SENSOR FOR CHEMICAL ANALYSIS

Abstract: An analysis electrode including a sensor on the sensitive surface of which a variable liquid flow has been applied into which the analysis substances diffuses through a semi-permeable membrane in connection with the electrode surface. By varying the composition and rate of the liquid flow it is gained, on one hand, that the analysis substance undergoes suitable modification, e.g., dissociation and, on the other hand, that the chemical environment around the sensor surface can be optimized, e.g. for an enzymatic reaction. In addition, the measuring range may be made variable by variation of the concentration of the analysis substance by changing the liquid flow rate.

Description: SENSOR FOR CHEMICAL ANALYSIS The present invention relates to a system in which a measuring chamber has been brought into connection with the sensitive surface of an analysis electrode. The measuring chamber, which together with the analysis electrode is submerged in the sample solution and is spaced from the latter by means of a membrane of a cer¬ tain permeability, is continuously flushed through by a liquid flow emanating from a specific outer reservoir. Among existing analysis electrodes those which are noticed in the first place today are the electrochemi¬ cal ones, the so-called enzyme electrodes and the mic- robial electrodes. Also so-called solid-state electrodes are coming into use. The electrochemical analysis electrodes may be di- vided up into ion-selective and membrane electrodes, where the ion-selective ones measure a specific elect¬ rochemical reaction on their sensitive surface and the membrane electrodes have a gas-permeable membrane which only allows gas molecules to pass into the electrolyte solution. Examples of the ion-selective electrode type are pH and NH. -electrodes and examples of the membrane type are NH-. and O ^ -electrodes. In practice problems may arise with these electrode types when measuring in samples of wholly or partly undefined contents. The problem may be illustrated with an example. In determin¬ ing NH. in a sample from a fermentation (pH = 7.0) a lon-selective NH. electrode cannot be used due to its sensitivity to K and other ions which are known to be present in the medium. A membrane electrode for deter- mining the percentage of NH_. cannot either be used since at pH 7.0 almost all NH-, is present as NH. according to the equation NH. + == * NH., + H + fp Λ K: = 9.3. The present invention allows direct measuring of the NH. content in the sample by placing in connection with the gas-permeable membrane of a NH-. electrode a ion-permeable membrane and laying between these mem- branes a flow of a buffer solution which holds so high a pH that the desired part of the NH. ions diffusing into the measuring chamber are converted into NH, form. This principle may be used in all systems of the type HA + -s≤ HA =*=* H + + A~ and HA H + A (g) where it is desired to change an environmental para¬ meter such as e.g. pH or buffer capacity from those prevailing in the sample but still perform a not sample- destroying analysis with a sensor placed in the sample. The present invention may also be applied to other ^ es of chemical reactions, e.g. redox reactions. An¬ other advantage is that, if it is desired to analyse percentages exceeding the measuring range of the elect- trode in question, it is possible by a suitable choice of flow rate of the external buffer to create a direct, continuous dilution of the analysis substance inside the membrane adjacent the sensor surface. Thus it is possible to obtain an optional measuring range in the instrument by adjustment of the liquid flow. In other words, the system can be used solely to create a vari¬ able measuring range in a certain electrode. Also other liquids and membranes than those mentioned above may be used in dependence upon the desired application. One may, for instance, let a reagent be contained in a constant percentage in the liquid flow in order to react with the analysis substance and form a measurable product. The principle for an electrochemical analysis electrode constructed according to the present inven¬ tion will appear from the following (see Fig. 1). (1) is an electrochemical sensor over the sensi- tive surface of which a membrane (2) has been mounted so that a liquid flow (F) is allowed to pass the mea¬ suring chamber (3) thus formed, through tubes (4) adap¬ ted therefor. An adjustable pump (5) drives the flow which comes from a specific reservoir (6). When the analysis substance diffuses from the sample through the membrane (2) into the measuring chamber (3) where, after dilution and possibly chemical conversion, the percentage is measured with the sensor (1) and the re- suit is obtained with the aid of the electronics (7). Enzyme electrodes have been the object of great, interest during the last decade (ref). They consist (see Fig. 2) in principle of an electrochemical sensor of membrane or ion-selective type (1) on the sensitive surface of which one has mounted one or more immobi¬ lized enzymes in the form of a membrane or on a carrier (2) and separated this from the sample solution by means of a semi-permeable membrane (3). The electrode signals is recorded in the electronics (4). The electrode (1) is chosen so that one of the reactants or products of the enzyme reaction will form analysis substance for the electrode. Ex. An enzyme reaction follows the formula A + H 2 0 + 0 2 E Z > C + H 2 0 2 and the substance A is that which is of interest to determine. However, A and C are complicated organic substances which cannot be measured directly electro¬ chemically. However, 0- and H-0-, being stoichiometri- cally related with A, can be measured with rescpect- ively a membrane and an ion-selected electrode. In this case therefore one of these electrodes are chosen as sensor ( (1) in Fig. 2). Certain disadvantages are en¬ tailed with enzyme electrodes: sensitivity to environ¬ mental parameters such as e.g. pH, sensitivity to de- naturating substances, product inhibition due to in¬ creased product percentages inside the enzyme layer etc. The present invention permits elimination of these disadvantages in that it makes it possible, by means of the flow system described above and an appropriate choice of liquid in the flow (F), to create optimum conditions for enzyme inside the measuring chamber even if the conditions in the sample are very unfavourable. Moreover, possibilities are provided, in the same way as described above, for simply varying the measuring range for the enzyme electrode. The principle for an enzyme electrode built ac¬ cording to the present invention appears from the fol¬ lowing (see Fig. 3). Fig. 3 A shows the build-up of the measuring chamber when the enzyme functions-as "active membrane", i.e. the analysis substance must diffuse -through a membrane with immobilized enzyme (1) while being transformed before it reaches the measuring chamber and the sensor ( (2) and (3) respectively). Fig. 3 B shows the situation when the enzyme (4) is contained immobilized in the chamber (2) and the sample is .. spaced from the measuring chamber by means of a membrane (1). The present invention may, in the same way as de¬ scribed above, also be applied to other electrode sys¬ tems with active and passive membranes, e.g. microbial electrodes and antigen-antibody- and carbohydrate-lec- tine electrodes etc. One may let a reagent accompany the liquid flow (F), which reagent takes part in the enzyme reaction while forming coloured or otherwise characteristic substances which then may be detected optically or in another way. Fig. 4 shows the electrode flow I as a function of the glucose concentration when the present invention has been applied to a glucose-sen¬ sitive enzyme electrode in 4 different flows (F) . Reference. Guilbault, G.G. Enz. Microb. Technol, 2, 258 (1980). OAIP "

Claims: CLAIMS 1. Analysis electrode including a sensor, c h a ¬ r a c t e r i z e d in that a variable liquid flow has been disposed in the vicinity of the sensitive sur¬ face thereof and that this liquid flow has been spaced from the sample solution by means of a membrane. 2. Analysis electrode according to claim 1, c h a r a c t e r i z e d in that said membrane is a semi-permeable or gas-permeable membrane. 3. Analysis electrode according to claim 1, c h a r a c t e r i z e d in that said membrane con¬ tains one or more of the following components: proteins, enzymes, other active substances, organelles or micro¬ organisms. 4. Analysis electrode according to claim 1, c h a r a c t e r i z e d in that said measuring cham¬ ber contains an immobilized preparation of one or more of the following components: proteins, enzymes, other active substances, organelles or micro-organisms.

Inventors: CLELAND NEIL FREDRIK, ENFORS SVEN OLOF, CLELAND, NEIL, FREDRIK, ENFORS, SVEN, OLOF
Applicants: CLELAND NEIL FREDRIK, ENFORS SVEN OLOF, CLELAND, NEIL, FREDRIK, ENFORS, SVEN, OLOF
Application year: 1984
Main classification: G01N27
IPC codes: C12Q1, G01N27