EP3491660A1

EP3491660A1 - Analysis device for gaseous samples and method for verification of analytes in a gas

Info

Publication number: EP3491660A1
Application number: EP17746047.4A
Authority: EP
Inventors: Jens Riedel; Andreas BIERSTEDT
Original assignee: Bundesministerium fuer Wirtschaft und Energie
Current assignee: Bundesministerium fuer Wirtschaft und Energie
Priority date: 2016-07-26
Filing date: 2017-07-25
Publication date: 2019-06-05
Also published as: DE102016113771B4; US20190267225A1; US10804092B2; WO2018019837A1; DE102016113771A1

Abstract

The invention relates to an analysis device for a gaseous sample, which analysis device comprises a mass spectrometer (6) having a measurement chamber and an inlet (5) leading into the measurement chamber, and a laser irradiation unit (30, 3). The analysis device is designed to convey the gaseous sample to the inlet by means of a current comprising the gaseous sample. The laser irradiation unit (30, 3) is designed to ignite a plasma (1) by means of a laser beam (2') in the current (4).

Description

Gaseous sample analysis apparatus and method for detecting analytes in a gas

The present invention relates to an analysis device for gaseous samples, in particular to an analysis device with a mass spectrometer, and to a method for detecting analytes in a gas, in particular gaseous and particulate analytes in a gas.

For the high-resolution characterization of chemical compounds, mass spectrometry, in which mass is determined to charge ratios (mz) of atoms or molecules, is widely used. For example, mass spectrometry can be used in environmental analysis, in biomedical and pharmacological investigations, in forensic investigations, and in doping controls, to name only a few fields of application.

The basis of mass spectrometric investigations is first of all the transfer of the analyte to be examined into the gas phase, as well as the subsequent ionization. For this a plasma can be used. For example, the inductively coupled plasma mass spectrometry (ICP-MS) of the Inductively Coupled Plasma (ICP-MS) uses plasma torches to ionize the sample, but plasma torches are very large, consume a lot of power and process gas, and are too Due to long switching times, it is very sluggish, which means that an IC plasma usually takes a few seconds to minutes to become stable.

The LAMMA (Laser Microscope Mass Analysis) or LIMS (Laser Ionization Mass Spectrometry) process uses a laser for direct solid-state detection. This results in the formation of a laser plasma directly on a micro-sample. Among other things, biological samples can be examined by means of LAMMA. However, LAMMA is not suitable for gaseous samples, but limited to solid micro samples with typical volumes of about 1 μL ·, which must also be stable in vacuum. The microprobe must therefore be introduced into or removed from the vacuum system of the measuring instrument before and after each measurement. In view of the above, the present invention proposes an analysis apparatus according to claim 1, a method according to claim 8, and a use according to claim 15.

According to one embodiment, an analysis device for a gaseous sample comprises a mass spectrometer comprising a measuring space and an inlet leading into the measuring space, and a laser irradiation unit. The analysis device is set up to convey the gaseous sample to the inlet of the mass spectrometer by means of a flow comprising the gaseous sample. The laser irradiation unit is set up to ignite a plasma for at least partial ionization of the gaseous sample with a laser beam in the flow in front of the inlet of the mass spectrometer.

An internal cross section of the inlet of the mass spectrometer may increase at least in sections towards the measuring space. Typically, an inner diameter of the inlet of the mass spectrometer tapers outwardly (increases toward the measurement space), typically by a factor of at least 10, more typically by a factor of at least 20. The inner diameter may taper monotonically or even strictly monotonically outwardly , The inlet of the mass spectrometer may in particular be designed as a nozzle which narrows outwards, typically with an internal diameter at the side remote from the measuring chamber of less than 500 μm, more typically less than 250 μm or even 200 μm. Such an inlet has proven to be particularly suitable for mass spectroscopic investigation for reasons of flow and vacuum technology.

Typically, the laser irradiation unit has a laser and / or a focusing optics for focusing the laser beam in the flow.

In addition, the laser irradiation unit is typically arranged at least partially in a flow direction in front of the inlet.

The laser is typically a pulsed laser, ie a laser operable in pulsed operation. With pulsed lasers particularly high laser powers can be achieved whose pulse peak power is typically in a range of 10 kW to 1 MW, and thus produce correspondingly favorable plasmas of high temperature in the gas flow in front of the mass spectrometer.

For example, it may be a pumped solid state laser that can emit laser pulses in the visible or near infrared. Although the use of a pulsed UV laser is likewise possible, plasmas which lead to good atomization and / or ionization of analytes contained in the carrier gas can also be generated in the flow of a carrier gas with longer-wavelength (and thus less expensive) pulsed lasers.

A decomposition of the analytes via a direct laser excitation is not required.

The pulse rate of the laser may typically be in a range of 50 Hz to 1 MHz, in particular in a range of 1 kHz to 1 MHz.

Instead of a laser, it is also possible to use two or even more lasers whose laser beams can intersect in the flow during operation.

The analyte or analytes may be dispersed in the carrier gas, typically in the form of nanoparticles or microparticles, e.g. be mixed as airborne aerosols, or in gaseous form with the carrier gas. In addition, the carrier gas, which may, for example, be nitrogen or air, may be mixed with a chemically inert process gas such as argon. The carrier gas may also be a noble gas, e.g. Argon, his.

By means of the laser beam, a plasma can be ignited in the carrier gas or the mixture of the carrier gas and the process gas. This is typically done contactless, i. not on macroscopic surfaces, e.g. Metal surfaces.

As a result, an influence on the subsequent mass spectroscopic analysis by ablated material of the surfaces (contamination or cross-contamination) can be avoided. By a high proportion of noble gases in the flow, a chemical impairment of the analysis result can be at least largely avoided.

Typically, the laser irradiation unit is adjusted to the mass spectrometer so that, during operation, the laser is sufficiently spaced from macroscopic surfaces Focus can generate in the flow. Typically, the distance of the focus from the macroscopic surfaces is greater than 1 mm or even 1 cm.

The term "macroscopic surface", as used herein, is to be understood as meaning a surface which, in at least one direction, has an extension which is greater than 0.1 mm, more typically greater than 1 mm.

The plasma ignited by the laser has a high temperature, typically greater than 1000 ° K or even greater than 5000 ° K, more typically greater than 10000 ° K, or even greater than 15000 ° K.

Compared with the inductively coupled plasma, a laser plasma can have a higher temperature (and thus a higher ionization efficiency), a better efficiency in its generation and a scalable size of a few micrometers up to a few centimeters.

The plasma thus has enough internal energy, charge and radiation to break the chemical and physical bonds in the analyte-molecule assemblies. After complete dissociation, further excess energy of the plasma can lead to a charge transfer to the generated analyte atoms. These can then be transferred with the flow through the inlet into the vacuum region (i.e., a vacuum region with a gas pressure below 300 mbar) of the measurement space of the mass spectrometer and analyzed there.

A direct decomposition of the analytes into atoms and ions by the laser, e.g. by multiphoton absorption, is not required. The laser therefore does not have to be matched to analytes.

In addition, it can be seen that plasmas ignited in the gas phase can be much more stable and can be maintained without direct contact with the sample.

With a suitable choice of the parameters laser power, pulse rate and flow velocity, the ionization can also be carried out without prior atomization of the analyte. Thus can be configure the analyzer for both elemental and molecular analysis.

Typically, the flow is generated or even controlled by the mass spectrometer, which is typically a time-of-flight mass spectrometer. For this purpose, the mass spectrometer typically has a suction pump, so that the gaseous sample can be sucked through the inlet into the measuring space. The suction pump may be a vacuum pump. In addition, the mass spectrometer typically has suitable electrostatic filters and lenses (ion optics), which allows the transfer of ions generated under atmospheric pressure in the measuring space.

The plasma can thus in the flow at atmospheric pressure or a slightly reduced pressure, for example in a pressure range of about 10 ⁴ Pa to about 10 ⁵ Pa done, particularly above 4 × 10 ⁴ Pa or even 5 * 10 ⁴ Pa. Since a separate vacuum technique is not required, the construction of the analyzer can be comparatively simple and / or inexpensive.

The chosen design of the analyzer allows for comparable or even higher ionization efficiency lower gas consumption and / or lower power consumption unlike ICP-MS. In addition, a rapid switching on and off of the plasma is made possible, so that the plasma can be better adapted to the actual sample entry. All of this can also have a favorable effect on the detection limits for analytes in gases. In addition, the analysis device can be comparatively compact.

In addition, existing mass spectrometers can be easily retrofitted. A corresponding retrofit kit for mass spectrometers therefore has at least one laser irradiation unit and an assembly instruction. In addition, the retrofit kit may have a data cable connectable to the laser irradiation unit and the mass spectrometer and / or a data carrier having program instructions which are suitable for causing a processor of the mass spectrometer to send control commands to the laser irradiation unit. In addition, the retrofit kit may have the further components of the analysis device described below, in particular fluidic components. In one embodiment, the analysis device consists of the mass spectrometer, and a laser irradiation unit, which is set up to generate a plasma in a flow leading into the measurement space in front of the inlet of the mass spectrometer. For example, the laser beam (in operation) may be focused to a point in front of the inlet (in the flow direction) that is at a distance of about 1 mm to about 5 cm, more typically at a distance of about 2 mm to about 1 cm in front of the inlet located.

The analysis device can have a separate evaluation unit, which is connected to the mass spectrometer and the laser irradiation unit and controls it (as a master). However, the control of the analysis device can also be provided by a controller of the mass spectrometer or the laser irradiation unit.

According to a development, the analysis device has a gas supply arranged in front of the inlet for the gaseous sample. As a result, the gaseous sample can be defined up to the area of plasma generation by means of the laser.

The gas supply may comprise a fluid channel for the gaseous sample, e.g. a hose and / or a tube, in particular a glass capillary, have or be formed by the fluid channel. In addition, the gas supply may additionally include a pressure pump for adjusting the flow rate of the gaseous sample through the fluid channel.

However, the gas supply may also be via a mixing cell having a first inlet for the gaseous sample, a second inlet for a process gas such as argon, which typically lead into an example. Tube-shaped mixing chamber, and with an outlet for a formed from the gaseous sample and the process gas Mixed gas, done. The outlet may be formed by one end of the mixing chamber. By means of the mixing cell can be added to the gaseous sample defined chemically inert process gas. For this purpose, a further pressure pump arranged in front of the second inlet and connected thereto can be provided.

To counteract cooling of the plasma by collisions with the inflowing cold process gas, the process gas can be preheated (thermally excited) and / or electronically excited (eg, pre-ionized). Therefore, a heating cell and / or discharge cell for the process gas can be provided in front of the mixing cell.

According to a development, the analysis device has a plasma cell, which is connected fluidically, typically even gastight, to the gas supply and the inlet, in which the laser can ignite the plasma in the flow. In the following, the plasma cell is also referred to as a plasma chamber.

Typically, in a radial direction perpendicular to the direction of flow, the plasma cell has a larger inner diameter than the mixing cell and / or a fluidic connection, e.g., a plasma cell, disposed between the plasma cell and the inlet. a hose connection or a glass capillary.

As a result, the plasma cell can be flowed through by the flow so that the flow is spaced in radial directions from a wall of the plasma cell. Thus, unwanted interactions of the plasma with the wall of the plasma cell and thereby causing impurities and cross-contamination can be at least largely prevented.

Surprisingly, when using the plasma cell, a significantly higher proportion of the analytes can both be atomized and the atoms formed during the atomization can be ionized. This leads to an increased measuring sensitivity in the subsequent analysis in the mass spectrometer. The higher efficiency of decomposition of the analytes in the plasma cell compared to the laser-mediated plasma decay in the free gas flow is mainly due to the fact that the analytes get into hotter plasma areas. With a suitable choice of parameters (laser power and flow velocity), at least nearly complete atomization and subsequent ionization of the atoms formed during atomization can be achieved in the plasma chamber.

In contrast, when laser-mediated plasma decarburization occurs in the free gas flow, not all analytes pass through the hottest plasma regions, but can be deflected by laser-focused pressure waves into cooler plasma regions where the analytes are ionized by indirect mechanisms rather than atomized. However, this mode of operation may also be desired. Compared to igniting the plasma on a liquid or solid electrode or other solid, the ignition of the plasma in the gas itself - regardless of whether it takes place in a free flow or in the plasma cell - in any case the advantage that no measurement by the plasma contaminating material is dissolved out. In addition, the regular replacement of the electrode or the solid is eliminated. Furthermore, plasmas which are ignited on surfaces of solids are subject to strong pulse-to-pulse fluctuations because the pulses are preferably ignited in stochastically distributed surface defects.

Typically, the plasma cell in radial directions has a larger internal diameter than the mixing cell and / or the fluidic connection by a factor of 1.5 to 5, more typically by a factor of 2 to 4.

According to one embodiment, a pulsed laser is used to ignite a plasma in a carrier gas of a gaseous sample before the gaseous sample in a mass spectrometer on gaseous analytes present in the gaseous sample and / or analytes present in the carrier gas as dispersed aerosol particles and / or dispersed aerosol particles present analyte is examined.

According to one embodiment, a method for analyzing a gaseous sample comprises generating a flow leading into a mass spectrometer, typically a time-of-flight mass spectrometer, comprising the gaseous sample and igniting a plasma in the flow with a laser beam.

The flow can be formed by the gaseous sample.

However, it is also possible to mix the gaseous sample with a process gas before the ignition of the plasma. The ignition of the plasma with the laser then takes place in the flow formed by the mixture of gaseous sample and process gas.

Since the gaseous sample typically comprises a carrier gas and an analyte, wherein the analyte may be dispersed in the carrier gas or mixed with the carrier gas, the plasma is typically ignited by the laser in the carrier gas, the process gas and / or a mixture of the carrier gas with the process gas. The ignition of the plasma with the laser beam is typically repetitive.

In addition, ignition of the plasma is typically contactless, i. directly in the gas and not on a surface of a solid or liquid (macroscopic) body.

Before mixing, the process gas can be excited thermally and / or electronically. In particular, the process gas can be heated. In addition, the process gas may be exposed to electrical discharges, typically partially ionized.

Typically, the plasma is generated so that a temperature of the plasma is above 1000 ° K, above 5000 ° K, above 10000 ° K, or even above 15000 ° K.

Depending on the choice of the parameters laser power (pulse peak power), laser pulse rate, flow composition and an existing or non-existent radial limitation of the plasma ignition of the plasma, at least almost complete atomization of the analyte and subsequent ionization of the resulting atomization Atoms take place or at least almost complete ionization of the (non-atomized) analyte done.

After passing the plasma-treated flow into the mass spectrometer, there may be an investigation for analytes, a detection of analytes or even their quantification.

The above-described embodiments may be arbitrarily combined with each other.

Further advantageous embodiments, details, aspects and features of the present invention will become apparent from the dependent claims, the description and the accompanying drawings. It shows:

1A is a schematic representation of an analysis device for gaseous samples according to an embodiment; FIG. 1B shows a mass spectrometer determined by means of the analysis device illustrated in FIG. 1A; FIG.

FIG. 1C shows a mass spectrogram determined by means of the analysis device shown in FIG. 1A; FIG.

FIG. 2A shows a mass spectrogram determined by means of the analysis device illustrated in FIG. 1A; FIG.

FIG. 2B shows a mass spectrogram determined by means of the analysis device shown in FIG. 1A; FIG.

3A is a schematic representation of an analysis device for gaseous samples according to an embodiment;

3B is a schematic representation of an analysis device for gaseous samples according to an embodiment;

3C shows a mass spectrogram determined by means of the analysis device illustrated in FIG. 3A;

FIG. 4A shows a mass spectrometer determined by means of the analysis device shown in FIG. 3A; FIG.

4B shows a mass spectrogram determined by means of the analysis device shown in FIG. 3A;

FIG. 5 shows ion chones determined by means of the analyzer shown in FIG. 3A; FIG.

6A is a schematic representation of a gaseous sample analysis apparatus according to an embodiment;

6B is a schematic representation of an analysis device for gaseous samples according to an embodiment; FIG. 7A shows a mass spectrogram determined by means of the analysis device shown in FIG. 6A; FIG.

FIG. 7B shows a mass spectrometer determined by means of the analysis device shown in FIG. 6B; FIG.

8A shows a mass spectrogram determined by means of the analysis device illustrated in FIG. 3B;

8B shows a mass spectrogram determined by means of the analysis device illustrated in FIG. 3B;

9A is a flowchart of a method for analyzing a gaseous sample according to an embodiment; and

9B is a flowchart of a method for analyzing a gaseous sample according to an exemplary embodiment.

In the figures, like reference numerals designate corresponding parts accordingly.

FIG. 1A shows a schematic representation of an analysis device 100 for gaseous samples. The analysis device 100 consists of a mass spectrometer 6 and a laser irradiation unit, which has a laser 30 and a focusing optics shown as a lens 3. The mass spectrometer 6 has an inner measuring space and an inlet 5 leading into the measuring space. For reasons of clarity, a detailed representation of the structure of the mass spectrometer 6, the laser 30 and the focusing optics 3 is dispensed with.

The experimental results presented below were obtained using a time-of-flight spectrophotometer API-HTOF MS (Tofwerk, Thun, Switzerland) as mass spectrometer 6 and a Conqueror 3-LAMBDA laser (Compact Laser Solutions GmbH, Berlin, Germany), ie a diode-pumped Nd : YV0 ₄ laser, determined as laser 30, wherein the wavelength of the laser beams used was λ = 532 nm, respectively. The time-of-flight mass spectrometer API-HTOF MS has internal pumps (three pump stages) with which gas can be sucked in through inlet 5. As shown in FIG. 1A, the time-of-flight mass spectrometer used was provided with a custom-made metallic inlet 5, which tapered conically towards the outside. On the side oriented to the atmospheric pressure, the inlet 5 has an exemplary inner diameter of 150 μm. This diameter increases uniformly in the direction of the measuring space (vacuum area) of the mass spectrometer 6 to an exemplary value of 4 mm, with an exemplary total length of 15 mm. The exemplary focusing optics used for the laser included three Nd: YAG laser mirrors (NB1-K13, Thorlabs, Dachau, Germany) and an aspherical lens (C240TME-A, Thorlabs, Dachau, Germany) with a numerical aperture of NA = 0.50 and a focal length of f = 8 mm. However, comparable results can also be achieved with other mass spectrometers and / or sufficiently powerful laser irradiation units.

In the exemplary embodiment, the mass spectrometer 6 may generate a flow 4 through the inlet 5 into the measurement space, the direction of which is indicated by the arrow shown, of ambient air. In addition, the laser 30 can emit a laser beam 2, which forms a laser focus after leaving the focusing optics 3 as a focused laser beam 2 'in the flow 4. The laser focus can ignite a plasma 1 in the flow 4.

By means of the plasma 1, constituents of the air and, in particular, analytes present in the air, typically airborne analytes in the form of molecules in the gas phase or in the form of liquid or solid particles as aerosol, can be at least partially converted into ions and / or element ions (ions of the atoms which the molecules consist).

In the case of solid or liquid aerosol particles, these are first evaporated in the laser-induced plasma 1, so that molecules of the analyte pass into the gas phase. The molecules in the gas phase can be atomized in the plasma 1, i. the chemical bonds are broken. The resulting atoms can be ionized in plasma 1, i. be converted into charged particles. These steps may occur in plasma 1 either simultaneously or sequentially.

The temperatures in plasma 1 can reach up to several thousand Kelvin. After the analytes have been decomposed into ions or elemental ions, these and any reaction products that may be formed can be analyzed in the mass spectrometer 6.

FIG. 1B shows a mass spectrogram of ambient air determined by means of the analysis device 100 shown in FIG. 1A. For this purpose, a flow 4 leading into the measuring space was generated by the mass spectrometer 6 and the laser beam 2, 2 'focused on a point located approximately 2 mm in front of the inlet 5 and the laser 30 operated in pulse mode. FIG. 1C shows a part of the mass spectrometer shown in FIG. 1A at higher resolution.

As is customary in mass spectrometry, in mass spectrograms, also referred to below for short as spectrograms, the relative abundance S in arbitrary units (au) of detected charged objects as a function of the unitless m / z, which is inversely proportional to the (absolute) specific charge (absolute charge per mass) is shown.

The spectrograms shown correspond to expected spectrograms for ambient air in the absence of analytes. The reactive species detected here also represent three possible ionization paths of an analyte or an analyte residue M as a function of its chemical properties: (1) formation of protonated species M + H +, (2) ammonium adduct formation M + NH4 +, and formation of radical cations M +. The symbol "+" indicates the positive charge of the cations.

In addition, other mechanisms such as electron impact, photoionization via UV photons, thermal ionization, and Penning ionization may be considered as potential ionization pathways.

FIG. 2A shows a mass spectrogram for a mixture of air with n-butanol as analyte determined by means of the analysis device 100 explained with reference to FIG. 1A. FIG. 2B shows a mass spectrogram for a mixture of air with toluene as analyte determined by means of the analyzer 100 described with reference to FIG. 1A. For both measurements, 1 ml of the respective analyte was distributed before the inlet 5 of the mass spectrometer. As a result, the ambient air accumulates with analyte molecules, which can then be ionized by interaction with the reactive species referred to above with reference to FIGS. 2B and 2C. In the case of n-butanol as an airborne analyte, both protonated and ammoniated ions can be detected.

The spectrogram for toluene as analyte shows the typical signals for the formation of radical cations.

FIG. 3A shows a schematic representation of a gaseous sample analysis device 200. The analysis apparatus 200 is similar to the analysis apparatus 100 explained above with reference to FIG. 1A, but additionally has a gas supply for the gaseous sample arranged in the direction of the flow 4 in front of the inlet 5.

In the exemplary embodiment, the gas supply has an unillustrated pressure pump and a fluid duct 7 supplied by the pressure pump and designed as a glass capillary. With the gas supply, the plasma generation region (1) arranged between the gas supply (more precisely the fluid duct 7) and the inlet 5 defined amounts of gaseous samples are supplied.

FIG. 3C shows an ambient air mass spectrogram (without added analytes) determined by analyzer 200, which was applied to the plasma generation region at a rate of 2 L / min.

The signal pattern obtained by means of the mass spectrometer 6 is comparable to that in FIG. IB. The spectrogram shown in FIG. 3C is dominated by protonated water clusters, while the ammonium-water clusters and 02+ have lower signal intensities S. The emergence of new, additional reactive species (e.g., ΝΟ +, N02 +, N03 +) is not observed.

For the examined gases (compressed air, N2, Ar) an increase of the signal intensities could be observed when using the gas supply, most of all with compressed air.

FIG. 3B shows a schematic representation of a gaseous sample analysis device 200 '. The analyzer 200 'is similar to the analyzer 200 described with reference to Figure 3A. Instead of the simple fluid channel, the analyzer has 200 'but provided a mixing cell 7c. For reasons of space, the laser irradiation unit and the mass spectrometer of the analyzer 200 'are not shown in FIG. 3B.

In the exemplary embodiment, the mixing cell 7c is substantially Y-shaped. The mixing cell 7c has a first inlet 71 for the gaseous sample and a second inlet 72 for a process gas, which open in a Y-shape into a mixing channel 7 'which has an outlet 73 for a mixed gas formed from the gaseous sample and the process gas forms in front of the plasma generation area. The mixing cell 7c may be made of glass, e.g. be formed of glass capillaries.

In order to produce well adjustable gas mixtures, a first pressure pump (not shown) for pumping the gaseous sample through the first inlet 71 and a second pressure pump (not shown) for pumping the process gas through the second inlet 72 may be provided.

In addition, it can be provided to supply the process gas to the second inlet 72 of the mixing cell 7c via a heating cell for the process gas, an electrical discharge cell or a combined heating discharge cell.

FIG. 4A shows a mass spectrogram determined by means of the analysis device 200 explained with reference to FIG. 3A for a mixture of air with n-butanol as analyte. FIG. 4B shows a mass spectrogram for a mixture of air with toluene determined by means of the analysis device 200 explained with reference to FIG. 3A. In both measurements, however, 2 ml each of the analyte in question was placed in a closed flask through which an air stream is passed. The air stream is able to entrain analyte molecules and is then transferred through the fluid channel 7 to the plasma generation region and finally into the mass spectrometer 6. In this embodiment, air forms the carrier gas of the gaseous sample.

In both cases signal amplifications of the respective analyte signals concerned can be observed. Analogously to the background spectrogram (see FIG. 1B and FIG. 1C), protonated ions are preferably observed in the n-butanol spectrogram in FIG. 4A. Nevertheless, ammonium clusters are formed, but in lower signal intensity. As can be seen in Figure 4B, radical cations are again detected for toluene; also here in higher intensity. FIG. 5 shows by means of the analysis device 200 explained with reference to FIG. 3A certain ion chromatograms for gaseous samples with n-butanol as analyte. For this purpose, n-butanol was added to a closed flask through which a gas stream was subsequently passed. The gas flow was Ar (upper part A), nitrogen (middle part B) and compressed air (lower part C). The respective gas stream is able to entrain analyte molecules. The gaseous sample formed was then transferred through the fluid channel 7 to the plasma generation area and finally into the mass spectrometer.

Shown in each case are obtained ion chromatograms for the protonated n-butanol trimer. The number I of ions detected per time t is shown in relative units.

The flow rate Q of the gas flow was varied at intervals of 60 s in each case. The laser generates plasmas in the flowing gaseous sample only in the time range marked by the arrows.

The measurement started with a flow rate of 2 L / min, but without ignited plasma (laser off). No ions were detected. From t = 60 s, the plasma was ignited with the laser and immediately after the analyte was detected. An increase in signal was also shown here depending on the selected carrier gas (highest for compressed air, lowest for Ar). As the flow rate Q decreases, the number of extracted analyte ions decreases again.

6A shows a schematic representation of an analysis device 300 for gaseous samples 300. The analysis device 300 is similar to the analysis device 200 explained above with reference to FIG. 3A and also has a gas feed 7b. The gas feed 7b may be designed like the gas feed 7 of the above-explained analysis device 200, but ends in a plasma cell 8, in which the plasma can be ignited by the laser radiation.

The plasma 1 is ignited in this embodiment by the laser 30 in operation not in a free gas flow but in a gas flow 4, which flows through a space which is bounded in the flow direction (arrows), radial direction, for example by a tubular wall 81 of Plasma cell 8, typically a glass wall. By means of the plasma cell 8, the plasma generation region which can be irradiated with the focused laser beam Γ is thus delimited in radial directions of the gas flow 4.

This structure can be used both for a further signal increase of the analyte signals for the molecular MS, as well as contribute to an increase of the decomposition of the analyte into (element) ions by targeted use of an excited carrier gas and thus used for the element MS become.

In addition, between the plasma cell 8 and the inlet 5 a connecting this fluid connection 7 is provided. Losses of the plasma-treated gaseous sample can be at least largely avoided by the fluidic connection 7 and thus the resolution limit of the analyzer 300 for analytes can be improved. The fluidic connection 7 may, for example, be a hose connection or a glass capillary.

FIG. 6B shows a schematic illustration of an analysis device 400 for gaseous samples. The analyzer 400 is similar to the analyzer 300 discussed above with respect to FIG. 6A, but has a mixing cell 7c, as discussed above with respect to FIG. 3B, whose outlet 73 opens into the plasma chamber 8.

FIG. 7A shows a mass spectrogram determined by means of the analyzer 200 described with reference to FIG. 6A for compressed air supplied at a pump rate of 2 L / min (without added analytes).

In comparison to FIG. 3C, an even higher signal amplification can be achieved by the plasma chamber 8. The composition of the reactive species remains unchanged.

FIG. 7B shows a mass spectrogram determined by means of the analysis device 200 explained with reference to FIG. 6A for a gaseous sample supplied with a pumping rate of 2 L / min with air as carrier gas and n-butanol as analyte.

Higher measurement signals could also be determined for this gaseous sample than for measurements without a plasma chamber (see FIGS. 2A and 4A). With reference to FIGS. 8A, 8B, the influence of an (electronic) excitation of the supplied process gas on the expected signal pattern in the spectrogram is explained.

FIG. 8A shows a mass spectrogram for air determined by means of the analysis device 200 'explained with reference to FIG. 3B, and FIG. 8B shows a mass spectrogram determined by means of the analysis device 200' explained with reference to FIG. 3B wherein the air in the mixing cell is transmitted electronically a discharge cell of stimulated helium was added.

Fig. 8A shows the typical known signal behavior in the mass spectrogram of ambient air. In particular, the emergence of the expected protonated water clusters, ammonium-water clusters, as well as the 02 + ions can be observed.

As can be seen from Fig. 8B, by mixing electronically excited helium, the species detected in Fig. 8A is no longer detected. Instead, signals in the lower mass range are detected for e.g. (m / z = 14) N +, (m / z = 16) 0+, (m / z = 28) N2 +.

Using the combination of an excited carrier gas (He) and the plasma ignited therein, atomization and subsequent ionization of analytes observed for element mass spectrometry can be observed with the flow and laser parameters used. Accordingly, the nitrogen and oxygen molecules contained in the ambient air can be detected as N + and 0+ ions, respectively. An analogous behavior is to be expected for other analytes.

Hereinafter, methods for analyzing gaseous samples which can be carried out with the above-mentioned analyzers will be explained.

9A shows a flow chart of a method 1000 for analyzing gaseous samples.

In a block 1100, a flow of gaseous sample into a mass spectrometer is generated.

Thereafter, or with the generation of the flow, a plasma is ignited directly in the flow in a block 1200 with a laser in front of the mass spectrometer. To ignite the plasma we typically use a focused, still typically focused, pulsed laser beam, in particular at a pulse rate that is in a range of 50 Hz to 1 MHz. The pulse peak power of the laser beam is typically above 10 kW and may be, for example, up to 1 MW.

The plasma may be in a free flow or in a flow-through plasma chamber, with the flow typically being spaced from lateral walls of the plasma chamber. The distance of the flow to the lateral walls of the plasma chamber in directions perpendicular to the flow direction is typically in a range of about 2 mm to about 10 mm.

In addition, the plasma can be ignited in an analyte comprising the carrier gas or a mixture of the carrier gas with an inert process gas.

It may be provided to mix the carrier gas before the block 1200 with an activated process gas.

Finally, in a block 1400, the laser-treated flow can be examined by mass spectroscopy, in particular on ions generated by the plasma.

9B shows a flow chart of a method 1000 'for analyzing gaseous samples.

In a block 1200 ', a plasma is generated in a gas flow with a laser. The generation of the plasma in block 1200 'can be carried out as explained above for block 1200.

Prior to block 1200 ', in a block 1100', the gas flow likely to be analytes may be generated.

After generating the plasma in the gas flow, the gas flow may be transferred to a mass spectrometer in a block 1300 '. Finally, the flow may be assayed in a block 1400 'in the mass spectrometer, with detection in the original gas flow of existing analytes.

With the methods described herein, gas-borne, in particular airborne analytes in the form of molecules in the gas phase or in the form of liquid or solid particles as an aerosol can be easily and reliably converted into elemental ions. This transfer can take place under atmospheric pressure. The generation of elemental ions can be used for downstream, mass spectrometric separation / detection for the qualitative and quantitative element determination of the analyte under investigation.

The atomization and / or ionization is carried out by a laser-induced, hot plasma, which is ignited in the gas. Direct interaction of the laser with the analytes (molecules, aerosol particles) is not required. Since gas-borne analytes often move very fast through the laser focus, these analytes can not be detected by other techniques based on a direct interaction, at least if they cross the focus volume in time between two laser pulses. With the methods and devices described herein, analytes present in gases can therefore be detected particularly sensitively.

Depending on the parameters used (flow parameters, laser parameters) either elemental or molecular spectrometry for gaseous samples is possible.

The laser-induced plasma has a hot core, which may be at least partially shielded for analytes due to interactions with the ambient air, as well as the formation of shockwaves.

At the periphery of the plasma, reactive species (e.g., protonated water clusters, ammonium-water clusters, O 2+ ions) are formed, which can cause ionization of an analyte by interaction with an analyte.

If the analyte does not reach the hot core of the plasma, typically there is no atomization of the analyte followed by ionization but ionization suitable for molecular spectrometry. When using a thermally and / or electronically excited carrier gas stream (which can be done, for example, by admixing an excited process gas to the gaseous sample or by exciting the gaseous sample), was also in the laser parameters used (wavelength: λ = 532 nm, repetition rate: 26 kHz , Average power: 15W, pulse width: 6 ns) has enough energy in the system to break through the corresponding bonds into the molecules, thus causing atomization and corresponding ionization of these atoms. The resulting ions can be analyzed in the mass spectrometer (element spectrometry).

According to one embodiment, an analysis device comprises a mass spectrometer comprising a measurement space and an inlet leading into the measurement space, a device for generating a flow of a gaseous sample through the inlet into the measurement space and a laser irradiation unit, the laser irradiation unit being set up with a laser beam in the Flow upstream of the inlet to ignite a plasma for at least partially ionizing the gaseous sample.

In this case, the device for generating the flow can be provided at least partially by the mass spectrometer and / or can have one or two external pressure pumps.

The present invention has been explained with reference to exemplary embodiments. These embodiments should by no means be construed as limiting the present invention. The following claims are a first, non-binding attempt to broadly define the invention.

Claims

An analyzer (100-400) for a gaseous sample, comprising:

- A mass spectrometer (6) comprising a measuring space and an inlet leading into the measuring space (5); and

a laser irradiation unit (30, 3),

wherein the analyzing device is arranged to convey the gaseous sample to the inlet (5) by means of a flow (4) comprising the gaseous sample, and wherein the laser irradiation unit (30, 3) is arranged with a laser beam (2 ') in the flow (4) in front of the inlet (5) to ignite a plasma (1) for at least partially ionizing the gaseous sample.

2. Analysis device (100-400) according to claim 1, wherein the laser irradiation unit (30, 3) comprises a laser (30) and / or a focusing optic (3), wherein the laser irradiation unit (30, 3) is arranged, the plasma (1 ) in a carrier gas of the gaseous sample, wherein the laser irradiation unit (30, 3) is arranged to ignite the plasma (1) in a mixture of the carrier gas with a process gas, and / or wherein the gaseous sample mixed with the carrier gas gaseous analytes and / or in the carrier gas dispersed aerosol particles.

3. Analysis device (100-400) according to one of the preceding claims, wherein the laser beam is a pulsed laser beam, in particular with a pulse rate which lies in a range of 50 Hz to 1 MHz, and / or wherein the laser beam has a pulse peak power of at least 10th kW.

4. Analysis device (100-400) according to one of the preceding claims, further comprising a gas supply (7, 7b, 7c) arranged in a direction of the flow (4) in front of the inlet (5).

The analysis device (100-400) according to claim 4, wherein the gas supply (7, 7b, 7c) comprises a fluid channel (7), a mixing cell (7c) having a first inlet (71) for the gaseous sample, a second inlet (7). 72) for a process gas, and an outlet (73) for a mixed gas formed from the gaseous sample and the process gas, a first pressure pump for pumping the gaseous sample through the fluid passage (7) or the first inlet (71), and or a second pressure pump for pumping the process gas through the second inlet (72).

6. An analysis device (100-400) according to claim 4 or 5, further comprising:

a plasma cell (8) connected fluidically to the gas supply (7, 7b, 7c) and the inlet (5), the laser irradiation unit (30, 3) coupling the laser beam (2 ') into an interior of the plasma cell (8) and / or in which the plasma cell (8) has a larger internal diameter than the mixing cell (7c) in a radial direction perpendicular to the direction of the flow (4), whereby the plasma cell (8) can be flowed through by the flow (4). that the flow (4) is spaced in the radial direction from a wall (81) of the plamaceous cell (8), the wall (81) being tubular, and / or the wall (81) being made of glass;

- A front of the mixing cell (7c) arranged heating cell for the process gas; and or

- A front of the mixing cell (7c) arranged discharge cell for the process gas.

7. Analysis device (100-400) according to one of the preceding claims, wherein the inlet (5) of the mass spectrometer (6) is a nozzle, wherein an internal cross section of the inlet (5) of the mass spectrometer (6) increases at least in sections, wherein the mass spectrometer (6) is a time-of-flight mass spectrometer, the mass spectrometer (6) having a suction pump fluidly connected to the measurement space, and / or the mass spectrometer (6) being arranged to inject the gaseous sample through the inlet (5) to suck in the measuring space, and / or to change a flow rate of the flow (4).

8. A method (1000, 1000 ') for analyzing a gaseous sample, comprising:

- generating a flow (4) leading into a mass spectrometer (6), which comprises the gaseous sample; and

- Igniting a plasma (1) in the flow (4) with a laser beam (2 ').

The method (1000, 1000 ') of claim 8, further comprising

- Mixing the gaseous sample with a process gas before igniting the plasma (1).

10. A method (1000, 1000 ') according to claim 9, further comprising - Thermal and / or electronic excitation of the process gas before mixing.

11. A method (1000, 1000 ') according to any one of claims 8 to 10, after ignition of the plasma (1) further comprising:

- Examining the flow (4) in the mass spectrometer (6); and or

- Detection of an analyte.

12. A method (1000, 1000 ') according to any one of claims 8 to 11, wherein a temperature of the plasma (1) is above 1000 ° K.

13. The method (1000, 1000 ') according to any one of claims 8 to 12, wherein the gaseous sample comprises a carrier gas and an analyte, wherein the analyte is dispersed in the carrier gas, wherein the analyte is mixed with the carrier gas, wherein the plasma (1 ) is ignited in the carrier gas, the process gas and / or a mixture of the carrier gas with the process gas, wherein the plasma in front of an inlet (5) of the mass spectrometer (6) is ignited, wherein the plasma in one of the flow (4). flowed through plasma cell (8) is ignited, which is fluidically connected to the inlet (5), and / or wherein the ignition of the plasma (1) with the laser beam (2, 2 ') is repetitive and / or contactless.

14. Method (1000, 1000 ') according to claim 13, wherein at least partial atomization and / or at least partial ionization of the analyte and / or atoms formed during atomization occur by the plasma (1).

15. Use of a pulsed laser (30) for igniting a plasma (1) in a carrier gas of a gaseous sample comprising gaseous analytes mixed with the carrier gas and / or aerosol particles dispersed in the carrier gas before the gaseous sample is analyzed in a mass spectrometer (6) becomes.