Chemistry: analytical and immunological testing – Optical result
Patent
1996-11-07
1998-06-23
Ludlow, Jan
Chemistry: analytical and immunological testing
Optical result
422 8205, 422 8209, 356 39, 356300, 356317, 600310, 600322, G01N 2100
Patent
active
057704546
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method and an apparatus for determining the concentration of an analyte in a biological sample.
The term "biological sample" refers to a body fluid or a tissue of a living organism. Biological samples in most cases are optically heterogeneous, i.e. they contain a large number of scattering centres at which irradiated light is scattered. In the case of biological tissue, in particular skin tissue, the scattering centres are formed by the cell walls and other heterogeneously optical components contained in the tissue.
Body fluids, in particular blood, are likewise optically heterogeneous biological samples, because they contain particles on which the primary radiation is scattered. Milk and other fluids subject to testing by food analysts often also contain a high concentration of scattering centres, for example in the form of emulsified fat droplets.
2. Description of the Related Art
For the qualitative and quantitative analytical determination of components of such biological samples, generally reagents or reagent systems are used that react chemically with the respective component. The reaction leads to a physically detectable change in the reaction solution, for example a change in its color, which can be measured as a measurement variable. By calibration with standard samples of known concentration, a correlation between the values of the measurement variable measured at different concentrations and the concentration is obtained. These methods, although permitting analyses of high accuracy and sensitivity, require that a liquid sample, in particular a blood sample, be taken from the body for analysis ("invasive analysis"). This sampling is unpleasant and painful and leads to a certain risk of infection.
A large number of methods and apparatuses have therefore been proposed for the in vivo and non-invasive determination of analytes in blood, tissue or other biological samples.
SUMMARY OF THE INVENTION
The invention relates to a group of such methods in which measurement light is irradiated by means of irradiation means as primary light at an irradiation site through an interface bounding the sample into the sample and light emerging out of the biological sample through an interface bounding the sample is detected by means of detection means at a detection site at a predetermined measuring distance, in order to determine (without the use of reagents) a physical property of the light which varies due to the interaction with the biological sample and which correlates with the concentration of the analyte in the biological sample. Such a method step is referred to below as a "detection step".
The physical property of the light that is determined (detected) in a detection step and correlates with the analyte concentration, which can also be referred to as a "quantifiable parameter", will for the sake of simplicity be referred to below as the "measurement variable". This term must not, however, be taken to mean that a particular amount of the measurement variable in a corresponding measurement unit has to be measured.
Insofar as the methods do not allow an absolute measurement, a calibration is required (as with the conventional methods of analysis based on chemical reactions). Customarily in at least one calibration step the measurement variable is determined on a biological sample with a known analyte concentration, which step is performed with the same measurement techniques as the detection step.
In an evaluation step of the analytical method the analyte concentration is determined from the measurement variable measured with at least one detection step, optionally in comparison with at least one calibration step. The evaluation step comprises an evaluation algorithm in which the concentration is calculated in a predetermined manner from the results of at least one detection step and as a rule at least one calibration step.
The wavelengths of the light which are discussed for such methods generally lie between some 300 nm a
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Boecker Dirk
Essenpreis Matthias
Haar Hans-Peter
Hein Heinz-Michael
Boehringer Mannheim GmbH
Ludlow Jan
Wallenhorst Maureen M.
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