ATOMIC ABSORPTION SPECTROMETER

Abstract

The present disclosure relates to an atomic absorption spectrometer for analyzing a sample, including a radiation source unit for generating a measuring beam, an atomization unit for atomizing the sample such that the atomized sample is located in a beam path of the measuring beam, and a detecting unit for detecting absorption of the measuring beam. The radiation source unit includes at least one light-emitting diode. According to the present disclosure, the detection unit includes a polychromator arrangement, in particular a high-resolution polychromator arrangement, as a spectrometric arrangement.

Claims

1-15. (canceled)

16. An atomic absorption spectrometer for analyzing a sample, the atomic absorption spectrometer comprising: a radiation source unit configured to generate a measuring beam, wherein the radiation source unit comprises at least one light-emitting diode; an atomization unit configured to atomize the sample such that the atomized sample is disposed in a beam path of the measuring beam; and a detection unit configured to detect an absorption of the measuring beam, wherein the detection unit comprises a polychromator arrangement as a spectrometric arrangement.

17. The atomic absorption spectrometer of claim 16, wherein a geometry of the radiation source unit is configured such that the radiation source unit is adapted to geometrical conditions of the detection unit.

18. The atomic absorption spectrometer of claim 17, wherein the geometrical conditions of the detection unit include an entrance aperture of the spectrometric arrangement.

19. The atomic absorption spectrometer of claim 16, wherein the at least one light-emitting diode of the radiation source unit comprises at least two light-emitting diodes, wherein a first light-emitting diode generates light of at least a first wavelength or with wavelengths within a predefined first wavelength range, and wherein a second light-emitting diode generates light of at least a second wavelength different from the first wavelength, or with wavelengths within a predefined second wavelength range differing at least partially from the first wavelength range.

20. The atomic absorption spectrometer of claim 19, wherein each of the at least two light-emitting diodes is individually switchable.

21. The atomic absorption spectrometer of claim 19, wherein the radiation source unit is configured such that the light of the first light-emitting diode is directed into a first partial region of the detection unit and such that the light of the second light-emitting diode is directed into a second partial region of the detection unit.

22. The atomic absorption spectrometer of claim 19, wherein the radiation source unit is configured such that the light of the first light-emitting diode and the light of the second light-emitting diode is directed to the detection unit as a combined measuring beam.

23. The atomic absorption spectrometer of claim 19, wherein the at least two light-emitting diodes are arranged together on a carrier element.

24. The atomic absorption spectrometer of claim 23, wherein the carrier element is part of a positioning device configured to enable the at least two light-emitting diodes to be positioned relative to the detection unit.

25. The atomic absorption spectrometer of claim 19, further comprising an optical system configured to direct the light generated by the first light-emitting diode and/or the second light-emitting diode to the detection unit.

26. The atomic absorption spectrometer of claim 25, wherein the optical system comprises at least one mirror, an optical waveguide, a light guide rod, a light mixing rod, a grating and/or a planar waveguide structure.

27. The atomic absorption spectrometer of claim 26, wherein the at least one mirror is configured as a mirror, and/or the optical waveguide is an optical fiber.

28. The atomic absorption spectrometer of claim 25, wherein the optical system comprises at least one interference filter.

29. The atomic absorption spectrometer of claim 25, wherein the optical system comprises at least one Y-coupler, at least two fibers fused together and/or a planar structure.

30. The atomic absorption spectrometer of claim 16, wherein the polychromator arrangement has a resolution capability in the picometer range or less.

31. The atomic absorption spectrometer of claim 30, wherein the polychromator arrangement has a resolution capability of R=50,000 to 150,000.

32. The atomic absorption spectrometer of claim 31, wherein the polychromator arrangement comprises an echelle spectrometer, a Rowland circle spectrometer, or a virtually imaged phased-array spectrometer.

33. The atomic absorption spectrometer of claim 16, wherein the radiation source unit comprises the at least one light-emitting diode and at least one hollow-cathode lamp or UV radiation source.

Description

[0047] The invention is explained in greater detail below based on figures FIG. 1-FIG. 5. Illustrated are:

[0048] FIG. 1: a schematic representation of an atomic absorption spectrometer according to the prior art, in the form of (a) an atomic absorption spectrometer based on graphite furnace technology, and (b) a flame atomic absorption spectrometer;

[0049] FIG. 2: possible embodiments of a radiation source unit, with (a) a light-emitting diode, (b) a plurality of light-emitting diodes, and (c-e) adaptation of the geometry to the geometry of the detection unit;

[0050] FIG. 3 possible embodiments of a radiation source unit using a carrier element (a) without and (b, c) with geometric adaptation to the detection unit, as well as various options for positioning individual light-emitting diodes relative to the detection unit;

[0051] FIG. 4 possible embodiments of a radiation source unit with a plurality of light-emitting diodes whose light is directed jointly to the detection unit; and

[0052] FIG. 5 a preferred embodiment of a detection unit in the form of a Littrow arrangement with crossed echelle grating structure.

[0053] In figures, identical elements are respectively provided with the same reference symbols.

[0054] Shown in FIG. 1a is a schematic representation of an atomic absorption spectrometer 1 that uses graphite furnace technology. Starting from the radiation source unit 2, a measuring beam 3 is emitted which passes through the atomizing device 4 in the form of a graphite tube. An atomized sample to be examined is located in the atomizing device 4. The radiation source unit 2 has at least one lamp which is selected such that the measuring beam 3 contains the spectral lines of the element being sought in the sample. Absorption of the measuring beam 3 results in an attenuation, which can be detected in a detection unit 5 that follows the atomization device 4. The detection unit 5 comprises a spectrometric arrangement 6 and an optoelectronic sensor 7, which optionally possesses integrated or connected evaluation electronics.

[0055] In contrast to the atomic absorption spectrometer 1 in FIG. 1a, the spectrometer 1 shown in FIG. 1b is a flame atomic absorption spectrometer 1. In addition to components already described in reference to FIG. 1a, the shown spectrometer 1 has a mirror system 8 with two mirrors 8a, 8b for guiding the measuring beam 3. Further, in FIG. 1b the spectrometric arrangement 6, which may be a monochromator or polychromator, for example, is by way of example represented by an entrance slit 6b through which the measuring beam 3 passes into the detection unit 5.

[0056] The following description relates to possible embodiments for the radiation source unit 2. According to the invention, the radiation source unit 2 comprises at least one light-emitting diode (LED) 9 as shown by way of example in FIG. 2a.

[0057] The most diverse embodiments known from the prior art can be used as light-emitting diodes in conjunction with the present invention. Planar light-emitting diodes, edge-emitting or side-emitting light-emitting diodes, or even dome-type light-emitting diodes are preferably used.

[0058] In FIG. 2a is a planar light-emitting diode 9 which generates light of wavelength λ.sub.1. The respective spectral range of the light-emitting diode 9 can thereby be selected specific to the application. The UV range is especially of interest since many elements which are of interest for an analysis have their spectral lines within this range.

[0059] In the context of the present invention, a plurality of light-emitting diodes 9a-9d can also be used, as depicted in FIG. 2b. These can in turn respectively generate light of different wavelengths λ.sub.1-λ.sub.4. In the instance of the embodiment according to FIG. 2b, the individual light-emitting diodes 9a-9d are selected, for example, in such a way that together they generate light in a broad wavelength range λ.sub.RGBW.

[0060] It is advantageous if the geometry of the light-emitting diode 9 is selected such that it is adapted to the geometric conditions of the detection unit 5. In the event that the spectrometric arrangement 6 has an entrance slit 6b, and/or in the event of a stigmatically imaging optical arrangement, it is accordingly advantageous if the light-emitting diode 9 has a geometry corresponding to the geometry of the entrance slit 6b, as depicted in FIG. 2c. This permits an optimum illumination of the sensor 7. However, an anamorphic arrangement can also be resorted to in order to be able to achieve optimum illumination of the sensor.

[0061] In the event that a plurality of light-emitting diodes 9a, 9b, . . . are used, it is conceivable on the one hand that each light-emitting diode 9 is adapted with regard to its geometry to the geometry of the detection unit. That is to say that each light-emitting diode 9a, 9b, . . . is designed corresponding to the variant illustrated in FIG. 2c. In this context, however, it is likewise conceivable to design the radiation source unit 2 such that the plurality of light-emitting diodes 9a-9c that are used are adapted in their entirety to the geometry of the detection unit 5, especially to the geometry of the entrance slit 6b of the spectrometric arrangement 6, as illustrated in FIGS. 2d and 2e for the instance of using three light-emitting diodes 9a-9c. Here, it is again conceivable on the one hand that all light-emitting diodes 9a-9c generate light of the same wavelength λ.sub.1 as in the instance of FIG. 2d. On the other hand, the light-emitting diodes 9a-9c may in part or all generate light of different wavelengths λ.sub.1-λ.sub.3, as in the instance of FIG. 2e.

[0062] Via the arrangement of a plurality of light-emitting diodes 9a, 9b, 9c next to one another, as in the instance of FIG. 2e, different partial regions T1, T2 of the sensor 7 can respectively be illuminated with the light of different wavelengths λ.sub.1-λ.sub.3. This allows a simultaneous multi-element analysis of the correspondingly designed atomic absorption spectrometer 1.

[0063] A further embodiment of the present invention includes the different light-emitting diodes 9a, 9b, being arranged together on a carrier element 10, as shown by way of example in FIG. 3 for the instance of an embodiment according to FIG. 2e. The embodiment in FIG. 3a is a carrier element 10 which can be fixedly positioned relative to the detection unit 5 since, with one position of the carrier element 10, all light-emitting diodes 9a-9c can be used for analyzing the respective sample.

[0064] However, it is also conceivable to configure the radiation source unit 2 in such a way that a sequential operation of the individual light-emitting diodes 9a, 9b, . . . is achieved, as shown in FIGS. 3b and 3c. For the embodiment from FIG. 3b, for example, six light-emitting diodes 9a-9f are arranged next to one another on the carrier element 10. The carrier element 10 here is part of a positioning unit (not shown) by means of which a lateral movement of the carrier element 10 relative to the detection unit 5 can be realized for the embodiment shown here, as indicated by the arrow. The different light-emitting diodes 9a-9f can thus be positioned one after the other in such a way that they respectively illuminate the sensor 7 to analyze different elements in the sample. In addition to a lateral movement, other possibilities for accomplishing a sequential positioning of the individual light-emitting diodes 9a-9f are also conceivable. By way of example, FIG. 3c shows an arrangement of four light-emitting diodes 9a-9d arranged on a round carrier element 10 which can respectively be positioned relative to the detection unit via a circular movement of the carrier element 10.

[0065] FIG. 4 shows four further possible embodiments for a radiation source unit 2 according to the invention, for which a respective optical system 11 which is designed to guide the light generated by the light-emitting diodes 9a, 9b to the detection unit 5. The light of the individual light-emitting diodes 9a, 9b, . . . is thereby respectively combined in such a way that all light-emitting diodes 9a, 9b illuminate the same surface of the sensor 7. The light of the individual light-emitting diodes 9a, 9b, . . . is especially combined to form a total measuring beam 9x.

[0066] According to FIG. 4a, the optical system 11 comprises two interference filters 12a, 12b; for FIG. 4b, the light of the individual light-emitting diodes is combined by means of three Y-couplers 13a-13c. By contrast, for FIG. 4c the optical system comprises a grating 14, and for FIG. 4d a light-mixing rod 15. The light-mixing rod 15 shown in FIG. 4d is of cylindrical form. It is to be noted that, in other embodiments, the light-mixing rod 15 can also be conical, for example, that is to say in the form of a taper.

[0067] Within the scope of the present invention, it is preferably that the spectrometric arrangement 6 have high spectral resolution; the resolution is preferably a few picometers. Various spectrometric arrangements which are fundamentally suitable in the context of the present invention are known to the person skilled in the art, for example from Wilfried Neumann, “Fundamentals of dispersive optical spectroscopy systems” (SPIE Monograph, ISBN: 9780819498243).

[0068] In the instance of a radiation source unit 2 having at least one light-emitting diode 9, conventional monochromatic spectral arrangements are generally rather unsuitable since they must be tuned sequentially according to the bandwidth of the light-emitting diode 9. Transient absorption events, as can be measured by the graphite furnace technique, especially require the use of spectral arrangements 6 in the form of polychromators, which are preferably used in combination with fast-readable optoelectronic multipixel sensors 7. Examples of such spectrometric arrangements 6 are, for example, the Rowland circle spectrometer, the virtually imaged phased-array spectrometer, or also the echelle spectrometer.

[0069] Echelle spectrometers with echelle gratings have a high spectral resolution, which is based on the use of high atomic numbers. However, due to the spectral overlap associated therewith, additional measures for order separation are respectively necessary. For this reason, echelle gratings are often combined in combination with prisms, gratings or grisms.

[0070] FIG. 5 shows a preferred embodiment for a detection unit 5 in the form of a Littrow arrangement with a crossed echelle structure, into which is integrated a transversely dispersive element for order separation. A measuring beam 3 travels through an entrance slit 6b of the spectrometric arrangement, is collimated at a concave mirror 16, passes the crossed echelle grating 17, and is then refocused via the concave mirror 16 to the sensor 7.

REFERENCE SIGNS

[0071] 1 Atomic absorption spectrometer [0072] 2 Radiation source unit [0073] 3 Measuring beam [0074] 4 Atomizing device [0075] 5 Detection unit [0076] 6 Spectrometric arrangement [0077] 6b Entrance aperture, entrance slit [0078] 7 Sensor [0079] 8 Mirror system [0080] 8a, 8b Mirror [0081] 9, 9a, 9b Light-emitting diode [0082] 9x Total measurement beam [0083] 10 Carrier element [0084] 11 Optical system [0085] 12a, 12b Interference filter [0086] 13a-13c Y-coupler [0087] 14 Grating [0088] 15 Light-mixing rod [0089] 16 Concave mirror [0090] 17 Echelle grating [0091] λ, λ.sub.1, λ.sub.2, . . . Wavelengths [0092] T1, T2 Partial regions [0093] F Surface