-flight mass spectrometer according to the present invention, a plurality of comparators set to different threshold levels to which a spectrum signal is input, and a signal discriminated by each of the comparators are input. A plurality of serial-in / parallel-out shift registers, a frequency dividing circuit for dividing the shift clock and generating an output every fixed number of shift clocks, a counter for counting the output of the frequency dividing circuit, and a frequency dividing circuit. A read signal generating means for generating a read signal by an AND signal of the output and the shift data; a first memory for storing a combination of the shift data and the output value of the counter based on the read signal from the read signal generating means; One based on the output value of the counter and the shift data among the shift data stored in combination. Alternatively, a decoder for creating a plurality of time data, and one or a plurality of time data created by the decoder and an output value of the counter stored in combination are recorded as one or a plurality of composite time data. And a second memory.

[0011]

Embodiments of the present invention will be described below. FIG. 1 is a diagram showing the overall configuration of a data collection and processing device for a time-of-flight mass spectrometer of the present invention, FIG. 2 is an explanatory diagram of the data collection circuit 1 in FIG.
FIG. 4 is a diagram illustrating the relationship between the TOF spectrum signal and the threshold of the comparator.

In FIG. 1, the TOF spectrum signal is
The threshold level is applied through a buffer amplifier 1 to a level discriminator 2 comprising comparators A to D, each of which is set separately. The threshold level of each comparator is set as shown in FIGS. 3 (a) and 4 (a) by a variable DC voltage source attached to each comparator.
As a result of comparison with the threshold level by the comparator, a digitized signal of “1” is obtained when the level is equal to or higher than the threshold level, and “0” is output when the level is lower than the threshold level. The output of the level discriminator 2 is an oscilloscope (OSC) 3 The data is taken into the data collection device 6 including the data collection circuits A to D as a lower digit of the flight time of the ion by the clock from the clock.

The TOF spectrum signal is generated by impact acceleration of a sample ion by a high voltage pulse, and the OSC 3 is started by a trigger signal of the impact acceleration. Since the time resolution of TOFMS is determined by the frequency of the OSC, the OSC generates a clock signal having the highest possible frequency (for example, 1 GHz). The clock of the OSC 3 is frequency-divided by a 1/2 ⁿ frequency ^dividing circuit 4, and the frequency-divided output is a write signal to the memory of the data collecting device 6. Is written to the data collection device 6.

Each of the data collection circuits A to A of the data collection device 6
Since D has the same configuration, the details will be described with reference to FIG. 2 taking the data collection circuit A as an example. The original clock (example 1 GHz) generated by the OSC 3 is a 2 ^n- bit shift register 10 (example n) = 4, the number of bits is 16).

The shift register 10 has a serial input
The digitized discrimination output of the comparator A, which is a parallel out and is input to the serial data in by the shift clock, is taken in as shift data indicating the lower digit of the flight time of ions. Shift register 10
Is a (m + 2 ⁿ ) -bit FIFO (First
In First Out) (for example, when m = 16 and n = 4, a 32-bit FIFO memory) is connected to the lower digit (lower 16 bits) of the data in.

On the other hand, the original clock generated by OSC3
(Example 1 GHz) is 1/2 divided by ⁿ frequency dividing circuit 4 (Example n = 4, the frequency 1 GHz / 16 = 62.5 MHz) is, m-bit counter 5 (m = 16 → 65536 binary) and AND circuit 13 Supplied to The contents of the m-bit counter 5 indicate the upper digit of the flight time of the ion, and this is sent to the upper digit (upper 16 bits) of the data-in of the FIFO memory 11 and written therein. The parallel output of the shift register 10 is ORed for all bits by an OR circuit 12 and input to an AND circuit 13.

That is, if there is at least one "1" in the shift data in the shift register, a clock of 62.5 MHz is applied to the write input (write clock) of the FIFO memory and the data (the upper digit of the flight time of ions) is applied. (16 bits) and shift data (16 bits))
Is written to. If there is no "1" in the shift data, data writing is not performed. The write clock (1 GHz / 16 = 62.5 MHz) has a shift bit number of 16
, Even one shift data is "1"
If there is, writing to the FIFO memory is performed once for every 16 shift data.

The conversion of the shift data into the lower digits of the flight time and the connection with the upper digits of the flight time are performed by the dime encoder 14. The time encoder 14 sends a read signal to the FIFO memory 11 every time it decodes 16 bits, decodes the data, and generates a time signal. As for the time relationship between the discrimination levels, since the upper digit of the time is recorded in the same word as the shift data, the histogram calculation device 7
In, data in which the upper digits of the time match can be recognized as one pulse, and when a plurality of scans are performed, a histogram is formed. The histogram calculation device 7 also has a role of controlling a DC voltage source attached to each of the comparators, and setting an appropriate threshold level for each comparator.

FIGS. 3 and 4 show the relationship between the TOF spectrum signal and the threshold level of the comparator when m = 16 and n = 4. When a TOF spectrum signal as shown in FIGS. 3 (a) and 4 (a) is detected (note that
For the sake of convenience, FIG. 3 and FIG. 4 are separated, but these are assumed to be continuous.) The first peak P1 is level 1 and level 2
Since the other small peaks do not reach level 1, only the peak P1 is written as "1" in the shift register, and the write clock (62.5 MHz) from the AND circuit 13 at the 16th bit is stored in the FIFO memory 11. The data is applied to the write clock, and the data (the upper digits of the flight time of the ions and the shift data (FIG. 3B)) are written.

At this time, 1 to the shift data of levels 2 to 4
Since there is no "1", no write clock is output from the AND circuit 13, and writing to the FIFO memory is not performed. At the next peak P2, it is between level 2 and level 3, at level 1, three "1" s are written continuously, at level 2, one "1" is written, and at levels 3, 4 it is shifted Since there is no "1" in the data, A
No write clock is output from the ND circuit 13, and the FI
Writing to the FO memory is not performed.

In the case of the peak P3, only the level 1 data is written as in the case of the peak P1. Peak P4
Similarly, in the case of level 3, two "1" s are continuously written in level 3, four "1" s are written continuously in level 2, and six "1" s are written in level 1 continuously. In the case of peak P5, , One “1” at level 4 and four “1” s at level 3
However, at level 2, six “1” s are continuously written, and at level 1, eight “1” s are written continuously. It can be seen from the data of FIGS. 3 (c) and 4 (c) that the data of "1" is extracted for each level, information on the height and width of each peak is obtained.

That is, the arrival time of the pulse from the detector, the pulse height and the pulse width are measured simultaneously. When this data is converted into a histogram, levels 1 to 1
Since the pulses are counted in duplicate in step 4, this correction is performed.

FIG. 5 is a block diagram showing a configuration example of the time encoder 14 described above. In FIG.
For convenience, the O memory 11 is illustrated as being divided into two FIFO memories 11a and 11b that store lower 16-bit data (shift data) and upper 16-bit data (time data), respectively. The FIFO memories 11a and 11
The time encoder that receives the data from b and converts it into time data includes a register H that receives the time data from the FIFO memory 11b, and the time data from the register H is supplied to the data-in (upper 16 bits).
A bit FIFO memory 21, a register S for receiving time data from the FIFO memory 11a, and a decoder 22 for receiving shift data from the register S and generating a write signal at a timing corresponding to a pulse position included in the shift data. It comprises an OR circuit 23, an AND circuit 24, and a 4-bit binary counter 25 that counts a time encode clock and supplies a count output to the data-in (lower 4 bits) of the FIFO memory 21 and to the decoder 22.

When a read pulse is applied to the read inputs of the FIFO memories 11a and 11b, shift data is written from the FIFO memory 11a to the register S, and time data is written from the FIFO memory 11b and latched.

Here, the shift data in the register S is
They are arranged as T0 to T15 in ascending order of time. Register H
Since the upper part of the time data is stored in H (m)
Then, when m = 16, H (m) takes a value of 0 to 65535, and H (m) is a value multiplied by 16 when the number of shifts is 2 ^n, which is higher in time data. Express. Therefore, T0-T1
When time is given to 5, T0 (H (m)) = (H (m) X16 + 0 [Clk], T1 (H (m)) = (H (m) X16 + 1 [Cl
k],... T15 (H (m)) = (H (m) X16 + 15 [Clk] where [Clk] is 1 nS if the original clock is 1 GHz.

Time encode clock (not necessarily synchronized with the original clock, but 20 MHz or more is desired because it is necessary to perform time encode processing at high speed)
Is a counter 25 that counts to determine the lower order of the time data ( ^{4 when} shift data is 2 ⁴ = 16 bits).
) Clock input and supplied to the AND circuit 24.

The count code output (A, / A,
(B, / B, C, / C, D, / D) is the binary code 0000,0001,0002,00
03,... Constituting the decoder 22 as 1110, 1111 16
Are supplied to the five 5-input AND circuits. And each AND
In the circuit, the output of the register S is ANDed and each A
The output of the ND circuit is ORed by an OR circuit and further supplied to an AND circuit 24 for ANDing with a time encoding clock.

FIG. 6 shows the time encode clock and T0 to
FIG. 9 is a diagram illustrating timings of T15 and a data write command pulse (Write Clock) to the FIFO memory 21. In this example, T0, T5, T6, and T12 are "1", that is, the timing at which ions reach the detector and are detected as pulses. The write command pulse is generated only at times t0, t5, t6, and t12. At that timing, 20-bit time data consisting of 4-bit lower data from the counter 25 and 16-bit upper data from the FIFO memory 11b is generated. FIF
The data is written to the O memory 21.

FIG. 7 is a diagram showing a state in which data (time data and shift data) before time encoding stored in the FIFO memories 11a and 11b are time-encoded and stored in the FIFO memory 21. . FIFO memory 1 underlined in FIG.
Data “0000000000001010” at the beginning of 1b and 11a,
“0001000001100001” is converted into four data “0000000000001010 0000”, “0000000000001010 0101”, “0000000000001010 0110”, and “0000000000001010 1100” from the beginning of the FIFO memory 21 underlined in FIG. 7B. The lower 4 bits of these four data are at the timings t0, t5, t6, and t12 described above.
Given by the count output of the counter 25,
It can be seen that the position where the four “1” s in the shift data “0001000001100001” are converted to time.

Thereafter, the FIFO memories 11a and 11b are sequentially
, And the time-encoded result is written to the FIFO memory 21. Then, the histogram calculation device 7 reads the time data from the FIFO memory 21 and performs a histogram process when repeated scanning (measurement) is performed.

FIG. 8 shows another configuration example of the time encoder. In this example, a parallel-in serial-out shift register 30 is used instead of the register S, the decoder 22, and the OR circuit 23 in the configuration shown in FIG.

The threshold levels need not be set at equal intervals as in the above-described example. For example, FIG.
As shown in FIG. 9, the first level may be set high and the rear may be set at regular intervals, or as shown in FIG. 9B, the initial level may be set low and the rear set at equal intervals. Alternatively, as shown in FIG. 9 (c), it may be gradually narrowed from level 1.

Further, when information on the height of each pulse is taken out, in the above example, the information is divided into four stages according to the four threshold levels. However, if more threshold levels are set, the information is divided into more stages. Can be taken out. In addition, even if the four threshold levels remain, by introducing the following idea,
It is also possible to extract the height information of each pulse by dividing it into stages or more.

For example, when the pulse width measured at the highest level 4 is wider than a certain level (for example, two clocks or more) as in the pulse P7 shown in FIG. Is not set, but the pulse level is estimated to exceed 5), and the level of the pulse is corrected to 5 instead of 4. By introducing such a concept, it is possible to extract pulse height information in a wide dynamic range with a limited number of comparators.

In addition, a D / A converter can be used as a variable voltage source for defining a threshold level in the comparators A to D. If a D / A converter is used,
Since the threshold level can be changed easily and quickly, the various settings described above can be arbitrarily selected.

[0036]

As described above, according to the present invention, by simultaneously measuring the arrival time, pulse width, and pulse height of a pulse from a detector, the dynamic range of a sample that can be handled by TOFMS can be increased as compared with a simple TDC method. , Just AD
Data can be collected with less memory, a smaller circuit scale, and lower cost than in the C method. .

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of a data acquisition and processing device for a time-of-flight mass spectrometer of the present invention.

FIG. 2 is an explanatory diagram exemplifying a data collection circuit 1 in FIG. 1;

FIG. 3 is a diagram illustrating a relationship between a TOF spectrum signal and a threshold of a comparator.

FIG. 4 is a diagram illustrating a relationship between a TOF spectrum signal and a threshold of a comparator.

FIG. 5 is a block diagram illustrating a configuration example of a time encoder 14.

FIG. 6 shows a time encoding clock, T0 to T15, and FIF.
FIG. 4 is a diagram showing the timing of a data write command pulse to the O memory 21.

FIG. 7 shows data before time encoding stored in FIFO memories 11a and 11b.
FIG. 3 is a diagram illustrating a state where the time-encoded data is stored in the storage unit 1;

FIG. 8 is a diagram illustrating another configuration example of the time encoder.

FIG. 9 is a diagram illustrating another example of setting a threshold level.

FIG. 10 is a diagram for explaining a concept of extracting pulse height information in a wide dynamic range using a limited number of comparators.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Buffer amplifier 2 ... Level discriminator 3 ... Oscillator 4 ... Division circuit 5 ... Counter 6 ... Data collection device 7 ... Histogram calculation device 10 ... Shift register 11,11a, 11b, 21 ... FIFO memory 12,23 ... OR circuit 13, 24: AND circuit 14: Time encoder 22: Decoder 25: Binary counter

Claims (6)

[Claims] 1. A spectrum signal is discriminated by a plurality of levels, each discriminated signal is inputted to each serial-in / parallel-out shift register, and discriminated by a shift register every time a predetermined number of bits are shifted by a shift clock. A data collection method for a time-of-flight mass spectrometer, wherein a time from a clock start and shift data are read out and recorded on condition that there is a signal input. 2. A spectrum signal is discriminated by a plurality of levels, each discriminated signal is inputted to each serial-in / parallel-out shift register, and discriminated to a shift register every time a predetermined number of bits are shifted by a shift clock. Under the condition that there is a signal input, the time and shift data from the clock start and shift data are read out and recorded, time data is created based on the recorded shift data, and the created time data corresponds to the shift data. A data processing method for a time-of-flight mass spectrometer, wherein the data is recorded in combination with the time recorded from the clock start. 3. A plurality of comparators set to different threshold levels to which spectral signals are input, a plurality of serial-in / parallel-out shift registers to which signals discriminated by the comparators are input, and a shift clock. A frequency divider that divides the frequency to generate an output at every fixed number of shift clocks, a counter that counts the output of the frequency divider, and a read that generates a read signal based on the logical product signal of the output of the frequency divider and the shift data A signal generation means, and a memory for storing a combination of shift data and an output value of the counter based on a read signal from the read signal generation means, and data acquisition for a time-of-flight mass spectrometer. apparatus. 4. The data collection device for a time-of-flight mass spectrometer according to claim 3, wherein the threshold level of each of the plurality of comparators is set by a D / A converter provided in each of the comparators. . 5. A plurality of comparators set at different threshold levels to which spectral signals are inputted, a plurality of serial-in / parallel-out shift registers to which signals discriminated by the respective comparators are inputted, and a shift clock. A frequency divider that divides the frequency to generate an output at every fixed number of shift clocks, a counter that counts the output of the frequency divider, and a read that generates a read signal based on the logical product signal of the output of the frequency divider and the shift data A signal generating means, a first memory for storing a combination of the shift data and the output value of the counter based on a read signal from the read signal generating means, and a first memory for storing the combined output value of the counter and the shift data. A decoder for generating one or more time data based on shift data in the decoder; And a second memory that combines the one or more time data created by the above and the output value of the counter stored in combination to record as one or a plurality of composite time data. Data processor for time-of-flight mass spectrometers. 6. The data processing apparatus for a time-of-flight mass spectrometer according to claim 5, wherein said first and second memories are FIFO memories.