Apparatus for measuring the light absorbance of a substance, computer-implemented method, computer program and non-volatile data carrier

Abstract

An apparatus 100 for measuring the absorbance of a substance contains: a sample cell 140 passing through a flow (F) of a solution (S) containing said substance, at least two light sources (D1, D2) emitting light in a respective waveband, a reference photo detector 151 registering a first signal (sR) representing respective reference light intensities of the light emitted by the at least two light sources (D1, D2), and a sample cell photo detector 152 registering a second signal (sD) representing an intensity of a light beam (LB) having passed through the sample cell 140, which light beam is produced based on light emitted by at least one of the at least two light sources (D1, D2). A respective bundle of optical fibers (BF1, BF2) receives light from each of the at least two light sources (D1, D2, Dn) via an originating end (BFi), and outputs light via a terminating end. The terminating ends of the bundles of optical fibers are arranged in a common bundle of optical fibers (BFC) forming an output interface (BFo) feeding light to the light beam (LB) through the sample cell 140 and to the reference photo detector 151.

Description

[0001] Apparatus for Measuring the Light Absorbance of a Substance, Computer- Implemented Method, Computer Program and Non-Volatile Data Carrier

[0002] TECHNICAL FIELD

[0003] The present invention relates generally to detecting the presence of and measuring the concentration of substances by studying their absorption of light. Especially, the invention relates to an apparatus for measuring the light absorbance of a substance according to the preamble of claim 1. The invention also relates to a computer-implemented method for controlling the proposed apparatus, a computer program and a non-volatile data carrier storing such a computer program.

[0004] BACKGROUND

[0005] Many substances absorb ultra violet or visible light due to their chemical composition. The absorption of light by substances has been used as the basis for detecting the presence of, and measuring the concentration of, such substances for many years. The concentration of the substance can be determined by use of the Beer Lambert Law:

[0006] A = Ebe where: A is light absorbance;

[0007] E is the molar light absorptivity with units of L mol- 1cm- 1; b is the light path length of the sample defined in cm; and c is the concentration of the compound in solution, expressed in mol- 1.

[0008] The Emax represents the maximum absorption of a substance at a given wavelength.

[0009] The UV region can be considered to consist of light of wavelength in the region of 1 nm to 400 nm, light of wavelength of 180 nm to 300 nm being known as deep UV.

[0010] Most analytical instruments for detecting substances which absorb in the deep ultra violet (UV) region use a mercury-lamp, deuterium lamp or xenon flash lamp as a light source. One example of such an instrument is a flow cell in which a solution containing one or more UV absorbing substances is passed between a UV light source (e.g. a mercury-lamp) and a UV detector (e.g. a photomultiplier or a photodiode) and changes in the intensity of UV light reaching the detector are related to the concentration of UV absorbing substances in the solution.

[0011] The detection of proteins, nucleic acids and peptides are of great importance in many sectors, including the environmental, biological and chemical sciences. Proteins have mainly two absorption peaks in the deep UV region, one very strong absorption band with a maximum at about 190 nm, where peptide bonds absorb, and another less intense peak at about 280 nm due to light absorption by aromatic amino acids (e.g. tyrosine, tryptophan and phenylalanine)

[0012] Nucleic acids absorb UV light at around 260 nm, some of the subunits of nucleic acids (purines) having an absorbance maximum slightly below 260 nm while others (pyrimidines) have a maximum slightly above 260 nm.

[0013] Almost all proteins have a maximum absorbance at about 280 nm due to the content of the light absorbing aromatic amino acids. The light source in the detectors of analytical systems used to detect and measure protein concentrations has historically been the mercury-line lamp. Mercury produces light with a wavelength of 254 nm but not at 280 nm, so a fluorescence converter is needed to transform the 254 nm light produced by the mercury lamp to longer wavelengths and a band pass filter is used to cut out a region around 280 nm. Mercury lamps have relatively short lifetimes and can prove unstable with time; furthermore, the disposal of these lamps can lead to environmental problems. The other lamps used to generate ultra violet light, such as the deuterium and the xenon flash lamps, disadvantageously require high voltages, need complicated electronics and often prove unstable with time. All of the currently used ultra violet light sources are relatively large and are consequently unsuitable for miniaturization of analytical instruments. Moreover, all of the lamps generate significant amounts of heat due to the high voltages required for their operation.

[0014] Light emitting diodes (LED) of type AlGaN / GaN with emissions in the 250 nm to 365 nm range have been developed. Sensor Electronic Technology, Inc. (Columbia, S.C., USA) have pioneered the development and use of these UV light emitting diodes, particularly for irradiating and sterilizing fluids such as biologically contaminated water. Other groups have also employed UV light emitting diodes for water purification systems (e.g. Phillips Electronics.

[0015] LEDs, which emit in the visible region of the spectrum, have been used for indirect photometric detection (Johns C., et al. (2004) Electrophoresis, 25, 3145-3152) and fluorescence detection of substances in capillary electrophoresis (Tsai C., et al. (2003) Electrophoresis, 24, 3083-3088). King et al. (Analyst (2002) 127, 1564- 1567) have also reported the use of UV light-emitting diodes which emit at 379.5 nm for indirect photometric detection of inorganic anions.

[0016] The use of deep UV light emitting diodes as light sources in detection systems for nucleic acids is disclosed in US 2005 / 0133724. A narrow bandwidth compared to the natural bandwidth of the sample, preferable a ratio of 1 to 10, provides a good linearity of the response and a broad dynamic range. (Practical Absorbance Spectrometry. Ed. A Knowles and C. Burgess, Chapman and Hall, New York).

[0017] WO 2017 / 144719 shows an apparatus for measuring the absorbance of a substance in a solution, which apparatus comprises least one sample cell arranged to contain said solution that is at least partially transparent to light of a predefined wavelength spectrum, at least two light passages through said at least one sample cell, each of said light passages having a known path length, an LED light source arrangement comprising at least two LEDs, each arranged to emit a light output with a wavelength within said predefined wavelength spectrum, wherein a plurality of optical fibers, one for each light passage, is arranged at each LED for receiving said light output and guiding it to the light passages.

[0018] US 9,322,772 discloses is an apparatus for measuring the absorbance of a substance in a solution, which apparatus comprises: a sample cell of known path length (b) for containing said solution, said cell being transparent to light of a predefined wavelength spectrum; ii) plural LED's each being independently operable by means of a controller each for emitting light, within said predefined wavelength spectrum, along a light path; iii) a band pass filter in the light path; iv) a beam splitter for dividing light from said source propagating along the path into a first portion and a second portion, said first portion being directable by the beam splitter toward a reference detector and said second portion being directable into the cell; v) a reference detector for detecting the intensity of said first portion of light directed by said beam splitter; and vi) a sample detector for detecting the intensity of the second portion propagating from the cell; the apparatus allowing a sample in the cell to be inexpensively subj ected to more than one wavelength of light for quicker or more accurate analysis.

[0019] Although the above apparatus provides many beneficial characteristics it has proven to have relatively low efficiency with respect to the amount of light from the LEDs entering the sample cell.

[0020] SUMMARY The obj ect of the present invention is therefore to offer a solution that addresses the above problem and provides a more efficient use of the emitted light.

[0021] According to one aspect of the invention, the obj ect is achieved by an apparatus for measuring the light absorbance of a substance. The apparatus contains a sample cell, at least two light sources, a reference photo detector, a sample cell photo detector and at least two bundles of optical fibers. The sample cell is configured to pass through a flow of a solution containing the substance to be examined with respect to its light absorbance. Each of the at least two light sources is configured to emit light in a respective waveband. The reference photo detector is configured to register a first signal representing respective reference light intensities of the light emitted by the at least two light sources. The sample cell photo detector is configured to register a second signal representing an intensity of a light beam having passed through the sample cell. Here, the light beam is produced based on light emitted by at least one of the at least two light sources, however only one light source at a time. Each bundle of the at least two bundles of optical fibers is configured to receive light emitted by a respective one of the at least two light sources via an originating end, and output light via a terminating end. The terminating ends of the at least two bundles of optical fibers are arranged in a common bundle of optical fibers forming an output interface that is configured to feed light to the light beam through the sample cell and to the reference photo detector.

[0022] The above apparatus is advantageous because the bundles of optical fibers enables feeding more light from each light source into the sample cell in a very efficient manner. Namely, it is relatively straightforward to arrange a number of optical fibers at a light source such that the amount of light received from that light source increases by a factor equivalent to the number of optical fibers used. Additionally, compared to a single-fiber design, it is easier to position the fiber connector with high accuracy in the center of the optical path and consequently attain high efficiency in the light transmission. Moreover, a bundle of optical fibers with a combined effective cross section area is more flexible, i.e. may be bent more sharply, than a single optical fiber of the same effective cross section area. Thus, the overall design of the apparatus can be made comparatively compact.

[0023] According to one embodiment of this aspect of the invention, the output ends of the at least two bundles of optical fibers are fused together in the output interface. This causes the emitted light energy to be more concentrated, which improves the detection capabilities of the light beam that is fed through the sample cell . According to another embodiment of this aspect of the invention, each of the at least two bundles of optical fibers contains at least three, preferably five to seven, optical fibers. Namely, these numbers of cooperating optical fibers have proven to strike a good balance between energy efficiency, quality and cost.

[0024] According to yet another embodiment of this aspect of the invention, a terminating optic filter is arranged at the output interface. The terminating optic filter is configured to only allow light in a first specified waveband to pass, which first specified waveband includes the respective wavebands of the light emitted from the at least two light sources. Consequently, it is ensured that exclusively light with the desired characteristics is fed through the sample cell, which, in turn, vouches for measurement results of high quality.

[0025] Alternatively, or in addition thereto, according to one embodiment of this aspect of the invention, a respective originating optic filter is arranged at the originating end of each of the at least two bundles of optical fibers. Here, each respective originating optic filter is configured to only allow light in a respective second specified waveband to pass, which respective second specified waveband is unique for the respective one of the at least two light sources from which the originating end receives emitted light.

[0026] According to further embodiments of this aspect of the invention, the apparatus either contains a beam-splitter or an optical waveguide configured to divert a portion of the output light from the output interface to the reference photo detector. Hence, the reference photo detector may register any intensity variations in the light emitted from the light source in an efficient manner.

[0027] According to yet another embodiment of this aspect of the invention, the sample cell contains a collimating lens that is configured to receive light from the output interface of the common bundle of optical fibers and produce the light beam being fed through the sample cell. Thereby, the light rays in the light beam are aligned to travel in parallel with one another through the sample cell. This improves the efficiency and the accuracy of the measurements.

[0028] According to a further embodiment of this aspect of the invention, the apparatus includes a controller configured to obtain the first signal registered by the reference photo detector while each of the at least two light sources emits light, and in response thereto calibrate the sample cell photo detector with respect to any changes in the intensities of the light emitted from the at least two light sources. Thus, consistent measurements may be ensured. Preferably, the controller is further configured to calibrate the sample cell photo detector with respect to a dark current registered by the sample cell photo detector when none of the at least two light sources emits light. Thus, for example, the dynamic range of measurements may be increased and / or non-linearity at high absorbance may be reduced.

[0029] According to another embodiment of this aspect of the invention, each optical fiber in the at least two bundles of optical is of multimode type. This allows a comparatively large amount of light energy emitted from the light source to be transferred to the sample cell. Preferably, each optical fiber in the at least two bundles of optical fibers further has a non-circular core, for example with a cross section shape being hexagonal or octagonal. Namely, this enables the light transmitting portions of the fibers to brought closer to one another in the originating and terminating ends. This, in turn, renders the transmission of light efficient and further concentrates the light energy being fed into the sample cell.

[0030] According to another aspect of the invention, the obj ect is achieved by a computer- implemented method for operating the above apparatus, which method is performed in at least one processor and which method involves: controlling light to be emitted from the at least two light sources, which each emits light in a respective waveband; obtaining a first signal via a reference photo detector, which first signal represents respective reference light intensities of the light emitted by the at least two light sources; and obtaining a second signal via a sample cell photo detector, which second signal represents an intensity of a light beam having passed through the sample cell, and which light beam is produced based on light emitted by at least one of the at least two light sources. Specifically, the method involves controlling the at least two light sources such that light is emitted from the at least two light sources according to a repeating sequence, wherein light is exclusively emitted from one of the at least two light sources at a time, and the repeating sequence has a repetition frequency above 5 Hz. Thereby, light of two or more different wavebands may be passed essentially simultaneously through the sample cell. This, in turn, allows for absorption measurements of very high quality and accuracy.

[0031] Further advantages, beneficial features and applications of the present invention will be apparent from the following description and the dependent claims.

[0032] BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The invention is now to be explained more closely by means of preferred embodiments, which are disclosed as examples, and with reference to the attached drawings.

[0034] Figures 1 -3 show schematic views of the apparatus according to embodiments of the invention;

[0035] Figures 4-9 illustrate how bundles of optical fibers may be arranged in the originating end according to embodiments of the invention;

[0036] Figures 10- 1 1 show graphs illustrating how the light sources may be controlled according embodiments of the invention;

[0037] Figure 12 depicts a cable- and connector arrangement for connecting two light sources to a sample cell according to one embodiment of the invention;

[0038] Figure 13 shows a perspective view of a light-producing module of the proposed apparatus according to one embodiment of the invention;

[0039] Figures 14- 16 exemplify how the bundles of optical fibers may be arranged in the connectors according to one embodiment of the invention; and

[0040] Figure 17 illustrates, by means of a flow diagram, a method according to one embodiment of the invention for operating the proposed apparatus.

[0041] DETAILED DESCRIPTION

[0042] Figure 1 shows a schematic view of an apparatus 100 according to a first embodiment of the invention, which apparatus is arranged for measuring the light absorbance of a substance. The apparatus 100 contains: a sample cell 140, first and second light sources D I and D2 respectively, a reference photo detector 151 , a sample cell photo detector 152 and two bundles of optical fibers BF 1 and BF2 respectively.

[0043] The sample cell 140 is configured to pass through a flow F of a solution S containing the substance whose light absorbance is to be measured.

[0044] Each of the light sources D I and D2, which may be implemented by LEDs, is configured to emit light in a respective waveband. The reference photo detector 151 is configured to register a first signal SR representing reference light intensities of the light emitted by the light sources D I and D2. Figure 10a shows graphs illustrating how the light intensity ID I and ID2 of the light emitted by the light sources D I and D2 respectively may vary as functions of time t. Figure 10b shows a graph that illustrates how a wavelength X of the light registered by the reference photo detector 151 varies between a first wavelength i (e.g. 260 nm) and a second wavelength 2 (e.g. 280 nm) depending on whether the first light source D I or the second light source D2 emits light.

[0045] The sample cell photo detector 152 is configured to register a second signal SD representing an intensity of a light beam LB having passed a known length through the sample cell 140. The light beam LB is produced based on light emitted by the light sources D I and D2.

[0046] Specifically, a respective bundle of optical fibers BF 1 and BF2 is arranged to transfer light from each of the light sources D I and D2 to the light beam LB as well as to the reference photo detector 151. Here, a first bundle optical fibers BF 1 is configured to receive light emitted by the first light source D I via an originating end BFi of the first bundle optical fibers BF 1 and output light via a terminating end of the first bundle optical fibers BF I . A second bundle optical fibers BF2 is configured to receive light emitted by the second light source D2 via an originating end BFi of the second bundle optical fibers BF2 and output light via a terminating end of the second bundle optical fibers BF2. Further, the terminating ends of the first and second bundles of optical fibers BF I and BF2 are arranged in a common bundle of optical fibers BFC forming an output interface BFo that is configured to feed light to the light beam LB through the sample cell 140.

[0047] According to the embodiments of the invention, the sample cell 140 contains a collimating lens 141 configured to receive light from the output interface BFo and produce the light beam LB being fed through the sample cell 140. The collimating lens 141 , causes the light rays in the light beam be aligned and travel in parallel with one another through the sample cell. This improves the efficiency and the accuracy of the measurements.

[0048] According to the embodiment of the invention illustrated in Figure 1 , the apparatus 100 contains a beam-splitter 131 , which is configured to divert a portion of the output light from the output interface BFo to the reference photo detector 151.

[0049] To attain small mutual distances between the light-transporting cores of the optical fibers in the bundles of optical fibers BF I and BF2, the output ends thereof may be fused together in the output interface BFo. One specific example of how the bundles of optical fibers BF I and BF2 may be organized in the output interface BFo will be described below with reference to Figure 16. According to one embodiment of the invention, a terminating optic filter 120 is arranged at the output interface BFo. The terminating optic filter 120 is configured to only allow light in a first specified waveband to pass. The first specified waveband includes the respective wavebands i and 2 of the light emitted from the light sources D I and D2, however, preferably just a minimum of other wavebands. Thus, the characteristics of the light passed through the sample cell 140 via the light beam LB may be kept well controlled. This, in turn, vouches for high- quality measurements.

[0050] Figure 2 shows a schematic view of the apparatus 100 according to a second embodiment of the invention. In Figure 2, all reference signs that also occur in Figure 1 designate the same entities and signals as described above with reference to Figure 1.

[0051] The apparatus 100 in the embodiment of Figure 2 contains an optical waveguide 132 that is configured to divert a portion of the output light from the output interface BFo to the reference photo detector 151. Preferably, the optical waveguide 132 is represented by at least one optical fiber connecting the output interface BFo with the reference photo detector 151.

[0052] In the embodiment of Figure 2, the apparatus 100 contains a respective originating optic filter 121 and 122, which is arranged at the originating end BFi of each of the at least two bundles of optical fibers BF I and BF2 respectively. The originating optic filter 121 and 122 are configured to only allow light in a respective second specified waveband i and 2 to pass. Here, the respective second specified waveband is unique for the respective one of the at least two light sources D I and D2 from which the originating end BFi receives emitted light. Thus, the characteristics of the light passed through the sample cell 140 via the light beam LB may be kept well controlled. The originating-filter design is especially advantageous if the second specified wavebands i and 2 are separated from one another by a comparatively large amount. Namely, in such a case, the terminating optic filter 120 would need to have a relative wide bandwidth and thus allow also a considerable amount of undesired wavebands between i and 2 to pass.

[0053] Naturally, according to embodiments of the invention, the terminating optic filter 120 may be combined with one or more originating optic filters, for example as illustrated in Figure 3. In Figure 3, all reference signs that also occur in Figures 1 and / or 2 designate the same entities and signals as described above with reference to Figures 1 and / or 2. Figure 3 shows a schematic view of the apparatus 100 according one embodiment of the invention, where the terminating optic filter 120 is arranged at the output interface BFo. Moreover, a respective originating optic filter 121 , 122, ... , 12n is arranged at the originating end BFi of each of a respective bundle of optical fibers BF 1 , BF2, ... , BFn configured to transfer light from a set of light sources D I , D2, ... , Dn to the output interface BFo.

[0054] Analogous to the above, each originating optic filter 121 , 122, ... , 12n is configured to only allow light in a respective second specified waveband i, 2, . . . , Xn to pass. The respective second specified waveband is unique for the respective light sources D I , D2, ... , Dn from which the originating end BFi receives emitted light. Thus, the characteristics of the light passed through the sample cell 140 via the light beam LB may be kept very well controlled.

[0055] Figure 4 shows a first example of how a bundle of optical fibers may be arranged in the originating end BFi according to one embodiment of the invention. Here, the end surfaces of seven optical fibers 401 , 402, 403, 404, 405, 406 and 407 respectively are arranged close together such that a central optical fiber 407 is encircled by the remaining six optical fibers 401 , 402, 403, 404, 405 and 406. Consequently, the light receiving portions of the optical fibers essentially form a conj oined light receiving surface equivalent to seven times the size the light receiving portion of each individual optical fiber.

[0056] Figure 5 shows a second example of how a bundle of optical fibers may be arranged in the originating end BFi according to one embodiment of the invention. Here, the end surfaces of three optical fibers 501 , 502 and 503 respectively are arranged close together, so that the light receiving portions of the optical fibers essentially form a conj oined light receiving surface equivalent to three times the size the light receiving portion of each individual optical fiber.

[0057] Figure 6 shows a third example of how a bundle of optical fibers may be arranged in the originating end BFi according to one embodiment of the invention. Again, the end surfaces of three optical fibers 601 , 602 and 603 respectively are arranged close together, so that the light receiving portions of the optical fibers essentially form a conj oined light receiving surface equivalent to three times the size the light receiving portion of each individual optical fiber. However, in contrast to Figures 4 and 5, each optical fiber in the bundle of optical fibers has a non-circular core. More precisely, in Figure 6, the cross section of the non-circular core has a hexagonal shape. This is beneficial because it enables the light receiving portions of the optical fibers to be arranged with even less distances from one another. Thus, the conj oined light receiving surface may receive light from the light sources in a more efficient manner.

[0058] Figure 7 shows a fourth example of how a bundle of optical fibers may be arranged in the originating end BFi according to one embodiment of the invention. Here, the end surfaces of five optical fibers 701 , 702, 703, 704 and 705 respectively with a hexagonal-shaped core cross section are arranged close together, so that the light receiving portions of the optical fibers essentially form a conj oined light receiving surface equivalent to five times the size the light receiving portion of each individual optical fiber.

[0059] Figures 8 and 9 show fifth and sixth examples of how a bundle of optical fibers may be arranged in the originating end BFi according one embodiments of the invention. In both cases, the end surfaces of seven optical fibers 801 , 802, 803, 804, 805, 806 and 807 respectively and 901 , 902, 903 , 904, 905, 906 and 907 respectively are arranged close together, so that a central optical fiber 807 and 907 respectively is encircled by the remaining six optical fibers and the light receiving portions of al the optical fibers essentially form a conj oined light receiving surface equivalent to seven times the size the light receiving portion of each individual optical fiber.

[0060] In Figure 8, the core of each optical fiber has a hexagonal shape, whereas in Figure 9, the core of each optical fiber has an octagonal shape. Analogous to the above, in both cases, the light receiving portions of the optical fibers may be located closer to one another than if the cores had been of circular shape.

[0061] In general, to allow a comparatively large amount of light from the light sources to be transferred into the sample cell 140, the optical fibers in the bundles of optical fibers are preferably of multimode type, i.e. where the core diameter is fairly large and wherein multiple light modes may be propagated.

[0062] As described above, Figures 10a and 10b illustrate how the light intensity ID I and ID2 of the light emitted by from two light sources may vary as functions of time t, for example D I and D2 respectively of Figures 1 and 2.

[0063] Figure I l a shows graphs illustrating how the light intensities IDI , ID2, . . . , IDU of the light emitted by n light sources may vary as functions of time t, for example D I , D2, ... , Dn of Figure 3.

[0064] Figure 1 lb shows a graph that illustrates how a wavelength X of the light registered by the reference photo detector 151 varies between a first wavelength i, a second wavelength 2 and up to an n:th wavelength Xn depending on whether the first light source D I , the second light source D2, the n:th light source emits light. Hence, provided that the repetition frequency according to which the light sources are sequentially activated is sufficiently high, the output interface BFo may appear to emit light of all the wavelengths i, 2, ... , n essentially simultaneously. Preferably, the repetition frequency is above 5 Hz.

[0065] According to one embodiment of the invention, to ensure consistent measurements, the apparatus contains a controller 1 10 that is configured to obtain the first signal SR registered by the reference photo detector 151 while each of the light sources D I and D2, or D I to Dn, emits light. In response thereto the controller 1 10 is configured to calibrate the sample cell photo detector 152 with respect to any changes in the intensities ID I or ID2, or ID I to Ion respectively, of the light emitted from the light sources D I and D2, or D I to Dn.

[0066] Additionally, inter alia to increase the dynamic range of measurements and / or reduce non-linearity at high absorbance, according to one embodiment of the invention, the controller 1 10 is configured to calibrate the sample cell photo detector 152 with respect to a dark current registered by the sample cell photo detector 152 when none of the light sources D I , D2, ... , Dn emits any light.

[0067] Preferably, the controller 1 10 includes processing circuitry in the form of at least one processor 1 13 and a memory unit 1 15, i.e. non-volatile data carrier, storing a computer program 1 17, which, in turn, contains software for making the at least one processor 1 13 execute the actions mentioned in this disclosure when the computer program 1 17 is run on the at least one processor 1 13.

[0068] Figure 12 depicts a first cable 1201 with a first connector 121 1 and a second cable 1202 with a second connector 1212, which first and second cables 1201 and 1202 are j oined to form a common cable 1203 with a connector 1213 for connecting two light sources D I and D2 to the sample cell 140 according to one embodiment of the invention. In accordance with what has been described above referring to Figures 1 , 2 and 4 to 9, each of the first and second cables 1201 and 1202 contains a respective bundle of optical fibers BF 1 and BF2 that each is configured to receive light emitted by a respective one of the at least two light sources D I and D2 via an originating end BFi and output light via a terminating end.

[0069] Figure 14 illustrates the first connector 121 1 with a first contact pin 1221 containing a first light input interface 1401 housing the originating end BFi of the first bundle of optical fibers BF I , which originating end BFi is configured to receive light emitted from the first light source D I .

[0070] Figure 15 illustrates the second connector 1212 with a second contact pin 1222 containing a second light input interface 1502 housing the originating end BFi of the second bundle of optical fibers BF2, which originating end BFi is configured to receive light emitted from the second light source D2.

[0071] Figure 16 illustrates the third connector 1213 with a third contact pin 1223 containing a light output interface 1603 housing the output interface BFo with terminating ends of the first and second bundles of optical fibers BF I and BF2. Preferably, in the output interface BFo, the terminating ends of the first and second bundles of optical fibers BF I and BF2 are mixed relative to one another in different rows, for example as illustrated in Figure 16.

[0072] Figure 13 shows a perspective view of a light-producing module of the proposed apparatus 100 according to one embodiment of the invention. Here, a first compartment 1310 containing the first and second light sources D I and D2 respectively is arranged on a PCB (printed circuit board) 1300. The PCB 1300, in turn, is fitted into a holder 1330 connected to a second compartment 1320 housing the reference photo detector 151 (not shown). The second compartment 1330 is further configured to be attached to the sample cell 140 by a connector member 1340 via which the light beam LB may be passed through the sample cell 140 to the sample photo detector 152 as described above. The cables 1201 , 1202 and 1203 and the connectors 121 1 , 1212 and 1213 interconnect the first and second compartments 1310 and 1320, such that light emitted by the first and second light sources D I and D2 may be fed to the sample cell 140 and the reference photo detector 151.

[0073] Figure 13 also shows a first set of connector pins 1301 configured to be connected to drive circuitry for driving the first light source D I and a second set of connector pins 1302 configured to be connected to drive circuitry for driving the second light source D2.

[0074] In order to sum up, and with reference to the flow diagram in Figure 17, we will now describe the computer-implemented method for operating the apparatus 100, which method is carried out by the controller 110 according to one embodiment of the invention.

[0075] In a first step 1710, a first light source D I is controlled to emit light in a first waveband i. In a step 1720 parallel to step 1710, first and second signals are obtained. The first signal SR represents a reference light intensity ID I of the light emitted by the first light source D I . The second signal SD represents an intensity of a light beam LB having passed a known length through the sample cell 140, and which light beam LB has been produced based on the light emitted by the first light source D I .

[0076] In a step 1730 subsequent to step 1710, the first light source D I is deactivated, i.e. controlled to stop emitting light.

[0077] Thereafter, in a step 1740, a second light source D2 is controlled to emit light in a second waveband 2. In a step 1750 parallel to step 1740, first and second signals are obtained again. Here, the first signal SR represents a reference light intensity ID2 of the light emitted by the second light source D2, and the second signal SD represents an intensity of a light beam LB having passed the known length through the sample cell 140, and which light beam LB has been produced based on the light emitted by the second light source D2.

[0078] In a step 1760 subsequent to step 1740, the second light source D2 is deactivated, i.e. controlled to stop emitting light.

[0079] Thereafter, the procedure loops back to steps 1710 and 1720. The procedure is repeated at a repetition frequency above 5 Hz.

[0080] All of the process steps, as well as any sub-sequence of steps, described with reference to Figure 17 may be controlled by means of a programmed processor. Moreover, although the embodiments of the invention described above with reference to the drawings comprise processor and processes performed in at least one processor, the invention thus also extends to computer programs, particularly computer programs on or in a carrier, adapted for putting the invention into practice. The program may be in the form of source code, obj ect code, a code intermediate source and obj ect code such as in partially compiled form, or in any other form suitable for use in the implementation of the process according to the invention. The program may either be a part of an operating system, or be a separate application. The carrier may be any entity or device capable of carrying the program. For example, the carrier may comprise a storage medium, such as a Flash memory, a ROM (Read Only Memory), for example a DVD (Digital Video / Versatile Disk), a CD (Compact Disc) or a semiconductor ROM, an EPROM (Erasable Programmable Read-Only Memory), an EEPROM (Electrically Erasable Programmable Read-Only Memory), or a magnetic recording medium, for example a floppy disc or hard disc. Further, the carrier may be a transmissible carrier such as an electrical or optical signal which may be conveyed via electrical or optical cable or by radio or by other means. When the program is embodied in a signal, which may be conveyed, directly by a cable or other device or means, the carrier may be constituted by such cable or device or means. Alternatively, the carrier may be an integrated circuit in which the program is embedded, the integrated circuit being adapted for performing, or for use in the performance of, the relevant processes.

[0081] The term “comprises / comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components. The term does not preclude the presence or addition of one or more additional elements, features, integers, steps or components or groups thereof. The indefinite article "a" or "an" does not exclude a plurality. In the claims, the word “or” is not to be interpreted as an exclusive or (sometimes referred to as “XOR”). On the contrary, expressions such as “A or B” covers all the cases “A and not B”, “B and not A” and “A and B”, unless otherwise indicated. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

[0082] It is also to be noted that features from the various embodiments described herein may freely be combined, unless it is explicitly stated that such a combination would be unsuitable.

[0083] The invention is not restricted to the described embodiments in the figures, but may be varied freely within the scope of the claims.

Claims

Claims:1 . An apparatus (100) for measuring the light absorbance of a substance, which apparatus (100) comprises: a sample cell (140) configured to pass through a flow (F) of a solution (S) containing said substance, at least two light sources (D I , D2, Dn) configured to emit light in a respective waveband ( i, 2, n), a reference photo detector (151) configured to register a first signal (SR) representing respective reference light intensities (IDI, ID2, IDU) of the light emitted by the at least two light sources (D I , D2, Dn), and a sample cell photo detector (152) configured to register a second signal (SD) representing an intensity of a light beam (LB) having passed through the sample cell (140), which light beam is produced based on light emitted by at least one of the at least two light sources (D I , D2, Dn), characterized in that the apparatus (100) comprises: at least two bundles of optical fibers (BF 1 , BF2, BFn), which each is configured to: receive light emitted by a respective one of the at least two light sources (D I , D2, Dn) via an originating end (BFi), and output light via a terminating end, wherein the terminating ends of the at least two bundles of optical fibers are arranged in a common bundle of optical fibers (BFC) forming an output interface (BFo) configured to feed light to the light beam (LB) through the sample cell (140) and to the reference photo detector (151).

2. The apparatus (100) according to claim 1 , wherein the output ends of the at least two bundles of optical fibers are fused together in the output interface (BFo).

3. The apparatus (100) according to any one of the claims 1 or 2, wherein the each of the at least two bundles of optical fibers (BF I , BF2, BFn) comprises at least three optical fibers (401 , 402, 403, 404, 405, 406, 407; 501 , 502, 503 ; 601 , 602, 603 ; 701 , 702, 703, 704, 705; 801 , 802, 803, 804, 805, 806, 807; 901 , 902, 903, 904, 905, 906, 907).

4. The apparatus (100) according to any one of the preceding claims, comprising a terminating optic filter (120) arranged at the output interface (BFo), which terminating optic filter (120) is configured to only allow light in a first specified waveband to pass, which first specified waveband comprises therespective wavebands ( i, 2, n) of the light emitted from the at least two light sources (D I , D2, Dn).

5. The apparatus (100) according to any one of the preceding claims, comprising a respective originating optic filter (121 , 122, 12n) arranged at the originating end (BFi) of each of the at least two bundles of optical fibers (BF 1 , BF2, BFn), which respective originating optic filter (121 , 122, 12n) is configured to only allow light in a respective second specified waveband ( i; 2; n) to pass, which respective second specified waveband is unique for the respective one of the at least two light sources (D I , D2, Dn) from which the originating end (BFi) receives emitted light.

6. The apparatus (100) according to any one of the preceding claims, comprising a beam-splitter (131) configured to divert a portion of the output light from the output interface (BFo) to the reference photo detector (151).

7. The apparatus (100) according to any one of the claims 1 to 5, comprising an optical waveguide (132) configured to divert a portion of the output light from the output interface (BFo) to the reference photo detector (151).

8. The apparatus (100) according to any one of the preceding claims, wherein the sample cell (140) comprises a collimating lens (141 ) configured to receive light from the output interface (BFo) and produce the light beam (LB) being fed through the sample cell (140).

9. The apparatus (100) according to any one of the preceding claims, comprising a controller (1 10) configured to: obtain the first signal (SR) registered by the reference photo detector (151) while each of the at least two light sources (D I , D2, Dn) emits light, and in response thereto calibrate the sample cell photo detector (152) with respect to any changes in the intensities (IDI, ID2, IDU) of the light emitted from the at least two light sources (D I , D2, Dn).

10. The apparatus (100) according to claim 9, wherein the controller (1 10) is further configured to calibrate the sample cell photo detector (152) with respect to a dark current registered by the sample cell photo detector (152) when none of the at least two light sources (D I , D2, Dn) emits light.1 1. The apparatus (100) according to any one of the preceding claims, wherein each optical fiber in the at least two bundles of optical fibers (BF 1 , BF2, BFn) is of multimode type.

12. The apparatus (100) according to any one of the preceding claims, wherein each optical fiber in the at least two bundles of optical fibers (BF 1 , BF2, BFn) has a non-circular core.

13. The apparatus (100) according to claim 12, wherein a cross section of the non-circular core has either a hexagonal shape or an octagonal shape.

14. A computer-implemented method for operating the apparatus (100) according to any one of the preceding claims, which method is performed in at least one processor (1 13) and which method comprises: controlling light to be emitted from the at least two light sources (D I , D2, Dn) which each emits light in a respective waveband ( i, 2, n), obtaining a first signal (SR) via a reference photo detector (151), which first signal (SR) represents respective reference light intensities (IDI, ID2, IDU) of the light emitted by the at least two light sources (D I , D2, Dn), and obtaining a second signal (SD) via a sample cell photo detector (152), which second signal (SD) represents an intensity of a light beam (LB) having passed through the sample cell (140), and which light beam (LB) is produced based on light emitted by at least one of the at least two light sources (D I , D2, Dn), characterized by controlling the at least two light sources (D I , D2, Dn) such that light is emitted from the at least two light sources (D I , D2, Dn) according to a repeating sequence wherein light is exclusively emitted from one of the at least two light sources (D I , D2, Dn) at a time, and the repeating sequence has a repetition frequency above 5 Hz.

15. The method according to claim 14, further comprising: calibrating the sample cell photo detector (152) with respect to any changes in the intensities (IDI, ID2, IDU) of the light emitted from the at least two light sources (D I , D2, Dn) reflected by the first signal (SR) while each of the at least two light sources (D I , D2, Dn) emits light.

16. The method according to any one of the claims 14 or 15, further comprising: calibrating the sample cell photo detector (152) with respect to a darkcurrent reflected by the second signal (SD) when none of the at least two light sources (D I , D2, Dn) emits light.

17. A computer program (1 17) loadable into a non-volatile data carrier (1 15) communicatively connected to a processing unit (1 13), the computer program (1 17) comprising software for executing the method according any of the claims14 to 16 when the computer program (1 17) is run on the processing unit (1 13).

18. A non-volatile data carrier (1 15) containing the computer program (1 17) of the claim 17.

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