DE19619226A1 - Sensor element and sensor for determining ozone concentrations - Google Patents

Abstract

A sensor element for determining ozone concentrations is characterised in that it contains at least one dye with conjugated double bonds contained in a polymer layer with at least one polymer. Also disclosed are a sensor that contains at least one sensor element of this type and a process for determining ozone concentrations.

Description

The invention relates to a sensor element for determining Ozone concentrations as well as a sensor that detects at least one of these Contains sensor elements.

It is known that conductivity sensors based on SnO₂ for the detection of Ozone can be used, e.g. B. disclosed in EP-A-0 311 439. This changes due to chemisorption of the ozone on the SnO₂ surface electrical resistance. The disadvantage of this analysis method is that Cross sensitivity to almost all oxidative gases, as well as the strong one Temperature sensitivity of these sensors, which is specially heated to approx. 400 ° C Need to become.

It is also known that ozone due to its absorption at 253.7 nm can be determined spectroscopically (VDI guideline: VDI 2468; VDI manual, keeping the air clean, volume 5). A disadvantage of this Analysis method is the cross sensitivity to hydrocarbons, which also absorb in this frequency range. Therefore, it is common in one parallel measurement in a second measuring channel a so-called Zero air measurement, d. H. an absorption measurement on an otherwise identical one Gas sample, which was only selectively freed from the ozone. With With the help of this reference measurement, the proportion of cross-sensitive gases be determined and eliminated. Because of the need to always have one Such a measuring device is complex to have to carry out reference measurement, expensive, sensitive and voluminous.  

It is also known that in the reaction of ozone with suitably prepared Weak lighting effects (chemiluminescence) occur (Journal of Atmospheric Chemistry, 14, 73-84, 1992; PTB-Mitteilungen, 103, 324-328, 1993). This measuring principle shows a good resolution. The disadvantage is but that a very sensitive photomultiplier and a High voltage source and sample temperature control are necessary.

From EP-A-0 665 427 it is known that ozone is determined gravimetrically can, in which it is on a polymer layer located on a quartz crystal is selectively bound. The adsorption causes an increase in mass caused by Change in the resonance frequency of the quartz crystal can be measured. One of the disadvantages of this method is sensitivity to outside Interferences, especially mechanical vibrations.

From DE-A-12 62 638 it is known that colorimetric ozone with a Sulfophthalein dye can be detected. A disadvantage of this Measuring system is that the sulfophthalein is only effective in its alkaline form is, d. H. that acidic air containing ozone cannot be demonstrated that the Dye must be impregnated on a powder (e.g. silica gel) and that a concentration can only be determined by comparison with one calibrated color scale is possible. This system is also aging in air, so that it must be filled with protective gas between measurements.

Furthermore, ozone can be colorimetrically measured in an indigo dye (Tekh. Misul (1988), 25 (2), 59-60) or Acid Chrome Violet K (Ozone: Sci. Eng. (1989), 11 (2), 209-15) containing solution. The disadvantage here is that the measurements must be carried out in liquid medium, which the Makes devices difficult to use. These systems also show a strong cross sensitivity to other contaminants of the Solvent.  

It is also known that ozone easily reacts with olefinic double bonds. In this reaction, so-called ozonides are formed, which are reductive Cleavage can be converted into aldehydes or ketones. The reaction will used in analytical organic chemistry for the detection of olefins (see e.g. Organikum, 16th ed., p. 262).

The object of the present invention was therefore to provide a new, simple, sensitive, inexpensive and compact sensor element as well as a sensor for Provide determination of ozone concentrations that are not those from the Disadvantages known in the prior art.

This task is solved by a sensor element for determining Ozone concentrations, which is characterized in that there is at least one Contains dye (chromophore), preferably in solid form, the conjugated Has double bonds and which is contained in a polymer layer, the has at least one polymer, preferably at least one of the conjugated double bonds is olefinic.

The particular advantage of the dye-containing polymers over z. B. pure Dyes are that sensitive to ozone can be improved or adapted to requirements. Because it was found that it is possible to introduce the dye into polymers, Produce layers that on the one hand have sufficiently high amounts of dye contain and on the other hand have the necessary permeability for ozone, so that the dye molecules within the layer are reached by ozone can.

Another advantage of dye-containing polymers over z. B. pure Dyes consist in that they are generally easier to process. This is a huge advantage when using special sensitive readout methods should be used, the special requirements for a dye-containing  Make shift such. B. special geometric shapes, exactly layer thickness to be observed, uniformity, absence of Light scattering centers and transparency.

The sensor according to the invention contains at least one according to the invention Sensor element and at least one readout system into which at least one a sensor element is integrated.

For the purposes of the invention, dye-containing polymers are those polymers where a dye group as a side group on a polymer chain is attached or is in the main chain of the polymer. Of the However, dye can also be used in a polymer or in a polymer mixture be dispersed or dissolved.

Through the use of dye-containing polymers, or in one Polymer matrix dispersed or dissolved dyes has succeeded in Disadvantages of the known detection systems for ozone and the desired properties, such as. B. high resolution and selectivity obtained, whereby detectors for the quantitative detection of ozone for Will be provided.

The choice of the suitable polymer or the polymer mixture is directed according to the special requirements. The selection criteria result e.g. B. from the required solubility of the dye used in the polymer from which required permeability for ozone, or from the desired Temperature stability, mechanical strength and from the required optical properties.

The dye-containing polymers change their optical appearance in the presence of ozone Properties and enable simply by measuring this Changes a quantitative determination of ozone.  

When using dye-containing polymers can also Mixtures of these with other polymers that are not necessarily one Chromophore included. This is for example possible, the absorbance of the system as well as its mechanical and elastic Properties and the degree of crystallization as well as the permeation properties to influence specifically.

Examples of particularly suitable polymers are polyimides, polysiloxanes, Polyesters, polyacrylates, polymethacrylates and polyolefins. But the invention is not limited to these polymers. In general, polymers are suitable which have an average molecular weight of 500 to 5,000,000, preferably 10,000 to 500,000, in particular 10,000 to 200,000.

Depending on the embodiment, it may be advantageous to add the dye Polymer plasticizers add to the mechanical properties and to improve the permeation behavior or to improve the solubility of the Improve dye in the polymer in case the dye is introduced into the polymer by solution. Are suitable as plasticizers all plasticizers used in plastics, such as B. phthalates and Cresols, the vapor pressure of which is sufficiently low that there is nothing worth mentioning Evaporation from the polymer occurs, and the solubility of the Can positively influence polymer properties.

Stilbenes or stilbene derivatives are preferred as dyes, Phenylvinyl heterocycles, vinyl diheterocycles, polyene systems such as B. oligomers α-phenyl-polyenes, oligomeric α-ω-diphenylpolyenes, oligomeric phenylvinylenes, Acetylene systems such as B. diphenylacetylene, azo compounds, hydrazones or Mixtures of these are used, with stilbene or stilbene derivatives in particular are preferred.  

In general, dyes are suitable whose absorption maximum is in the range from 300 nm to 1 200 nm, preferably from 350 nm to 700 nm, in particular from 400 nm to 500 nm.

A preferred sensor element contains the dye-containing polymer as one of its components or even consists entirely of it. The shape of the Polymers and the type of other constituents that may be used depend among other things on how the change of the optical properties to be measured under the influence of ozone.

The sensor element can be made entirely of the dye-containing polymer exist if, for example, it is suitable for the intended purpose Moldings, e.g. B. a film, a fiber or a body with other suitable geometric shape is produced. Suitable manufacturing processes for this are known in principle to the person skilled in the art. Can be used for example casting processes from solution, injection molding, extrusion and Spinning process.

In the event that the dye-containing polymer is part of the sensor element, there are one or more other constituents, whereby as further Components, in particular, carrier materials for the dye-containing polymer are called. For example, plates, foils, fibers or come as supports differently shaped bodies in question. These can be made of glass, plastic, metal and / or other transparent, reflective or light scattering Carrier materials exist. In some cases, it may be advantageous to To provide carriers with dielectric layers.

The supports are coated with the dye-containing polymer. For Increase in the surface area available for the coating, can be provided with other porous coatings beforehand will. These porous coatings can, for example, consist of particles  Titanium dioxide, silicon dioxide or other materials contain the appropriate one optical properties and a high specific, open-pore surface exhibit.

The carriers can be coated in different ways. Suitable processes for this are known to the person skilled in the art. For the production extremely thin and uniform layers is e.g. B. the Langmuir-Blodgett Technology particularly well suited. But there can also be adsorption layers by immersing the carrier in a solution of the dye-containing polymer getting produced. Other suitable methods are diving and Flow coating, laminating, knife coating and printing processes, screen printing and spray coating in particular are. The thickness of the applied layer of the dye-containing polymer is preferably between 2 nm and 500 μm, particularly preferably in the range of 10 nm to 20 µm and in particular in the range from 20 nm to 5 µm.

The sensor element according to the invention can, for example, in a Flow cell overflows with a defined volume flow of ozone-containing air or simply exposed to the air containing ozone.

The dyes in the sensor element change their presence in the presence of ozone optical properties. The change can e.g. B. by determining the optical absorption can be detected. How to proceed is known in principle to the person skilled in the art. This can e.g. B. happen that Sensor element is irradiated by light, the wavelength of which is in the range of Dye absorption lies.

The change in absorption behavior due to the effects of ozone can then by determining the change in intensity of the light passing through be measured.  

The invention consequently also relates to a method for determining Ozone concentrations using at least one according to the invention Sensor element, which is characterized in that the concentration by changing the optical properties, preferably the absorption, certainly.

But it is also possible to use the change in optical properties of reflectance measurements. In this case you choose for Measuring an optical arrangement that determines a change in light that is reflected on the sensor element. It is particularly advantageous here if as a support for the dye-containing polymer layer, a reflective plate e.g. B. silicon is used with a coating of silicon dioxide is provided. The thickness of this layer is such that for one certain range of the angle of incidence of the incident on the layer Light interference amplification occurs. In such an arrangement usually monochromatic, linearly polarized light is used. This is a particularly sensitive measurement of the change in given optical properties by the influence of ozone. Like one Measuring arrangement to be executed in detail is known to the person skilled in the art.

Furthermore, you can change the optical properties using the Determine the attenuation of evanescent waves from optical fibers. Here will the sensor element in the form of a planar, a strip or one fibrous optical waveguide, in which the otherwise usually existing or partially removed waveguide jacket and by the dye-containing polymer is replaced, so that evanescent waves from the Waveguide core get into the area of the dye and thereby can be weakened. If light is now conducted in the waveguide, whose wavelength is in the range of dye absorption, one has an effect Change in dye properties as a change in Waveguide attenuation and can be detected easily and sensitively.  

The detailed execution of such a measuring arrangement is also known to the person skilled in the art known in principle, as well as an arrangement for the detection of Dye changes plasmonic surface waves can be used. In In this case, the sensor element according to the invention usually contains one thin metal layer e.g. B. of gold or silver, which in turn with a layer of the dye-containing polymer is provided. Under defined conditions, that depend on the detailed execution of the arrangement can in the Metal layer surface plasmons are excited, for example affect that a light beam striking the sensor element with significantly reduced intensity is reflected, with part of the energy of the incident light beam to excite the surface plasmons is being used. The conditions under which this is the case will be sensitive to the dye properties on the metal layer and serve as an easily determinable and sensitive measure of their Change.

From the change in the optical properties of the dye-containing Polymers that are continuous or, for example, two in time successive measurements can be determined, one obtains a measure for the ozone concentration in the air to which the sensor element was exposed.

The invention is explained in more detail below on the basis of exemplary embodiments explained, but without being limited thereby.

example 1

To produce a sensor element, 0.4 ml of a solution of 4- [N- (2-hydroxyethyl) -N-methylamino] -4'-nitrostilbene in cyclohexanone (8 mg / ml) with 0.3 ml of a 4% polyimide solution in cyclohexanone and with 1.8 ml Cyclohexanone mixed. The polyimide is a polymerization product made of 2,2-  bis [3,4-dicarboxyphenyl] hexafluoropropane dianhydride and 2,3,5,6- tetramethylphenylenediamine monomer (described in EP-A-0 355 367). With this solution is a squeegee film on a glass plate 25 mm × 75 mm, 1 mm thick) with a wet film thickness of about 10 microns. The coated Glass plate is placed on a hot plate with a temperature of approx. 5 minutes 70 ° C. After evaporation of the solvent, a uniform dye-polyimide film. There are none in the optical microscope Observe signs of crystallization of the dye.

Example 2

A glass plate (25 mm × 75 mm, 1 mm thick) is made on both sides as in Example 1 coated and dried for approx. 15 minutes in a drying cabinet at approx. 80 ° C. The glass plate is then placed in a measuring chamber with two opposite windows are provided with light for radiation and themselves in an optical measuring arrangement for determining the absorption spectrum located. Air flows through the chamber with ozone. The move the air with ozone is done by irradiating the air with a low pressure Mercury vapor lamp before the air enters the measuring chamber. The Ozone concentration in the measuring chamber is measured using an ozone analyzer from the company Horiba determines and is 0.7 ppm. After the onset of ozone the sensor element in the measuring chamber clearly detects the dye absorption from. At a wavelength of 470 nm, the initial rate for the decrease is about 0.6% per minute.  

Example 3 Synthesis of poly - [(succinic acid-4- [2- (methyl- {4- [2- (4-nitrophenyl) vinyl] phenyl} amino) ethyl] ester) - (1-octadecene)]

In a 200 ml round bottom flask, 2.98 g of 4- [N- (2-hydroxyethyl) -N- methylamino] -4′-nitrostilben dissolved in 30 ml dry THF. 1.064 g potassium t Butylate are suspended in 20 ml of dry THF and added to the Solution of the Stilben dripped. The mixture becomes viscous and after 5 minutes a precipitation begins to fall. The mixture is stirred at 22 ° C. for 30 minutes, then a solution of 3.5 g of poly (maleic anhydride-1-octadecene) in 30 ml of dry THF added dropwise. The piston comes with a Provide drying tube and the reaction mixture is at 22 ° C for 18 hours touched. The reaction mixture is then refluxed for 6 hours and then cooled to 22 ° C. The dark red solution becomes drop by drop with stirring in a solution of 800 ml of methanol and 2 ml of 37% HCl registered. The polymeric product separates out as a red oil. The product is taken up in diethyl ether and introduced into 800 ml of methanol. The the resulting suspension is centrifuged. 3.31 g of product are obtained. Of the Chromophore content is determined by UV / VIS measurements and is 18 % By weight.

The polymer produced is dissolved in cyclohexanone, the concentration Is 72 mg / ml. The solution will run at a speed of 100 Revolutions per minute on cleaned glass substrates (microscope slide) spun with a size of 37.5 mm × 25 mm. Then be the films by heating on a hot plate at approx. 100 ° C Removes solvent residues.

A support coated in this way is mounted in the test chamber of a spectrophotometer (Perkin-Elmer Lambda 9) in the measuring beam. An uncoated carrier is mounted in the reference beam. The measuring chamber is flushed with ozone-enriched air, with an estimated concentration of approx. 2 ppm. The absorption spectrum of the polymer films is measured before exposure to ozone and repeatedly during exposure to ozone. A significant decrease in the absorbance of the polymers under the influence of ozone can be found within minutes. The absorption spectra are shown in Fig. 1. During the measurement, the chamber is ventilated and the flow of ozone is interrupted. Without the influence of ozone, no decrease in absorption by light irradiation can be observed. Similarly, no change in the rate of degradation can be observed when the sample is exposed to ozone under radiation or in the dark.

Example 4

A support coated according to Example 3 at 1000 revolutions per minute is mounted in the measuring beam of the sample chamber of the spectrophotometer. The absorbance at the absorption maximum of the chromophore at 433 nm is constantly measured under the influence of ozone at a concentration of 75 ppb on average. The decrease in absorbance at 433 nm is shown in FIG. 2. A decrease in absorption can be clearly demonstrated within less than 2 minutes.

Example 5

5 mg 2- [7- (2- {4 - [(2-hydroxyethyl) methylamino] phenyl} vinyl) -4,4-dimethyl- 4,4a, 5,6-tetrahydro-3H-napthalene-2-ylidenes] malonitrile (preparation disclosed in: I. Cabrera, O. Althoff, H.T. Man, H.N. Yoon, Adv. Mater. 1994, 6, 43) and 95 mg PMMA are dissolved in 2 ml cyclohexanone. The solution is one Speed of 100 revolutions per minute on cleaned glass substrates  (Microscope slide) with a size of 37.5 mm × 25 mm spun on. The films are then heated on a Removes solvent residues from the heating plate at approx. 100 ° C.

A coated carrier is in the measuring beam of the sample chamber Spectrophotometer mounted. The absorbance at the absorption maximum of Chromophors at 536 nm is constantly under the influence of ozone at a Concentration measured at an average of 800 ppb.

The decrease in absorbance at 536 nm is shown in Fig. 3. A decrease in absorption can be clearly demonstrated within less than 2 minutes.

Example 6

0.5 ml SY409® (as a 75% solution in xylene) and 0.2 ml SY430® (as 25% solution in xylene) with 0.4 ml of a solution of 4- [N- (2-hydroxyethyl) -N- methylamino] -4'-nitrostilbene mixed in chloroform (8.4 mg / ml).

SY409® and SY430® are two different phenylmethyl silicone resins from Wacker company used as polymers. With this mixture a squeegee film on a glass plate (25 mm × 75 mm, 1 mm thick) with one Wet film thickness of about 10 microns. The coated glass plate is used for 5 Minutes on a hot plate with a temperature of 70 ° C. After that a uniform dye-polymer film is obtained on the glass plate.

The glass plate is placed in a measuring chamber similar to that in Example 2, with the difference that the light transmission at a wavelength of 450 nm can be continuously recorded by a compensation recorder. The measuring chamber is flushed with ozone-free air for a few minutes. The measuring chamber is then flushed with air containing ozone (ozone concentration between 0.6 ppm and 0.7 ppm) for approx. 55 minutes. The chamber is then flushed with ozone-free air for about 35 minutes and then flushed again with ozone-mixed air (ozone concentration 0.7 ppm) for about 25 minutes. Fig. 4 shows a clerk diagram the timing of the light transmission and the ozone concentration in the measuring chamber. One can clearly see the decrease in absorption (absorption (in%) = 100 - transmission) at times of ozone exposure. It can also be seen that the absorption does not change when the measuring chamber is flushed with ozone-free air.

Example 7

1 ml SY409® (as a 75% solution in xylene) and 0.5 ml SY430® (as 25 % Solution in xylene) with 2 ml of xylene and with 0.5 ml of a solution of 4- [N- (2- hydroxyethyl) -N-methylamino] -4′-nitrostilbene in chloroform (8 mg / ml) mixed. This mixture is used to make a squeegee film on two glass plates (25 mm × 75 mm, 1 mm thick) with a wet film thickness of approx. 10 µm. The coated glass plates are left to dry on a hot plate for 5 minutes placed at a temperature of 70 ° C. Then the glass plates in subjected to measurements in succession in the measuring chamber according to Example 6, at which the measuring chamber with ozone-mixed air of different Concentration is flushed out. The mean ozone concentrations are in the first case 0.17 ppm and in the second case 0.26 ppm. Due to the Ozone effects with different concentrations result different initial rates for the decrease in dye absorption (measured at 450 nm). In the first case, the initial rate is 0.23% per Minute and in the second case 0.32% per minute based on the Light intensity I₀ in front of the glass plate without absorption.  

Example 8

0.5 ml of a UV-crosslinkable silicone (P52061 from ABCR, Stuttgart) with 0.3 ml dioctyl phthalate, 1 ml chloroform and 0.3 ml of a solution of 4- [N- (2-hydroxyethyl) -N-methylamino] -4′-nitrostilbene in cyclohexanone (25 mg / ml) mixed. With this solution, a squeegee film is placed on a glass plate (25 mm × 75 mm, 1 mm thick) with a wet film thickness of about 10 microns. The coated glass plate is placed on a hot plate with a Temperature of approx. 90 ° C. Then the coated glass plate to crosslink the layer 30 seconds with UV light Medium pressure mercury lamp irradiated. During the irradiation, the Gaseous nitrogen washes around the glass plate to keep out atmospheric oxygen. There is an even film on the glass plate that shows no signs of crystallization of the dye.

The glass plate is placed in a measuring chamber as in Example 6. The transmission at a wavelength of 450 nm is continuously recorded by a compensation recorder. The measuring chamber is flushed with ozone-free air for a few minutes. The measuring chamber is then flushed several times with ozone-mixed air with different ozone concentrations between 0.1 ppm and 0.5 ppm. In between, rinsing is carried out with ozone-free air. Fig. 5 shows a chart recorder the time course of dye absorption (absorption (in%) = 100 - transmittance) and the ozone concentration in the measuring chamber. You can clearly see the decrease in absorption at the time of ozone exposure. The steepness of the decrease depends on the respective ozone concentration. It can also be seen that the absorption does not change when the measuring chamber is flushed with ozone-free air.

Claims (11)

1. Sensor element for determining ozone concentrations, characterized in that it contains at least one dye which has conjugated double bonds and which is contained in a polymer layer which has at least one polymer. 2. Sensor element according to claim 1, characterized in that at least one of the conjugated double bonds is olefinic. 3. Sensor element according to claim 1 or 2, characterized in that the dye is stilbene or a stilbene derivative. 4. Sensor element according to one of claims 1 to 3, characterized characterized in that the dye is in solid form. 5. Sensor element according to one of claims 1 to 4, characterized characterized in that the dye covalently to at least one polymer of Polymer layer is bound. 6. Sensor element according to one of claims 1 to 4, characterized characterized in that the dye is dissolved or dispersed in the polymer layer is. 7. Sensor element according to one of claims 1 to 6, characterized characterized in that the polymer layer on a support of at least a carrier material is arranged. 8. Use of a sensor element according to one of the present Claims in one sensor.   9. Sensor for determining ozone concentrations, thereby characterized in that it has at least one sensor element according to one of the Claims 1 to 7 contains. 10. Method for determining ozone concentrations using at least one sensor element according to one of claims 1 to 7, characterized characterized in that the concentration can be changed by changing the optical Properties determined. 11. The method according to claim 10, characterized in that the Concentration determined by changing the absorption.