Chemistry: analytical and immunological testing – Measurement of electrical or magnetic property or thermal... – By means of a solid body in contact with a fluid
Patent
1992-06-23
1994-06-07
Johnston, Jill A.
Chemistry: analytical and immunological testing
Measurement of electrical or magnetic property or thermal...
By means of a solid body in contact with a fluid
422 88, 436124, 436166, G01N 2125, G01N 2712
Patent
active
053189124
DESCRIPTION:
BRIEF SUMMARY
This invention relates to gas sensors and to certain novel compounds which are suitable for use in gas sensors.
The ability of phthalocyanines, and certain other semiconducting complex ring systems, to act as gas sensing materials has been known for some years. Thus GB-A-2111987 and GB-A-2186087 disclose the use of multi-ring organic semi-conducting compounds in the detection of "NOX" gases. The use of organometallic derivatives of phthalocyanine, meso-tetraarylporphin and dihydrodibenzotetraazaannulene to detect chlorine and NOX gases is also discussed in J. Chem. Socl, Faraday Trans. 1, 80, No. 4, 1984, 851-863, J. Phys. Chem. Solids, 49, No. 9, 1988, 1003-1008 and Sensors and Actuators, 15, No. 4, 1988, 359-370, while FR-A-2383440 discloses the use of symmetrical phthalocyanine and porphyrin organometallics in the detection of a range of gases. Gas detection is effected by virtue of changes in conductivity and/or spectral properties of the semi-conductors.
There is a need to develop further improved methods of detecting the presence of gases, for example the presence, and preferably also the concentration, of industrial pollutant gases in order to distinguish therebetween. The present invention therefore seeks to provide gas sensors exhibiting improved sensitivity and selectivity.
According to the present invention a gas sensor comprises as the gas-sensing component, which changes colour and/or electrical conductivity on exposure to certain gases, a (mono, di or tri) azatetrabenzoporphyrin. The benzoporphyrin may optionally contain a metal. Mixtures of the macrocycles may be employed. A bank of such sensors may be provided, of graded sensitivity, to reveal (by how many in the bank were affected) the concentration of any temporary exposure to gas.
We have surprisingly found that, while it is known that phthalocyanine is easier to oxidise than is prophyrin, the mono-, di- or triazatetrabenzoporphyrins of the invention are even easier than either phthalocyanine or porphyrin. The oxidation potentials of these various compounds are different, and this can be exploited by using a specific compound of appropriate oxidation potential to respond selectively to desired gases. In furtherance of such selectivity, the compound may be appropriately substituted.
An oxidant/reductant sensor according to the invention, which can sense dissolved gases such as chlorine, nitrogen oxides, SO.sub.2, H.sub.2 S and bromine in water and also ions resulting therefrom and other ions which may be present such as perchlorate and dithionite, comprises a tetrabenzoazaporphyrin as set forth above, which tetrabenzoazaporphyrin covers an area of a support which is stationed in or which is capable of being moved into and out of a location in which it is exposed to the oxidant/reductant. The sensors may be passive or active. Thus passive sensors (such as badges or coated dipsticks) will show a colour change on exposure to a gas or a solution of oxidant or reductant (such as a chlorine-contaminated water reservoir) which change can be monitored by subsequent measurement of optical absorption change. Alternatively, means may be provided to apply a potential difference across the macrocycle component and measure the current required to restore the original colour as a measure of the oxidant/reductant content of the environment. Active sensors may monitor a change in either or both of optical absorption and electrical conduction in an on going manner.
The tetrabenzoazaporphyrin preferably contains at least one metal. Suitably, the metal is in the form of a transition metal ion, optionally associated with an anion or anionic ligand.
Certain triazatetrabenzoporphyrins have previously been prepared. Thus J. Chem. Soc., 1938, 1-6 discloses the preparation of copper tetrabenzotriazaporphyrin as a pigment. Copper, zinc, magnesium and iron (II) tetrabenzotriazaporphyrins were investigated by Barrett, Linstead and Tuey, J. Chem. Soc., 1939, 1809-1820. The properties of highly conducting molecular crystals of (triazatetrabenzoporphyrinato) copper (II)
REFERENCES:
patent: 5135717 (1992-08-01), Renzoni et al.
Honeybourne et al "Use of Thin Films of Conjugated . . . " J. Chem. Soc. Faraday Trans. 1, (1984), 80, pp. 851-863.
Honeybourne et al "Thin Films of Conjugated . . . " Sensors & Actuators, vol. 15, No. 4 (1988), pp. 359-373.
Ahmet Mustafa T.
Rickwood Kenneth R.
Silver Jack
British Technology Group Limited
Johnston Jill A.
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