Patent Application
20060248942
The present application claims priority from Japanese Patent Application No. JP 2005-50102 filed on Feb. 25, 2005, the content of which is hereby incorporated by reference into this application.
The present invention relates to a mass spectrometry technology. More particularly, it relates to a technology effectively applied to data processing technologies for mass spectrometry using an A/D converter in a Time-of-Flight Mass Spectrometer (TOF-MS).
The TOF-MS is an apparatus in which a sample is ionized and accelerated in a space and a time of flight in the space, which depends on its mass, is measured, thereby analyzing components contained in the sample. The sample is ionized in an interface 1, and is then reached to a Time-of-Flight (TOF) region 2.
The ion fed to the TOF region 2 is accelerated at a timing of a pulse signal 11a generated from a pulser 11. The accelerated ion flies through the course represented by an arrow in the drawing inside the TOF region 2, and then reaches (collides with) a detector (micro channel plate) 21, thereby generating a detection signal 2a. A gain adjuster 4 connected to a stage previous to the data acquisition circuit 5 adjusts the amplitude of the detection signal 2a, and a detection signal 4a after the amplitude adjustment is inputted to the data acquisition circuit 5.
In the data acquisition circuit 5, the time of flight of the ion is repeatedly measured with this detection signal 4a, and acquired addition data (measurement results) 5b is outputted to a user interface unit 62 via a CPU 61.
Here, systems of acquiring time-of-flight data in the data acquisition circuit 5 include a Time to Digital Converter (TDC) system and an Analog to Digital Converter (ADC) system. In the apparatus for quantitative analysis of each component contained in the sample, the ADC system is often used.
The amplitudes of the detection signal 2a are different in accordance with the number of ions reaching (colliding with) the detector (Micro Channel Plate) 21. In the TDC system, a time and the number of detections are acquired when the data exceeds a certain level (threshold level) regardless of the magnitude of the amplitude of the detection signal 2a. Meanwhile, in the ADC system, the amplitude data is acquired at predetermined time intervals.
The gain adjuster 4 connected to the stage previous to the data acquisition circuit 5 adjusts the amplitude of the detection signal 2a, and then the detection signal 4a after the amplitude adjustment is inputted to an A/D converter 51 of the data acquisition circuit 5. The detection signal 4a after the A/D converter 51 at the timing of a reference converts the amplitude adjustment clock 50a generated by a clock generator 50 into digital data 51a representing a voltage value, and the digital data 51a is stored in a signal intensity addition memory 53.
Here, since the next measurement (process 1) cannot start during the data transfer, all of the time of the process 2 corresponds to a measurement suspension time. In this example, approximately 40% of the measurement time is a measurement suspension time, which leads to a degradation in measurement efficiency.
Also, in the above-described ADC system, since it is required that n-bit sampling data from the A/D converter 51 representing the amplitude of the detection signal is obtained on the order of M points and further the obtained data is subjected to an addition process, the entire amount of data is increased in comparison with the TDC system. For the solution of this problem, for example, Japanese Patent Application Laid-open Publication No. 11-287807 discloses the technology of removing unnecessary sampling data, and United States Patent Application Publication No. 2003-0173514 discloses a data compression process such as the noise reduction by means of threshold levels.
In
Sampling data from an A/D converter includes not only a peak spectrum but also a lot of unnecessary data such as a noise level, for example. Therefore, in this data compression technology, a threshold level is set and the sampling data equal to or lower than the threshold level is cut off without being written in the memory, and only data exceeding the threshold level is transferred.
There are a variety of schemes for processing the data at the points which are cut off because the data is equal to or lower than the threshold level, which include an offset operation system in which data equal to or lower than a predetermined level (in the drawing, the threshold level) is offset uniformly to the threshold level as shown in
In these data compression processes, when data compression is performed to the addition data, since it is required that all pieces of measurement data are transferred to the CPU and then a compression process is performed by the CPU, a problem of increasing a measurement suspension time (data transfer time) occurs.
Moreover, in the technologies discussed in the above-mentioned Japanese Patent Application Laid-Open Publication No. 11-287807 and United States Patent Application Publication No. 2003-0173514, processor processing or hardware multiplexing is performed. Therefore, a problem that the process becomes complicated and the cost is increased occurs.
Accordingly, the present invention is to solve the above-described problems, and an object thereof is to provide a mass spectrometry technology capable of achieving a reduction in data transfer time by extracting and transferring only the data exceeding a threshold level, in an ADC data processing function of a time-of-flight mass spectrometer. Note that, in the present invention, simultaneously with a reduction in data transfer time, removal of noise data can be achieved.
Furthermore, another object of the present invention is to provide a mass spectrometry technology capable of achieving an improvement in analytical efficiency by extracting only the stored data required for the analysis.
The above and other objects and novel characteristics of the present invention will be apparent from the description of this specification and the accompanying drawings.
The typical ones of the inventions disclosed in this application will be briefly described as follows.
In the present invention, in an ADC data processing function of a time-of-flight mass spectrometer, as means for extracting only a signal required for the analysis in a short time, a voltage value frequency addition memory circuit for adding frequencies of voltage values is provided, and a predetermined process is performed to determine a threshold level based on the noise distribution represented by the stored contents of the memory circuit. Then, only the data exceeding this threshold level is extracted and transferred. By doing so, a reduction in data transfer time can be achieved.
Also, in the present invention, the user of the apparatus refers to the contents of the above-described voltage value frequency addition memory circuit and a signal intensity addition memory circuit, and based on the reference result, a threshold level for discriminating between a noise value and a signal value is set, and then, only the stored data required for analysis is extracted. By doing so, an analytical efficiency can be improved.
More specifically, the present invention is applied to a time-of-flight mass spectrometer having a data processing function, in which an ionized sample is accelerated and allowed to fly and a detection signal obtained by detecting the flying ion is processed, and to a mass spectrometry method in this mass spectrometer, and the present invention has the following features.
(1) A time-of-flight mass spectrometer comprises: an A/D converter that samples a detection signal; a first memory circuit that stores sampling data from the A/D converter while performing an addition process of the sampling data; a second memory circuit that performs an addition process of frequencies of voltage values from the A/D converter and stores an addition result; a computing unit that performs a predetermined process based on the result of addition process in the second memory circuit to calculate a threshold level; and a third memory circuit that extracts only the data exceeding the threshold level, which is an output signal from the computing unit, from an addition process result in the first memory circuit, and stores the extracted data.
(2) In another aspect of the time-of-flight mass spectrometer described in (1), the computing unit performs a predetermined process based on the addition process result in the second memory circuit to calculate a threshold level and an offset value, and a third memory circuit extracts only the data obtained by performing an adding/subtracting process equivalent to the offset value to the data exceeding the threshold level, which is the output signal from the computing unit, from the addition process result in the first memory circuit, and stores the extracted data.
(3) In another aspect of the time-of-flight mass spectrometer described in (1), a register is provided instead of the computing unit, and the register calculates and sets a threshold level by performing a predetermined process after the apparatus user reads the addition result in the second memory circuit. Also, the third memory circuit extracts only the data exceeding the threshold level set in the register, and stores the extracted data.
(4) In another aspect of the time-of-flight mass spectrometer described in (1), a register group is provided instead of the computing unit, and the register group calculates and set a threshold level and an offset value by performing a predetermined process after the apparatus user reads the addition process result in the second memory circuit. Also, the third memory circuit extracts only the data obtained by performing an adding/subtracting process equivalent to the offset value to the data exceeding the threshold level set in the register group, and stores the extracted data.
The effects obtained by typical aspects of the present invention will be briefly described below.
According to the present invention, in an ADC data processing function, a voltage value frequency addition memory circuit for determining a threshold level and a data compression memory circuit for extracting only a signal exceeding the threshold level are provided. Therefore, data required for analysis can be easily compressed and a data transfer time can be reduced. As a result, a measurement suspension time of the apparatus can be reduced.
Also, according to the present invention, the determination and the setting of a threshold level at the time of data compression can be made by the apparatus user performing an arbitrary computation based on the time-based voltage value addition results and the voltage value frequency addition results. Therefore, the user can set an arbitrary discrimination value of a noise value and a signal value, and the efficiency of the analytical operation can be improved.
These and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.
According to the present invention, in an ADC data processing technology for mass spectrometry in which time-of-flight data is measured and acquired, a memory circuit for performing the time-based voltage value addition process for the sampling data of each measurement and a voltage frequency addition memory circuit for performing the addition of the frequencies of voltage values during the measurement simultaneously with the above-mentioned addition process are provided. After all measurements are finished, a predetermined process is performed to determine a threshold level based on the voltage value frequency data. Further, a memory circuit for data compression for extracting only a signal exceeding the threshold level is provided, and only the compressed data is transferred to a CPU. Accordingly, a reduction in data transfer time is achieved.
Also, in the data compression process according to the present invention, after the measurements using the memory circuit for performing time-based voltage value addition process and the voltage value frequency addition memory circuit are finished, only the voltage value frequency addition results are transferred to the CPU, and an apparatus user then performs a predetermined process based on those addition results to determine a threshold level, thereby generating compressed data by the memory circuit for data compression.
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted.
The mass spectrometer according to this embodiment typically includes a sample interface 1, a pulser 11, a time-of-flight (TOF) region 2 provided with a detector (micro channel plate) 21, a gain adjuster 4, a data acquisition circuit 5, a CPU 61, and a user interface (I/F) unit 62.
The data acquisition circuit 5 includes a clock generator 50 for generating a reference clock 50a, an A/D converter 51 for sampling a detection signal 4a, a counter 52 for generating a measurement start signal 5a and a control signal 52a for data storage, data computation, and data extraction, a signal intensity addition memory (first memory circuit) 53 for storing sampling data 51a while performing an addition process, a voltage value frequency addition memory (second memory circuit) 54 for storing frequencies of voltage values in the sampling data 51a while performing an addition process, a compression memory (third memory circuit) 55 for extracting only the data exceeding a threshold level 56a from addition process results 53a of the sampling data 51a and storing the extracted data, and a threshold level computation circuit (computing unit) 56 for performing a predetermined process based on voltage value frequency addition results 54a to calculate the threshold level 56a.
In this mass spectrometer, the interface 1, the pulser 11, the TOF region 2, and the gain adjuster 4 have the same functions as those of the respective components depicted in
In the operation of the voltage value frequency addition memory 54, with using a digitized voltage value itself outputted from the A/D converter 51 as an address of the memory, how many times that voltage value is outputted from the A/D converter 51 is counted. For example, when a sampling speed of the A/D converter 51 is 1 GHz, a sampling time is 1 μsec, and a voltage input to the A/D converter 51 is 0 V, 1 k digitized voltage values indicating 0 V are outputted from the A/D converter 51. In the voltage value frequency addition memory 54, 1 k count values remain at an address indicating 0 V.
Next, the operation of the threshold level computation circuit 56 will be described with reference to
Here, the output 56a from the threshold level computation circuit 56 is σ and is used as a threshold level of the compression memory 55 described next. Next, in the compression memory 55, an addition is performed n times, and then, after performing a σ-value computation in the threshold level computation circuit 56, time data having an ion intensity (voltage value) exceeding the a value and voltage value data indicating the ion intensity are extracted from the signal intensity addition memory 53. An example of such data is shown in
Next,
A process 1 is the case where the number of measurements is 100, a measurement range is 1 ms, a sampling speed of the A/D converter 51 is 1 Gsps, and the signal intensity addition memory 53 has an address of 1 M points, and the time required for the process 1 is 100 ms. Also, in the process 1, simultaneously with the completion of the 100-th measurement, an average value and a σ value of the voltage values outputted from the A/D converter 51 are calculated by the voltage value frequency addition memory 54 and the threshold level computation circuit 56, and therefore, the average value and the σ value are calculated from the results obtained from up to the 99-th measurement. Therefore, upon the completion of the 100-th measurement, the average value and the σ value can be obtained. Next, in a process 2, voltage values exceeding the σ value (threshold level) are extracted, and this extraction is performed for the time equal to the time of a process of reading the signal intensity addition memory 53 once, which corresponds to one measurement time, that is, 1 ms.
Next, in a process of data transfer to the CPU 61, since the number of points is assumed to be one-tenth of 1 M points as described above, the number of points is 100 k points. Here, since the extracted data includes time data and voltage value data, two data transfers are required and it is assumed that two-point transfer is performed. Therefore, the data transfer rate to the CPU 61 is 8 ms (100 K points×2 data/25 MHz).
As described above, in contrast to the conventional example described with reference to
Note that, in this embodiment, the threshold level computation circuit 56 calculates a standard deviation value (σ). However, the threshold level computation circuit 56 can perform not only this σ-value computation but also a desired computation defined by apparatus specifications or the like.
Furthermore, in this embodiment, the threshold level 56a, which is the output from the threshold level computation circuit 56, is inputted to the compression memory 55. Alternatively, the threshold level 56a can also be inputted to the signal intensity addition memory 53. In this case, when a measurement is performed, a threshold level measurement is performed in advance by using only the voltage value frequency addition memory 54, and then, signals exceeding the threshold level is stored by using the signal intensity addition memory 53. Furthermore, upon the completion of the measurement using the signal intensity addition memory 53, data can be extracted by the compression memory 55 by using the same threshold level, and then, the extracted data can be transferred to the CPU 61.
Also, the data acquisition circuit 5 has functions similar to those of the data acquisition circuit shown in
Next, the operation of the compression memory 55-1 will be described with reference to
As a result, in this embodiment, an ion spectrum analysis can be performed with using the values closer to actual voltage values.
Note that, in this embodiment, the offset value 59b outputted from the threshold level computation circuit 59 is inputted to the compression memory 55-1. Alternatively, the offset value 59b can be inputted to the signal intensity addition memory 53. In this case, a measurement for outputting the offset value is performed before data is stored in the signal intensity addition memory 53. Also, after data is stored in the signal intensity addition memory 53, data may be extracted by using only the threshold level 59a.
First, a normal measurement is performed to store the data in the signal intensity addition memory 53 and the voltage value frequency addition memory 54. Thereafter, the contents of the voltage value frequency addition memory 54 (and the signal intensity addition memory 53) are read by the user via the CPU 61 to determine an offset value and a threshold level based on the histogram results of noise values. Then, these values are set in a threshold level setting register 57 and an offset value setting register 58, respectively, and then, data exceeding the threshold level is extracted by using a compression memory 55-2. This assumes a case where an ion signal and the amount and distribution of noise levels are determined by the apparatus user (or determined through software) to set a desired threshold level and a desired offset value for data acquisition.
As a result, according to this embodiment, the apparatus user can perform a flexible measurement.
Note that the threshold level and the offset value may be used for the decision or as a correction value at the time when data is stored in the signal intensity addition memory 53.
Also, this embodiment can also be applied to a case where only a register that allows the apparatus user to set a threshold level is provided.
In the foregoing, the invention made by the inventors of the present invention has been concretely described based on the embodiments. However, it is needless to say that the present invention is not limited to the foregoing embodiments and various modifications and alterations can be made within the scope of the present invention.
The present invention relates to a mass spectrometry technology. More particularly, it is effectively applied to a data processing technology for mass spectrometry using an A/D converter in a time-of-flight mass spectrometer.
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-050102 | Feb 2005 | JP | national |
