Miniature and High-Resolution Monochromatic Light Source for Measuring the Concentration of a Fluid Sample

Abstract

A small light source for coupling to a movable optical probe may include a light emitting diode (LED) for generating a probe signal of a first bandwidth, an optical coupler disposed adjacent to the LED and configured to couple the probe signal into the movable probe, and a narrow band pass filter configured to receive the probe signal of the first bandwidth and output the probe signal to the movable probe at a second bandwidth smaller than the first bandwidth.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the benefit of priority under 35 U.S.C. § 119 to U.S. Provisional Application No. 63 / 343,361, filed on May 18, 2022, entitled "COMPACT HIGH RESOLUTION MONOCHROMATIC LIGHT SOURCE FOR FLUID SAMPLE CONCENTRATION MEASUREMENT", the disclosure of which is hereby incorporated by reference in its entirety.

[0002] Embodiments of the present disclosure generally relate to spectroscopy, and more particularly, to solution analysis using a light source coupled to a variable path - length measurement system.

Background Art

[0003] Absorption spectroscopy is used to measure the composition and / or properties of materials in any phase, gaseous, liquid, or solid. For example, the optical absorption spectrum of a liquid substance may be measured to determine the concentration or other properties of a target species within the liquid medium. The absorption spectrum may provide a distribution of light attenuation (due to absorbance) as a function of light wavelength. In known spectrophotometers, the sample substance to be studied is placed in a transparent container, and electromagnetic radiation (light) of a known wavelength λ (i.e., ultraviolet, infrared, visible, etc.) and intensity I is then measured using an appropriate detector after passing through the transparent container.

[0004] Known ultraviolet (UV) / visible spectrophotometers utilize a container such as a standard cuvette, which may have a standard cm path length through which incident light is directed into the liquid containing the substance being measured. For a sample consisting of a single homogeneous substance with concentration c, the light transmitted through the sample follows the relationship known as Beer's law: A = εCL, where A is the absorbance (also known as the optical density (OD) of the sample at wavelength λ, where OD = -log of the ratio of transmitted light to incident light), ε is the absorption or extinction coefficient (usually constant at a given wavelength), C is the concentration of the sample, and L is the path length of the light through the sample. Thus, in principle, information regarding the concentration of a homogeneous substance can be determined based on the recorded light intensity of the signal passing through the sample container. However, under some circumstances, determination of concentration in such an apparatus can become difficult. In many cases, the target compound in the solution is very highly concentrated. For example, certain biological samples such as proteins, DNA, or RNA are often isolated at concentrations outside the linear range of the spectrophotometer when absorbance is measured. Therefore, in many cases, dilution of the sample is required to measure an absorbance value within the linear range of the instrument. Multiple dilutions of the sample are frequently required, which leads to both dilution errors and the removal of the diluted sample for any downstream applications. Therefore, it is useful to obtain existing samples without knowledge of their possible concentrations and measure the absorption of these samples without dilution. One resulting characteristic common to these known UV / visible spectrophotometers is that an accurate path length L must be known in order to perform accurate concentration measurements.

[0005] To address these issues, measurement techniques based on spectrophotometers with variable path lengths have been developed in recent years. This type of spectroscopy system may generally use a known light source such as a light source based on a UV / visible spectrophotometer. The light from the UV / visible spectrophotometer is then directed to a special probe of an analytical instrument configured to vary the path length L in a special sample chamber to facilitate the performance of multiple absorbance measurements. Thereby, during a series of measurements, while the probe is moved through a plurality of different positions so as to vary the path length L, the radiation generated from the light source of the UV / visible spectrophotometer is detected after passing through the sample chamber. Therefore, a series of measurements are made that generate different values of A for each value of different L without the need for knowledge of any specific path length L to determine the concentration C.

[0006] Such variable path length spectroscopy may be adapted to perform in-line measurements of samples while being guided through, for example, a production system, but the equipment required for such a measurement scenario may require significant installation effort and a substantial amount of space. For example, a UV / visible photospectrometer system used as a light source may occupy a space of tens of thousands of cubic centimeters (several cubic feet) and may have a weight of about several tens of kilograms. Therefore, the placement and operation of the spectroscopy system with respect to a production system or other experimental system that generates the fluid sample to be measured may be limited. Also, even when the UV / visible photospectrometer system is placed remotely, collecting data for each measurement of a given path length L may increase the overall measurement time for measuring changes in absorbance over multiple path lengths. In view of the above and other considerations, the present disclosure is provided. SUMMARY OF THE INVENTION

[0007] In one embodiment, a small light source for coupling to a movable optical probe is provided. The small light source includes a light emitting diode (LED) for generating a probe signal of a first bandwidth; an optical coupler disposed adjacent to the LED and configured to couple the probe signal into the movable probe; and a narrow band pass filter configured to receive the probe signal of the first bandwidth and output the probe signal to the movable probe at a second bandwidth smaller than the first bandwidth.

[0008] In another embodiment, a measuring device includes a small light source having a light emitting diode (LED) for generating a probe signal; and measuring equipment for receiving the probe signal. The measuring equipment may include a sample cell for containing a fluid sample, the sample cell including a cell wall. The measuring device may also include a probe configured to direct the probe signal through the sample cell, where the probe is movable along the probe direction relative to the cell wall to reduce the path length of the probe signal through the fluid sample, and a detector arranged to receive the probe signal after it has passed through the cell wall.

[0009] In another embodiment, a system for measuring the concentration of a material in a fluid sample is provided. The system may include a small light source having a light emitting diode (LED) for generating a probe signal, and measuring equipment for receiving the probe signal. The measuring equipment may include a sample cell for containing a fluid sample, the sample cell chamber including a cell wall. The measuring equipment further includes a probe including a probe tip configured to direct the probe signal through the sample cell, where the probe is movable along the probe direction relative to the cell wall to reduce the path length of the probe signal through the fluid sample; and a detector arranged to receive the probe signal after it has passed through the cell wall.

Brief Description of the Drawings

[0010] The accompanying drawings illustrate preferred embodiments of the disclosed method devised for practical use of the principle.

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Figure 1A

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Figure 1B

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Figure 2

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Figure 3

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Figure 5

DETAILED DESCRIPTION OF THE INVENTION

[0017] This embodiment presents a novel approach to variable path length spectroscopy and related measurement systems, including a small light source device. In particular, these embodiments may be based on absorption spectroscopy where changes in absorbance are used to determine the concentration of materials within a fluid sample.

[0018] According to embodiments of the present disclosure, a small light source is provided to be coupled to a variable path length measurement (VPT) device. The small light source and the VPT device together provide a flexible absorption spectroscopy apparatus that can be easily integrated into various production, research, and measurement systems, including chromatography systems, protein purification systems, filtration systems, and other fluid processing systems. In particular, the small light source device of the present embodiment may require a size of approximately 4 inches × 1.5 inches × 1.5 inches (10 centimeters × 3.75 centimeters × 3.75 centimeters) according to one non-limiting embodiment. The overall system size including the small light source and the VPT device may be approximately 12 inches × 12 inches × 6 inches (30 centimeters × 30 centimeters × 15 centimeters) in one non-limiting embodiment.

[0019] FIG. 1A shows an absorption spectroscopy apparatus shown as system 100 according to an embodiment of the present disclosure. System 100 may include a small light source 102, a measuring instrument 110 coupled to the small light source 102, and a detector 112 disposed adjacent to the measuring instrument 110.

[0020] The small light source 102 may include a light emitting diode (LED) 104, an optical coupler 106 disposed adjacent to the LED 104, and a narrow band pass filter 108 disposed adjacent to the optical coupler 106. According to an embodiment of the present disclosure, the LED 104 may represent a single LED or an array of LEDs that emit radiation at a single wavelength. In other embodiments, a plurality of LEDs may be provided, in which case a given LED emits radiation at a wavelength different from that of another LED.

[0021] Like known LEDs, LED 104 may emit radiation whose intensity as a function of wavelength is characterized by a single peak, which may be associated with a given type of LED such as a 272 nm LED, a 310 nm LED, etc. According to different embodiments of the present disclosure, LED 104 may emit unfiltered radiation 105 having a peak with a bandwidth or full width at half maximum between 10 nm and 50 nm. According to an embodiment of the present disclosure, when the unfiltered radiation 105 from LED 104 passes through the narrow band pass filter 108, the bandwidth of the filtered radiation 107 may be reduced to less than 1 nm, which is essentially monochromatic radiation. Therefore, the small light source 102 may be referred to as a monochromatic light source. In various embodiments of the present disclosure, the filtered radiation may have a peak wavelength in the range from ultraviolet (UV) to infrared (IR) wavelengths, more particularly between 250 nm and 1000 nm, and may have a bandwidth of less than 1 nm after exiting the small light source 102.

[0022] During operation, the filtered radiation 107 may be directed through the measuring device 110 and appear as attenuated radiation 111, which is detected by the detector 112. Although shown separately in FIG. 1A, in some embodiments, the detector 112 may form part of the measuring device 110. The operation of the measuring device 110 or its variants will be described in detail below.

[0023] However, briefly, the measuring device 110 uses a movable optical probe (not shown separately) to vary the path length L of the filtered radiation 107 passing through a given fluid sample (not shown) present within the measuring device 110. The detector 112 is configured to detect the intensity of the radiation shown as attenuated radiation 111 that has passed through a given fluid sample. According to Lambert-Beer's law, the concentration C of the material in the sample may be determined as A / eL, where A is the absorbance and e is the molar extinction coefficient. Further, A is determined as log 10 (I 0 / I), where I 0is the intensity of the filtered radiation 107, and I is the intensity of the attenuated radiation 111. Since the intensity of the attenuated radiation 111 varies according to the change in the path length L, the change in the absorbance A as a function of the change in the path length L can be directly determined using the change in I as a function of the change in the path length L. For example, the first path length L 1 at the intensity measurement value (I 1 ) and the second path length L 2 at the intensity measurement value (I 2 ), assuming that the change in I 0 can be ignored between them, DA can be directly determined as logI 1 -logI 2 . Further, from Lambert-Beer's law, DA / DL is equal to eC, where DL or its absolute value is equal to L 1 -L 2 . Thus, using the system 100, when the radiation passes through the measuring device 110, by varying the path length of the filtered radiation 107 (determining DL) and detecting the change in the intensity of the attenuated radiation 111 (determining DA), the concentration C of the material in the fluid sample may be easily determined.

[0024] According to an embodiment of the present disclosure where the bandwidth of the filtered radiation 107 is less than 1 nm, the system 100 may determine the concentration of the sample in the measuring device 110 in a wavelength range narrow enough to be regarded as single-wavelength or monochromatic radiation.

[0025] To highlight the advantages of the system of FIG. 1A, FIG. 1B shows a reference absorption spectroscopy apparatus shown as system 150. System 150 includes a known light source, where light source 152 may be referred to as a UV / visible spectrophotometer. Light source 152 may generate radiation over a range of wavelengths extending from near ultraviolet to the visible wavelength range. The radiation may be guided through an optical fiber or similar structure to measurement device 158. In some embodiments, measurement device 158 may operate to vary the path length L of the radiation from light source 152 passing through the fluid sample within measurement device 158. For each path length L, the absorption spectrum may be collected over a range of wavelengths between 200 nm and 700 nm, or any suitable wavelength. Again, concentration C may be determined by determining the change in absorbance. However, collecting intensity information at detector 112 for a given path length L may require a much longer duration over the spectral range from 200 nm to 700 nm compared to the system 100 detecting the intensity of monochromatic radiation. For example, collection of the absorption spectrum in the apparatus of FIG. 1B may be performed by continuously scanning a grating to generate different optical wavelengths guided through the fluid sample as a function of time. As an example, absorbance measurements using the apparatus shown in FIG. 1B may require about 20 seconds.

[0026] The inventors recognize that, for the purpose of measuring the concentration of a target material, in many cases, measurement of the change in the intensity of absorbance of a fluid sample containing the target material need only be performed over a narrow spectral range using essentially monochromatic radiation. Therefore, system 100 of FIG. 1A, by using an LED as the light source, can collect absorbance data almost instantaneously after triggering the LED, and the duration required to obtain each new absorbance measurement value at the new path length L is limited only to the time required to adjust the path length L of the radiation. Also, by having a small size, system 100 may provide an advantage in terms of flexibility of integration into processing systems including chromatographic systems, protein purification systems, filtration systems, and other fluid processing systems, as described above.

[0027] Figure 2 shows a side cross-sectional view of a small light source according to an embodiment of the present disclosure. The small light source 102A may be a modified form of the small light source 102 described above. In this embodiment, the small light source 102A includes a housing 202 that includes an LED 104, an optical coupler 106, and a narrow band pass filter 108.

[0028] The small light source 102A may also include a connector 204 for reversibly coupling to a measuring device such as the measuring device 110. In particular, the connector 204 functions as an adapter configured to reversibly couple the light source 102A to a movable optical probe, as will be further considered below. According to some embodiments, the small light source 102A may represent one light source of a set of similar light sources that are interchangeable to be connected to the measuring device 110. Each light source of the set of light sources may include an LED configured to emit radiation at a selected wavelength. Thereby, the small light source 102A can represent, according to non-limiting embodiments of the present disclosure, a 272 nm light source, a 280 nm light source, a 310 nm light source, etc. Thus, the small light source 102A may be easily interchangeable to adjust the wavelength of the filtered radiation 107 according to a given application. Thereby, a radiation source with a wavelength of 272 nm may be appropriate for examining the absorbance of the first material, while a radiation source with a wavelength of 310 nm may be appropriate for examining the absorbance of the second material. Of course, the characteristics of the narrow band pass filter 108 may also be adjusted in conjunction with the selection of the wavelength of the LED 104.

[0029] Figure 3 shows one modified form of the system of Figure 1. The system 100A includes a small light source 102 and a measuring device 110A connected to the small light source 102. In some embodiments, the small light source 102 may be configured similarly to Figure 2, where the housing 202 houses an LED, an optical coupler, a narrow band pass filter, and a connector. Therefore, the small light source 102 may be reversibly connected and separated from the measuring device 110A.

[0030] The measurement device 110A may include a movable optical probe, where the operation of the movable optical probe is described in detail with respect to FIG. 4 below. The measurement device 110A may include a sample cell 160, an inlet port 161 for containing a fluid sample, and an outlet port 163 for guiding the fluid sample out of the sample cell 160. Therefore, the measurement device 110A may be coupled to a processing system (not shown separately) and used to provide a dynamic measurement of the concentration C of the material in the sample fluid as the sample fluid passes through the measurement device 110A.

[0031] FIG. 4 shows another measurement system shown as a measurement system 250 according to a further embodiment of the present disclosure. The measurement system 250 is shown as being coupled to an external processing system represented as a processing system 180. Therefore, the processing system 180 may represent any suitable system that generates a fluid sample to be measured, such as the chromatographic system, protein purification system, filtration system, or other fluid processing system described above. The measurement system includes a measurement device 110B, as well as a small light source 102A and a drive component 176 coupled to the measurement device. According to some embodiments, the drive component 176 may be considered part of the measurement device 110B.

[0032] In the scenario of FIG. 4, the processing system 180 is shown as generating a fluid sample 182 that is directed through the measuring device 110B to measure the concentration C of the material in the fluid sample 182. In operation, the small light source 102A emits radiation from an LED selected to emit radiation at a target wavelength suitable for measuring the material in the fluid sample 182. The radiation may be provided as monochromatic radiation as a result of passing through the narrow bandpass filter in the small light source 102A as discussed above. The radiation is directed to enter and pass through the movable probe 172 along the probe axis 178. The movable probe 172 may be formed of a single optical fiber or a plurality of fibers suitable for transmitting radiation over a suitable wavelength range generated by the small light source 102A. These fibers may have different diameters depending on the use of the measuring device 110B. In various non-limiting embodiments, the diameter of the fiber ranges from about 0.005 mm to about 20.0 mm. The movable probe 172 may be fused silica, glass, plastic, or any transmissible material suitable for the wavelength range of the small light source 102A and the detector 112. After passing through the window 170, the radiation is detected using the detector 112, where suitable examples of the detector 112 include, among others, a photomultiplier tube, a photodiode, an avalanche photodiode, a charge-coupled device (CCD), and an intensified CCD.

[0033] In particular, the movable probe 172 is translatable along the probe axis 178 so as to move within the sample cell 160. As shown in FIG. 4, the movable probe may translate relative to the cell wall 162 of the sample cell 160 so as to vary the path length L of the radiation. In particular, the path length L represents the distance between the probe tip 172A and the lower portion of the cell wall 162. Thus, the value of L may correspond to the distance that the radiation travels through the fluid sample 182 when the fluid sample is disposed within the sample cell 160.

[0034] According to various embodiments of the present disclosure, a transparent window, shown as window 170, may be provided opposite to probe tip 172A. The window 170 may form, for example, a part of the lower portion of the cell wall 162 and may be suitable for transmitting wavelengths within the range of the measuring device 110B, such as from 200 nm to 1100 nm. For example, in embodiments where the wavelength of the radiation is within the ultraviolet range, a quartz window may be required. In various non-limiting embodiments where the sample cell 160 is coupled to a fluid line external to the processing system or apparatus, the volume of the fluid sample within the sample cell 160 may be in the range between microliters and multiple milliliters, while the path length L may be variable between 0 cm and several centimeters.

[0035] To facilitate concentration measurements using the technique where DA / DL is equal to eC, the drive component 176 may be a motor that translates the probe tip 172A along the probe axis 178. The drive component 176 may provide continuous movement or may be set to vary the path length L in precise steps. In various non-limiting embodiments, suitable examples of the drive component 176 include stepper motors, servos, piezoelectric, electric, and magnetic motors, or any device controllable to provide a variable path length L through the sample. The drive component 176 may be coupled to translate the movable probe 172 relative to the sample cell 160, while in some embodiments, the drive component 176 may drive the stage on which the sample cell 160 is placed such that the probe tip 172A moves relative to the sample cell 160. In some embodiments of gradual or stepwise movement, the movable probe 172 is moved relative to the sample cell 160 in increments in the range of 0.2 μm to 1 cm, and more particularly, in the range of 1 μm to 50 μm.

[0036] Note that FIG. 4 shows an embodiment of the measuring instrument 110B for "vertical alignment". Here, the sample cell 160 is disposed above the detector 112, and the probe tip 172A can move vertically, inside and outside the sample cell 160, such that the radiation emitted from the probe tip 172A travels through the fluid sample 182 in the sample cell 160 and impinges on the detector 112 disposed below. In a further embodiment, other orientations are possible, such as a flow cell system in which the detector and the probe tip are substantially horizontally aligned with respect to each other and the probe axis is horizontal along a horizontal plane. Regardless of the absolute spatial orientation or the movable probe 172 and the detector 112, according to various embodiments of the present disclosure, the probe axis generally extends perpendicular to the main plane of the detector 112.

[0037] Advantages obtained by the foregoing embodiments include the ability to provide higher quality light to the sample being measured as compared to systems based on known broadband spectrometers. The improved quality includes a more stable light source for a given radiation and a narrower full width at half maximum. The monochromatic light source of the present embodiment achieves better spectral resolution than a broadband spectrometer and maintains a much smaller form factor, making such a light source device particularly useful for applications where only a selected few wavelengths are used daily.

[0038] Furthermore, the size reduction and environmental design requirements (IP65+ / chemical compatibility) are unique to this type of device, enabling such a device to be placed in a GMP manufacturing environment, where such placement is not practical for conventional broadband spectrometers.

[0039] FIG. 5 shows an exemplary absorption spectrum according to an embodiment of the present disclosure. In this example, the graph of FIG. 5 shows the detected radiation intensity as a function of wavelength in the near UV range. Three spectra are shown, namely the spectrum shown as curve 502, the spectrum shown as curve 504, and the spectrum shown as curve 506, each of which is composed of a single monochromatic peak showing the detected intensity of the UV light emitted at 272 nm from the monochromatic source.

[0040] In accordance with various embodiments of the present disclosure, consistent with the foregoing embodiments, the peak may have a full-width at half-maximum of less than 1 nm. The spectrum represents data collected after radiation is emitted from a UV LED source and passes through a narrow-bandpass filter. Thus, spectrum 502 presents data collected in a first case, where, in that first case, the path length of the multi-monochromatic radiation is the path length L through the fluid sample disposed at a first position 1 and is directed through a probe that defines it. Similarly, curve 504 presents data collected in a second case, where, in that second case, the path length of the multi-monochromatic radiation is the path length L through the fluid sample disposed at a second position 2 and is directed through a probe that defines it, while curve 506 presents data collected in a third case, where, in that third case, the path length of the multi-monochromatic radiation is the path length L through the fluid sample disposed at a third position 3 and is directed through a probe that defines it. As described above, assuming that the concentration C is equal to DA / (DLe), since DL is given by L 2 -L 1 it follows that determining the difference in absorbance (DA) between curve 504 and spectrum 502 is directly related to C. Also, since DL is given by L 3 -L 2 it also follows that determining the difference in absorbance (DA) between curve 506 and curve 504 is directly related to C.

[0041] Note that the intensity of the 272 nm peak essentially corresponds to intensity I as discussed above, and the rate of increase of the intensity of the 272 nm peak with a change in the value of L is proportional to the change in absorbance DA / DL, or the slope coefficient m. Thus, in one case, the value of DA / DL or m may be determined by the measured values of the differences in I and L (curve 504 - curve 502) between the first case and the second case. Similarly, the value of m may be determined by the measured values of the difference in I (curve 506 - curve 504).

[0042] In summary, by providing a small monochromatic light source in combination with a VPT device, the present embodiment has demonstrated a novel and useful alternative to systems based on known broadband spectrometers, particularly for specific applications. Measurements performed using broadband optical scanning can provide the user with all the information necessary to analyze a sample, but such measurements require long data acquisition times and data analysis times. By providing individual wavelengths for analysis, the present embodiment enables the user to obtain only the information needed, without including irrelevant information. By thus focusing on a single individual wavelength, the acquisition time is reduced, enabling the user to make real-time process decisions and ensure the quality of the product being measured.

[0043] This configuration has been disclosed with reference to specific embodiments, but many modifications, alternatives, and changes to the described embodiments are possible without departing from the spirit and scope of the disclosed configuration as defined in the appended claims. Accordingly, this configuration is not intended to be limited to the described embodiments, but rather is intended to have the full scope defined by the language of the following claims and their equivalents.

Claims

1. A small light source for coupling to a movable probe, comprising: A light emitting diode (LED) for generating a probe signal with a first bandwidth; An optical coupler disposed adjacent to the LED and configured to couple the probe signal into the movable probe; and A narrow band pass filter configured to receive the probe signal with the first bandwidth and output the probe signal to the movable probe with a second bandwidth smaller than the first bandwidth The small light source is provided.

2. The small light source according to claim 1, wherein the first bandwidth is at least 10 nm and the second bandwidth is less than 1 nm.

3. The small light source according to claim 1, further comprising a housing for accommodating the LED, the optical coupler, and the narrow band pass filter.

4. The small light source according to claim 3, further comprising a connector for reversibly coupling to the movable probe.

5. The small light source according to claim 1, wherein the LED, the optical coupler, and the narrow band pass filter form a monochromatic light source.

6. The small light source according to claim 5, wherein the probe signal is characterized by a wavelength in the range from ultraviolet (UV) to infrared (IR), and has a monochromatic signal with a bandwidth of less than 1 nm after leaving the small light source.

7. A small light source having a light emitting diode (LED) for generating a probe signal; and A measuring device for receiving the probe signal, the measuring device comprising: A sample cell for accommodating a fluid sample, the sample cell including a cell wall; A probe configured to direct the probe signal through the sample cell, wherein the probe is movable along the probe direction with respect to the cell wall so as to reduce the path length of the probe signal through the fluid sample; and A detector arranged to receive the probe signal after passing through the cell wall Having The measuring device is provided.

8. The small light source is An optical coupler disposed adjacent to the LED; and A narrow band pass filter configured to receive the probe signal with the first bandwidth and output the probe signal with a second bandwidth smaller than the first bandwidth The measuring device according to claim 7, further comprising.

9. The measuring device according to claim 8, wherein the second bandwidth is less than 1 nm.

10. The measuring device according to claim 8, wherein the LED, the optical coupler, and the narrow band pass filter are arranged in a common housing.

11. The measuring device according to claim 10, wherein the small light source is reversibly attachable and detachable to / from the measuring device.

12. The measuring device according to claim 7, wherein the measuring device is configured to guide the fluid sample through the sample cell.

13. The measuring device according to claim 7, wherein the probe signal is characterized by wavelengths in the range from ultraviolet (UV) to infrared (IR), and has a monochromatic signal with a bandwidth of less than 1 nm after exiting the small light source.

14. A system for measuring the concentration of a material in a fluid sample, comprising: A small light source having a light emitting diode (LED) for generating a probe signal; A measuring device for receiving the probe signal, the measuring device comprising: A sample cell for containing the fluid sample, the sample cell including a cell wall; A probe including a probe tip configured to direct the probe signal through the sample cell, wherein the probe is movable along the probe direction with respect to the cell wall so as to reduce the path length of the probe signal through the fluid sample; and A detector arranged to receive the probe signal after passing through the cell wall. A system comprising.

15. The small light source further comprises: An optical coupler arranged adjacent to the LED; and A narrow band pass filter arranged to receive the probe signal of a first bandwidth and output the probe signal with a second bandwidth smaller than the first bandwidth. The system according to claim 14.

16. The system according to claim 15, wherein the probe signal is characterized by wavelengths in the range from ultraviolet (UV) to infrared (IR), and has a monochromatic signal with a bandwidth of less than 1 nm after exiting the small light source.

17. The system according to claim 15, wherein the LED, the optical coupler, and the narrow band pass filter are arranged in a common housing.

18. The system according to claim 14, wherein the small light source is reversibly attachable and detachable to / from the measuring device.

19. The system according to claim 14, wherein the measuring device is configured to guide the fluid sample through the sample cell.

20. The sample cell is An inlet port for receiving the fluid sample; An outlet port for guiding the fluid sample out of the sample cell; and A transparent window disposed between the probe tip and the detector The system according to claim 14, further comprising.

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