Chemistry: analytical and immunological testing – Including titration or ph determination
Patent
1997-01-02
1999-07-13
Lipman, Bernard
Chemistry: analytical and immunological testing
Including titration or ph determination
436172, 526248, 526320, G01N 3116
Patent
active
059226129
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an optical method for determining the pH value and the ionic strength of an electrolyte solution, to optical sensors for carrying out the method, to polymers and to a polymerisable composition, and to fluorescent dyes.
It is known that the pK.sub.a value of an indicator changes with the ionic strength of a solution and that that change is dependent upon the level of charge on the indicator. It has therefore already been proposed in DE-A-3 430 935 to use in the determination of the pH value the difference between the measured values of two sensors M.sub.1 and M.sub.2 having different ionic strength dependencies, which is a complex function of the ionic strength J, after calibration with known standard solutions by computation using a process control computer.
The optical determination of the ionic strength at a given pH value in accordance with the fluorescence method using two optical sensors is described in DE-A-3 430 935. In that instance the fluorescent dye of the sensors, which is the same for each sensor, is immobilised via bridge groups directly on the surface of glass carriers, one sensor containing additional charges for achieving a high polarity and ionic strength dependency, and the other sensor being so modified that it is substantially non-polar, hydrophobic and independent of the ionic strength. A very considerable disadvantage of those sensors is that the fluorescent dye is directly exposed to external effects of the measuring solutions, and influences both of a physical nature (for example dissolution of the dye, deposits on the surface) and of a chemical nature (decomposition of the dye) rapidly render the sensors unusable. In addition, in the case of excitation in an evanescent field, interference between the evanescent measurement field and the fluorescence of the test sample cannot be completely avoided, which reduces the accuracy of measurement. The response time of those sensors is short, however, since the fluorescent dye bonded to the surface immediately comes into contact with the electrolyte solution. The sensitivity is regarded as adequate.
It is also known from WO 93/07483 to use as pH indicators carriers coated with hydrophilic polymers containing a polymer-bonded dye, optical measurements being based on the absorption method. Fluorescence detection is not mentioned.
It has now been found that the service life and usable life of sensors for determining ionic strength and pH value can be considerably increased, that the sensitivity is not reduced but is actually increased and that the response times are not reduced but are even slightly increased when measurements are carried out with sensors in which the fluorescent dye is embedded in a polymer membrane and the membrane layers of the two sensors used for measurement have different polymer compositions. Those different compositions bring about, for example, differences in the hydrophilicity, polarity and/or dielectric constant and therewith a different dependency on ionic strength, without it being necessary to make provision for high charges in at least one sensor. It has been shown, surprisingly, that it is not necessary to use charged sensors but that even measurement in a virtually uncharged environment is possible. The embedding of the indicator dye in the sensor membrane brings about effective protection against damage and interference from the measuring medium, so that the usable life is extended also. In addition, in sensors that measure in an evanescent field of the substrate, the membrane keeps the sample solution geometrically remote from the detection zone on the surface of the waveguide, which in contrast to the sensors described in DE-A-3 340 935 prevents interference with the fluorescence of the sample solution. The photostability is surprisingly high, which ensures a longer usable life. The response times and the conditioning times correspond, despite the embedding of the fluorophore, to the short time periods required for optical measuring systems, those parameters being substantially dep
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Alder Alex
Barnard Steven
Berger Joseph
Blom Nils
Rouilly Marizel
Kalinchak Stephen G.
Lipman Bernard
Novartis Corporation
Sarofim N.
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