Field of the invention

The present invention relates to a breath analyzing system and method. In particular the invention relates to a breath analyzing system and method arranged to provide absorption information in at least two different wavelength bands and using the information from the wavelength bands to identify an unidentified substance from a set of preselected substances.

Background of the invention

Breath analyzing equipment is becoming increasingly common, not at least in vehicles as a measure to detect and prevent driving under the influence of intoxicating substances. The breath analyzing equipment may be a stand-alone, even handheld, unit that gives a measured value of the content of a substance or substances in the driver’s breath. Alternatively, breath analyzing equipment may be part of a system wherein also including equipment for identifying the driver and/or immobilizing the vehicle. Such breath analyzing equipment is typically permanently mounted in the vehicle and may be an integral part of the dashboard, for example. Breath analyzing equipment may also be stationary systems used to control access to a work area, a vehicle fleet depot or the like.

To provide a breath analyzer that has an appropriate sensitivity, is reliable and provides a reasonable fast analysis is far from trivial. This is especially true if the breath analyzing equipment should be able to detect a plurality of substances and not being disturbed by variation in moisture, CO2 content etc. Breath analyzing equipment that fulfills these requirements are described in for example US7919754 and US9746454, hereby incorporated by reference.

Breath alcohol analyzers based on non-dispersive infrared (NDIR) sensors commonly operate in the 9.4-9.6 pm wavelength range, as exemplified in the above referred patents. In this wavelength range ethyl alcohol has a strong absorption band with minor cross sensitivity to other substances. There are, however, challenges related to signal resolution, availability of infrared sources and detectors with adequate performance, and bulky design related to the long optical paths required. Operation in the 3.3-3.6 pm range offers several advantages but has been hampered by high cross sensitivity to many substances which may occur in breath due to endogenous or exogenous origin. Current state of the art breath alcohol analyzers operating in the 3.3-3.6 pm range are typically equipped with a chopper wheel with several optical filters to perform the analysis. US 4,268,751 discloses a breath alcohol analyzer with a chopper wheel with several optical filters and has the capability of distinguishing between ethyl alcohol and acetone by means of two narrow-band filters at 3.39 and 3.48 pm. The chopper wheel design, incorporating plurality of moving parts, is not suitable outside a laboratory environment. Additionally a multiplicity of narrow-band filters would be needed to discern between more substances than ethyl alcohol and acetone. This would make the detector even more complicated, costly and unsuited for vehicle mounted or handheld devices.

Summary of the invention

The object of the invention is to provide a breath analyzing system and method of operation that overcomes the drawbacks of operating in the 9.4-9.6 pm wavelength range and is suitable for being used in the field.

This is achieved by the breath analyzing method as defined in claim 1, and the breath analysis apparatus as defined in claim 20.

The breath analysis apparatus according to the invention for non-dispersive breath analysis operating in a preselected wavelength range of an unidentified substance , the breath analysis apparatus comprises:

- a measuring cell comprising non-dispersive infrared elements , the measuring cell comprising:

- a source configured to transmit an infrared beam and at least first detector (6) and a second detector of infrared radiation within said wavelength range,

- at least two concave mirrors arranged to control an infrared beam from said source to traverse the cell multiple times, thereby extending the optical path well beyond the physical dimensions of the cell,

- a first interference filter with a first characteristic transition wavelength combined with a first infrared detector arranged in the optical path and configured to transmit a first wavelength band within the preselected wavelength range through the filter to the first infrared detector while reflecting a second wavelength band within the preselected

wavelength range to be passed on to a second infrared detector, thereby the first infrared detector is configured to generate a first absorption signal associated to the first wavelength band and the second infrared detector is configured to generate a second absorption signal associated to the second wavelength band, wherein the first and second wavelength bands are at least to a major part separated by a preselected transition wavelength, li, in the wavelength range between 3.3 and 3.6 pm, and preferably between 3.4 and 3.5 pm.

According to an aspect of the invention the breath analysis apparatus further comprises a control unit arranged to receive at least the first and second absorption signals, the control unit configured to determine an absorption comparative value representing a comparison at least between the absorption in the first wavelength band and the absorption in the second wavelength band and a total absorption value representing a total absorption in at least the combined first wavelength band and the second wavelength band, and to compare the absorption comparative value and the total absorption value with tabulated data for a preselected set of substances arranged with corresponding values, and identifying the unidentified substance as the substance from the set of preselected substances representing the best match in terms of the absorption comparative values and the total absorption values.

According to an aspect of the invention the breath analysis apparatus further comprises an auxiliary sensor unit configured to identify the reception of a human breath sample by means of peak detection of at least one tracer gas and determining a tracer gas concentration value. The control unit is typically configured to also determine breath concentration value of the identified substance using the tracer gas concentration value.

The method according to the invention of identifying an unidentified substance from a set of preselected substances during breath analysis of a human breath sample in a measuring cell using non-dispersive spectroscopy in a preselected wavelength range comprises the steps of:

- recording at least a first signal from a first infrared detector and a second signal from a second infrared detector, wherein the first signal represents the absorption in a first wavelength band in the in the preselected wavelength range and the second signal represents the absorption in a second wavelength band in the preselected wavelength range, wherein the first and second wavelength bands are at least to a major part separated by a preselected transition wavelength, l ₍ ;

- determining an absorption comparative value representing a comparison of at least the absorption in the first wavelength band and the absorption in the second wavelength band; and

- determining a total absorption value representing a total absorption in at least the combined first wavelength band and the second wavelength band;

- comparing the absorption comparative value and the total absorption value with tabulated data for the preselected set of substances arranged with corresponding values, and

- identifying the unidentified substance as the substance from the set of preselected substances representing the best match in terms of the absorption comparative values and the total absorption values. According to an aspect of the invention the preselected transition wavelength of the measuring cell, l ₍ , is given by transition wavelength of the first interference filter, li, the first interference filter being a high-pass filter and transmitting wavelengths above the preselected transition wavelength, l ₍ , to the first infrared detector and passing wavelengths below the preselected transition wavelength, l ₍ , to at least the second infrared detector. Alternatively the first interference filter is a low-pass filter transmitting wavelengths below the preselected transition wavelength, l ₍ , to the first infrared detector and passing wavelengths above the preselected transition wavelength, l ₍ , to at least the second infrared detector.

According to an aspect of the invention the non-dispersive spectroscopy is infrared non- dispersive spectroscopy and the preselected wavelength range is 3.3 to 3.6 pm.

According to an aspect of the invention the method further comprises a step of identifying the reception of a human breath sample by means of peak detection of at least one tracer gas and determining a tracer gas concentration value. A breath concentration value of the identified substance may be determined using the tracer gas concentration value.

According to an aspect of the invention if the identified substance is not ethanol, an error indication is issued.

According to an aspect of the invention a subset from the set of preselected substances has been predefined and a further step of determining a breath concentration value of the identified substance wherein the tracer gas concentration value is utilized is performed only if the identified substance is one of the substances in the subset. The predefined subset typically comprises substances for which regulations defining a maximum allowed concentration in breath or blood exists.

According to an aspect of the invention the absorption comparative value is a ratio between the absorption in the first wavelength band and the absorption in the second wavelength band.

According to an aspect of the invention the total absorption is the sum of the absorption in the first wavelength band and the second wavelength band normalized with the tracer gas concentration value.

According to an aspect of the invention the tabulated data for the preselected set of substances has been arranged as tensor elements with coordinates representing absorption comparative values and a total absorption values for respective substance, and the step of comparing and determining comprises arranging the absorption comparative value and the total absorption value of the unidentified substance as coordinates in a corresponding multidimensional tensor, and quantifying the distance from the coordinates of the unidentified substance to at least a portion of the substances in the set of preselected substances and selecting the closest substance as the identified substance. The distances may be quantified by calculating the magnitudes and directions of the multidimensional tensors.

According to an aspect of the invention if a deviation in magnitude and direction between the unidentified substance and the identified substance is larger than a predetermined value, a notification is issued that identification of the unidentified substance could not be performed.

According to an aspect of the invention the preselected transition wavelength, l ₍ , is between 3.3 and 3.6 pm, and preferably between 3.4 and 3.5 pm.

According to an aspect of the invention the first wavelength band and the second wavelengths band overlaps partly.

According to an aspect of the invention a specific target substance has been preselected and by that selection a number of potential interfering substances are identified, and the selection of interferences filters, as well as the numbers of filters and detectors, has been performed to optimize the separation of the target substance from the identified potential interfering substances. The specific target substance is typically ethyl alcohol and the identified potential interfering substances includes at least one of the substances: methyl alcohol, acetone, isopropyl alcohol and 1 -propanol

According to an aspect of the method according to invention of the of recording comprises recording a first signal from a first infrared detector provided with a first interference filter with a first characterizing transition wavelength, a second signal from a second infrared detector provided with a second interference filter with a second characterizing transition wavelength and a third signal from a third infrared detector, wherein the first signal represents the absorption in a first wavelength band, the second signal represents the absorption in a second wavelength band and the third signal represents the absorption in a third wavelength band in the preselected wavelength range, wherein the first and second wavelength bands are at least to a major part separated by a preselected first transition wavelength, li,

corresponding to the first transition wavelength associated with the first interference filter and the second and third wavelength bands are at least to major part separated by a preselected second transition wavelength, i, corresponding to the second transition wavelength associated with the second interference filter; and

in the steps of determining the absorption comparative value and the total absorption value, the absorption values of the first, second and third wavelength bands are utilized.

According to an aspect of the invention the breath analysis apparatus further comprises:

- a second interference filter with a characteristic transition wavelength combined with the second infrared detector; and

- a third infrared detector, and the control unit is configured to:

-record a first signal from a first infrared detector, a second signal from a second infrared detector and a third signal from a third infrared detector, wherein the first signal represents the absorption in a first wavelength band, the second signal represents the absorption in a second wavelength band and the third signal represents the absorption in a third wavelength band in the preselected wavelength range, wherein the first and second bands are at least to a major part separated by the preselected first transition wavelength, li, and wherein the second and third bands are at least to a major part separated by the preselected second transition wavelength, li, given by the characteristic transition wavelength of the second interference filter; and

-to determine the absorption comparative value representing a comparison between the absorption in the first wavelength band, the absorption in the second wavelength band and the absorption in the third wavelength band and the total absorption value represents a total absorption in the combined first wavelength band, the second wavelength band and the third wavelength band.

Thanks to the invention it is possible to provide a breath analysis apparatus operating in the 3.3-3.6 pm range. Thereby the breath analysis apparatus for non-dispersive breath analysis can be made in a compact format due to a shorter optical path. It is further possible to use components such as radiation sources and detectors that are less costly than in higher wavelength ranges.

One advantage afforded by the present invention is to identify a substance from a set of preselected substances in a efficient manner and with equipment that is comparably simple, and therefore robust and less costly compared to prior art techniques. One further advantage is that it is possible to provide an accurate and reproducible separation of the 3.3-3.6 pm wavelength range into a first and second wavelength band by the uses of only one interference filter.

One further advantage is that it is possible to identify and discern between ethyl alcohol (ethanol) and a number of known“disturbing substances” by dividing the 3.3-3.6 pm wavelength range into only a first and second wavelength band and compare the absorption values according to the invention.

In the following, the invention will be described in more detail, by way of example only, with regard to non-limiting embodiments thereof, reference being made to the accompanying drawings.

Brief description of the drawings

Fig. l is a schematic illustration of a breath analysis apparatus according to the present invention;

Fig. 2 is a graph showing absorption of ethyl alcohol in the 3.3-3.6 pm wavelength range;

Fig. 3a is a graph showing interference filter characteristics with one interference filter with a cutoff wavelengths of 3.5 pm, 3b is a graph showing interference filter characteristics with two interference filter with a cutoff wavelengths of 3.5 pm 3.4 pm respectively, and 3c 3b is a graph showing bandpass interference filter characteristics with two interference filter with bandpass wavelengths centered around 3.35, 3.45 and 3.55 pm, respectively;

Fig. 4 is a graph illustrating the mapping of absorption characteristics of selected substances based on data of Table 1;

Fig. 5a-e are schematic graphs illustrated the timing pattern of breath related signals; and Fig 6 is a flowchart of the method according to the present invention.

Detailed description

Terms such as’’top”,“bottom”, upper”, lower”,“below”,“above” etc are used merely with reference to the geometry of the embodiment of the invention shown in the drawings and/or during normal operation of the helmet and are not intended to limit the invention in any manner.

The breath analysis apparatus 100 according to the invention is schematically depicted in Fig. 1, and comprises a non-dispersive infrared (NDIR) measurement cell 1. The measuring cell 1 is configured to be operative in a preselected wavelength range, the preselected wavelength range typically governing the majority of other design parameters such as light source, detectors, filters, optical path etc. The measuring cell 1 according to the invention intended for detection of ethyl alcohol is optimized for a wavelength range of 3.3 to 3.6 pm. Fig 2 shows the absorption spectrum of ethyl alcohol in the wavelength range of 3.3-3.6 pm The double peaks indicate that the CH bonds are affected by the presence of an OH-group in one of the two carbon atoms of the molecule. In the spectra of other substances, it is possible to find other characteristics of the spectrum connecting to the molecular structure.

As apparent for the skilled person a breath analysis apparatus also comprises for example a housing, a mouthpiece, air ducts, a power unit and typically one or more fans and steerable vents. The basic designs of breath analysis apparatuses for different purposes, e.g. stationary, handheld and vehicle mounted are known in the art, for example from US7919754 and US9746454 and are therefore not depicted or elaborated on herein.

The breath analysis apparatus 100 is provided with an inlet portion 100a for receiving a breath sample from a human being and an outlet portion 100b for the breath sample to exit from the measuring cell 1. The breath sample is passing through the measuring cell 1 as indicated by the vertical arrows at the inlet and outlet portions la, lb of the measuring cell 1. A beam of infrared radiation, indicated by dashed lines, is passing through the measuring cell in the transverse direction, starting from the light source 5 and being reflected multiple times I, II, III, IV, V, VI, VII VIII by concave mirrors 2, 3, 4 which are preferably designed and arranged according to the principles disclosed by J. U. White, J. Opt. Soc. Amer. 32 (1942), 285-288, a so called White cell configuration.

The light source 5 is an IR source being a black body emitter or light emitting diode, LED, operating within the preselected wavelength range. A suitable LED is made from multiple hetero-structures of III-V compounds with various constitution to operate as active layer and layers transparent to the emitted radiation. Both black body emitters, such as dedicated light bulbs and LEDs fulfill the necessary requirements for acting as suitable emitters in the system according to the invention.

The measuring cell 1 is provided with at least a first infrared detector 6 provided with a first interference filter 7 to precisely control the transmission and reflection of the infrared radiation. The transmitted portion of the infrared radiation is received by the first infrared detector and the reflected portion will after a number of reflections by the concave mirrors 2, 3, 4 be received by a second infrared detector 8. The infrared detectors/interference filters are typically provided on or near one of the concave mirrors 2, 3, 4. The second infrared detector 8 may be provided with a second interference filter 9 and further infrared detectors may be provided in the measuring cell 1. The interference filters 7, 9 typically include a transparent substrate with a multilayer thin film structure in which the layers have interchanging high and low index of refraction. The effect of this multilayer structure is to control the transmission and reflection properties of the filter. The transition wavelength, l*, is selectable by choice of materials and thicknesses of the multilayer structure. Typically interference filters suitable in the measuring cell 1 are high-pass or low-pass filters characterized by a transition wavelength l above which the filter is transmitting (reflecting) radiation, and below which the filter is reflecting (transmitting). The transition wavelength may also be referred to as the cut-off wavelength. Alternatively the interference filters are bandpass filters which transmit wavelengths in a defined portion of the spectra and reflects outside of that defined portion. Suitable filters are commercially available. The first and second wavelength bands should to the major part not overlap, although a minor overlapping portion is acceptable. The selection of first and second wavelength band will be further discussed below.

According to one embodiment of the invention the first and second wavelength bands are completely separated. This may be achieved by using bandpass interference filters for the first and second interference filters with their transmitting portions sufficiently far apart.

According to one embodiment of the invention the first and second wavelength bands overlap at the most 20 %, and e preferably at the most 10%.

According to one embodiment of the invention the first interference filter 7 is a high-pass or low-pass filter with a characteristic transition wavelength, li, and the second infrared detector 8 is not combined with any interference filter. The measuring cell 1 will facilitate detection in a first wavelength band and in a second wavelength band with only the first interference filter 7. The measuring cell 1 will be characterized by a preselected transition wavelength, l ₍ , separating the first and second wavelength bands. The preselected transition wavelength, l ₍ , is in this configuration given solely by the transition wavelength of the first interference filter, li.

To achieve a separation of the preselected wavelength range into two bands using only one interference filter could be advantageous according to some aspect since it is a simple and robust design and high reproducibility between different measuring cells 1 could be expected. This is of particular importance since the method of the invention utilizes comparison with tabulated values in the performed analysis to identify an unidentified substance. This comparison is sensitive to variations in the cells preselected transition wavelength, l ₍ , and therefore a simple, yet stable, configuration is advantageous. According to one embodiment of the invention the measuring cell 1 is provided with a first interference filter 7 with a first transition wavelength, li, a second infrared detector 8 provided with a second interference filters 9 with a second transition wavelength, %2, and a third infrared detector (not shown). Similar to what has been described above the measuring cell 1 will in this embodiment have a first, a second and a third wavelength band defining three regions in the preselected wavelength range 3.3 to 3.6 pm. The measuring cell 1 is characterized by a first preselected transition wavelength, la, separating the first and second wavelength band and a second preselected transition wavelength, X _& , separating the second and third wavelength band. The measuring cells first preselected transition wavelength, la,ΐb given by the transition wavelength of the first interference filter, li, and the second preselected transition wavelength, X _& , is given by the transition wavelength of the second interference filter, X2.

Detectors covering the 3.3-3.6 pm band are commercially available. Such detectors are typically photonic devices, e g photodiodes, having selective properties regarding responsivity to infrared radiation compared to e g thermopiles which are sensitive also to thermal effects due to convection or conduction.

Typical dimensions of the measuring cell 1 range between 14 x 16 x 6 mm and 90 x 50 x 30 mm with an optical path of 300 - 1000 mm depending on the actual application.

The measuring cell 1 may include an auxiliary sensor unit 11 with sensors 12 and control elements 13 with the objective of identifying a human breath and controlling the air flow through the measuring cell. These elements could preferably include means for the detection and quantification of a tracer gas, for example carbon dioxide or water vapor, which is inherently included in human breath.

The signals to and from the measuring cell 1 are controlled by an control unit 10 which is capable of real time signal processing and to execute preloaded and/or downloaded instructions. The control unit 10 may also be provided with communication means or connected to communications means for communication with for example a vehicle communication unit, a remote server etc. The communication may be wireless or wirebound.

As discussed in the background section a challenge in using the 3.3-3.6 pm range is the overlap of absorption signal between substances that could be present in a person’s breath sample or in the environment wherein the sample is taken. The latter is particularly problematic if so called passive breath analysis is utilized, i.e. breath analysis performed without the person blowing into a mouthpiece. It has commonly been believed that a detailed spectrum analysis measurement, as exemplified in Fig. 2, is needed to discern for example ethyl alcohol from acetone or methyl alcohol. This requires expensive and complicated equipment. The inventors have realized that a careful selection of a limited number of wavelength bands within the 3.3-3.6 pm range is sufficient to identify and discern between a substantial number of substances that are either known volatile substances, target substances” or substances that are commonly known to disturb the measurements of target substances.

Fig. 3a shows the two spectra, 32 and 33 associated with the embodiment using only one interference filter, in this case a high-pass interference filter with a transition wavelength, li, of 3.5 pm. The overlapping portion is depending on how sharp the transition is at the transition wavelength.

Fig. 3b shows the three spectra, 3 G, 32’ and 33’ associated with the embodiment a second interference filter and a further infrared detector (without filter), the second interference filter having a transition wavelength at 3.4 pm.

As discussed previously also bandpass interference filters could be used and Fig. 3c illustrates an embodiment wherein each three sensors are provided with bandpass interference filters: I the first interference filter 7 is configured to have the characteristic transmission illustrated by curve 33”, i.e. a center wavelength of 3.55 pm and a width of 0.10 pm. Interference filter 9 is configured to have the characteristic transmission illustrated by curve 32”, i.e. a center wavelength of 3.45 pm and a width of 0.10 pm. The third 9 is configured to have the characteristic transmission illustrated by curve 31”, i.e. a center wavelength of 3.35 pm and a width of 0.10 pm.

Both the embodiment referring to Fig 3b and 3c give two transition wavelengths at 3.4 and 3.5 pm, dividing the wavelength range 3.3-3.6 into three wavelength bands.

In table 1 spectroscopic data from thirty substances, representing a preselected set of substances, have been combined with the filter spectra 31731”, 32732” and 33733” to simulate absorption signals from the various wavelength bands, all normalized to ethanol (EtOH). The substances have been selected to represent gases which could be present in human breath for both endogenous and exogenous reasons. The spectroscopic data were obtained from Pacific Northwest National Laboratory, USA.

The six columns of Table 1 represent name of substance (left column), normalized absorption of the three wavelength bands (columns 2-4), the combined normalized absorption of the bands 3.4-3.5 pm and 3.5-3.6 pm (column 5), and the ratio between the absorption of the bands (column 6).

Fig. 4 is a graph using the data in column 5 in table 1 as x-axis and column 6 as y-axis. Each substance is represented by their coordinates in this two-dimensional graph. The coordinates are uniquely related to any one of the substances, although some of them are clustering in certain areas. To each coordinate a tensor can assigned and the magnitude and direction of the tensor is a unique property of each one of the listed substances and can be used to identified an unidentified substance. With the objective of identifying a certain unidentified substance, for example ethyl alcohol, its closest neighbors in the graph are isopropyl alcohol and methyl alcohol. Even though the magnitudes of their respective tensors do not differ very much, they may be distinguished from each other by different directions in the two-dimensional graph. Conversely, the tensors of 1 -propanol and pentane have almost the same direction as that of ethyl alcohol, but their magnitudes differ significantly.

The embodiment described in relation to figures 1 and 3a-b utilizing one interference filter provides absorption signals which may directly be compared to the graph of Fig. 4. From absorption signals from a breath sample comprising one or more unidentified substances, its coordinates can be calculated and compared with the library obtained from columns 5 and 6 of table 1. It is thus possible to identify a substance by its coordinates by measuring the distance between the coordinates of the unidentified sample and any of the substances in the library. Zero distance means unambiguous identification. A finite distance could either mean that more than one substance is present in the sample, or that there is a remaining

measurement error. By taking more samples, errors can be reduced.

The embodiment in relation to Fig 3c utilizing three wavelength bands is an extension by which a third dimension is added to the graph of Fig. 4. This implementation is useful to avoid the tendency of coordinate clustering illustrated in the graph of Fig. 4, and to improve the reliability of substance identification. These embodiments are illustrating the basic principle of using a multidimensional property to be represented as a tensor having the rank of the actual dimensionality of the implementation, the first and second embodiment having rank two and three, respectively.

Fig. 5a-e shows a typical timing pattern of signals from two consecutive breath samples obtained from the auxiliary sensor unit 11, see Fig. 1 and from the measuring cell 1. Peaks of carbon dioxide CO2 (a), water vapor H2O (b), air flow (c), and the NDIR bands below (d) and above 3.5 pm (e) occur almost simultaneously. By recording these signals their origin from a human breath can be established. The signal baselines between breaths provide important information concerning eventual background concentration of any of the key substances.

The method of identifying an unidentified substance from a set of preselected substances is illustrated in the flowchart of Fig. 6. The method is performed during breath analysis of a human breath sample in a measuring cell according to the invention with a preselected wavelength range, and the method comprises the steps of:

61 : recording at least a first signal from a first infrared detector provided with a first interference filter and second signal from a second infrared detector, wherein the first signal represents the absorption, Ai, in a first wavelength band in the in the preselected wavelength range and the second signal represents the absorption in a second wavelength band, A2, in the preselected wavelength range, wherein the first and second wavelength bands are at least to a major part separated and a preselected transition wavelength, l ₍ , is separating the first and second wavelength band

62: determining an absorption comparative value representing a comparison of at least the absorption, Ai, in the first wavelength band and the absorption, A 2, in the second wavelength band;

63 : determining a total absorption value representing a total absorption in at least the combined first wavelength band and the second wavelength band;

64: comparing the absorption comparative value and the total absorption value with tabulated data for the preselected set of substances arranged with corresponding values;

65: identifying the unidentified substance as the substance from the set of preselected substances representing the best match in terms of the absorption comparative values and the total absorption values. According to one embodiment the first infrared detector is provided with a first interference filter and the preselected transition wavelength, li, is the transition wavelength of the first interference filter thereby transmitting wavelengths above/below the preselected transition wavelength, li, to the first infrared detector and passing wavelengths below/above the preselected transition wavelength, li, to at least the second infrared detector. If wavelengths above/below the transmission wavelength is transmitted or reflected by the first interference filter 7 depends on if a high-pass or a low-pass configuration is utilized.

According to one embodiment, if the identified substance is not a predetermined target substance, for example ethyl alcohol, the method comprises the additional step, step 66, of issuing an error signal or message. Such an error message could include instructions to the user to move closer to the detector, to use a mouthpiece, if the first attempt was using passive detection, for example.

Typically the method also comprises a step, step 60a, of identifying the reception of a human breath sample by means of peak detection of at least one tracer gas, for example carbon dioxide and/or water vapor and a step, step 60b, of determining a tracer gas concentration value. This is preferably performed utilizing the auxiliary sensor unit 11. The identification of the reception of a human breath sample is used as a trigger for the further steps, which is exemplified in Fig. 5. In a step 67 a breath concentration value of the identified substance may be determined using the tracer gas concentration value is utilized.

According to one embodiment the absorption comparative value is a ratio between the absorption in the first wavelength band and the absorption in the second wavelength band, for example the ratio: A i/A 2.

According to one embodiment the total absorption is the sum, A1+A2 _, of the absorption in the first wavelength band and the second wavelength band preferably normalized with the tracer gas concentration value.

According to one embodiment a subset from the set of preselected substances has been predefined. The predefined subset could be a set of detectable substances for which legal regulations, limit values stipulated by an industrial standard, limits imposed by an employer or equivalent exists. Such substances will be referred to as substances for which a regulation defining a maximum allowed concentration in breath or blood exists. A further step of the method, step 67, comprises checking if the identified substance is one of the substances in the predefined subset. The step of determining a breath concentration value of the identified substance wherein the tracer gas concentration value is utilized may be performed only if the identified substance is in the subset.

According to one embodiment and with reference to the discussion referring to Table 1 and Fig. 4, the tabulated data for the preselected set of substances has been arranged as tensor elements with coordinates representing absorption comparative values and a total absorption values for respective substance The steps of comparing 64 and determining 65 comprises arranging the absorption comparative value and the total absorption value of the unidentified substance as coordinates in a corresponding multidimensional tensor, and quantifying the distance from the coordinates of the unidentified substance to at least a portion of the substances in the set of preselected substances and selecting the closest substance as the identified substance. Computationally this can be done by a number of known routines, for example transformation of the coordinates of the tensor to place the coordinates of the unidentified substance in origo and calculating the distances to the other substances. The distances may be quantified by calculating the magnitudes and directions of the

multidimensional tensors.

According to one embodiment if a deviation in magnitude and direction between the unidentified substance and the identified substance is larger than a predetermined value, a notification is issued that identification of the unidentified substance could not be performed.

According to one embodiment the preselected transition wavelength ,l ₍ , is between 3.3 and 3.6 pm, and preferably between 3.4 and 3.5 pm.

As discussed referring to Table 1 and Fig. 4 the choice of the characteristics of the interferences filters, as well as the numbers of filters (detectors) greatly effects the multidimensional separation of substances. According to one embodiment a specific target substance is identified, for example ethyl alcohol, and the selection of interferences filters, as well as the numbers of filters, is done to optimize the separation of the target substance from known“close neighbors”. According to one embodiment the specific target is ethyl alcohol and the filter parameters are selected to give a first preselected transition wavelength, la, of 3.5 pm. Alternatively the filter parameters are selected to give a first preselected transition wavelength, l ₍ , of 3.5 pm and a second preselected transition wavelength, l ₍ 2, of 3.4 pm. The control unit 10 of the breath analysis apparatus 100 according to the invention is configured to control and/or perform the method according to the invention. In particular the control unit 10 is configured to receive the signals (61) discussed in the method according to the invention and to perform the steps of determining an absorption comparative value 62, determining a total absorption value 63, comparing the absorption comparative value and the total absorption value with tabulated data 64 and identifying 65. The control unit 10 may further be configured to identify the reception of a human breath sample 60a and to determine tracer gas concentration value 60b.

According to one embodiment of the breath analysis apparatus 100 according to the invention, the first interference filter 7 is arranged in the optical path and configured to transmit a first wavelength band within the preselected wavelength range through the filter to be passed on to the first infrared detector 6 while reflecting a second wavelength band within the preselected wavelength range to be passed on to a second infrared detector 8, thereby the first infrared detector is configured to generate a first absorption signal, Ai, corresponding to the first wavelength band and the second infrared detector is configured to generate a second absorption signal, A2, corresponding to the second wavelength band. The control unit 10 is arranged to receive at least the first and second absorption signals and to output a result indicating the quantified presence or absence of the unidentified substance within the breath sample. The control unit 10 is configured to determine an absorption comparative value representing a comparison at least between the absorption in the first wavelength band and the absorption in the second wavelength band and a total absorption value representing a total absorption in at least the combined first wavelength band and the second wavelength band, and to compare the absorption comparative value and the total absorption value with tabulated data for a preselected set of substances arranged with corresponding values, and identifying the unidentified substance as the substance from the set of preselected substances representing the best match in terms of the absorption comparative values and the total absorption values.

The embodiments described above are to be understood as illustrative examples of the system and method of the present invention. It will be understood that those skilled in the art that various modifications, combinations and changes may be made to the embodiments. In particular, different part solutions in the different embodiments can be combined in other configurations, where technically possible.

Table 1 Absorption characteristics of selected substances relative to ethanol using three filters with center wavelengths 3.35, 3.45, and 3.55 pm, respectively defined by Fig. 3. Absorption data from Pacific Northwest National Laboratory, USA were used in the calculations. The entity A3.4-3.6 /AewH is the total absorption within the wavelength range 3.4 -3.6 pm normalized to the corresponding absorption of ethanol. A 3.s/A>3.s is the ratio between the absorption in the wavelength bands below and above 3.5 pm. * Carbon dioxide and Carbon monoxide do not show any absorption in these wavelength ranges and are not included in the graph of Fig. 4.