Abstract: A universal standard chemical reagent for quantitative visual and spectrometric analysis of compounds having reactive functional groups, including mixtures and homologs of said compounds, said reagent comprising a compound of the general formula Q-B-f, wherein: Q stands for an organic moiety which can be measured quantitatively, visually by color, spectroscopically, or fluorometrically; B represents a non-reactive organic bridging unit linking the moiety Q to a reactive functional group f, said bridging unit being of sufficient length or size to prevent any possible interaction of Q that might alter its spectroscopic properties even upon derivatization; and f is a reactive group which can react with a compound to form covalently bonded derivatives.

Abstract: A D-allose specific dehydrogenase has been isolated which can be used with NAD as a cofactor in a sensitive, specific, quantitative assay for D-allose in aqueous media. A qualitative, color-based test for the presence of D-allose results when an election-accepting dye is coupled to NAD.

Abstract: The compound 2,3,5,6-tetrahydroxy-1,4-quinone, its derivatives and structural analogs are used as activators for intrinsic blood coagulation and as diagnostic reagents for the activated partial thromboplastin time test of blood coagulation.

Abstract: The present invention provides a process for determining the content of hirudin or of a synthetic thrombin inhibitor in the blood. A prothrombin intermediate, or a compound that splits prothrombin into meizothrombin, or a mixture thereof, is added to a blood sample and a measurement is taken of the time that elapses between the addition of the reagent to the sample and the beginning of coagulation. Comparison is then made, where necessary, with a standard calibration curve.

Abstract: The invention relates to a method of analyzing the viability of a sample of cells using an aqueous solution comprising two fluorescent dyes. Dye I has the formula: ##STR1## where R.sup.2 is C.sub.1-6 alkyl; Z.sup.- is a biologically compatible counterion;X is O; S; Se; or NR.sup.15, where R.sup.15 is H or C.sub.1-6 alkyl; or CR.sup.16 R.sup.17, where R.sup.16 and R.sup.17, which may be the same or different, are independently H or C.sub.1-6 alkyl, or the carbons of R.sup.16 and R.sup.17 taken in combination complete a five or six membered saturated ring; and the benzazolium is optionally further substituted;n=0, 1, or 2;Y is --CR.sup.3 .dbd.CR.sup.4 --; p and m=0 or 1, such that p+m=1;R.sup.5 is a C.sub.1-6 alkyl, C.sub.1-6 alkenyl, C.sub.1-6 polyalkenyl, C.sub.1-6 alkynyl or C.sub.1-6 polyalkynyl group; or R.sup.5 is an OMEGA;R.sup.3, R.sup.4, R.sup.6 and R.sup.7, which may be the same or different, are independently H; or a C.sub.1-6 alkyl, C.sub.1-6 alkenyl, C.sub.1-6 polyalkenyl, C.sub.1-6 alkynyl or C.

Abstract: The present invention relates to a method of determining the metabolic state of neutrophils present in the body of a patient. In particular, the present invention involves the measurement of the rates of in vitro glycolysis in blood samples taken from individuals as a function of the number of selected cells present in the blood sample, including neutrophils and red blood cells. The physiologic information provided by the present method, which, for example, indicates whether an individual's neutrophils are in a quiescent, primed or activated state, allows the medical practitioner to attain a better understanding of the patient's condition and, consequently, assists in the diagnosis and formulation of proper treatment.

Abstract: A method for rapidly collecting kinetic rate data from a temperature scanning reactor for chemical reactions. The method, which is particularly useful for studying catalytic reactions, involves ramping (scanning) of the input temperature to a reactor and recording of output conversion and bed temperature without waiting for isothermal steady state to be established.

Abstract: A method for the determination of the activated partial thromboplastin time (APTT) in a one-step reaction, in which the determination of APTT is initiated by contacting a reagent that contains the substances necessary for the APTT determination in a premixed form, with the sample to be tested. A reagent which contains the substances necessary for the APTT determination is also disclosed.

Abstract: Air reactivity, CO.sub.2 and soot index of a carbon product is determined. The air reactivity and CO.sub.2 reactivity of a sample of a carbon product are determined on the basis of the same test of the same sample. Air reactivity is analyzed first and, when such analysis is finished, CO.sub.2 reactivity is automatically analyzed on the same sample. The soot index is determined by collecting and weighing soot dust. A vertical tube furnace includes an inlet for the introduction of gas, and a sample holder which is freely suspended from a weighing device and extends down into the tube furnace. The sample holder is provided with one or more thermocouples for registering temperature of a carbon product.

Abstract: A method and a device for measuring detailed decomposition rate characteristic of special material gas such as silane gas. After inert gas is supplied from a gas purifier(1)(a first gas-supply source) into a reaction pipe(20) to provide a high purity atmosphere in the pipe, the inside of the pipe is baked by heater (25 or 27). Then, the inside of the reaction pipe(20) is kept in an atmosphere at a specified temperature and special material gas with a specified purity is supplied from a bomb(10)(a second gas-supply source) into the reaction pipe at a fixed flow rate. When the inside of the reaction pipe (20) reaches a specified terminal temperature, a decomposition rate of the special material gas at the temperature is measured by a gas chromatography (12) by, for example, extracting a part of gas in the reaction pipe. Afterward, a flow rate of the special material gas is successively varied and a decomposition rate at every time of variation is measured.

Abstract: A control loop and fluidization quality analyzer for a fluidized bed utilizes time varying pressure drop measurements. A fast-response pressure transducer measures the overall bed pressure drop, or over some segment of the bed, and the pressure drop signal is processed to produce an output voltage which changes with the degree of fluidization turbulence.

Abstract: This invention relates to an enzyme assay for quantitative analysis of biochemical substances using NAD(P)-NAD(P)H system and utilizing hydrogen peroxide, in which isocitric acid, metal ions and isocitrate dehydrogenase are previously added to a test sample, thereby consuming the endogenous substances that interfere the analysis, and at the same time regenerating NAD(P)H reduced.The isocitrate dehydrogenase is then inactivated by addition of a chelating agent, an enzyme or substrate that generates hydrogen peroxide as reaction product is added simultaneously or thereafter, and the amount of hydrogen peroxide thus formed is measured.Biochemical substances that generate hydrogen peroxide as reaction product can be correctly analyzed by this method with no adverse effect of endogenous substances because these interfering substances have been removed prior to measurement.

Abstract: Method for the analytical determination of the concentration of a component of a medical sample, in which a reaction of the sample with reagents leads to a time-dependent change S(t) in a measured quantity S and the concentration C correlates according to an evaluation curve C(X) with an input variable X derived from S(t), in which the calibration curve is ambiguous for at least a portion of the possible X values. In order to assign an input variable X to one of the sub-sections and thereby to obtain an unambiguous correlation to a particular concentration C, a training run and an analysis run are performed. In the training run, a discrimination algorithm is performed at least once, in which a discriminator set is generated from measurements of S(t), a score is generated in each case from the latter with a multivariate statistical technique and it is checked whether the scores can be divided into separate subsets, in which the concentrations are correctly assigned to the sub-sections of the calibration curve.

Abstract: A system for detecting the presence of bacterial growth in a plurality of sample vials incorporates a single test station moveable along each of the plurality of sample vials. In one embodiment, the sensor station is movably mounted on a rod, and that rod is movably mounted on a pair of spaced rods. The rod which carries the test station may move along the spaced rods to change the location of the test station in a first dimension and the test station is moveable along its rod to change location in a second dimension. In this way, the test station may be moved through two dimensions to move serially to the location of each of the plurality of sample vials. In another aspect of this invention, a bar code is associated with each of the sample vials, and the test station makes a reading of that bar code concurrent with a determination being made as to whether there is any bacterial growth in the sample vial.

Abstract: A method for identifying, characterizing, categorizing and enumerating cells within a cell population. The survivorship characteristics of the different cell populations is used to obtain quantitative and qualitative information about the cell populations initially present in the sample solution before conditions were imposed on the sample solution to elicit a response. The monitored cell survivorship response may be either direct disappearance of intact cells or the appearance of cell structures, carcasses, ghosts or residuum. In a preferred embodiment, a leukocyte cell decay rate in the presence of an erythrolytic agent is determined by monitoring leukocyte counts at several time intervals after the addition of the erythrolytic agent to the sample solution. The leukocyte decay rate is then used to indicate the presence of a fragile leukocyte population, and to accurately estimate the number of leukocytes initially present in the whole blood sample.

Abstract: Process for the sequential observation of the successive states of a chemical reaction taking place in a high vacuum or under a low pressure or the determination of the nature of a substance or the composition of a mixture which can be liquid, solid or gaseous, or alternatively aerosols contained in air, by dissociation in a dissociation box or case (20) filled with a neutral gas from the molecules of the compounds formed, followed by energy filtration of the dissociation fragments in an electrostatic analyzer (22) and detector (24), characterized in that the molecules of the compounds to be analyzed are formed on a target (4), whose conductive walls are raised to a high d.c.

Abstract: An apparatus and method for measuring an amount of gas adsorbed on or desorbed from a solid and for analyzing and surveying reactions of a gas with a solid. Governing parameters include pressure, temperature and gas flow rate. The apparatus and method provide accurate measurement utilizing temperature programmed characterization and the volumetric method. The method is useful at both very high and very low pressures.

Abstract: A catalytic converter has an inner region and a jacket surface surrounding the inner region and being disposed approximately parallel to a given flow direction. The inner region conducts a flow of a fluid containing ingredients to be converted in the inner region by a catalyzed exothermic reaction. The flow passes through the inner region in the given flow direction. The reaction zone is defined as a part of the inner region in which a reaction predominantly takes place. A method for detecting a reaction zone in the catalytic converter includes detecting the reaction zone by measuring a distribution of temperature over the jacket surface along a measurement path being aligned approximately parallel to the given flow direction. The reaction zone is determined by a segment of the measurement path at which the temperature deviates by less than a predetermined limit value from a maximum value of the temperature over the measurement path.

Abstract: A method for rapidly collecting kinetic rate data from a temperature scanning reactor for chemical reactions. The method, which is particularly useful for studying catalytic reactions, involves ramping (scanning) of the input temperature to a reactor and recording of output conversion and bed temperature without waiting for isothermal steady state to be established.

Abstract: Apparatus and methods for accurately determining the gel time of oxygen inhibited polymerizable compositions is provided. Gel times in these compositions are related to dissolved oxygen concentration. The inventive method and apparatus use a small diameter capillary tube filled with the composition and sealed thereafter at one end to include an air space between the end of the liquid column and the sealed end of the tube. A pulsed force of air is applied to the unsealed end of the tube which causes the column of liquid and air/liquid interface to move in accordance with the amplitude of the pulsed air force. A motion detector sensor is located at the air/liquid interface. A light source is then applied to the polymerizable column within the tube causing it to gel. Recording equipment appropriately connected to the motion detector sensor visually describes the motion of the air/liquid interface which becomes zero at the gel point.

Abstract: A system (10) for in vivo measuring chemical and physical parameters of a patient's blood includes a probe (12), a sensing system (14), and flush interference warning devices (20). The system measures pH, pCO.sub.2, and temperature values, and determines a base excess value using the measured pH and pCO.sub.2. The time rate of change of the base excess value is also determined, as is the time rate of change of temperature. The warning devices are activated, indicating that the measured parameters are likely affected by the presence of flush solution flowing past the probe, when either: (a) the base excess value is less than a predefined threshold base excess; (b) the absolute value of the time rate of change of the base excess value is greater than a predefined threshold time rate of change of base excess; or, (c) the absolute value of the time rate of change of temperature is greater than a predefined threshold time rate of change of temperature.

Abstract: A method and reagent for determining fibrinogen from undiluted plasma samples. The use of undiluted plasma as sample is made possible by the use of a specific peptide inhibitor of fibrin aggregation in a concentration which permits aggregation of fibrin but with reduced speed, so that coagulation time can be measured easily. The range of fibrinogen concentrations which can be measured is increased as compared to that of known methods, and the measurement can be fully automated without prediluting the sample. A biological fluid, e.g., undiluted plasma, is incubated with a reagent containing at least one inhibitor of fibrin aggregation in an amount effective to increase coagulation time to allow measurement of the fibrin concentration, e.g., a coagulation time of about 50 to 150 seconds at a fibrin concentration of 1 gram/liter, and thrombin, or a protease of analogous activity in an amount, which immediately converts all the fibrinogen into soluble fibrin, e.g., in an excess of at least 20 U per ml of plasma.

Abstract: A method and apparatus for verifying the operating accuracy of an instrument (10) for detecting the concentration of a medically significant component of a body fluid. The instrument (10) operates by determining the remission of a reacted chemistry contained on a substrate (106) after the chemistry has reacted with the medically significant component of the body fluid. The instrument (10) includes a radiation source (182), a radiation detector (300) and a pathway (164) from the radiation source (182) to the chemistry (106) and from the chemistry (106) to the radiation detector (300) when the substrate (106) is properly inserted into the instrument (10). The remission of the chemistry (106) determines the radiation detected by the radiation detector (300).

Abstract: A method of determining the critical vapor pressure of a hygroscopic material, such as a drug. A drug sample is placed in a substantially isothermal environment. A vapor, such as water vapor, at a given pressure is then placed in the ambient air over the drug. The rate of heat production from this sample at the given water vapor pressure, or the humidity of the air above the sample, is then measured. The water vapor pressure over the drug is gradually increased. Simultaneously, the rate of increase in heat production from the drug sample, or the rate of change of the relative humidity of the air above the drug sample, is measured. A marked increase in the rate of heat production generated by the drug, or a marked change in the relative humidity of the air over the sample, signals the attainment of the critical water vapor pressure.

Abstract: Disclosed are an apparatus and a method for carrying out and studying catalysis and catalyzed chemical reactions. Disclosed is a reactor with a catalyst zone, under vacuum, into which a very rapid pulse of reactant gas is pulsed. The products are analyzed by a real-time method of analysis, such as mass spectrometry. The apparatus and method can detect reaction intermediates and products, and can indicate their sequence of production.

Abstract: A method and apparatus (10) for determining the remission of a chemistry (106) which reacts with a medically significant component of a body fluid. The remission of the chemistry (106) changes as it reacts. The method and apparatus (10) include irradiating the chemistry (106) with a radiation source (182), detecting remissions of radiation from the chemistry (106) with a radiation detector (300), providing a radiation pathway (164) between the source (182) and the chemistry (106), providing a remission pathway (164) between the chemistry (106) and the detector (300), and detecting the rate of change of remission of the chemistry (106) with respect to time.

Abstract: A test apparatus for studying the behavior of chemical reactants is disclosed.

Abstract: A method of determining levels of extrinsic and intrinsic clotting factors and protein C based upon the reaction rate of the observed clot formation and the first derivative of the reaction rate of observed clot formation is provided. In accordance with the teachings of the invention, the reaction rate of the observed clot formation in a prothrombin time test or an activated partial thromboplastin time assay is determined for both test and normal plasma samples and the reaction rates compared. In another embodiment, the first derivative of the reaction rate of the observed clot formation is determined and the results compared.

Abstract: A method for measuring the concentration of hydroxides in alkaline solutions in a remote location using the tendency of hydroxides to absorb carbon dioxide. The method includes the passing of carbon dioxide over the surface of an alkaline solution in a remote tank before and after measurements of the carbon dioxide solution. A comparison of the measurements yields the absorption fraction from which the hydroxide concentration can be calculated using a correlation of hydroxide or pH to absorption fraction.

Abstract: Process for the specific determination of the serum fructosamine content in blood or in samples obtained from blood by reaction with an appropriate color reagent and measurement of the color change thereby brought about, in which before the color reaction sample components with a non-specific reducing action and/or causing turbidity are removed and subsequently the color reagent is added at a pH value of from 10 to 12. The sample components are removed by treatment at approximately neutral pH value with a reagent composition comprising at least one enzymatic oxidation agent, optionally together with peroxidase and/or catalase and/or lipase, as well as with at least one SH group-blocking substance. A kit for the specific determination of the serum fructosamine content in blood or samples obtained from blood, comprises said reagent composition, a rebuffering reagent with a buffer which has an alkaline pH value and a color reagent for the detection of fructosamine.

Abstract: A chemical analyzer in which the measurement of the change in attenuation of RF radiation propagated through a sample is used as the basis for calculating the change in concentration of a given chemical in the sample. Also disclosed are various probe and system designs which facilitate the use of RF attenuation as a basis for measurement of certain chemical characteristics of a sample.

Abstract: Serum is reacted with a dinitrohalobenzene compound and the rate of halogen formation is measured. This rate is in proportion to the amount of albumin in the sample. Other proteins like the globulins, as well as free aminoacids and urea, do not interfere with this reaction.

Abstract: Disclosed is a method for measuring the rate and extent of cure of a resin system undergoing polymerization which entails adding at least one multifunctional fluorescent dye to the resin system undergoing polymerization, the dye being one which initially forms a complex with itself or other components of the system and subsequently chemically reacts with the resin and whose degree of fluorescent emission varies in accordance with the degree of reaction with the resin, polymerizing the resin, simultaneously measuring the fluorescence of the resin system, and comparing the measured fluorescence with pre-existing data correlating the observed values with the rate and extent of polymerization, thereby enabling the rate and extent of polymerization of the resin system under evaluation to be determined.

Abstract: An apparatus and a method is provided for measuring the rate of flow of gas from a sample of a peroxygen, such as, hydrogen peroxide, thereby indicating the stability of the peroxygen. The invention overcomes the disadvantages of the prior methods which are less precise and have a long time delay.

Abstract: A method for studying the rate and type of hydrocarbon generated from a hydrocarbon source utilizes hydrous pyrolysis to generate hydrocarbons from the sample and then utilizes cryogenic methods to remove the fluid portions to a transfer vessel. The gaseous components are removed to a further vessel of known dimensions for determination of weight. The hydrocarbons in the transfer vessel are passed through a dryer to separate the water and their makeup determined. The hydrocarbons remaining in the reactor vessel are removed by working with solvents and their weights are determined after separation and evaporation of the solvents.

Abstract: A method is provided for testing the activity of a catalyst for a chemical reaction in which naphthalene is reversibly hydrogenated by gaseous hydrogen into tetralin, which avoids the need to pressurize a test vessel with hydrogen, enables simple apparatus to be used and gives good accuracy. Tetralin and catalyst are introduced into a sealed container, the container is heated to a reaction temperature for a predetermined time, and the amount of naphthalene formed by dehydrogenation is determined. The method is applicable to the measurement of catalyst activity for catalysts used in the production by hydrogenation of coal-derived liquids.

Abstract: A process for the determination of fructosamine in body fluids by the reaction of a sample solution with a color reagent, wherein the sample liquid is mixed with a buffer solution having a pH value of from 9 to 12, a color-forming reagent and uricase, as well as with at least one detergent, and the chronological change of the extinction is measured kinetically in a temperature range of from 20.degree. to 40.degree. C. at the earliest after 5 minutes.

Abstract: A method and apparatus for analyzing a sample to determine an analyte content has a sensor for sensing the analyte positioned between a first and second transducer. The analyte or derivatives thereof are reciprocated between the first and second transducer to reciprocate at the sensor and allow instantaneous sensing of an indication of the analyte's presence at a point between the first and second transducer. Rapid analysis can be carried out in many different systems including for example where the transducers are enzyme reactors and the analytes are body metabolites.

Abstract: An article such as a drawn optical fiber (21) or an array of optical fibers is provided with a curable coating material. The array of optical fibers may be held together with a curable matrix material (45). Included in the coating material or the matrix material is a fluorescent constituent the fluorescence emission of which changes as a function of the degree of cure of the coating or matrix material. After the in-line curing of the coating material or of the matrix material, the fluorescence emission of the fluorescent constituent is monitored to determine the degree of cure of the curable material.

Abstract: Disclosed are an apparatus adapted for use in a temporal analysis of products (TAP) system for studying catalytic reactions, a catalytic reactor provided with heat exchange capability and useful in the TAP system, and an apparatus for use in gas processing which can also be used in a TAP system. The gas processing apparatus includes a manifold for introduction of a plurality of gases into a gas processing system. The manifold comprises a plurality of channels through which gas may flow toward the gas processing system, and a mixing chamber having an inlet in communication with the plurality of channels and an outlet in communication with the gas processing system. At least one of the channels has a rapidly operable feed valve at the terminus of the channel at which it communicates with the chamber inlet. The mixing chamber has a void volume that is small relative to the working volume of the gas processing system.

Abstract: A method for determining the extent of polymerization of a polymer system consisting of adding a fluorescent label, the label having a reactivity similar to the reactivity of the curing agent, to the polymer system and measuring the fluorescence intensity proportional to cure species concentration during polymerization. The fluorescence intensity of the label exhibits sensitive changes throughout the polymerization process, allowing one to follow cure reactions in a quantitive way by measuring fluorescence, especially in the latter stages of cure. The cure species composition, reactivity ratio, activation energy and weight-average molecular weight can also be determined by adding a label and measuring the UV-VIS spectra in addition to the fluorescence intensity.

Abstract: Two methods of determination of the chemical changes induced in a film of material such as photoresist that has been exposed to electromagnetic radiation. Two methods use measurement of polarized light reflected by the film mounted on a substrate to determine a real refractive index or a complex refractive index of the film. Two other methods use measurement of polarized light by the film mounted on a (partly) transparent substrate to determine a real refractive index or a complex refractive index of the film.

Abstract: The lamellar body solubilization test (LBST) is a rapid and simple indicator of fetal lung maturity. The amniotic fluid contains lamellar bodies, the presence of which can be correlated to maturation of lung tissue. The test is conducted by measuring a difference in an optical property (turbidity, light scatter, innate or added fluorescence) of a sample of amniotic fluid or other physical property affected by the presence of particulate bodies suspended in a liquid, either 1) kinetically (rate method) or 2) as an end point method (pre- and post-), due to the unravelling or solubilization of the lamellar bodies caused by subjecting the sample to a physical or chemical agent, e.g., detergent or heat. The change in that property either rate of change or delta, by the destruction of the lamellar body structure provides an accurate indication of the concentration and size of the lamellar bodies in the sample of amniotic fluid, which in turn provides a good indication of fetal lung maturity.

Abstract: The present invention is a device to measure the degree of cure of fiberglass using only infrared radiation. Particular frequencies of infrared radiation are used to determine the value of a cure-sensitive function and also the value of as cure-insensitive function and from a combination of the values of the functions, a property of fiberglass is determined.

Abstract: A photometric method and apparatus for measuring agglutination in a biological agglutination reaction system test sample using a laser beam source and at least one photodetector for detecting light scattered by the test sample. The method includes the following steps: (1) arranging the at least one photodetector so as to be capable of detecting scattered light from the test sample at a scatter angle of 30 to 60 with respect to a laser beam directed at the test sample from the laser beam source; (2) irradiating the test sample with the laser beam from the laser beam source; (3) selectively detecting the intensity of scattered light from the test sample at the scatter angle of 30 to 60 using the at least one photodetector which provides an output indicative thereof; and (4) determining the first derivative of the output of the at least one photodetector with respect to time and obtaining the maximum value thereof.

Abstract: The invention comprises a method for determining the corrosion rate of metals in contact with a liquid system which is capable of causing corrosion of such metals which comprises adding to the liquid system an electrochemically active compound having a reduction potential more positive than the metal in contact with the liquid system and then monitoring the system thus treated with the electrochemically active compound to determine its rate of reduction which is proportional to the corrosion rate of the metal.

Abstract: A system and protocol for performing cytotoxicity studies including apparatus and methods for culturing the biopsied cells, for providing oxygenated nutrients, for removing cell-waste products, for introducing a fluorogenic substrate, for introducing cytotoxic agents including anticancer drugs, for measuring the released fluorescence and for measuring intracellular accumulation of fluorescein. Cytotoxicity can be determined by measuring fluorescence in the efflux of the vessel and concommitantly by direct photometric comparisons of the cells in the vessel before and after exposure to the cytotoxic agent.

Abstract: The present invention provides a process for the photometric determination of prekallikrein in plasma, wherein plasma is incubated with a surface activator, the extinction obtained is measured, a chromogenic thrombin substrate is then added thereto, the optically determinable group liberated therefrom is measured at short time intervals or continuously and the gradient of the linear part of the curve obtained by plotting the time against the extinction is determined as a measure of the prekallikrein content. The partial thromboplastin time of plasma is simultaneously determined by carrying out the incubation in the presence of calcium ions and a phospholipid and measuring the time it takes the extinction to reach a predetermined level.

Abstract: A reagent of the type comprising an acid, a molybdate salt, a non-ionic surfactant, and polyvinylpyrrolidone (PVP). The reagent is characterized in that it further comprises an enhancing amount of at least one sugar alcohol. Also, a method for assaying inorganic phosphorus of the type which comprises mixing a sample of biological fluid with a reagent and measuring the absorbance of the resulting solution. The method is characterized in that the above reagent is employed therein. The method can further be characterized in that the measurement can be made via a rate technique.

Abstract: An analyte in solution is made to react with a specific reactant coated on the wave-guide thus modifying the optical properties thereof. The index of refraction of the wave-guide material is higher than that of the reaction medium which ensures that a light signal injected into said guide be carried by multiple total reflection, the distance of penetration of the evanescent wave associated with the totally reflected signal being of the same order of magnitude or greater than the thickness of the analyte-reactant product layer.