WO2016092156A1

WO2016092156A1 - Method and device for detecting ambient clusters

Info

Publication number: WO2016092156A1
Application number: PCT/FI2015/050875
Authority: WO
Inventors: Heikki JUNNINEN; Mikko SIPILÄ
Original assignee: University Of Helsinki
Priority date: 2014-12-12
Filing date: 2015-12-11
Publication date: 2016-06-16

Abstract

An arrangement (100) for determining mobility of molecules or clusters of an ambient atmosphere by an ion mobility spectrometer comprises a first flow tube (101) and an ion mobility chamber (102) with an inlet (103). The first flow tube is configured for providing sample gas flow (104) for the ion mobility chamber (102) via the inlet (103). The arrangement comprises also an electric field generating device (105) for applying an electric field between the inlet (103) and outlet (110) of the ion mobility chamber, and a generator for producing ionized clusters by ionising the clusters of the gas flow by a non-radioactive soft X-ray radiation source (106). The generator is configured to produce said ionized clusters in an ion formation region (108, 108A), which is arranged after the inlet (103) in the direction of the sample flow (104) and after the electric potential wall of the inlet (103) and inside the electric field of the ion mobility chamber (102).

Description

METHOD AND DEVICE FOR DETECTING AMBIENT CLUSTERS

TECHNICAL FIELD OF THE INVENTION

The invention relates to a method and device for detecting properties, such as masses or concentrations, of gas phase samples or especially molecules or ambient clusters, especially clusters of an ambient atmosphere in an ion mobility spectrometer.

BACKGROUND OF THE INVENTION An accurate mass spectrometry methods for determining of properties of gas phase samples are in very important role e.g. in atmospheric studies, such as studying e.g. roles of different chemical substances, such as ammonia, amines, sulphuric acid and oxidized organics, in atmospheric nanoparticle formation. Especially there is a need for better known of low concentrations and variability of atmospheric amines and highly oxidized organics as well as also many other bases and acids.

However, measurement of trace amounts of gaseous compounds for example from air is extremely difficult, as their concentration is minimal compared to the total air molecule concentration, and due to the large variety of the different gases compounds and their isotopes. However, some of these molecules have a significant effect on the air chemistry and aerosol formation, even in small amounts. Therefore exact measurements are needed for instance in atmospheric aerosol research.

Very often gas phase samples are analysed by a mass spectrometer, but also other detecting devices can be used, such as IMS-device (Ion Mobility Spectrometry) or DMA-device (Differential Mobility Analyzers). The mass spectrometer is detecting the mass to charge ratio of an ion or ion cluster, whereas IMS and DMA devices are based on the electrical mobility of the sample particles. As majority of sample particles, such as airborne molecules and clusters are initially neutral, they need to be charged before a measurement. The ions move in an electric field and in a certain media, such an in a gas flow inside the ion mobility spectrometer by a certain velocity, depending e.g. on the size and shape of the ions. The ion mobility spectrometer determines the ions based on the mobility of the ions using the electric field generated inside the spectrometer. In order to provide the electric field an inlet of the spectrometer is in a very high electric potential, typically in order of 10kV. The high electric potential, however, naturally prevents access or flow of the ionized particles being outside the inlet into the spectrometer, so in other words the access of the ionized clusters or other particles before the inlet in the direction of the flow into the through the spectrometer.

SUMMARY OF THE INVENTION

An object of the invention is to alleviate and eliminate the problems relating to the known prior art. Especially the object of the invention is to provide an arrangement and device for allowing particles to flow into the spectrometer from the outside of the inlet of the spectrometer.

The object of the invention can be achieved by the features of independent claims.

The invention relates to an arrangement for determining properties, such as masses or concentrations, of gas phase samples and especially mobility of molecules or ambient clusters of an ambient atmosphere by an ion mobility spectrometer according to claim 1. In addition the invention relates to a corresponding method for determining ambient clusters according to claim 15. According to an embodiment of the invention an arrangement for determining properties of the molecules or clusters of an ambient atmosphere by an ion mobility spectrometer comprises a first flow tube and an ion mobility chamber with an inlet. The first flow tube is configured to provide a sample gas flow with the ambient molecules or clusters for the ion mobility chamber via the inlet. In addition the arrangement comprises an electric field generating device for applying an electric field in the ion mobility chamber, and essentially between the inlet, an ion gate and outlet of the ion mobility chamber. The arrangement comprises also a generator for producing ionized clusters for the ion mobility chamber by ionising said clusters of the gas flow by a non-radioactive soft X-ray radiation source.

It is to be noted that according to the invention the ambient molecules or clusters are not yet ionized in the first flow tube, but the generator produces the ionized clusters in an ion formation region, which is located after the inlet in the direction of the sample flow and therefore also after the electric potential wall of the inlet. This offers great advantages over the prior art, namely previously the particles were ionized already before the inlet and because of the high electric potential wall of the inlet, the introducing of the ionized particles into the ion mobility chamber has been very difficult and aggressive often decomposing the particles to be determined. According to the invention the electrically neutral clusters can be introduced easily and gentle way to the other side of the high electric potential wall of the inlet portion, because the electric potential wall does not introduce any forces to the electrically neutral clusters. The ionizing of the electrically neutral clusters just after the high electric potential wall of the inlet is very gentle, easy and effective way to introduce ionized clusters for the ion mobility chamber of the ion mobility spectrometer.

The ion gate comprises or functions advantageously as an electrode providing an electrical potential. The electrical potential is advantageously controllable so an access of said ionized clusters from the ion formation region into the portion of said ion mobility chamber after said ion gate is controlled by the controllable electrical potential. Thus the ions can be generated in said ion formation region and when switching an appropriate electrical potential to said ion gate, the ions are dragged from the ion formation region into the ion mobility chamber.

The ionizing generator for producing the ionized clusters is advantageously a soft X-ray radiation source. According to the invention the focal point of the X-ray radiation source is focused into the ion formation region, which is located after the inlet. The energy of the used soft X-ray photons is typically in a range of 1 -10 keV, most advantageously about 1 -5 keV. This area is very appropriate, because it does not decompose the clusters to be ionized. The X-ray radiation source offers also additional advantages, namely it can be switched in operation mode and off mode due to need, whereupon it is much safer way to ionize the clusters than e.g. radioactive sources. In addition the focusing of the X-ray radiation beam is quite easy and accurate. According to an advantageous embodiment the X-ray radiation used is focused to a certain focal point or focal point area. The point or accurate area, where the ionized clusters are produced, is located in said ion formation region after the inlet but before the ion gate.. The mobility determination can only performed to ions that are produced before the ion gate, namely ions that are formed after the ion gate are only disturbing and are harmful to the mobility determination. Thus, according to an embodiment tthe arrangement is configured to determine the properties, such as masses or concentrations, by determining the mobility and travelling time of the ionized clusters between the ion gate and outlet.

According to an embodiment also ionized reagent particles can be provided into the sample flow in order to stabilize desired chemical reactions so that only desired chemical charging reactions are produced. By this e.g. unwanted charging reactions can be effectively eliminated. This is because it is most likely that that sample ion will interact first with the desired ions the amount or concentration of which is increased and thereby the collision probability of these ions are maximized. The ionized reagent particles can be provided into the sample flow for example after the inlet electrical potential wall, where the mixing of the ionized reagent particles into the sample flow can be implemented electrically. Thus, there is no need for mixing the reagent particle flow and sample flow mechanically with each other, which makes the process very fast and minimize un-wanted turbulences.

In addition, according to an embodiment the inlet of the ion mobility chamber may be configured to minimize losses at a wall region of the ion mobility chamber. This is possible, for example, by providing a large diameter flow tube and providing laminar sample flow so that the sample flow flowing essentially at the centre area of the large diameter flow tube does not interact with the wall of the tube. According to an example a sub- sample is taken from the sample flow just before actual detection (so where the losses are negligible or even zero).

Additionally the inlet of the ion mobility chamber may be configured to introduce only proportion of the sample flow of the first flow tube into the ion formation region and ion mobility chamber, whereupon the arrangement comprises an outlet channel before the ion mobility chamber for removing the excess sample flow. In addition, the arrangement may also comprise a laminarizer for producing an essentially laminar flow for the inlet area and again into the ion formation region and ion mobility chamber in order to additionally minimize wall contacts of the ionized clusters.

The present invention offers advantages over the known prior art, such as the possibility to measure neutral clusters from the ambient atmosphere and additionally essentially at atmospheric pressure. Additionally, the invention increases the detection sensitivity, and losses including wall losses can be effectively minimized, because the clusters can be transferred as electrically neutral over the inlet high potential wall directly to the ion formation region after the said inlet portion.

BRIEF DESCRIPTION OF THE DRAWINGS

Next the invention will be described in greater detail with reference to exemplary embodiments in accordance with the accompanying drawings, in which:

Figure 1 illustrates a principle of an exemplary arrangement for determining ambient clusters according to an advantageous embodiment of the invention,

Figure 2 illustrates another example of an arrangement for determining ambient clusters according to an advantageous embodiment of the invention, and

Figure 3 illustrates an exemplary inlet portion of the arrangement according to an advantageous embodiment of the invention.

DETAILED DESCRIPTION

Figures 1 -2 illustrate principles of exemplary arrangements 100 for determining ambient clusters, and Figure 3 illustrates an exemplary inlet portion 103 of the arrangement according to an advantageous embodiment of the invention. The arrangement 100 comprises a first flow tube 101 and an ion mobility chamber 102 with an inlet 103, as well an ion gate 1 1 1. The sample gas flow 104 is led via the first flow tube 101 to the ion mobility chamber 102 via the inlet 103 and ion gate 1 1 1. In addition the arrangement comprises an electric field generating device 105 for applying an electric field 105 in the ion mobility chamber 102, and essentially between the inlet 103, ion gate

1 1 1 and outlet 1 12 of the ion mobility chamber 102.

According to an embodiment the inlet 103 (or the wall structure around the pin hole of the inlet), ion gate 1 1 1 and outlet 1 12 are configured to function as electrodes providing said electric field 105. As an example the electrical potential of the inlet 103 is greater than the electrical potential of said outlet

1 12 so that the ions formed in the ion formation region are effectively dragged towards the ion mobility chamber 102 and again to the outlet 1 12. As an example the potential of said inlet 103 might be e.g. 9000 V, the potential of said ion gate when accessing the ions in to the mobility chamber e.g. 4800 V and the potential of the output 1 12 electrode e.g. 400 V. However, these are just examples and are not to be understood as having any limitative effects. In addition according to an exemplary embodiment the electrical potential of the ion gate 1 1 1 is controllable, whereupon the access of the ionized clusters from the ion formation region 108 into the portion of said ion mobility chamber 102 after said ion gate 1 1 1 can be controlled by the controlling said electrical potential of said ion gate 1 1 1 .

The arrangement comprises also a generator 106 for producing ionized clusters for the ion mobility chamber 102 by ionising said clusters of the gas flow 104 by a non-radioactive soft X-ray radiation source 106 emitting X-ray beams 107, which are focused into the ion formation region 108, or advantageously to a focal point or focal point area 108A, located before the ion gate 1 1 1 , and where the clusters are ionized. The ion formation region 108 locates, according to the invention after the inlet 103 in the direction of the sample flow and therefore also after the electric potential wall of the inlet 103.

The inlet 103 of the ion mobility chamber may be configured to introduce only proportion 109 (sub-sample) of the sample flow 104 of the first flow tube into the ion formation region 108 and ion mobility chamber 102. This is implemented by an outlet channel 1 10, which is advantageously provided just before the ion mobility chamber 102, or even before inlet wall 103 for removing the excess sample flow.

Figure 2 illustrates another example of an arrangement 100 for determining ambient clusters according to an advantageous embodiment of the invention comprising essentially the same components and functionalities as described in connection with the Figure 1. The arrangement 100 additionally comprises a suction portion 1 13 arranged in the ion formation region 108 to generate under-pressure and thereby to deflect the sample gas flow 104 trajectory so that the sample gas flow 104 elongates to or along the focal point area 108A of the X-ray radiation source 106, thereby providing longer ion formation region 108 and to provide ions more effectively. In addition the arrangement may also comprise a counterflow generating device 1 14 for generating counterflow 1 15. The counterflow may comprise e.g. N₂, He or Ar, and the purpose is to remove undesired components, such as water, from the sample gas flow 104.

The invention has been explained above with reference to the aforementioned embodiments, and several advantages of the invention have been demonstrated. It is clear that the invention is not only restricted to these embodiments, but comprises all possible embodiments within the spirit and scope of the inventive thought and the following patent claims. Especially, it is to be noted that the properties of the ambient molecules or clusters to be studied may be e.g. masses or concentrations of gas phase samples and especially mobility of molecules or ambient clusters of an ambient atmosphere. The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated.

Claims

1. An arrangement (100) for determining properties, such as masses or concentrations, of gas phase samples and especially mobility of ambient clusters by an ion mobility spectrometer,

wherein the arrangement comprises:

- a first flow tube (101 ) and an ion mobility chamber (102) with an inlet

(103), where said first flow tube is configured for providing sample gas flow (104) for the ion mobility chamber via said inlet, said sample gas comprising said ambient clusters to be determined by the ion mobility spectrometer,

- an electric field generating device for applying an electric field (105) between the inlet (103), an ion gate (1 1 1 ) and outlet (1 12) of the ion mobility chamber,

- a generator (106) for producing ionized clusters by ionising said clusters of the gas flow by a non-radioactive soft X-ray radiation source,

wherein

- said generator is configured to produce said ionized clusters in an ion formation region (108), which is arranged after the inlet (103) and before the ion gate (1 1 1 ) and inside the electric field (105), and

- said electrical potential of said ion gate (1 1 1 ) is controllable so that an access of said ionized clusters from the ion formation region (108) into the portion of said ion mobility chamber (102) after said ion gate (1 1 1 ) is controlled by the controllable electrical potential of said ion gate (1 1 1 ).

2. An arrangement of claim 1 , wherein said generator (106) for producing said ionized clusters is a soft X-ray radiation source, the focal point area (108A) of which is focused into the ion formation region (108) being after the inlet (103) but before said ion gate (1 1 1 ).

3. An arrangement of any of previous claims, wherein said inlet (103), ion gate (1 1 1 ) and outlet (1 12) is configured to function as electrodes providing said electric field (105).

4. An arrangement of any of previous claims, wherein the electrical potential of said inlet (103) is greater than the electrical potential of said outlet (1 12).

5. An arrangement of any of previous claims, wherein the arrangement is configured to determine the properties, such as masses or concentrations, by determining mobility and travelling time of the ionized clusters between the gate (1 1 1 ) and outlet (1 12).

6. An arrangement of any of previous claims, wherein the arrangement comprises a suction portion arranged in the ion formation region (108) to generate under-pressure and thereby to deflect the sample gas flow (104) trajectory so that said sample gas flow (104) elongates to the focal point area (108A) of the X-ray radiation source, thereby providing longer ion formation region (108) and to provide ions more effectively.

7. An arrangement of any of previous claims, wherein the arrangement comprises a suction portion arranged in the ion formation region (108) and a counterflow generating device (1 14) for generating counterflow (1 15) in order to remove undesired components.

8. An arrangement of any of previous claims, wherein the energy of the used soft X-ray photons is in a range of 1 -10 keV, most advantageously about 1 -5 keV, and wherein said X-ray radiation source is configured to be switched in operation mode and off mode.

9. An arrangement of any of previous claims, wherein the arrangement is further configured to provide ionized reagent particles into the sample flow in order to stabilize desired chemical reactions so that only desired chemical charging reactions are produced.

10. An arrangement of claim 9, wherein the arrangement is configured to provide said ionized reagent particles into the sample flow after the inlet electrical potential wall (103) and mixing said ionized reagent particles electrically into the sample flow (104).

1 1. An arrangement of any of previous claims, wherein the inlet (103) of the ion mobility chamber (102) is configured so to minimize losses at a wall region of the ion mobility chamber.

12. An arrangement of any of previous claims, wherein the inlet (103) of the ion mobility chamber (102) is configured so introduce only proportion of the sample flow (104) of the first flow tube (101 ) into the ion formation region (108) and ion mobility chamber, whereupon the arrangement comprises an outlet channel (1 10).

13. An arrangement of any of previous claims, wherein the arrangement comprises a laminarizer for producing an essentially laminar flow for the inlet area and again into the ion formation region and ion mobility chamber in order to minimize wall contacts of the ionized clusters.

14. An arrangement of any of previous claims, wherein the mobility determination process is implemented essentially at atmospheric pressure.

15. A method for determining properties, such as masses or concentrations, of gas phase samples and especially mobility of ambient clusters by an ion mobility spectrometer,

wherein the method comprises steps of:

- providing a sample gas flow from a first flow tube (101 ) for the ion mobility chamber (102) via an inlet (103) of the ion mobility chamber, said sample gas comprising said ambient clusters to be determined by the ion mobility spectrometer,

- applying an electric field (105) between the inlet (103), an ion gate

(1 1 1 ) and outlet (1 12) of the ion mobility chamber,

- producing ionized clusters by ionising said clusters of the gas flow (104) by a non-radioactive soft X-ray radiation source (106),

wherein

- said ionized clusters are produced in an ion formation region (108) after the inlet (103) and before the ion gate (1 1 1 ) and inside the electric field,

- an access of said ionized clusters from the ion formation region (108) into the portion of said ion mobility chamber (102) after said ion gate (1 1 1 ) is controlled by a controllable electrical potential of the ion gate