JPS5924379B2 - Paramagnetic gas concentration detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new device for detecting the concentration of paramagnetic gas molecules.

More specifically, we will use the phenomenon of quenching of fluorescence emitted from the electronically excited states of organic and inorganic compounds by paramagnetic gas molecules to quickly and sensitively detect paramagnetic gas concentrations in gases and liquids. This relates to a simple device. Oxygen plays an extremely important role in fields that require oxygen gas for fuel such as the chemical industry, steel, and thermal power generation, as well as fields that require a controlled and constant oxygen concentration such as fine chemicals, food industry, medicine, and the environmental field. is playing.

Therefore, accurate and rapid detection and control of oxygen concentration is an important problem in each field, and various types of oxygen concentration detection devices have been devised and put into actual use. Typical of these are ■ (a) Solid state battery method (measurement of electromotive force of concentration batteries using solid electrolytes) ■ (b
) Magnetic type (measurement of magnetic susceptibility or magnetic pressure of O2)■(c)
An example is an electrochemical method (measurement of current or electromotive force by cathodic reaction of O2). In method (a), the operating temperature of the solid electrolyte, which is an oxygen ion conductor (usually 800
Since the temperature is raised to 1000°C (1,000°C to 1,000°C) for measurement, explosion-proofing is the most important issue. The oxygen meter of type (b) is most commonly used for process applications, but it is said to have drawbacks in measurement accuracy and sensitivity. Further, although the oxygen meter of the method (c) is inexpensive, it is said to have problems with stability, maintainability, sensitivity, response speed, etc. On the other hand, No, N02 (hereinafter N
The NOx meter, which measures the concentration of NOx (abbreviated as Ox), has recently become increasingly important as a pollution measurement device in terms of environmental regulations, and various types of NOx meters have been developed.
Measurement of NO2 fluorescence using 03→NO2*+02) is becoming mainstream in terms of maintainability, sensitivity, etc.

However, devices capable of detecting low concentrations (around 1 pμm) are expensive, and the development of a new type of low-cost, high-sensitivity NOx meter is in demand, especially for measuring environmental concentrations.
Paramagnetic gas molecules with high electron affinity (large charge transfer interaction) such as O2, No, and N02 emit fluorescence (emission from an excited singlet state) and phosphorescence of organic compounds in the gas, liquid, and solid phases. It is well known that it exhibits an extremely significant quenching effect on (emission from an excited triplet state).

To explain the case of 02 as an example, there is a relationship between the emission intensity and the oxygen concentration as shown by the following equation.
It has been confirmed that the formula rnVOlmer) holds true for many organic compounds.

10/I-1+K “τ(i)2〕・・・・・・・・・(
1) 10 is the emission intensity in the absence of oxygen molecules (e.g. under N2), I is the emission intensity under a certain oxygen concentration, K
, is the quenching reaction rate constant (usually the rate constant of diffusion-limited reaction in the liquid phase or gas phase), and τ is the fluorescence or phosphorescence lifetime.

Under certain conditions, the term K ・τ in equation (1) becomes equal to
Considered to be q constant and N2 other than 02, C
O2, H2, Ar. Since ordinary gas molecules such as H2O and hydrocarbons have almost no quenching effect, IO, I
By measuring , it becomes possible to measure the 02 concentration.

Recently, one or two proposals have been made regarding a practical 02 concentration detection device that utilizes such a quenching phenomenon.

Although there are slight differences in terms of optical methods and electrical circuits, the device can be broadly divided into the following three components: (1
) Holds a fluorescent material and its luminescence releases surrounding 02 or NOx
It is composed of a sensor section that quenches light in proportion to the concentration; (2) an excitation source for exciting the fluorescent substance; and (3) a measuring section that detects and records changes in fluorescence intensity. (2) and (
Regarding 3), since various light sources and photometry techniques, etc., which have been significantly advanced in recent years, can be easily applied, this method can be used to
The challenge in developing a NOx meter is said to be a stable sensor with high sensitivity and fast response speed. Regarding the sensor part, which is the key point of this method, the following three types of sensor forms have been proposed so far: (a) Porous glass (PO
rOusVycOrGlass) A material in which a fluorescent substance is adsorbed onto a porous material with a large surface area, such as silica gel;
(b) A fluorescent substance dissolved in a solvent in the form of a uniform film on a substrate; (c) A fluorescent substance dispersed in a wafer-like polymer such as polyethylene.

Although method (a) is simple and highly sensitive, it is extremely unstable as a sensor because not only the sensor characteristics are easily affected by the adsorption of moisture and organic substances, but also the light resistance is significantly reduced by the adsorption.

Since the method (b) uses an organic solvent, there is a problem in that the sensor changes over time due to evaporation and outflow of the solvent. Furthermore, it is impossible to measure dissolved O2 in the liquid because of the dissolution and flow of the solvent into the liquid. Method (c) is stable with little change over time, but because the gas permeability coefficient of the matrix polymer greatly affects sensitivity and response speed, it cannot function as a sensor with a general polymer matrix such as polyethylene. cannot be done (see below).

The present invention was achieved through detailed spectroscopic studies on the gas permeability coefficients and sensor properties of various polymers, and is a further improvement and development of the method (c) above. SUMMARY OF THE INVENTION An object of the present invention is to provide a small, lightweight, and inexpensive paramagnetic gas concentration meter for gases and liquids that has improved the above-mentioned drawbacks and has a highly sensitive, fast response, and stable sensor section.

These objects of the present invention include: a sensor section consisting of a film-like material in which a fluorescent substance is dispersed in a polymer matrix; an excitation source for exciting the fluorescent substance; and a sensor for detecting and recording changes in fluorescence intensity. This is achieved by using a matrix made of silicone rubber as the polymer matrix in a paramagnetic gas molecule concentration detection device constituted by a measuring section. The silicone rubber referred to in the present invention refers to a polymer compound containing a Si-0- bond in its main chain.

Among these, particularly desirable polymers include methyl group, ethyl group,
Various RTVs (ROOmTemperature V
ulcanizatiOn) silicone rubber, LTV (
LOWTemperatureVulcanizati
On) Silicone rubber, heat-curable silicone rubber, etc. alone or a mixture thereof.

In the present invention, polyethylene, polypropylene, polysulfone, polystyrene, polymethyl methacrylate, polyvinyl chloride, polyethylene terephthalate, polycarbonate, polyamide, polytrimethylvinylsilane, It is also possible to use a polymer such as trimethylsilylstyrene by adding it to the silicone rubber. Furthermore, blocks, alternating copolymers, and graft polymer compositions having a siloxane skeleton, such as polysulfone-polydimethylsiloxane block copolymers, polycarbonate-polydimethylsiloxane block copolymers, etc., can be used as matrix polymers. You can also do it. On the other hand, various inorganic fillers such as aerosil, silica, and methane oxide, and organic additives such as higher alcohols, epoxy-modified silicones, and silicone surfactants may be added to the extent that they do not affect the fluorescent properties of the fluorescent material. It is also possible to add it to the matrix polymer.
Table 1 shows the 02 transmission coefficients of various matrix polymers and the sensor characteristics (sensitivity, response speed) for 02 when pyrene is used as the fluorescent material.

Desirable quenching sensitivity and response speed (99%) t that can be instrumented as a normal 02 meter are (IN2-1air
)/1aIr〉0.5, t×5sec More preferably (
IN2-1air)/1a1r〉2,tku1sec'(
'However, the RTV of the present invention has a significantly large 02 transmission coefficient.
Polymer matrices other than silicone rubber (having a dimethylsiloxane skeleton) matrix cannot satisfy this condition.

Dirt occurs when the sensor is exposed to air. In the case of RTV silicone rubber with a large 02 transmission coefficient (dissolution/diffusion), the 02 molecules in the air quickly dissolve and diffuse into the matrix film that holds the fluorescent molecules. Collisions with fluorescent molecules (
This is thought to be due to the fact that the fluorescence is quenched in proportion to the 02 concentration in the matrix and a steady state is quickly reached by the generation of EncOunterCOMplex. On the other hand, in the case of a matrix film such as polymethyl methacrylate, which has a small O2 permeability coefficient, both the dissolution and diffusion of O2 are low and slow, making it impossible to satisfy the required characteristics as a sensor in terms of both sensitivity and response speed. The results in Table 1 show the characteristics for 02 in the gas phase, and using the same principle, the sensor unit is brought into contact with the liquid and dissolved oxygen is detected by utilizing the dissolution and diffusion behavior of dissolved 02 into the matrix film. It is also possible to measure. The fluorescent substance used in the present invention preferably has as high a fluorescence quantum yield (high fluorescence intensity) as possible and a long fluorescence lifetime (high sensitivity, see formula (1)), but usually aromatic hydrocarbons, dyes, Organic phosphors such as dyes and inorganic phosphors such as tungstates, molybdates, uranyl salts, silicates, oxides, and sulfides are used.

Among these, 30
A fluorescent material having a fluorescence spectrum in the wavelength range of 00λ to 8000λ and a fluorescence quantum yield of 0.1 or more is preferably used. In particular, from the viewpoints of sensor quenching sensitivity, light fastness, stability, reproducibility, compatibility and dispersibility with matrix polymers, silicone rubbers using aromatic hydrocarbons with a long fluorescent life as the fluorescent substance are preferred. By combining with the present invention, the remarkable features and effects of the present invention can be brought out.

Table 2 shows the sensitivity when four types of aromatic hydrocarbons having different fluorescence lifetimes are dispersed in an RT silicone rubber film having a dimethylsiloxane skeleton, which is a typical matrix polymer of the present invention.

When the quenching reaction can be handled by a diffusion model as shown in equation (1), a linear relationship between sensitivity and fluorescence lifetime is expected at a constant 02 concentration, but the results shown in Table 2 This is also confirmed by.

This is considered to indicate that most of the quenching reaction of fluorescent molecules is caused by the diffusion of 02 (generation of EncCounterComplex) because 02 diffuses quickly in the silicone matrix. By the way, K calculated from the slope of the straight line (see equation (1)) is 1
．． It was 3×105 sec-1·TOrr-1. As mentioned above, the desirable quenching sensitivity for instrumentation is at least (
Since N2-1ai, )/1aIr>0.5,
In the present invention, aromatic hydrocarbons having a fluorescent life of 20×10 −9 sec or more are preferably used. Aromatic hydrocarbons that meet these conditions include triphenylene,
Examples include naphthalene, phenanthrene, chrysene, pyrene, coronene, ovalene, and derivatives thereof. 0.1% to 100%, the above-mentioned ordinary fluorescent substance is often used to detect NOx concentration, but 1
For detection of low concentrations around ppm (~10-3T0rr in the gas phase), extremely long-lived (several seconds) delayed fluorescent materials such as acridine orange and tripaflapine are used.
A phosphor emitting uOrecenee is used.

In this case, it is necessary to remove short-lived non-light components using a rotating sector or the like. In the present invention, a film-like material made of matrix polymer alone can be used as the sensor part, but it is easier to stabilize the film and make a thinner film (improved response speed) by using the basic method. Become. Suitable substrates include glass, mirrors, plastic films, porous plastic films, silk nets, nylon nets, chromatography paper, porous glass, pressure-molded plates of silica gel, alumina, molecular sieves, and the like. When assembling the device in a transmission type (see FIG. 1), it is desirable to use a substrate with as high a transmittance as possible.
A method for producing a sensor using these substrates, fluorescent molecules, etc. will be described below, taking an RTV silicone rubber matrix as an example.

Liquid silicone polymer used in RTV silicone rubber (degree of polymerization: 200-100001η: 1000-1
00000CS) has a siloxane bond as a skeleton and terminal reactive groups as -SlOH, -SiOMelSiCl, -Sl
Those having CH=CH2, -SlOCOR, etc. and containing a methyl group, ethyl group, phenyl group, etc. as side chain groups are used.

The above liquid silicone polymer (5 to 60 wt%), a crosslinking agent such as acetoxysilane, alkoxysilane, or aminosilane (0 to 20 wt%), and a catalyst such as an organotin compound that becomes a catalyst for condensation or addition reaction (0 to 5 wt%). naphtha, benzene, toluene, chloroform, cyclohexane,
After dissolving in an organic solvent such as hexane (40 to 90 wt%) and curing the fluorescent material, the concentration range is 10, at which crystals do not precipitate.
Soluble between -6M and 10-2M (based on silicone polymer).

These solutions are spread on a suitable substrate and allowed to stand at 0 to 100°C to harden. In view of the response speed of the sensor, etc., the thickness of the film on the substrate is preferably 300 μm or less. In order to improve the compatibility of fluorescent molecules with the silicone matrix and the sublimation resistance, various additives such as higher alcohols, epoxy-modified silicones, and silicone surfactants are often added before curing. In addition, in order to efficiently deactivate the active singlet oxygen generated by the quenching reaction with 02, add a singlet oxygen quencher such as β-carotene or triethylenediamine to the curing solution within a range that does not affect the fluorescent properties. can be added to improve the light resistance of the sensor. In the case of a fluorescent substance that is difficult to dissolve in the liquid silicone polymer solution, the two are mixed and kneaded and then spread on a substrate and cured. To protect the sensor surface from dust, water droplets, etc., or to measure dissolved oxygen, add a thin porous film layer such as polytetrafluoroethylene, polyvinylidene fluoride, or polyethylene on the sensor surface. This is preferable because it is more stable and can extend the life of the sensor. The device of the present invention is effectively used for detecting the concentration of paramagnetic gases, especially 02 and NOx.
) in the atmosphere (21%, about 20
0,000 ppm) acts as an interfering component, it becomes necessary to have a device that removes 02 from the measurement gas in advance and separates and/or concentrates the NOx component, as well as a converter for converting NO→NO2 or NO2→NO.

As such devices, separation using an oxygen pump using a solid electrolyte, adsorption separation concentration using various adsorbents, etc. are used. 0.1% to 100 when used as a 02 meter
%, so the interference caused by the coexisting NOx (0.01% or less, normally 0.0001% or less in the atmosphere) can be completely ignored.

N2, CO2, H2O. Since there is almost no interference from coexisting gas molecules such as H2, Ar, and hydrocarbons, the 02 meter according to the present invention is a highly sensitive 02 meter with extremely excellent selectivity.
It can be said that it is a meter. As the excitation source of the present invention, a low-pressure or high-pressure mercury lamp, a Xe lamp, various fluorescent tubes, a tungsten lamp, a laser beam, electroluminescence, etc. are used.

As the fluorescence detection element, a photoelectric conversion element such as a photomultiplier, a photodiode, a phototransistor, or a photocell is used. Devices can be roughly classified into transmission type and reflection type depending on the fluorescence detection method, but in order to deepen the understanding of the present invention, FIG. 1 shows a side sectional view and a system diagram of the transmission type 02 meter. Reference numeral 1 is a low-pressure mercury lamp, and light other than the excitation wavelength of the fluorescent substance is cut out by a filter 2.

Reference numeral 4 denotes a sensor film having a glass plate 9 as its base, and its fluorescence intensity changes in accordance with the 02 concentration in the gas entering the gas chamber from the gas inlet 8.

Only the fluorescent light component is taken out by a filter 3 and inputted to a photoelectric conversion element (silicon photocell) 5, passed through an amplifier 6, and a recorder 7 records changes in fluorescent light intensity. In the method of the present invention, the fluorescence intensity is 1 when 02 is not present (for example, under N2). The ratio of fluorescence intensity under a certain 02 concentration is 1. Since the 02 concentration will be detected by /I, two sets of sensors and detection elements are arranged in parallel, one sensor is supplied with N3 gas (or is evacuated), IO and I are measured simultaneously, and the processing circuit is used to detect 02 concentration. . It is also possible to display or record /I at the same time. Figure 2 shows an example of coronene/R.
TV silicone rubber film (on 200μ glass substrate)
The sensitivity characteristics with respect to the 02 concentration in N2 gas when the sensor is incorporated into the apparatus shown in FIG. 1 as a sensor are shown.

It can be seen that the detection of 02 concentrations around 0.1% and above is excellent.

The 90% response speed was 0.1 sec.

As described above, the 02 concentration and NOx concentration detection device obtained by the present invention has extremely few interfering components, has high sensitivity, fast response speed, and operates stably. It is also inexpensive, small, and lightweight, so it can be easily carried by the user.

Also, since it is possible to measure dissolved O2 in liquids, it is useful in medicine, food industry, fine chemicals, chemical industry, marine development,
This detection device can be used in various fields such as space development and the environment.

[Brief explanation of drawings]

FIG. 1 is a side sectional view and a system diagram of a transmission type device according to the present invention.

Claims (1)

[Claims] 1 Consists of a sensor section made of a film-like material in which a fluorescent material is dispersed in a polymer matrix, an excitation source for exciting the fluorescent material, and a measuring section that detects and records changes in the intensity of the fluorescent light. 1. A paramagnetic gas concentration detection device, characterized in that the polymer matrix is a matrix made of silicone rubber.