EP2135059A2

EP2135059A2 - Measuring device and method for optically determining the concentration of blood sugar and/or lactate in biological systems

Info

Publication number: EP2135059A2
Application number: EP08734378A
Authority: EP
Inventors: Reinhard D. Beise
Original assignee: Biocomfort Diagnostics GmbH
Current assignee: BIOCOMFORT DIAGNOSTICS VERWALTUNGS-GMBH
Priority date: 2007-03-16
Filing date: 2008-03-16
Publication date: 2009-12-23
Also published as: DE102007032849A1; DE112008000683A5; WO2008113328A2; WO2008113328A3; US20100041969A1

Abstract

The invention relates to a measuring device for optically determining the concentration of blood sugar and/or lactate in biological systems, comprising at least one IR radiation source (3), that radiates IR light on a volume (1) that is to examined, and at least one measuring detector (10) that detects light coming from the volume (1) that is to be examined in order to determine the concentration of blood sugar and/or lactate, also by laymen in a simple manner and anywhere. According to the invention, the IR light radiated on the volume (1) that is to be examined is supplied, prior to entry into the volume (1), to a reference detector.

Description

Measuring device and method for optical concentration determination of blood sugar and / or lactate in biological systems

The invention relates to a measuring device for the optical concentration determination of blood sugar and / or lactate in biological systems with at least one IR (infrared) - radiation source that emits IR light on a volume to be examined, with at least one measuring detector, the from receiving volume outgoing light, and with at least one reference detector, which is supplied to the volume to be examined radiated IR light before entering the volume, wherein the radiation source, the reference detector and the measuring detector connected via a lock-in and between the IR radiation source and the measuring detector is an optical measuring path with a first Meßwegcharakteristik and formed between the IR radiation source and the reference detector, an optical reference path with a second, deviating from the first Meßwegcharakteristik Meßwegcharakteristik. The invention also relates to a method for the optical concentration determination of blood sugar and / or lactate in biological systems, in which IR light along an optical measuring path irradiated to a volume to be examined and from the light emanating from the volume of a value relevant to the concentration using a Reference measurement of the IR light irradiated to the volume to be examined and a lock-in method is determined via an optical reference path, the optical reference path having a measurement path characteristic which deviates from the measurement path characteristic of the optical measurement path.

In the present context, as a relevant value for the concentration, on the one hand, for example, a value proportional to the concentration or inversely proportional to the concentration can be determined. This can in particular serve the output of an analytical measured value. However, depending on the requirements, a digital output with a lower information content, for example for displaying a normal, a critical and a critical concentration value, or merely a binary signal, for example when a critical concentration value is exceeded, can be referred to as "relevant value". be determined. In this respect, in the present context the term "relevant value" denotes a value which serves as a function of the concentration for detecting the information content desired with the present concentration determination.

[03] To date, such concentration determinations are relatively expensive. They either require a complex chemical-analytical measurement setup or they are calculated back to concentration using spectral analysis. It is understood that such measuring methods are extremely expensive already because of their equipment cost and in particular can not be performed easily by laymen suburb. The same applies to chemical measuring methods, which also require a high level of wear on auxiliary equipment, such as measuring strips or measuring chemicals.

Thus, WO 2005/112740 A2 and EP 0 670 143 B1 disclose comparatively simply constructed measuring devices which may possibly be operated on by a medical layman and, in particular, require no further aids, such as measuring strips or measuring chemicals. However, WO 2005/112740 A2 dispenses with a reference measurement, so that it is not generic for this reason alone.

On the other hand, DE 100 20 615 C2 discloses a more complex measuring setup, which in particular requires a reference sample, ie a measuring chemical, and thus ensures that the optical paths between light source and measuring detector on the one hand and light source and reference detector on the other hand each have identical Meßwegcharakteristika, so that in particular sample and reference sample can be reversed. For simple measurements such a non-generic measuring device is not suitable.

A generic arrangement is disclosed in EP 0 670 143 B1, in which an amplitude-modulated as well as wavelength-modulated radiation source is used, de amplitude modulation for varying a penetration depth of the light into a medium to be examined and the wavelength modulation for determining the first derivative of the Spectrum at a selected wavelength is used, including a lock-in is used. Ultimately, however, one must deduce exactly one wavelength from the concentration, which is associated with considerable uncertainties. [07] It is an object of the present invention to remedy this situation.

[08] As a solution, the invention proposes, on the one hand, a measuring device for optically determining the concentration of blood sugar and / or lactate in biological systems with at least one IR radiation source, which radiates IR light to a volume to be examined, with at least one measuring detector, which the light to be examined receives, and with at least one reference detector, which is supplied to the volume to be examined radiated IR light before entering the volume before, wherein the radiation source, the reference detector and the measuring detector via a lock-in with each other connected and between the IR radiation source and the measuring detector, an optical measuring path having a first Meßwegcharakteristik and between the IR radiation source and the reference detector, an optical reference path with a second, deviating from the first Meßwegcharakteristik Meßwegcharakteristik are formed and wherein the measuring device distinguished thereby t that the IR radiation source emits IR light in at least two discrete wavelengths or in at least two discrete wavelength bands on the volume to be examined.

[09] It should be pointed out in this connection that purely physically, the photons of the light which is fed to a detector are not available for further measurement. As used herein, the term "light" refers to a beam of photons from which a portion is or may be branched off for a reference measurement, so it is quite clear that photons used for the reference measurement are the volumes to be examined Nevertheless, relevant statements can be made about the nature of the IR light radiated onto the volume to be examined, since these photons originate from one and the same radiation source.

[10] On the other hand, the invention also proposes a method for the optical concentration determination of blood sugar and / or lactate in biological systems, in which IR light is irradiated along an optical measuring path to a volume to be examined and from the light emanating from the volume for the concentration of relevant value taking advantage of a taking place via an optical reference path reference measurement of the radiated to the volume to be examined IR light and a lock-in method is determined, wherein the optical reference path has a measurement path characteristic which deviates from the measurement path characteristic of the optical measurement path and which is characterized in that at least one component from a previously determined or known spectrum is selected at least one peak of interest and the value relevant for the concentration is determined by at least two within this peak, discrete wavelengths or wavelength bands are determined.

By reference measurement, it is possible to determine fluctuations in the radiated to the volume to be examined IR light and correct in this way the value determination accordingly. Thus, it is possible to minimize any temperature influences or even natural Liehe fluctuations of the radiation source and thus to increase the accuracy of the relevant value in relation to the actual concentration. By such a measure, the apparatus construction, which is indeed increased by the reference measurement per se, considerably simplify the effect that lower requirements can be made of the radiation source, so that it can be chosen much smaller and more manageable. In particular, it is possible to dispense with temperature-stabilizing measures or other measures which appear necessary for stabilizing the radiation source, which considerably reduces the apparatus design as a whole.

A structurally simple embodiment can be realized by a beam splitter, which is arranged between the volume to be examined and the radiation source. In this case, the beam splitter is preferably aligned such that a part of the light emitted by the radiation source is directed to the reference detector. In this way structurally very simple a reference measurement can be made.

It may also be advantageous if the beam splitter is aligned such that at least a portion of the outgoing of the volume of light is directed to the measuring detector. Such a configuration can for example be selected such that the volume to be examined, such as a finger, an earlobe or an arm, is arranged between the beam splitter and the measuring detector. This applies in particular to the case that an absorption measurement of the ER light is made. On the other hand, a reflection measurement and / or a measurement of otherwise emitted light, which by the stimulating IR light is stimulated to be measured, especially when this outgoing from the volume of light reaches the beam splitter and is guided by this starting to the measuring detector.

Accordingly, the measurement detector may, for example, be oriented linearly with respect to the volume-radiated HI light, which is advantageous in particular for absorption measurements. In particular, for reflection measurements, however, it may be particularly advantageous if the measurement detector is oriented at an angle with respect to the radiated IR radiation to the volume. By means of the latter measure, it can be avoided, in particular, that the ER light radiated onto the volume passes directly through the volume and reaches the measuring detector uninfluenced.

[15] A beam splitter is not mandatory for reference measurement. In an alternative embodiment, the reference detector may be directed, for example, to scattered light of the IR radiation source. Regardless of which light source is used, the generation of scattered light can hardly be avoided in light generation, since the resulting light is already partly refracted or otherwise distracted slightly in the radiation source itself. This applies in particular to laser light sources. In addition, due to the linear nature of photon propagation, laser light sources require two opposing mirrors, between which the laser state can form. One of the mirrors is chosen to be semi-permeable, so that the laser light can be coupled out for further use by means of this mirror. However, other coupling-out mechanisms are also conceivable, but they in turn generate scattered light which can be used for the reference measurement. Since, however, even an impermeable mirror usually allows a small amount of light to pass through or, if appropriate, be made slightly translucent, it is also readily possible for a laser to produce stray light or a small fraction of light from the side opposite the exit solid of the laser for reference measurements to use. The use of such stray or extraneous light for the reference measurement has the advantage that the main ray path between the IR radiation source and the volume is not hindered by the reference measurement. In this way, losses can be minimized, which in turn leads to a simplification of the equipment required for the desired measurement accuracy. [16] The lock-in method according to the invention and a lock-in according to the invention are known per se from the prior art in order to be able to eliminate statistical fluctuations which influence measurement results. In this case, an excitation signal which is directed to a sample is modulated, it being assumed that a response of the sample induced by the modulated excitation is modulated accordingly, so that in the detector all measurement signals which do not have a corresponding modulation are correspondingly eliminated and measuring signals which have the same modulation can be amplified accordingly. For such a modulation come, depending on the specific embodiment, both an amplitude and a frequency modulation in question. However, such lock-in methods are unusual in spectroscopic investigations, since such a modulation in the Fourier transform leads to disturbances. Even with chemical concentration determinations, such lock-in methods can not naturally be used.

By combining an optical concentration determination or the concentration determination via IR light with a lock-in method, however, statements can be made in great detail about the light emanating from the volume to be examined, which despite a relatively small outlay on equipment still lead to meaningful relevant values.

[18] Preferably, the reference detector is also connected to the IR radiation source via the lock-in, so that disturbance effects, such as, for example, noise, can also be detected here.

[19] As already indicated above, an amplitude modulation can be carried out for the lock-in method, which can be embodied in particular binary, that is to say "light on" and "light off". However, in particular in the case of an electronic embodiment of the lock-in, the amplitude modulation can be chosen to be much less aggressive and, for example, to a small amplitude fluctuations, for example in a window of less than 50% of the maximum strength, preferably less than 35% or less than 25%. In particular, the amplitude modulation can also be designed as a sine wave, and thus less aggressive than the square wave of a binary signal. [20] On the other hand, a wavelength modulation can be made, wherein the bandwidth of the wavelength modulation is preferably less than 20 nm, preferably less than 18 or less than 15 nm, which can be ensured in particular by the lock-in or by the wavelength modulation a meaningful peak of the spectrum of the component whose concentration is to be determined is not left. In this case, it goes without saying that supplementary measures may have to be provided in order to be able to determine absolute values from a lock-in absolute value generated via wavelength modulation, since in this case the first derivative of a spectrum is usually first measured. On the other hand, it is precisely the first derivative of a spectrum, in particular at suitable wavelengths, that can be at least as meaningful in terms of concentration as the spectrum itself.

[21] In the present case, in particular laser diodes can be used as radiation sources. At first glance, laser diodes are unsuitable for spectroscopic investigations, which are usually used to determine concentration, since they do not have the necessary bandwidth for spectroscopic investigations. On the other hand, such laser diodes have the advantage of a relatively good luminous efficacy, so that with relatively little equipment expense excellent radiation performance, especially in the IR range, can be achieved. Also, laser diodes can readily provide light for reference measurements, as has been generally explained in more detail above with reference to laser light sources.

Because of the low modulation capabilities of the laser diodes, it may be advantageous to provide two or more laser diodes, which may be particularly advantageous for time reasons, since a modulation of a laser diode, in particular over a bandwidth of more than 20 nm addition, is relatively time-consuming, because The laser diode takes some time to stabilize. In addition, the expenditure on equipment increases disproportionately with such a large bandwidth.

[23] If at least one second peak is selected and one of the two wavelengths or one of the two wavelength bands lies in this second peak, the measurement accuracy can be increased if necessary. Similarly, when selecting multiple peaks, too several components, in particular a biological system, are checked for their concentration.

[24] Depending on the specific implementation, it is particularly advantageous if different laser diodes or different IR radiation sources are used for the measurement at the different peaks.

[25] The relevant peaks, which are easily accessible with IR measurements, generally have a width of well over 200 nm. By using a wavelength band within a respective peak, a demand profile is created that is relatively inexpensive In particular, can also be realized by a laser diode. Thus, the effort to modulate the wavelength of a laser diode, but also another IR radiation source, in a wavelength band of less than 200 nm, preferably less than 170 nm, much lower than when several peaks detected - and therefore several 100 nm as bandwidth provided for the ER radiation source.

[26] The present invention is particularly suitable for embodiments in which the wavelength bands or the emission frequency of the IR radiation source is between 1000 nm and 2000 nm and / or between 2000 nm and 3000 nm. In these wavelength ranges, water, the major constituent of most biological systems, has a relatively low interaction with light. As a result, components that can be found in such an environment, better accessible to a measurement. It is understood that in other environments, where appropriate, other wavelength ranges can be used to advantage.

In concrete implementation of the method described here, it may on the one hand be advantageous to record only two measuring points at the selected peak, of which one measuring point is in a concentration-independent region of the selected peak, while the other one is as strong as possible from the concentration dependent region of the peak. From the slope between these two measuring points, a statement can then be made about the absolute concentration of the component to be examined in the volume, the measuring point then serving as a reference in the concentration-independent region. It It is understood that the two measuring points or the two corresponding wavelength bands do not necessarily have to be found in the same peak.

In this case, these two measuring points are controlled discretely, which can be realized on the one hand, for example, by two laser diodes or on the other hand by a laser diode whose wavelength is changed according to leaps and discretely. Although laser diodes can be stabilized relatively accurately to a few nanometers, this is relatively time-consuming, so that in particular two laser diodes are suitable for a discrete activation. On the other hand, the accuracy of the selection of the measuring points is not necessarily limited to less than one nanometer. Rather, it may be sufficient if the measurement points lie within a wavelength bandwidth below 20 nm. In this case, it is also possible in particular to modulate the frequency of the IR radiation source within the bandwidth of 20 nm in order to use this modulation for a lock-in method. On the other hand, it may also be advantageous to stabilize the IR radiation sources to less than 8 nm, preferably to less than 6 nm or less than 4 nm, and to adjust them accordingly in order to carry out the lock-in with a lower modulation or else by an amplitude-modulated lock. To realize in.

On the other hand, depending on the specific IR radiation source used, it may be advantageous to continuously modulate the IR radiation sources in a range below 170 nm, preferably below 150 nm or below 120 nm, and from this modulation the shape of the selected peak determine from which of the value relevant for the concentration can be determined. By means of such a large wavelength band, in particular a wavelength-modulated or wavelength-modulated lock-in can be realized very well.

[30] Although the above individually explained solutions are in themselves advantageous regardless of the other features of the other solutions. In practice, however, it has been found that, in particular through the combination of discrete wavelength measurements, reference measurements and lock-in in the absence of a reference sample, an apparatus construction can be created which is very small and ensures sufficient measurement accuracy and therefore also On-site measurements, especially by laymen, allows. [31] In particular, the omission of the measurement of a complex spectrum but the restriction to one or more individual peaks in the concentration determination allows a measurement with laser diodes, which only limited in their wavelength must be changed. Optionally, it is possible to dispense entirely with a change in wavelength by selecting only two measuring points or narrow wavelength bandwidths on a peak of interest, and exciting these by means of one respective laser diode. It goes without saying that by increasing the number of laser diodes, even more complex measuring operations can be carried out without significant loss of time.

Regardless of the asymmetry of the optical paths, ie the optical measuring path and the optical reference path, the use of multiple discrete wavelength bands, each of which is wavelength modulated, in an optical concentration determination of blood sugar and / or lactate in biological systems with at least one IR Radiation source, which radiates IR light to a volume to be examined, with at least one measuring detector, which receives light emitted from the volume to be examined, and with at least one reference detector, which the radiated to the volume to be examined IR light before entering the Volume is supplied, wherein the radiation source, the reference detector and the measuring detector connected via a lock-in, correspondingly advantageous. The same applies to a measuring method for the optical concentration determination of blood sugar and / or lactate in biological systems, in which IR light is irradiated to a volume to be examined and from the light emanating from the volume of a value relevant to the concentration using a reference measurement of the volume of irradiated IR light to be examined and a lock-in method are determined.

[33] In the present context, the term "peak" refers to a significant variation of a spectrum, which is characterized in particular by a maximum or minimum, ie an extremum, and two foot points, where the foot points do not have to be at identical levels, however As a rule, the concentration of the substance whose spectrum is being examined is much less dependent than the respective extreme points, In particular, as already explained in detail above, it is possible to have several peaks, possibly also only the extreme point of a peak and the base point of one peak other peaks, for the erfϊnstungsgemäßen measurements. Further advantages, objects and objects of the present invention will become apparent from the following description of the appended drawing, in which exemplary measuring devices according to the invention and process guides are shown. In the drawing: FIG. 1 shows a schematic structure of a first measuring arrangement; FIG. 2 shows a schematic structure of a second measuring arrangement;

FIG. 3 shows a schematic structure of a third measuring arrangement;

FIG. 4 shows a first possible process control;

Figure 5 shows a second possible process control; and

FIG. 6 shows a third possible procedure.

[35] The measuring arrangement according to FIG. 1 comprises a volume 1 in which the concentration of a component is to be determined. For this purpose, IR light 2 is irradiated to the volume 1, which is generated by an IR laser diode 3, via an optical fiber 4 and a Kolima- torlinse 5 and a beam splitter 6 to the volume 1 is supplied. The IR light 2 passes through the volume 1, the light 7 emanating from the volume 1 being bundled correspondingly into an optical fiber 9 via a collimator lens 8 and fed to a measuring detector 10.

[36] A portion of the IR light from the IR laser diode 3 is fed via the beam splitter 6 as reference light 11 via a further collimator lens 12 and a further optical fiber 13 to a reference detector 14. The light beam 2 and the detectors 10, 14 are metrologically connected to each other via a lock-in connection, not shown.

[37] In the case of the arrangement according to FIG. 2, which substantially corresponds to the measuring structure according to FIG. 1, so that identically effective assemblies are also numbered identically, slightly different assemblies are marked with the letter A, instead of an absorption measurement a reflection measurement takes place. The light 7A emanating from the volume 1 is directed to the collimator lens 8 at the beam splitter 6A, which is therefore effective both for the IR light 2 radiated to the volume 1 and for the light 7A emanating from the volume 1 already described above manner the measuring detector 10 supplied. With this arrangement, also other light, which is induced by the IR light 2, can be detected without further. In this respect, this arrangement is not based on reflection limited. It is understood that the detection arrangement of the collimator lens 8, optical fiber 9 and detector 10 can be provided elsewhere to detect light emanating from the volume 1.

In a departure from the arrangement according to FIG. 1, the arrangement of FIG. 3 utilizes scattered light or light 1 IA issuing through the rearward part of the IR laser diode 3 as the reference light. Incidentally, this arrangement corresponds to the embodiment of Figure 1 and is designed for absorption measurement.

[39] Figure 4 shows a section of a peak, which is selected from the known per se spectrum of the component whose concentration is to be determined. The section comprises a wavelength range of approximately 200 nm. As described above, a measurement is performed at two measurement points Pl and P2 whose wavelength separation is approximately 150 nm. Here, the measurement point Pl is selected to be within a range of the peak which is relatively independent of the concentration. The measuring point P2 has been placed in a range which, on the other hand, is as significant as possible in terms of concentration, so that the difference between these two measuring points can be deduced from the concentration, the measuring point P1 serving as a reference, so that external influences, in particular the influences other components of the biological system can be excluded or minimized. Even with this measure, the measurement setup can be realized cumulatively or alternatively substantially simply.

[40] As can be readily appreciated, such a measurement can be performed with the measurement arrangements outlined above by tuning the IR laser diode 3 to the respective wavelengths, respectively. On the other hand, it is immediately apparent to any person skilled in the art that, instead of an IR laser diode 3 or instead of an IR radiation source, two IR radiation sources which are tuned to the corresponding wavelengths can also be used.

[41] While in this embodiment, the IR laser diode is relatively accurately tuned and preferably kept constant with fluctuations of less than 1 nm when the measuring points Pl and P2 are recorded, the laser diode in the method example according to Figure 5 with a bandwidth of approx. 15 nm modulated to produce a lock In-V experience implement. The latter can be realized in the process control of Figure 4 via an amplitude modulation. In this respect, in the method example according to FIG. 5, wavelength bandwidths B1 and B2 are used instead of measuring points.

[42] On the other hand, the wavelength of the IR radiation source can also be modulated over a larger range, for example of approximately 150 nm, so that, in particular, the ranges B1 and B2, within which measurement results are recorded or used for concentration determination, are swept over can. Also from these measurements, which, however, will usually be very time consuming, relevant values can be determined via the concentration, whereby a lock-in can be realized by the appropriate modulation. However, it is also conceivable, despite a possible wavelength modulation with such a bandwidth to make an amplitude modulation and to use for the lock-in, while the modulation is used only for sweeping a corresponding wavelength band. In this context, it can be seen, in particular, that further wavelength bands, in particular also through the use of further IR radiation sources, can be tapped without further ado.

[43] As can be seen immediately, in the method examples according to FIGS. 4 and 5, the measuring points or wavelengths P1 and P2 or wavelength bandwidths B1 and B2 are discretely spaced from one another. The same applies to the wavelength bandwidths Bl and B2, within which the measurement takes place in the embodiment according to FIG.

[44] As can be seen immediately, the characteristic of the path which the light passes from the IR laser diode 3 to the measuring detector 10 and which can be referred to as the optical measuring path 15 differs in all embodiments from the characteristic of the path which the light from the IR laser diode 3 to reference detector 14 passes through and which can be referred to as optical reference path 16, since the measuring path 15 with a medium, which is located in the volume 1, comes into contact, the optical reference path 16 are not affected becomes. List of reference numbers:

1 measuring volume 8 collimator lens

2 IR light 9 optical fiber

3 IR laser diode 10 measuring detector

4 optical fiber 11 reference light

5 Kolimatorlinse I IA through the rear part of the IR

6 beam splitter laser diode 3 emitted light

6A beam splitter 12 collimator lens

7 out of the measuring volume outgoing 13 optical fiber

Light 14 reference detector

7A 15 optical measuring path starting from the measuring volume

Light 16 optical reference path

Claims

Patent claims:

1. Measuring device for the optical concentration determination of blood sugar and / or lactate in biological systems with at least one IR radiation source that radiates IR light onto a volume to be examined, with at least one measuring detector that records light emanating from the volume to be examined, and with at least one reference detector, to which the IR light radiated onto the volume to be examined is supplied before entering the volume, the radiation source, the reference detector and the measurement detector being connected to one another via a lock-in and an optical one between the IR radiation source and the measurement detector Measuring path with a first measuring path characteristic and between the IR radiation source and the reference detector an optical reference path with a second measuring path characteristic deviating from the first measuring path characteristic are formed, characterized in that the IR radiation source IR light in at least two discrete wavelengths or in at least two discrete wavelength bands onto the volume to be examined.

2. Measuring device according to claim 1, characterized in that a beam splitter is arranged between the volume to be examined and the radiation source in such a way that part of the light emanating from the radiation source is directed towards the reference detector and that at least part of the light emanating from the volume is directed at the measuring detector.

3. Measuring device according to claim 1, characterized in that the reference detector is directed towards scattered light from the IR radiation source.

4. Measuring device according to one of claims 1 to 3, characterized in that the measuring detector is aligned linearly with respect to the IR light radiated onto the volume.

5. Measuring device according to one of claims 1 to 3, characterized in that the measuring detector is aligned at an angle with respect to the IR light radiated onto the volume.

6. Measuring device according to one of the preceding claims, characterized in that the radiation source is a laser diode.

7. Measuring device according to claim 6, characterized in that the laser diode has an emission frequency between 1,000 nm and 2,000 nm and / or between 2,000 nm and 3,000 nm.

8. Measuring device according to claim 6 or 7, characterized by means for modulating the laser diode over a bandwidth of less than 170 nm, preferably less than 20 nm.

9. Measuring device according to claim 8, characterized by two laser diodes.

10. Measuring device according to one of the preceding claims, characterized by means for modulating the wavelength of the IR radiation source at least within a discrete wavelength band.

11. Measuring device according to claim 10, characterized in that the modulation means are operatively connected to the lock-in.

12. Method for the optical concentration determination of blood sugar and/or lactate in biological systems, in which IR light is irradiated along an optical measuring path onto a volume to be examined and a value relevant to the concentration is derived from the light emanating from the volume using an optical Reference measurement of the IR light radiated onto the volume to be examined as well as a lock-in method is determined, the optical reference path having a measurement path characteristic that deviates from the measurement path characteristic of the optical measurement path, characterized in that at least one component consists of a At least one peak of interest is selected from the previously determined or known spectrum and which contributes to the concentration ration relevant value is determined based on at least two discrete wavelengths or wavelength bands located within this peak.

13. The method according to claim 12, characterized in that at least one second peak is selected and one of the two wavelengths or one of the two wavelength bands lies in this second peak.

14. The method according to claim 12 or 13, characterized in that the relevant value is determined from the absorption of the IR light radiating through the volume.

15. The method according to any one of claims 12 to 14, characterized in that the relevant value is derived from the reflection of the IR light radiated onto the volume and/or from the light emission stimulated by the IR light radiated onto the volume

Volume is determined.

16. The method according to one of claims 12 to 15, characterized in that an amplitude modulation is carried out for the lock-Pn method.

17. The method according to any one of claims 12 to 15, characterized in that wavelength modulation is carried out for the lock-in method.

18. The method according to claim 17, characterized in that the wavelength modulation has a bandwidth of less than 20 nm, preferably less than 18 nm or less than 15 nm.

19. The method according to any one of claims 12 to 18, characterized in that the wavelength bands are each between 1,000 nm and 2,000 nm and / or between

2,000 nm and 3,000 nm.

20. The method according to any one of claims 12 to 19, characterized in that the width of the wavelength band is in a range below 170 nm, preferably below 150 nm or 120 nm.

21. The method according to any one of claims 12 to 20, characterized in that the wavelength band is traversed by a substantially continuous modulation of the wavelength.

22. Method according to one of claims 12 to 20, characterized in that at least two discretely spaced wavelength bandwidths are controlled within the wavelength band

23. The method according to claim 22, characterized in that at least one wavelength bandwidth is below 20 nm.

24. The method according to claim 23, characterized in that at least one wavelength bandwidth is below 8 nm, preferably below 6 nm or below 4 nm.