GB2611576A

GB2611576A - Sample introduction system

Info

Publication number: GB2611576A
Application number: GB2114481.1A
Authority: GB
Inventors: Schlüter Hans-Jürgen; Murtazin Ayrat
Original assignee: Thermo Fisher Scientific Bremen GmbH
Current assignee: Thermo Fisher Scientific Bremen GmbH
Priority date: 2021-10-11
Filing date: 2021-10-11
Publication date: 2023-04-12
Also published as: GB202114481D0

Abstract

A sample introduction system 10 for an analytical apparatus, such as a mass or optical spectrometer. The introduction system comprises a sample inlet 11 for receiving a sample to be nebulized, a nebulizer 20 for nebulizing the sample and a gas inlet 12 for receiving gas for transporting the nebulized sample. A conduit 15 provides the nebulized sample to the spectrometer. The nebulizer comprises at least one transducer for providing an ultrasonic vibration and at least one ultrasonic horn for amplifying the ultrasonic vibration. The at least one ultrasonic horn may be a Fourier horn.

Description

Sample introduction system

Field of the invention

The present invention relates to nebulization in spectroscopy, chemical analysis and physical analysis. More in particular, the present invention relates to a sample introduction system for an analytical apparatus, such as a spectrometer, and to a method of introducing a sample into an analytical apparatus, such as spectrometer.

Background of the invention

In spectrometry systems and many other types of analytical apparatus, a sample must be introduced into the analytical apparatus. Various types of samples can be used, such as solid samples, liquid samples and gaseous samples. Many types of analytical apparatus require a gaseous input. That is, the sample must be contained in a gas stream which is introduced into the analytical apparatus Liquids may be introduced into an analytical apparatus by means of a gas stream if the liquid is nebulized, that is, if the liquid is provided as droplets which are small enough to be carried by the gas stream of a carrier gas. To this end, nebulizers have been developed which serve to convert a flow of liquid into an aerosol, a stream of tiny droplets. Such droplets may, for example, have a diameter between land 100 pm.

Several parameters of a nebulizer are important to determine its suitability for a particular application. One of these parameters is the total amount of aerosol produced. Another parameter is droplet size distribution (DSD), indicating how the droplet diameter is distributed around its mean value. Other important parameters are the stability of the total aerosol amount and droplet size distribution over time and the robustness of the target diameter and of the droplet size distribution when variations in the properties of the liquid sample occur. Sometimes mechanical droplet size filters, such as spray chambers, are used to remove droplets having larger diameter than desired, but such filters introduce a significant amount of waste and can also cause memory and matrix effects.

To improve the properties of the generated aerosol, sample introduction systems based upon ultrasonic nebulizers have been proposed.

United States patent application US 2015/165466 Al (Agilent) discloses an example of an ultrasonic nebulizer including a piezoelectric element that vibrates responsive to a drive signal having an alternating voltage. A nebulizing layer that may be a passive resonator is bonded to a first surface of the piezoelectric element and has an outer surface that transforms a liquid into a mist responsive to vibration of the piezoelectric element. The surface of the passive resonator may be textured to guide the liquid flow.

Most sample introduction systems based upon ultrasonic nebulizers have several disadvantages, such as the need for a drained spray chamber, large dimensions, a high power consumption, the need for external cooling and a relatively high price. To overcome these disadvantages, alternative sample introduction systems have been proposed which have smaller dimensions and are more efficient and less expensive. United States patent US 8 642 954 (PerkinElmer) discloses a sample introduction system for an atomic spectrometer which utilizes a spray head including a vibrating mesh. Other techniques have also been proposed.

British patent GB 2 548 071 (Thermo Fisher Scientific), for example, discloses a liquid sample introduction system for a plasma spectrometer. The liquid sample introduction system comprises a sample container for a liquid sample, a surface acoustic wave (SAW) nebulizer, an electronic controller for supplying power to the SAW nebulizer so as to produce an acoustic wave on a surface of the nebulizer for generating an aerosol from the liquid, and an aerosol transport arrangement for receiving the aerosol and carrying it into a plasma or flame of a spectrometer. The SAW nebulizer comprises a substrate with apertures and an electrode arrangement. The entire contents of British patent GB 2 548 071 are herewith incorporated by reference in this document.

Although such arrangements have several advantages, they appear to be less suitable for acidic sample solutions as the separation between the electrical current delivery zone and aerosol generating zone is typically insufficient. In addition, the choice of suitable materials is limited, thus increasing their cost of production and restricting the range of analytical applications.

Summary of the invention

The invention seeks to overcome the above-mentioned and other disadvantages of sample introduction systems of the prior art. Accordingly, the invention provides a sample introduction system for an analytical apparatus, such as a spectrometer. The sample introduction system may comprise: - a sample inlet for receiving a sample to be nebulized, - a nebulizer for nebulizing the sample, - a gas inlet for receiving gas for transporting the nebulized sample, and - a conduit for providing the nebulized sample to the spectrometer.

The nebulizer can comprise at least one transducer configured for providing an ultrasonic vibration and at least one ultrasonic horn for amplifying the ultrasonic vibration.

By providing a nebulizer arranged for providing an ultrasonic vibration, the advantages of ultrasonic nebulizers are retained. By using at least one ultrasonic horn configured for amplifying the ultrasonic vibration, further advantages are achieved. In particular, the amplification due to the one or more ultrasonic horns allows a lower power consumption, a lower cost and an increased stability of the aerosol properties. In addition, an ultrasonic horn allows to spatially separate the source or sources of the ultrasonic vibration and the nebulization zone or zones.

The nebulizer of the invention may comprise at least two ultrasonic horns. That is, the nebulizer may comprise two, three, four, five, six or more ultrasonic horns. The at least two ultrasonic horns may be arranged in series. Additionally, or alternatively, the at least two ultrasonic horns may be arranged in parallel. Providing two or more ultrasonic horns in series has the advantage of a greater amplification of the ultrasound. Providing two or more ultrasonic horns in parallel has the advantage of spreading out the nebulization over multiple ultrasonic horns, which can result in a better control of the particle size.

The present invention also provides a nebulizer having ultrasonic horns both in series and in parallel. An arrangement of four ultrasonic horns, for example, may consist of two parallel sets of each two ultrasonic horns in series.

It is noted that United States patent US 6 669 103 (Tsai) discloses a device for atomizing a liquid for ultrasonic spray pyrolysis. The prior art device includes cascaded ultrasonic horn stages. As is well known, ultrasonic spray pyrolysis is used for producing ultra-fine powders, for instance for thin film coating. US 6 669 103 fails to disclose or suggest the use of ultrasonic horn stages in sample

introduction systems for analytical apparatus.

In the sample introduction system of the invention, each ultrasonic horn, or each series arrangement of ultrasonic horns, could be provided with an individual transducer. In some embodiments of the present invention, however, two or more parallel ultrasonic horns, or two or more parallel arrangements of ultrasonic horns, may share a transducer. Thus, at least two ultrasonic horns may have a single common transducer. Conversely, a single ultrasonic horn or each series arrangement of ultrasonic horns may be provided with more than one transducer, for example two, three, four, or more transducers.

At least some of the transducers may be piezo-electric transducers. The ultrasonic vibration produced by at least some of the transducers may have a frequency between 15 kHz and 200 kHz, for example between 50 kHz and 100 kHz, although other frequencies are also possible, such as frequencies up to 1 MHz or above 1 MHz, for example 2 MHz, 5 MHz, 10 MHz or higher frequencies.

Thus, in embodiments of the invention the frequency of the ultrasonic vibration may be between 15 kHz and 10 MHz, in particular between 100 kHz and 5 MHz, more in particular between 1 MHz and 5 MHz, although other ranges can also be envisaged.

The at least one ultrasonic horn may have a suitable cross-section, for example round, oval, square, hexagonal or octagonal. In some embodiments, the at least one ultrasonic horn may have a rectangular cross-section. The at least one ultrasonic horn may comprise a Fourier horn.

The nebulizer may be made using MEMS technology. As is well known, the term MEMS stands for micro-electro-mechanical systems. This technology enables very small structures to be made to a high precision. Suitable materials for making nebulizers using MEMS technology or another technology may for example be silicon, silicon nitrides, silicon carbides, other ceramics, silicon dioxides (quartz), aluminium oxides, polymers, metals (such as, but not limited to, aluminium and copper), PTFE (polytetrafluoroethylene) or PFA (perfluoroalkoxy alkanes).

The sample introduction system may be configured for receiving a liquid sample. In some embodiments, the sample introduction system may be configured for receiving a solid sample. The conduit may comprise a spray chamber. In other embodiments, the conduit may be constituted by a pipe section or a similar tubular conduit.

The present invention also provides a nebulizer for use in a sample introduction system as described above, the nebulizer comprising at least one transducer configured for providing an ultrasonic vibration and at least one ultrasonic horn for amplifying the ultrasonic vibration.

The present invention further provides an analytical apparatus, such as a spectrometer or a gas chromatograph, comprising a sample introduction system as described above. A spectrometer according to the present invention may further comprise at least one mass analyser, mass separation device or wavelength disperser and at least one detector unit.

A spectrometer according to the present invention may be an optical spectrometer or a mass spectrometer. A spectrometer according to the present invention may further comprise a plasma source, such as a plasma torch.

The present invention further provides a sample introduction system for an analytical apparatus, comprising: - a sample inlet for receiving a sample to be nebulized, - a nebulizer for nebulizing the sample, - a gas inlet for receiving gas for transporting the nebulized sample, and - a conduit for providing the nebulized sample to the analytical apparatus.

The nebulizer can comprise at least one transducer configured for providing an ultrasonic vibration and at least one ultrasonic horn for amplifying the ultrasonic vibration. Such a nebulizer may have small dimensions and may use a small amount of power. The transducer may be a piezo-electric transducer, for example.

The present invention additionally provides a method of introducing a sample into an analytical apparatus, such as a spectrometer, the method comprising: - receiving a sample to be nebulized, - nebulizing the sample, receiving gas for transporting the nebulized sample, and providing the nebulized sample to the spectrometer, wherein nebulizing the sample comprises utilizing at least one transducer configured for providing an ultrasonic vibration and at least one ultrasonic horn for amplifying the ultrasonic vibration.

In a method according to the present invention, nebulizing the sample may comprises utilizing at least two ultrasonic horns arranged in series. Alternatively, or additionally, nebulizing the sample may, in a method according to the present invention, comprise utilizing at least two ultrasonic horns arranged in parallel. At least one ultrasonic horn may be a Fourier horn.

Brief description of the drawings

Fig. 1 schematically shows a first embodiment of an analytical apparatus in which a sample introduction system according to the present invention is used.

Fig. 2 schematically shows a second embodiment of an analytical apparatus in which a sample introduction system according to the present invention is used.

Fig. 3 schematically shows a third embodiment of an analytical apparatus comprising a sample introduction system according to the present invention.

Fig. 4 schematically shows a first embodiment of a nebulizer for a sample introduction system according to the present invention.

Fig. 5 schematically shows a second embodiment of a nebulizer for a sample introduction system according to the present invention.

Fig. 6 schematically shows a third embodiment of a nebulizer for a sample introduction system according to the present invention.

Fig. 7 schematically shows a fourth embodiment of a nebulizer for a sample introduction system according to the present invention.

Fig. 8 schematically shows a fifth embodiment of a nebulizer for a sample introduction system according to the present invention. Fig. 9 schematically shows a sixth embodiment of a nebulizer for a sample introduction system according to the present invention.

Fig. 10 schematically shows various cross-sections of nebulizers for a sample introduction system according to the present invention.

Detailed description of the drawings

The present invention provides a sample introduction system for analytical apparatus, such as spectrometers. A sample introduction system according to the invention may comprise a nebulizer having at least one transducer configured for providing an ultrasonic vibration. A sample introduction system according to the invention may further comprise at least one ultrasonic horn for amplifying the ultrasonic vibration. This will be further explained with reference to the drawings.

An embodiment of an analytical apparatus comprising a sample introduction system according to the present invention is schematically shown in Fig. 1. The analytical apparatus 100 of Fig. 1 comprises a sample introduction system 10 comprising a nebulizer unit 20 according to the invention, which will later be explained in more detail. The sample introduction system of Fig. 1 is constituted by a sample introduction unit 10 configured for receiving a sample, such as a liquid sample, and converting this sample into an aerosol AS. This aerosol may optionally be conditioned by desolvation, charging or atomization. The aerosol is provided to a further unit, for example an analyzer unit 30, such as an analyzer unit of a mass spectrometer or of an elemental analyzer. The analyzer unit 30 of this embodiment provides an analyte-specific physical output AO, such as light or ions, to the detector unit 50 of the analytical apparatus 100. In response to the analyte-specific physical output AO of the analyzer unit 30, the detector unit 50 produces a detection signal DS which is supplied to the signal processing unit 60. The processed detection signal DS results in an output signal OS, which may also be referred to as analytical signal and which describes the chemical and/or isotopic composition of the sample.

Another embodiment of an analytical apparatus comprising a sample introduction system according to the present invention is schematically shown in Fig. 2. The analytical apparatus 100 of Fig. 2 also comprises a sample introduction system according to the invention. In this example, the analytical apparatus 100 is an optical emission spectrometer. The sample introduction system of Fig. 2 is constituted by a sample introduction unit 10 configured for receiving a sample, such as a liquid sample, and converting this sample into an aerosol AS. This aerosol is provided to a plasma unit 40 for exciting the aerosol constituents. The plasma unit 40 provides a physical output PO, such as light, to the analyzer unit 30. The analyzed physical output AO is supplied to the detector unit 50 of the analytical apparatus 100. In response to the physical output PO of the plasma unit 40, the detector unit 50 produces a detection signal DS which is supplied to the signal processing unit 60. The processed detection signal DS results in an output signal OS which describes the chemical or isotopic composition of the sample. In some embodiments, the analyzer unit 30 may be absent. In the embodiment of Fig. 2, for example, the plasma unit 40 may be coupled to the detector unit 50 without an intermediate analyzer unit 30.

A desolvation unit may be used with a sample introduction system comprising a plasma unit to decrease the solvent load of the plasma and thereby improve the sensibility and matrix robustness of the analysis.

Fig. 3 schematically shows an embodiment of an analytical apparatus in more detail. The analytical apparatus 100 is shown to comprise a sample introduction unit 10 according to the invention. In addition, the analytical apparatus 100 is shown to comprise a plasma unit or plasma chamber 40 and a detector unit 50. A connection tube 15 connects the sample introduction system 10 to the plasma chamber 40, while an optical guide 49 connects the plasma chamber 40 to the detection unit 50. The analytical apparatus 100 may comprise further components, such as a signal processing unit, which are not shown in Fig. 3 for the sake of clarity of the drawing. An analyzer unit (30 in Figs. 1 & 2) may be arranged between the plasma chamber 40 and the detector unit 50.

The sample introduction system 10 of Fig. 3 is shown to comprise a sample introduction tube 11, a nebulizer 20 and a carrier gas introduction tube 12, as well as the connection tube 15 mentioned above. The sample introduction tube 11 is, in the embodiment shown, configured for receiving a liquid sample to be nebulized and supplying the liquid sample to the nebulizer unit 20. The carrier gas introduction tube 12 is configured for receiving a carrier gas CG, for example argon, for carrying the nebulized sample from the nebulizer unit 20 to the plasma chamber 40. In the embodiment shown, the introduction tube 12 is shown to be connected to the nebulizer unit 20 so as to feed carrier gas directly to the nebulizer. In this way, coaxial gas and liquid flows may be provided in some embodiments. In other embodiments, however, the carrier gas introduction tube 12 may be space apart from, and thus not be in contact with the nebulizer 20. Such embodiments may have a so-called cross flow geometry.

The nebulizer unit 20 comprises in accordance with the invention one or more transducers for producing ultrasound and one or more ultrasonic horns for amplifying the ultrasound, as will be further explained later with reference to Fig. 4. In some embodiments, the sample introduction unit 10 may additionally comprise a spray chamber arranged between the nebulizer unit 20 and the connection tube 15.

The plasma chamber 40 may be a plasma chamber according to the prior art. An example of a suitable plasma chamber is disclosed in WO 2020/208085 (Thermo Fisher Scientific), the entire contents of which are herewith incorporated by reference in this document. The plasma chamber 40 comprises a plasma torch 41, which in the embodiment of Fig. 3 is an inductively coupled plasma (ICP) torch. This ICP torch comprises a coil 42 for inducing an alternating magnetic field to excite the gas and thus to generate a gas plasma 45. Alternatively, or additionally, the plasma may be generated using microwaves, at least one laser, DC electrical discharges, RF (radio frequency) electric discharges, and/or other techniques which may be known as such The connection tube 15 is arranged so as to direct the gas stream containing the aerosol to the plasma torch 41. The aerosol (that is, the nebulized sample) contained in the gas stream entering the plasma chamber 40 is excited by the high temperature of the plasma 45 (in some applications approximately 8000 K) and will emit electromagnetic radiation, such as light. At least part of the emitted light can be guided to the detector unit 50 by the optical guide 49, which may be constituted by a so-called periscope. Although the optical guide 49 is shown here to be arranged along the axis of the plasma torch 42 (axial view), the optical guide 49 or a further optical guide (not shown) may alternatively, or additionally, be arranged perpendicularly to the plasma torch 41 (radial view).

As mentioned above, the optical guide 49 transmits light from the plasma chamber 40 to the detector unit 50, which in this embodiment is an optical detector unit. The detector unit 50 may comprise one or more detector arrays, for example CCD (charge coupled device) detector arrays, for detecting the emitted light and converting the detected light into one or more digital images.

As mentioned above, the nebulizer unit 20 comprises at least one transducer for generating a high-frequency vibration of at least one surface of the nebulizer. The nebulizer unit 20 further comprises, in accordance with the invention, at least one acoustic horn for amplifying the high-frequency vibration. Such nebulizer units will further be explained with reference to Figs. 4 -10 An exemplary embodiment of a nebulizer unit 20 for use in a sample introduction system of an analytical apparatus is schematically shown in Fig. 4. The embodiment of Fig. 4 comprises a nebulizer body 21 having a hollow interior 24. In the embodiment shown, the interior 24 is open to the exterior via an aperture 25. In other embodiments, the aperture 25 may be closed off or absent.

A transducer 22 is shown to be arranged in the interior 24, in the embodiment shown against a side wall of the interior 24 of the nebulizer body 21. In the embodiment shown, a feed tube 23 passes through a back wall of the nebulizer body 21 into the interior or cavity 24 so as to provide a liquid sample. In the embodiment shown, the open end 29 of the feed tube 23 is arranged axially with respect to the longitudinal axis of the interior 24, and also with respect to the feed direction of the aerosol AS. In addition, the open end 29 is shown in Fig. 4 to extend beyond the aperture 25 and thus beyond the nebulizer body 21. As a result, the sample S will be nebulized outside of the nebulizer body 21. This is, however, not essential and in some embodiments the feed tube 23 may have an open end inside the interior 24, for example closer to the transducer 22. Alternatively, or additionally, the open end 29 of the feed tube 23 may be located in the same plane as the aperture 25 of the nebulizer body 21. The feed tube 23 may be connected to the sample introduction tube 10 shown in Fig. 2.

It will be understood that in addition to the aperture 25, the nebulizer is provided with at least one aperture in the back wall of the nebulizer body 21 through which the feed tube 23 passes and may be provided with further apertures for feeding through electrical leads towards the transducer 22.

However, these apertures are typically closed off by the parts they are provided for. The nebulizer body 21 may be made of silicon or a silicon dioxide compound, for example.

According to an aspect of the invention, the nebulizer unit 20 is shaped so as to constitute at least one ultrasonic horn. To this end, the interior 24 tapers towards its aperture 25, having sides 26 which slope over at least part of their length, thus decreasing the internal diameter of the interior 24 towards the aperture 25. The sloping sides thus define a horn section 27, while the transducer is located in a drive section 28 having substantially parallel side walls in the embodiment shown. It is noted that the horn section 27 may extend beyond the sloping side walls 26 and that part of the horn section 27 may have substantially parallel side walls. This may also be the case in embodiments with a curved cross-section, where the transition from slanting side walls to parallel side walls is not defined by a corner.

An ultrasonic horn is also known as acoustic horn or acoustic waveguide and its shape serves to amplify the ultrasonic vibrations. Due to the amplification, the nebulizing process is more effective and more droplets may be obtained while requiring less energy to produce the droplets.

The ultrasonic horn is provided by the tapering of the side walls 26, resulting in a reduced cross-section towards the aperture 25. It is noted that the interior of the nebulizer need only be tapered in one dimension. That is, in a dimension perpendicular to the drawing the cross-section may be constant over the length of the hollow nebulizer body 21. Alternatively, the cross-section of the interior 24 may also be tapered in a second dimension. A constant cross-section is preferably rectangular, for example square, but may also be round, oval, or polygonal (for example hexagonal or octagonal), as will later be explained with reference to Fig. 10. As an example of a non-constant cross-section in a second dimension, a conical interior 24 can be envisaged.

To provide a desired amplification of the ultrasound, the interior 24 may have a specific length. In particular, the horn section may have a length of approximately half a wavelength of the ultrasound produced by the transducer 22. The length of a horn section may thus be proportional to the wavelength and therefore inversely proportional to the frequency. It will be understood that the wavelength is not only dependent on the frequency, but also on the material of the nebulizer body. At a frequency of 1 MHz, for example, the wavelength X may be equal to approximately 10 mm, resulting in a half wavelength 212 of approximately 5 mm. Thus, the nebulizer unit 20 shown in Fig. 4 may have an overall length of less than 10 mm. An advantage of the ultrasonic nebulizer of the invention is the small amount of power that is required to achieve the desired nebulization.

Due to the small dimensions of the nebulizer, it can suitably be produced using MEMS (MicroElectro-Mechanical Systems) technology, which is well known to those skilled in the art. Suitable materials are, for example, silicon, glass, quartz, and silicon composites.

The transducer 22 may be a piezo-electric transducer, which is well known in the art. More than one transducer 22 per interior 24 may be used, in which case the two or more transducers may be arranged against the same wall or against different walls of the interior 24.

The nebulizer of the present invention may be configured for producing droplets having a diameter between 1 pm and 50 Jim, preferably droplets having a diameter less than 20 pm, more preferably droplets having a diameter less than 10 p.m, although other droplet sizes are also possible. The droplet size may depend on the transducer frequency and other parameters, such as the flow of the sample S through the feed tube 23, the diameter of the feed tube 23 and/or the location of the open end 29 of the feed tube 23 relative to the nebulizer body 21.

The embodiment of Fig. 5 comprises two ultrasonic horns arranged in series. The nebulizer body 21 has an interior comprising two cavities, a first cavity 24A in which the transducer 22 is arranged and a second cavity 24B in which no transducer is accommodated. The second cavity 24B received ultrasound from the first cavity 24A and, due to its shape, further amplifies the ultrasound. Due to the double acoustic horn, a greater amplification of the ultrasound can be achieved. Each acoustic horn section has a horn length HL. The cavity 24A is shown to comprise a horn section 27 having sloping side walls 26 and a drive section 28 in which the transducer 22 is accommodated. Thus, the embodiment of Fig. S comprises two horn sections 27 and a single drive section 28.

As can be seen in Fig. 5, the feed tube 23 is absent from the interior of the nebulizer body 21. Instead, the feed tube 23 extends along the exterior of the nebulizer body 21, the open end 29 of the feed tube 23 being located adjacent to the aperture 25 of the nebulizer body 21. In the embodiment shown in Fig. 5, the feed tube 23 is L-shaped, in contrast to the substantially straight feed tube 23 of Fig. 4.

The aperture 25 may in some embodiments have a surface area between 0.1 mm2 and 4 mm2, although both smaller and larger surface areas are feasible. The aperture 25 may be an actual opening but may in some embodiments be closed off. Thus, in the embodiment of Fig. 4 where the feed tube 23 extends through the aperture area 25, the actual opening may have the same diameter as the feed tube, the remainder of the aperture area 25 being closed off by an end wall or ultrasonic transmission surface. In some embodiments, such as the embodiment of Fig. 5, the aperture area 25 may have a wider opening, corresponding to the entire aperture area, that is, corresponding to the entire surface area of the intersection of the tapered acoustic horn and the outer edge of the nebulizer body 21.

If the aperture area 25 is closed off, its outer surface may be structured. A structured outer surface of the aperture area 25, on which the sample liquid may be supplied, allows the nebulization to have a more localized character, which can further improve both the efficiency of the aerosol generation and the properties of the generated aerosol. The structured outer surface may comprise a single channel or a plurality of channels, and/or a single ridge or a plurality of ridges. The channels and/or ridges may be straight or curved, parallel and/or crossing, and may have the same or different aspect ratios. The aperture area 25 may be round, oval, rectangular (including square), polygonal (including hexagonal), or have another shape. The diameter of the aperture area 25 may for example be between 0.1 mm and 10 mm, preferably between 0.5 mm and 2 mm, although other diameters may also be used.

The embodiment of Fig. 6 comprises a series arrangement of three ultrasonic horns having cavities 24A, 24B and 24C respectively. The feed tube 23 is shown to be arranged outside the nebulizer body 21, near the aperture 25.

The embodiment of Fig. 7 comprises a series arrangement of four ultrasonic horns having cavities 24A, 24B, 24C and 24D respectively. The interior of the nebulizer body 21 is shown to comprise two transducers, of which a first transducer 22 is arranged against the back wall of the interior, while a second transducer 22' is arranged against a side wall.

The embodiment of Fig. 8 comprises two parallel arrangements, each comprising three ultrasonic horns in series. The nebulizer 20 of Fig. 8 is provided with an individual transducer and an individual feed tube for each arrangement. The first series arrangement comprises cavities 24A, 24B and 24C, while the second series arrangement comprises cavities 24D, 24E and 24F. Two feed tubes 23 are provided, each ending near a respective aperture 25. It will be understood that parallel arrangements of ultrasonic horns are also possible with one, two, four, five, six or more ultrasonic horns per arrangement. In addition, instead of two parallel arrangements, three or more parallel arrangements of one, two, three, four, five, six or more ultrasonic horns each can be envisaged.

The embodiment of Fig. 9 comprises a tapering cross-section constituted by side walls 26 which are not straight but curved. In the example shown, the side walls are convex, when viewed from the interior 24. It will be understood that the cross-section may be shaped differently and may for example have a stepped cross-section. Alternatively, or additionally, Bezier curves may be used to define the cross-section of the interior 24. A Baler curve is a parametric curve used in computer graphics and other fields to provide smooth shapes.

Fig. 10 schematically shows various cross-sections of a nebulizer according to the invention, taken along the line C-C in Fig. 9. The first cross-section 61 is rectangular, which the second cross-section CS2 is oval. The third cross-section 63 is square and the fourth cross-section 64 is substantially circular. The fifth cross-section SC5 is polygonal, the present example shows a hexagon.

The invention may be utilized in, for example, optical spectrometry and mass spectrometry.

Although the invention has been mainly explained with reference to spectrometry systems, the invention is not so limited and may be utilized in other technical fields, for example chemical analysis in general and/or physical analysis in general.

Examples of chemical analysis in which the teachings of the present invention may be utilized include elemental analysis, isotope ratio analysis, and other analysis applications.

It will be understood by those skilled in the art that the invention is not limited to the embodiments shown and that many additions and modifications can be made without departing from the scope of the invention as defined in the accompanying claims.

Claims

Claims 1. A sample introduction system for a spectrometer, comprising: - a sample inlet for receiving a sample to be nebulized, - a nebulizer for nebulizing the sample, - a gas inlet for receiving gas for transporting the nebulized sample, and - a conduit for providing the nebulized sample to the spectrometer, wherein the nebulizer comprises at least one transducer configured for providing an ultrasonic vibration and at least one ultrasonic horn for amplifying the ultrasonic vibration.
2. The sample introduction system for a spectrometer according to claim 1, wherein the nebulizer comprises at least two ultrasonic horns.
3. The sample introduction system according to claim 2, wherein the at least two ultrasonic horns are arranged in series.
4. The sample introduction system according to claim 2 or 3, wherein the at least two ultrasonic horns are arranged in parallel.
5. The sample introduction system according to claim 4, wherein at least two ultrasonic horns have a single common transducer.
6. The sample introduction system according to any of the preceding claims, wherein the ultrasonic vibration has a frequency between 15 kHz and 10 MHz, preferably between 100 kHz and 5 MHz, more preferably between 1 MHz and 5 MHz.
7. The sample introduction system according to any of the preceding claims, wherein the at least one ultrasonic horn has a rectangular cross-section.
8. The sample introduction system according to any of the preceding claims, wherein the at least one ultrasonic horn comprises a Fourier horn.
9. The sample introduction system according to any of the preceding claims, wherein the at least one transducer is a piezo-electric transducer.
10. The sample introduction system according to any of the preceding claims, wherein the nebulizer is made using MEMS technology.
11. The sample introduction system according to claim 10, wherein the nebulizer is at least partially made from a material chosen from the groups consisting of: silicon, silicon nitrides, silicon carbides, other ceramics, silicon dioxides, aluminium oxides, polymers, metals, PTFE, PFA or composites of any of these materials
12. The sample introduction system according to any of the preceding claims, which sample introduction system is configured for receiving a liquid sample.
13. The sample introduction system according to any of the preceding claims, wherein the conduit comprises a spray chamber.
14. The sample introduction system according to any of the preceding claims, wherein the at least one acoustic horn has an ultrasonic transmission surface closing off its aperture area.
15. The sample introduction system according to claim 14, wherein the ultrasonic transmission surface is structured and preferably comprises at least one channel and/or at least one ridge.
16. The sample introduction system according to claim 14 or 15, wherein the ultrasonic transmission surface has a diameter between 0.1 mm and 10 mm, preferably between 0.5 mm and 2 mm.
17. The sample introduction system according to any of claims 14 to 16, wherein the ultrasonic transmission surface is round, oval, rectangular or polygonal.
18. A nebulizer for use in a sample introduction system according to any of the preceding claims, the nebulizer comprising at least one transducer configured for providing an ultrasonic vibration and at least one ultrasonic horn for amplifying the ultrasonic vibration.
19. A spectrometer comprising a sample introduction system according to any of claims 1 to 17.
20. The spectrometer according to claim 19, which is an optical spectrometer.
21. The spectrometer according to claim 19, which is a mass spectrometer.
22. The spectrometer according to claim 21, further comprising a plasma source.
23. A sample introduction system for an analytical apparatus, comprising: - a sample inlet for receiving a sample to be nebulized, - a nebulizer for nebulizing the sample, - a gas inlet for receiving gas for transporting the nebulized sample, and - a conduit for providing the nebulized sample to the analytical apparatus, wherein the nebulizer comprises at least one transducer configured for providing an ultrasonic vibration and at least one ultrasonic horn for amplifying the ultrasonic vibration.
24. An analytical apparatus comprising a sample introduction system according to claim 23.
25. A method of introducing a sample into an analytical apparatus, such as a spectrometer, the method comprising: - receiving a sample to be nebulized, - nebulizing the sample, - receiving gas for transporting the nebulized sample, and - providing the nebulized sample to the analytical apparatus, wherein nebulizing the sample comprises utilizing at least one transducer configured for providing an ultrasonic vibration and at least one ultrasonic horn for amplifying the ultrasonic vibration.
26. The method according to claim 25, wherein nebulizing the sample comprises utilizing at least two ultrasonic horns arranged in series.
27. The method according to claim 25 or 26, wherein nebulizing the sample comprises utilizing at least two ultrasonic horns arranged in parallel.
28. The method according to any of claims 25 to 27, wherein at least one ultrasonic horn is a Fourier horn.
29. The method according to any of claims 25 to 28, wherein the at least one transducer is a piezo-electric transducer.