Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1998-11-25
2001-03-13
Tung, T. (Department: 1743)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S416000
Reexamination Certificate
active
06200444
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a cation-selective sensor which has a cation-selective coating. As a result of cations to be detected coming into contact with this layer, a detectable change in the electrical properties of the layer is brought about.
2. Description of the Prior Art
For the determination of ions in solutions, use is frequently made of the potentiometric ion-selective electrode (Cammann, K., Die Arbeit mit Ionenselektiven Elektroden [Working with ion-selective electrodes], 2nd ed., Springer Verlag: Berlin, Heidelberg, New York, 1977). Ion-selective electrodes are electrochemical sensors with which the concentration or activity of specific ions can be determined by means of a potential difference. The ion-selective potential difference occurs at the phase boundary between active electrode material/electrolyte and depends according to the Nernst equation on the activity of a specific ion in the solution. One example of sensors of this type are ion-selective field-effect transistors (for example DE 29344005 C2).
Unlike the case of resistance and capacitance, the absolute values of the electrical potential have no physical meaning, since the potential can only be defined in relation to a reference value. In electrochemistry, such a reference value is customarily given by the potential of the reference electrode. The need for a reference electrode is the critical disadvantage with the use of potentiometric measurements for the determination of ion activities in solution.
Another fundamental limitation with the potentiometric analysis methods relates to the composition of the ion-selective membrane. The requirements made of the nature of the specific binding and/or of the complexing sites within the membrane should be such that the potential difference at the membrane/solution interface is generated selectively as a function of the presence of a particular species in the solution. For example, this binding should not be too strong, in order to permit sufficiently fast exchange of the detected species between the membrane phase and the solution.
Besides the potentiometric analysis methods, the most frequently used electrochemical analysis methods are those which measure the current through a suitably prepared or modified conducting or semiconducting working electrode. The potential of this electrode is set by that of the reference electrode. The measured current results from the electrochemical redox reaction which takes place at the working electrode/solution interface. In addition to the reference electrode which is needed, the use of this measurement method is further limited by the fact that the measured species must be electroactive at the working potential applied to the working electrode. Furthermore, this potential must be different from that of the interfering species. The latter point often causes a problem since many chemical compounds or large groups of chemical compounds have very similar redox properties. In addition, the required electrode potentials for many compounds lie outside the range which is practically usable.
The non-electrochemical methods usually employed for the specific recognition of charged and neutral species include the various types of liquid chromatography. In this case, the sample to be analysed is brought into contact with a so-called stationary phase, for example a polymer layer, which specifically binds or retains the detected species. The strength of this binding determines the retention time of the analyte within the chromatography column. When tailor-made stationary phases are used, very many species can be identified. However, this type of analytical measurement arrangement is highly complex and very expensive.
A further possibility for the determination of ions in solutions is given by ion-selective optodes. Ion-selective compounds and indicators, which contain structural elements that change their optical properties in the UV/VIS range, can be used as chromoionophores and fluoroionophores in corresponding ion-selective sensors with optical signal transmission. An overview of the way in which ion-selective optodes function is given in the following articles: K. Seiler, Ionenselektive Optodenmembranen [Ion-selective optode membranes], Fluka Chemie AG, Buchs, Switzerland (1991), ISBN 3-905617-05-6, W. Morf, K. Seiler, P. P. Sörensen, W. Simon, Ion-Selective-Electrodes, Vol. 5, Pergammon Press, Oxford, New York, Akademiai Budapest (1989), p. 141.
Interaction of ions with the chromophore components, or fluorescent components, in a membrane which is applied to an optical transducer system, leads to absorption or excitation of the fluorescence, and it has in this way been possible to develop chemical sensors for colourless or non-fluorescent substances.
The optical sensor systems have fundamental disadvantages. For example, the optical systems are disturbed by background light and, compared with electrochemical sensors, have relatively narrow dynamic measurement ranges. Furthermore, the long-term stability of immobilized components is limited by photolytic breakdown and leaching, and the response times of optical sensors are relatively long. Further disadvantages of ion-selective optodes include incompatibility with microelectronics and the lack of possibilities for integration.
The synthesis of chromophore compounds or fluorescent compounds is very time-consuming and cost-intensive, which is likewise highly disadvantageous.
A further possibility for the determination of ions in solutions is given by test rods and test papers. This involves a microchemical investigation method, in which chemical reactions, visible to the naked eye, of small quantities of elements (in the form of their ions) or compounds can be identified. The analytes can be identified by virtue of their colour reactions (colour changes). In this case, all the reagents needed for the specific detection reaction are applied to a support and, on exposure to an aqueous analyte solution, the analyte in question can be assigned to a concentration range according to the intensity or the hue of the respective coloration. The reagents used in test papers and test rods for the specific colour reactions or colour changes are also used in colorimetric test systems. In colorimetry, the colour intensity of a sample solution is visually compared with the intensity of standard solutions whose concentrations are known. Problems and disadvantages are found with the accuracy in these determination methods, which often only give semiquantitative conclusions. It is not possible to use test strips in on-line measurement systems, and so test strips cannot function as sensors. EP 0 153641 A2 presents the structure and measurement method for some test strips.
Another important class of analytical methods for the detection of charged or uncharged species in a gas or liquid medium employs the measurement of resistance or capacitance. Variations in the conductance or the dielectric properties of a layer of a sensitive material are exhibited as a function of the interactions with the detected species. In the field of gas detection, resistive and capacitive sensors are thus widely used.
In contrast to this, the use of such sensors is encountered only infrequently for chemical analyses in liquids. Measurements of the total conductance of electrolyte solutions are of only limited analytical meaning, because they generally lack specificity. Notwithstanding, in GB 2204408 A, R. S. Sethi et al. described a conductimetric enzyme biosensor which has finger-like interdigital electrodes (IDEs) that are covered by a membrane of immobilized urease. When urea is present in the test solution, the use of densely arranged electrodes makes it possible to measure the conductance of the solution with which the enzyme layer is saturated, so long as the conductance changes specifically with respect to the urea hydrolysis which is catalysed by urease. The shortcomings of biosensors of this type includes the drastic reduction in the sensitivity of
Ahlers Benedikt
Cammann Karl
Choulga Alexandre
Institut fuer Chemo und Biosensorik Muenster e.V.
Marshall & Melhorn
Noguerola Alex
Tung T.
LandOfFree
Cation-selective sensor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Cation-selective sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cation-selective sensor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2520832