Chemical apparatus and process disinfecting – deodorizing – preser – Analyzer – structured indicator – or manipulative laboratory... – Means for analyzing liquid or solid sample
Patent
1992-07-31
1994-05-03
Warden, Robert J.
Chemical apparatus and process disinfecting, deodorizing, preser
Analyzer, structured indicator, or manipulative laboratory...
Means for analyzing liquid or solid sample
422 8206, 422 8205, 436169, 359123, G02B 600, G01N 3394
Patent
active
053085817
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to an indicator for use in a luminescence-optical configuration for continuous and reversible measurement of the pH of a sample within a relevant measuring range, the sample being at least in indirect contact with the indicator provided as an acid or base, and the luminescence decay time .tau. of the indicator depending on the pH of the sample, and to a sensor comprising such an indicator.
DESCRIPTION OF THE PRIOR ART
Measuring the pH is an essential task in many fields of science and technology, for instance in chemistry, process engineering, manufacturing or environmental analysis. Optical methods and devices for pH measurement have been proposed frequently. A survey of the latest state of the art is given by LEINER & WOLFBEIS: Fiber Optic pH Sensors, in CRC Book on Fiber Optic Chemical Sensors and Biosensors, O. S. WOLFBEIS (ed.), CRC Press Inc., Boca Raton, Fla. 1991. In particular, two methods have proved useful: pH measurement via the change in absorption, and via the change in luminescence of a suitable indicator. Absorption-optical sensors are simpler in design, but in practice are prone to considerable technical problems (low signal change, high straylight, poor long-term stability, etc.). In luminescence-optical sensors some of these problems are avoided, though their long-term stability often is unsatisfactory, as the concentration of the indicator changes over time due to various influences, thus giving rise to signal changes biasing the measured result.
A method of improving long-term stability of luminescence-optical sensors to a considerable extent, in particular the long-term stability of optical fluorosensors, is characterized by using fluorescence decay time rather than fluorescence intensity for measurement (LIPPITSCH et al., Analytica Chimica Acta 205 (1988), 1-6). As luminescence, or rather, fluorescence decay time is largely independent of indicator concentration, measuring errors due to concentration are eliminated. So far luminescence-optical sensors based on decay time measurement have mainly been developed for measuring physical variables (e.g., temperature) and oxygen concentration. For a long time it has not been possible to produce luminescence-optical pH sensors, as no indicator media were known that would respond to a change in pH by a reversible change in luminescence decay time.
So far only two attempts have been made to develop fluorescence-optical pH sensors based on decay time measurement.
An arrangement is known from AT-PS 393 035, where two substances in close contact with each other are provided in an optical sensor, the first substance being a fluorophore insensitive to the pH value to be determined, and the other one being a chromophore influencing the fluorescence of the fluorophore. The reduction in fluorescence decay time .tau. due to the energy transfer between chromophore and fluorophore is employed for quantitative determination of the pH value. The extent of energy transfer is determined by the overlap of the fluorescence spectrum of the fluorophore (donor) and the absorption spectrum of the pH indicator (acceptor) and their distance in space, and is thus dependent on the spatial distribution and the concentration of the two substances. In this way the major advantage of decay time sensors, i.e. their independence of indicator concentration, is lost.
The second attempt at developing a decay time sensor for pH measurement is described in "New luminescent metal complex for pH transduction in optical fiber sensing", by M. C. MORENO-BONDI et al., SPIE 1368, 1990, 157-164. In this device an indicator material is used, for instance, a ruthenium complex, whose fluorescence is dynamically quenched by acids, which will result in a change in fluorescence decay time. The degree of quenching, however, is determined by the type and concentration of the buffer, as well as by the chemical composition of the quenching acid, and only indirectly by the pH value. For this reason use of the device as a pH sensor is of limited
REFERENCES:
patent: 4767718 (1988-08-01), Meyers
patent: 4925268 (1990-05-01), Iyer et al.
patent: 5047351 (1991-09-01), Makiuchi et al.
Aldrich Catalog; 1988, pp. 33, 34, 60, 147, 152, 174, 416, 552, 977, 1059, 1089, 1304, 1321.
Wolfbeis et al.; "A Study on Fluorescent Indicators . . . "; Fresenius Z Anal. Chem; 314; 1983; 119-124.
Wolfbeis et al.; "Syntheses of Fluorescent Dyes"; Journal of Heterocyclic Chem.; 19; 1982; 841-843.
Karpf Hellfried
Leiner Marco J.
Lippitsch Max
AVL Medical Instruments AG
Torres Ramon
Warden Robert J.
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