JP2005338057A - Apparatus and method for identifying substance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique of specifying a very small amount of chemical substances for monitoring environment for conserving environment, since environmental pollution due to dioxins, environmental hormones, etc. has caused serious social problems in recent years. <P>SOLUTION: In the technique using at least one type of frequency converting element for identifying substances, the substances are identified through the use of a frequency-converting element, such as a quartz oscillator, by determining a differential coefficient of an initial change rate of an approximate curve due to frequency changes, caused when substances are adsorbed. By using two or more types of frequency-converting elements, a technique capable of further improving identification accuracy is provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a substance identification method using a frequency conversion element, and more particularly to a measurement apparatus useful for easily identifying a volatile organic compound or the like defined in environmental standards.

  In recent years, a QCM (Quartz Crystal Microbalance) type sensor has attracted attention as a highly sensitive gas sensor that can be measured relatively easily in a room temperature environment. This sensor has a structure in which an electrode formed on the surface of a frequency conversion element such as a crystal resonator and an organic material is formed on the aforementioned electrode as a gas substance trapping film. The change in mass of the detected gas is detected as a change in resonance frequency of a frequency conversion element such as a crystal resonator.

  In Japanese Patent Laid-Open No. 1-244335, a plurality of quartz oscillators having receptors formed on their surfaces are combined in a plurality of different types, and the frequency change values of individual quartz crystal resonators are patterned to have a predetermined substance. There are proposals for chemical sensors that make it possible to distinguish odors and tastes from patterns.

In JP-A-5-72093, in identifying a chemical substance using a frequency conversion element coated with an organic thin film, preferably a crystal oscillator, a frequency change amount and an adsorption amount due to adsorption of adsorbed molecules adsorbed on the organic thin film. Or, by finding the distribution coefficient and analyzing the data, it is easy and efficient to select organic thin films that can be applied to many chemical substances, and there is a proposal to identify substances by using the selected organic thin films. is there.
JP-A-1-244335 JP-A-5-72093

  However, in JP-A-1-244335, it is only possible to identify the frequency change amount for each film of a plurality of frequency conversion elements having different films by patterning, and the whole substance can be quantified and discriminated. In addition to the difficulty of discriminating the chemical substances constituting the substance, it is essential to provide a plurality of frequency conversion elements in order to perform pattern recognition.

  In JP-A-5-72093, when identifying a substance, it is necessary to obtain values such as a frequency change amount, an adsorption amount, a distribution coefficient, etc., and to select an organic film having a correlation with the substance to be identified. There is a problem that it is difficult to identify unless an organic film is selected on the assumption of an identification object in the range.

  The present invention has been made in order to solve the above-described problems. In identifying a substance, a frequency conversion element such as a crystal resonator is used, and a frequency change that occurs when the substance is adsorbed is started. Thus, a substance identification apparatus and a substance identification method for identifying a substance are provided by obtaining a time derivative of a frequency change after a predetermined time (common name, referred to as an initial velocity method).

  In the present invention, a substance is detected by a detection unit having a frequency conversion element composed of an inorganic material, an electrode provided on the frequency conversion element, and an organic film provided on the electrode, and a change in oscillation frequency begins. And an analysis unit for calculating a time derivative (initial velocity method) of a frequency change after a predetermined time as a measurement value, and comparing with a clear numerical value as a measurement value without depending on pattern recognition as disclosed in JP-A-1-244335. Is possible.

  In pattern recognition as disclosed in JP-A-1-244335, a plurality of frequency conversion elements are required. However, the present invention relates to the polarity of each adsorbed substance, the adsorbing force, and the chemical affinity with the film (especially in the initial stage of adsorption). It is this chemical affinity of the substance that contributes the most to the magnitude of the quantity), and paying attention to the fact that the slope of the adsorbed substance varies depending on the relationship such as chemical bond strength, Based on the approximate expression, the amount of frequency change with time in the initial adsorption process of the adsorbed material is approximated by a logarithmic function, and the theoretical value obtained by time differentiation (initial velocity method) after a predetermined time from the start of adsorption is calculated. In the determination unit, the measured value and the theoretical value are collated to determine the substance.

  The present invention measures a change in oscillation frequency obtained by adsorption of a target substance on an organic film, obtained from a substance identification sensor having an organic film, and measures the frequency change after a predetermined time from the start of the change in oscillation frequency. The time derivative (initial velocity method) is calculated as a measured value, and further, the time derivative (initial velocity) of the frequency change after a predetermined time from the start of the oscillation frequency change based on a known approximate expression specific to each substance. Method) is calculated as a theoretical value, the measured value is compared with the theoretical value, and the substance corresponding to the frequency change is determined. Accordingly, in JP-A-5-72093, there is no need to select an organic film having a correlation with a substance to be identified, which is indispensable for identifying a substance. It is possible to identify regardless.

  By using the substance identification method using an organic film according to the present invention, it is possible to easily identify a target substance by obtaining a differential coefficient by using at least one type of frequency conversion element formed of an organic film. The effect that can be obtained.

  Further, by using at least two kinds of frequency conversion elements formed of different organic thin films, it is possible to obtain the effect of improving the identification accuracy of the substance identification method using the organic film according to the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of a substance identification device. The configuration of the substance identification device will be described below with reference to FIG.

  The substance identification device has a detection unit (E1) composed of three elements of a crystal resonator 1, an electrode 3, and an organic film 2 as a frequency conversion element, an oscillator (E4) as an oscillation unit, a frequency measurement unit (E5), and a calculation unit. The following four elements corresponding to (E10), that is, an analysis unit (E6), a determination unit (E7), a display unit (E8), and a storage unit (E9) are included.

  FIG. 3 is a cross-sectional view of the crystal resonator detector. As shown in FIG. 3, the detection unit (E1) is configured, for example, by attaching an organic film 2 to one surface of the electrode 3 provided on both surfaces of the crystal resonator 1. The organic film 2 has an adsorption site that can adsorb a wide range of substances.

  The organic film 2 corresponds to a sensitive part in the detection part (E1), and examples thereof include known polymer compounds, polyion complex lipids, and phospholipids. In addition, as long as it is an organic substance which functions as a sensitive part, the material of the organic film 2 is not limited to the above.

  Examples of the method for forming the organic film 2 include a method in which a liquid obtained by dissolving an organic substance using a suitable solvent such as dichloromethane is applied using a microsyringe, a non-contact despacer, or the LB method (Langmuir-Blodgett). Film).

  An example of the frequency measurement unit (E5) is a device that can obtain data on the passage of time and frequency change, such as a frequency counter.

  The calculation unit (E10) includes an analysis unit (E6), a determination unit (E7), a display unit (E8), and a storage unit (E9), and is connected to the frequency measurement unit (E5). As the calculation unit (E10), for example, a PC terminal device and a display can be used.

  The storage unit (E9) stores mathematical formula data that identifies a known approximate formula unique to each substance. The approximate expression is an approximate expression for calculating a time derivative of the frequency change after a predetermined time from the start of the change of the oscillation frequency, and is specified by mathematical formula data which is a set of numerical values. The storage unit (E9) is configured by a memory such as a RAM or a ROM. Moreover, you may be comprised by the hard disk etc.

  The analysis unit (E6) calculates a time derivative of the frequency change after a predetermined time from the start of the change of the oscillation frequency as a measured value. The analysis unit (E6) reads mathematical formula data from the storage unit, and based on the mathematical formula data, calculates a time derivative of the frequency change after a predetermined time from the start of the change of the oscillation frequency as a theoretical value. The analysis unit (E6) is composed of a CPU.

  The determination unit (E7) determines the substance corresponding to the frequency change by comparing the measured value with the theoretical value. The determination unit (E7) is composed of a CPU. The display unit (E8) displays the determination result. For example, a display such as a liquid crystal, a CRT, or an organic EL can be used for the display unit (E8).

  The measurement method of the present invention will be described with reference to FIG. FIG. 2 is a flowchart showing each process of the measurement method of the substance identification device.

  A constant frequency is input from the oscillator (E4) to the detector (E1) to oscillate (step S1). Next, the target substance is adsorbed on the detection unit (E1) having the organic film 2 (step S2). When the target substance is adsorbed on the organic film 2 of the detection unit (E1), the frequency changes. This frequency change is measured by the frequency measuring unit (E5). (Step S3). The analysis unit (E6) receives the information on the frequency change, and calculates the time derivative (initial speed method) of the frequency change after a predetermined time from the start of the change of the oscillation frequency as a measured value (S4). Furthermore, the mathematical data that identifies the known approximate expression specific to the nuclear material is output from the storage unit (E9), and the time derivative of the frequency change after a predetermined time (initial velocity method) as a theoretical value based on the mathematical data described above Calculate (step S5). The predetermined time is preferably 300 seconds. It should be noted that the order of steps 4 and 5 may be either before or after.

  The determination unit (E7) determines the substance by comparing the measured value with the theoretical value (step S6). When obtaining an approximate curve for step S4, a logarithmic function is generally obtained for a portion that can be approximated by a linear curve, except for a portion that is complex and non-linear in frequency change after a predetermined time from the start of change of oscillation frequency. Approximate using The display unit (E8) displays the determination result.

  Regarding step S5, as a criterion for specifying a substance that has caused a frequency change, a substance can be specified if the slope of the theoretical value calculated from the approximate value is within ± 5% of the slope of the measured value.

  Hereinafter, embodiments of the present invention will be described in detail using examples. FIG. 4 is a diagram showing a section obtained by logarithmic approximation using trichloroethylene used as an example in the embodiment according to the present invention. FIG. 5 shows the frequency change with time of the sample gas by the polyion complex lipid used in the examples according to the present invention. FIG. 6 shows the result of obtaining the value of the differential coefficient from the approximate curve of the sample gas.

  The test conditions are as follows. As shown in FIG. 3, a 9 MHz At-CUT crystal resonator 1 in which 10,000 ng of polyion complex type lipid (2C12N + / PSS-MW = 865.47) is coated on an electrode is used, and trichloroethylene which is a volatile organochlorine compound and a sample gas are used. Frequency changes in the gas phase were measured using dichloromethane, toluene, 1,1,1-trichloroethane, and carbon tetrachloride.

  The measurement of the sample was performed by performing a sample gas flow for 300 seconds after a nitrogen gas flow for 180 seconds, and again performing a nitrogen gas flow for 600 seconds. Here, FIG. 4 shows a section where logarithmic approximation is obtained.

  FIG. 5 shows measurement data from the start of adsorption by the sample gas flow to immediately before the nitrogen gas flow again.

  Next, the logarithmic function was approximated in this section, and after calculating the approximate expression, the differential coefficient of the tangent line after 4 seconds and 50 seconds after the start of the gas flow was calculated for each sample (FIG. 6).

  As a result of FIG. 6, the magnitude of the differential coefficient after 4 seconds and the ranking of the sample gas are as follows: dichloromethane (−94.395)> trichloroethylene (−44.3925)> toluene (−35.0275)> carbon tetrachloride (− 34.356)> 1,1,1-trichloroethane (-33.025).

  As a result of FIG. 6, the differential coefficient and the ranking of the sample gas after 50 seconds are as follows: dichloromethane (−7.5518)> trichloroethylene (−3.5514)> toluene (−2.8802)> carbon tetrachloride (− 2.7492)> 1,1,1-trichloroethane (-2.642).

  From FIG. 5, toluene and 1,1,1-trichloroethane have substantially the same frequency change amount, but when comparing the differential coefficients at 4 seconds, toluene is 35.03, 1 in absolute value from FIG. , 1,1-trichloroethane = 33.03, the identification was confirmed by the differential coefficient from the approximate curve. The identification was confirmed from the result after 50 seconds.

  Next, when comparing toluene with carbon tetrachloride, the differential coefficient up to 50 seconds after the result of FIG. 6 was almost the same, but the maximum frequency change amount was different, so that from the approximate curve up to 300 seconds. It was confirmed that identification was possible by obtaining a differential coefficient.

  Next, it will be described in detail as a second embodiment that the present invention enables gas identification with high accuracy. FIG. 7 is a comparison of frequency variation when the sample gas is measured with three different types of adsorption films.

  As shown in the column of the prior art, the adsorbed substance has a correlation between the organic membrane, the adsorbed amount, and the frequency change. In this example, the polyion complex type lipid (2C12N + / PSS-MW = 865.47) Of phosphoric acid (2C12O-POOH MW = 434.6) and its mixed film were compared with trichlorethylene and dichloromethane, toluene, 1,1,1-trichloroethane, carbon tetrachloride, and approximated by the difference in frequency change by the film We verified that it was possible to identify with high accuracy by comparing the differential coefficients in the curves.

  The embodiment in this example used the same measurement method as in the first example. The measurement results are shown in FIG.

  In the first example, it was confirmed that the discrimination by the differential coefficient was possible. However, the fact that the differential coefficient is different indicates that the adsorption rate is different depending on the polarity of the gas.

  Therefore, in the different organic films in FIG. 7, the difference in adsorption speed due to the magnitude of the gas polarity and the frequency change amount due to the adsorption amount show different values, so that the differential coefficient is obtained from the approximate curve and compared. Gas identification can be performed with higher accuracy.

  In this example, using a mixed film of a polyion complex type lipid (2C12N + / PSS- = 865.47) and a phospholipid (2C12O-POOH MW = 434.6), the frequency change due to adsorption of formaldehyde was compared, and toluene etc. It was confirmed that even substances other than the organochlorine compounds can be adsorbed by these films.

  In the embodiment of the present example, the same measurement method as in the first example was used. The measurement results are shown in FIG.

  In FIG. 8, even with formaldehyde, although there was a difference in the amount of adsorption due to the difference in membrane, the adsorption reaction could be confirmed.

  The application field of the present invention is the field of measuring minute substances, environmental pollutants, DNA sensing, time-dependent quantitative analysis of enzyme reactions, detection of drugs and poisons, detection and quantification of trace components by antigen-antibody reaction, nosocomial infections This is the field of measurement.

It is a block diagram of the present invention. It is the flowchart which showed each process of the measuring method. It is a block diagram of a crystal oscillator detection part. It is the area which calculated | required the approximation by the logarithm which used the trichlorethylene used in the Example concerning this invention as an example. FIG. 4 shows a change in frequency with respect to time of a sample gas due to a polyion complex lipid used in Examples according to the present invention. It is the result of having calculated | required the value of the differential coefficient from the approximated curve of sample gas. It is a comparison of the amount of frequency change when measuring sample gas with three different kinds of adsorption films. It is a figure which shows the result of Example 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crystal oscillator 2 Organic film 3 Electrode E1 Detection part E4 Oscillator (oscillation part)
E5 Frequency measurement unit E6 Analysis unit E7 Determination unit E8 Display unit E9 Storage unit E10 Calculation unit

Claims (4)

A detection unit having a frequency conversion element made of an inorganic material, an electrode provided on the frequency conversion element, and an organic film provided on the electrode;
An oscillation unit connected to the detection unit;
A frequency measurement unit connected to the oscillation unit and measuring an oscillation frequency of the oscillation unit;
A substance identification device comprising: an analysis unit that is connected to the frequency measurement unit and calculates a time derivative of the frequency change after a predetermined time from the start of the change of the oscillation frequency as a measurement value. A storage unit for storing mathematical formula data for identifying a known approximate formula specific to each substance, which is an approximate formula for calculating a time derivative of a frequency change after a predetermined time from the start of the change of the oscillation frequency,
A determination unit for determining a substance corresponding to the frequency change,
The analysis unit reads the mathematical formula data from the storage unit, calculates a time derivative of a frequency change after a predetermined time from the start of the change of the oscillation frequency as a theoretical value based on the mathematical formula data, and the determination 2. The substance identification device according to claim 1, wherein the unit determines the substance corresponding to the frequency change by comparing the measured value with the theoretical value.   3. The substance identification device according to claim 1, wherein the predetermined time from the start of the change of the oscillation frequency to the calculation of the time derivative of the frequency change as a measurement value is 300 seconds. Oscillation that oscillates an electric signal of a constant frequency from an oscillator to a substance identifying sensor comprising a frequency conversion element made of an inorganic material, an electrode provided on the frequency conversion element, and an organic film formed on the electrode Process,
An adsorption process for adsorbing a target substance on the organic film of the substance identification sensor;
A measurement process for measuring a change in oscillation frequency caused by the adsorption;
A calculation process for calculating a time derivative of the frequency change after a predetermined time from the start of the change of the oscillation frequency as a measurement value;
Based on a known approximate expression specific to each substance, a theoretical value calculation process for calculating a time derivative of the frequency change after a predetermined time from the start of the change of the oscillation frequency as a theoretical value;
A substance identification method comprising: a step of comparing the measured value with the theoretical value to determine a substance corresponding to a frequency change.

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