WO2011073206A1

WO2011073206A1 - Device and method for producing a sample from a liquid

Info

Publication number: WO2011073206A1
Application number: PCT/EP2010/069661
Authority: WO
Inventors: Frédéric Chartier; Michel Tabarant; Olga Victorova-Leclerc
Original assignee: Commissariat A L'energie Atomique Et Aux Energies Alternatives
Priority date: 2009-12-14
Filing date: 2010-12-14
Publication date: 2011-06-23
Also published as: FR2953927A1; EP2513625A1; FR2953927B1

Abstract

The invention relates to a device (1) for preparing a sample from a liquid including analytes, said device comprising a glow discharge lamp that includes a cathode (2) and an anode (3), a glow discharge (5) being formable therebetween. The device (1) is characterized in that it also comprises an injector (4) comprising an inlet (40) and an outlet (41). The inlet (40) is suitable for receiving the liquid and a nebulizing gas such that the injector (4) forms a nebulizer for distributing the liquid, in aerosol form, directly onto the cathode (2). The outlet (41) is directed toward the cathode (2) and suitable for distributing the liquid directly onto the surface of the cathode (2) such that the analytes can interact with the glow discharge (5) so as to form the sample. The invention also relates to a corresponding method for producing a sample by means of glow discharge.

Description

DEVICE AND METHOD FOR MANUFACTURING SAMPLE FROM A LIQUID

Field of the invention

The invention relates to the field of sample preparation from a liquid comprising glow discharge analytes. More specifically, the invention relates to a device for preparing samples by glow discharge from a liquid and comprising a cathode.

The invention also relates to a glow discharge sample manufacturing method, using a device for preparing samples from a liquid, comprising a cathode.

State of the art

It is known to use glow discharge lamps coupled to mass spectrometry for the elemental and isotopic analysis of samples, and glow discharge lamps coupled to optical spectrometry for the elemental analysis of samples.

The operation of a glow discharge lamp is as follows.

The glow discharge lamp comprises a cathode and an anode between which an electric field of the order of one kilovolt is applied after injection of a plasma gas, usually argon. The electric field causes ionization of the plasma gas atoms under reduced pressure (from 0.1 to 10 millibars), forming a plasma also called "glow discharge".

The glow discharge interacts with a solid comprising analytes. This solid is often the cathode itself of the glow discharge lamp cathode which is eroded as and when analysis.

More precisely, the plasma gas atoms are accelerated by the electric field towards the cathode and cause the ejection of constituent atoms of the material of the cathode, and therefore of the solid.

These atoms are then excited and ionized in the glow discharge, then directed to an analyzer (usually a mass spectrometer or optical spectrometer).

This technique is usually used for the characterization of solids, but its properties also make it very interesting for the direct characterization of liquids containing analytes to be characterized.

Indeed, it allows not only the elemental, but also molecular characterization of the liquids containing analytes and the solvent; which makes it perfectly suited to speciation studies, that is, to the analysis of the different chemical forms under which an element exists in a given environment.

However, the major disadvantage of liquid characterization is the lack of available energy in the glow discharge to remove the solvent. It is then important to completely remove the solvent before reacting (injecting) the analytes with (in) the glow discharge.

To allow the introduction of liquid for interaction with a glow discharge for elemental characterization purposes and molecular, intermediary devices between the liquid and the glow discharge lamp have been developed.

In particular, the intermediate devices of the "Particle Beam" type (or "Partide Beam" in English) have been developed essentially for speciation studies at the separation output of the different species by chromatographic techniques, as described in US Pat. No. 5,447,553. .

The principle described in US Pat. No. 5,447,553 consists in nebulizing, using a nebulizing gas, a liquid sample comprising analytes to be characterized, in order to form an aerosol. The aerosol is thus formed of the liquid from the sample and the nebulizing gas. The aerosol is then vaporized in a heated chamber, the latter allowing the separation of solvent molecules and analytes present in the form of desolvated particles. The solvent molecules and the analyte particles are then aspirated through a double chamber under reduced pressure, having a first chamber and a second chamber, where differential pumping (1 to 10 millibars for the first chamber and 0.1 to 1 millibar for the second chamber) allows the removal of solvent molecules and nebulizing gas before the introduction of the analytes into a glow discharge lamp.

The intermediate device is an element intended to be positioned upstream of the glow discharge source, which limits the compactness of all the equipment.

Another disadvantage is the need for an additional pumping system to provide vacuum in the double chamber; the device is thus a particularly complex equipment with a large number of parts, with complicated use, which increases its cost and reduces its maneuverability for the operator. Finally, it is not possible to use the device dynamically; which limits the analytical possibilities, in particular, it is not possible to pre-concentrate the analytes. Description of the invention

The object of the invention is to overcome at least one of the above disadvantages.

For this purpose, it is proposed according to the invention a device for preparing a sample from a liquid comprising analytes, comprising:

a glow discharge lamp comprising a cathode and an anode, between which a glow discharge can be formed,

the device being characterized in that it further comprises an injector comprising an inlet and an outlet;

the inlet being adapted to receive the liquid and a nebulizing gas, so that the injector forms a nebulizer for distributing the liquid in aerosol form directly on the cathode, the outlet being directed towards the cathode and adapted to distribute the liquid directly on the surface of the cathode, so that the analytes can interact with the glow discharge to form the sample.

Other optional and non-limiting features of the device are:

the cathode is a cylinder having a longitudinal axis and comprising:

^■ a base at one end of the cylinder having a center through which the longitudinal axis passes; ^■ a free end opposite the base having a tapered portion defined by a plane oblique to the longitudinal axis;

^■ a shaft extending parallel to the longitudinal axis between the base and the free end;

A central recess within the barrel and extending parallel to the longitudinal axis from the oblique plane;

the free end having a peripheral edge to the recess, the edge defining a glow discharge initiation tip at the point of the edge whose projection on the longitudinal axis is furthest from the center of the base;

and wherein the outlet of the injector is arranged to deposit the liquid droplets upstream of the glow discharge primer tip;

the oblique plane forms an acute angle with the longitudinal axis; the angle being between 40 ° and 60 °;

the barrel comprises a housing bore of the injector extending from the base and opening into the recess; and

- The bore through the barrel has a longitudinal axis of bore forming an angle between 20 ° and 30 ° with the longitudinal axis of the cylinder.

There is also provided a method for producing a sample by discharge using the device according to the invention, characterized in that it comprises the step of:

injecting at least once a liquid comprising analytes directly onto the surface of the cathode using a nebulizer.

Other optional and non-limiting features of the process are:

the method further comprises the step of, after the injection of the liquid, forming a glow discharge between the cathode, optionally the glow discharge primer tip of the cathode, and an anode for ionizing the analytes injected on the cathode;

the method further comprises the step of sending the ionized analytes to an analysis device;

the method further comprises, between the injection of the liquid and the formation of the glow discharge, the step of injecting a plasmagenic gas between the cathode and the anode to feed the glow discharge and optionally to facilitate desolvation of the analytes; and

the liquid injection step is repeated more than once in order to concentrate the analytes.

The invention has many advantages.

The device according to the invention is very compact, since the preparation of the sample takes place in the glow discharge source.

The invention does not require any additional pumping system

The device according to the invention is thus a particularly simple equipment with a reduced number of parts, a simple use, which reduces its cost and increases its maneuverability for the operator.

Finally, it is possible to use the device dynamically; this increases the analytical possibilities, in particular, it is possible to pre-concentrate the analytes.

Description of the drawings Other features, objects and advantages of the invention will appear on reading the detailed description which follows, with reference to the drawings given by way of non-limiting illustration, among which:

FIG. 1 is a diagram of the device for preparing samples from a liquid comprising analytes, according to the invention;

FIG. 2A is a longitudinal sectional view of a first example of a cathode used in the device of FIG. 1;

- Figure 2B is a top view of the cathode of Figure 2A viewed in the axis A-A side of the free end of the cathode;

FIG. 2C is a side view of the cathode of FIG. 2A;

FIG. 3A is a longitudinal sectional view of a second example of a cathode used in the device of FIG. 1;

- Figure 3B is a top view of the cathode of Figure 3A viewed in the axis A-A side of the free end of the cathode;

FIG. 3C is a side view of the cathode of FIG. 3A; FIG. 4 is a diagram showing the main steps of the glow discharge sample manufacturing method according to the invention;

FIG. 5 is a graph showing the spectra of europium Eu and europium hydroxide EuOH made with, on the one hand, a method and a cathode of the prior art and, on the other hand, a method and a cathode comprising a tip according to an exemplary embodiment of the invention.

Detailed description of the invention Device

A device 1 for preparing a sample from a liquid comprising analytes according to the invention is described below with reference to FIGS. 1, 2A to 2C and 3A to 3C.

The device 1 for preparing a sample from a liquid comprising analytes comprises a glow discharge lamp.

The glow discharge lamp comprises a cathode 2 and anode 3, between which a glow discharge 5 may be formed.

The device 1 further comprises an injector 4 comprising an inlet 40 and an outlet 41.

The outlet 41, through which the liquid in aerosol form, is directed towards the cathode 2 and is adapted to distribute the liquid directly on the surface of the cathode 2.

The inlet 40 is adapted to receive the liquid and a nebulizing gas, so that the injector 4 forms a nebulizer for distributing the liquid in aerosol form directly on the cathode 2.

Thus the analytes can interact with the glow discharge to form the sample.

The nebulizer is a droplet forming device, for example a pneumatic micro-nebulizer known to those skilled in the art. A nebulizer comprises two concentric capillaries each carrying the liquid or the gas respectively. At the outlet 41 of the nebulizer, the gas makes it possible to break up the liquid into droplets whose volume varies from a few microliters to a few hundred microliters depending on the diameters of the capillaries used for a gas flow rate of between a few tens and a few hundred milliliters per minute. minute. The nebulizing gas may be argon, helium, or any other gas. Preferably, the nebulizing gas may also serve as plasma gas for the formation of the glow discharge. In this case, the nebulizing gas will be a rare gas.

For example, by using a pneumatic micro-nebulizer with an internal capillary diameter of the order of a hundred microns, it is possible to spray the liquid at a flow rate of between 10 L.min ^-1 and 30 L.min ¹ , for a nebulization gas flow (argon) of between 20 mL.min ^-1 and 50 mL min ^-1 .

With such a device, it is possible to manufacture samples by glow discharge from liquid.

The cathode 2 is made of a metal that does not interact with the analytes contained in the liquid, for example nickel. The metal is preferably of very high purity, for example greater than 99.9%, to avoid any pollution of the sample by the residual elements that it could contain.

Also, the metal preferably has a low level of sputtering, for example less than 0.1 g / s, i.e. the percentage of ions from the metal to glow discharge ions is very weak. The cathode 2 is electrically conductive to allow the creation of the glow discharge.

Here, the anode 3 has a conical shape. An electrical insulator is used to electrically isolate the anode 3 from the cathode 2. This insulator can also allow the centering of the cathode 2 relative to the anode 3 by virtue of its shape. The insulation is for example alumina.

The injector 4 is inserted in a sealed manner in the device 1 by means of sealing means 9 of the O-ring type for example, to ensure the seal between the injected liquid, while the device 1 is placed under reduced pressure. order of 100 Pa. The cathode 2 is advantageously a cylinder having a longitudinal axis AA.

The cylinder comprises a base 21 at one of its ends. On this base 21 is defined a geometric center 21A through which the longitudinal axis A-A passes.

The base 21 may have a disc shape, polygonal regular or not, or any shape.

In all cases, the center 21A can be defined as the center of gravity of the surface of the base 21, if this center of gravity is included in the surface of the base 21. For example, for a disc, the center 21A is the center of the disc ; for a square, the center 21A is the intersection of the medians or diagonals of the square; for a regular polygon, the center 21A is the center of the circumscribed circle of the regular polygon; etc.

The base 21 is preferably perpendicular to the axis A-A, but may also be non-perpendicular to the axis A-A.

The cylinder also includes a free end 22 opposite the base 21 and having an outer surface.

The free end 22 comprises an oblique portion 222 delimited by an oblique plane P with respect to the longitudinal axis A-A, that is to say that the oblique plane P does not form a right angle with the longitudinal axis A-A.

The oblique plane P can form an acute angle α with the longitudinal axis A-A. This angle a is between 40 ° and 60 °.

A barrel 23 of the cylinder extends parallel to the longitudinal axis

A-A between the base 21 and the free end 22.

The cylinder further comprises a central recess 24 inside the barrel 23 and extending parallel to the longitudinal axis A-A from the oblique plane P. The central recess 24 may be of revolution about the longitudinal axis AA or have a polygonal shape or other.

The free end 22 has, on the oblique portion 222, an edge 220 peripheral to the recess 24 and closed.

Due to the oblicity of the plane P, the edge 220 defines a point 221 of glow discharge primer at the point of the edge 220 whose projection 22A on the longitudinal axis AA is furthest from the center 21 A of the base 2.

In the embodiments of the cathode shown in Figures 2A-C and 3A-C, the free end 22 also comprises a straight portion 223 relative to the longitudinal axis A-A of the cathode. The recess 24 and the straight portion 223 intersect at most at a point which is the glow discharge primer tip 221 (as in Figs. 2A-C).

As shown in FIG. 1, the outlet 41 of the injector 4 is arranged to deposit the liquid droplets upstream of the glow discharge primer tip 221.

For this purpose, the barrel 23 of the cylinder 2 may comprise a bore 25 for housing the injector 4. The bore 25 extends from the base 21 and opens into the recess 24.

The bore 25 through the barrel 23 may have a longitudinal bore axis forming an angle β between 20 ° and 30 ° with the longitudinal axis of the cylinder A-A.

The asymmetrical shape of the cathode 2 described above (with the free end 22 delimited by an oblique plane P with respect to the longitudinal axis AA) makes it possible to locate the glow discharge 5 between the anode 3 and the tip 221 of the cathode 2, where the analytes were deposited.

Indeed, the shape with a tip makes it possible to ionize optimally the analytes: what is not possible to obtain with a simple tipless recess (that is to say when the plane delimiting the free end 22 of the cathode is perpendicular to the longitudinal axis AA of the cathode).

Example of sizing

The cathode 2 is for example a straight cylinder with a circular base. The recess 24 is also cylindrical with a circular base with a diameter of between 4 mm and 6 mm. The distance between the tip 221 and the bottom of the recess 24 is between 8 mm and 12 mm. The distance separating the tip 221 and the anode 3 is between 2 mm and 4 mm, this distance is chosen according to the experimental conditions of the glow discharge used. The distance upstream 6 of the tip 221 on which the liquid is deposited is between 3 mm and 4 mm.

Sample manufacturing process

A method of making a sample from a liquid by discharging using the device 1 for preparing a sample from a liquid comprising analytes according to the invention is described below with reference to the In this process, the liquid is directly injected onto the surface of the cathode 2 of the preparation device 1.

The method mainly comprises the following steps:

E1 - a first glow discharge lasting a few seconds in order to increase the temperature of the solid cathode 2; E2 - the injection of the droplets of the liquid comprising analytes to be analyzed directly on the surface of the cathode 2;

E3 - the injection of a plasmagene gas between the cathode 2 and the anode 3 to feed a glow discharge 5;

E4 - the formation of the glow discharge 5 between the cathode

2 and the anode 3 for interaction with the analytes so as to atomize, excite and ionize the atoms.

E5 - the sending of ions or photons in an analysis device.

The injection E2 of the liquid is carried out by spraying an aerosol comprising the liquid directly on the surface of the cathode using a nebulizer 4.

The liquid can be introduced through the inlet 40 of the injector 4 via a peristaltic pump or a syringe pump. The liquid introduced may also come from a liquid chromatography apparatus for separating the compounds contained in the starting solution.

The analytes can be concentrated on the cathode 2. The concentration of the analytes is obtained by repeating the injection steps E2 of the liquid droplets.

The plasmagenic gas during the injection step E3 of this gas makes it possible to feed the glow discharge 5 and possibly to facilitate desolvation of the analytes.

When the injector 4 is a micro-nebulizer, the gas used to form the aerosol can also serve as plasma gas. In this case, the step E3 of injecting the plasma gas may have begun during the injection E2 of the liquid and end after the injection of liquid E2, for example 5 minutes after liquid has stopped being injected on the cathode, with a gas flow rate of 50 mL.min ^-1 for a deposited volume of 30 microns of liquid. The formation of the glow discharge 5 is performed in a manner known to those skilled in the art. The ions of the glow discharge interact with the analytes present on the cathode 2 or the tip 221 of the cathode 2 to atomize and ionize the analytes.

In order to continuously supply the glow discharge 5, the injection step E3 of the plasma gas is prolonged, but possibly with a lower gas flow rate.

The ions or photons resulting from the interaction of the plasma with the analytes are then sent to an analysis device for characterization, for example a mass spectrometer or an optical spectrometer.

The advantages of the device 1 and the method of manufacturing a sample from a liquid are, among others:

- the simplicity of use;

- the possibility of working on volumes of low volume liquid;

the possibility of determining the chemical form of the elements in a sample as well as studying the evolution of the speciation as a function of the nature of the medium (ratio of element / molecule concentrations, pH, etc.); and

the possibility of studying speciation after separation of the different complexes by separation techniques in the liquid phase by stopping the separation between each separated species in order to analyze it.

Another advantage is the possibility of determining the concentration of majority, minority or trace elements in the liquid and their isotopy by the pre-concentration of the sample by iteration of the injection step E2 of liquid, with a possible separation of the previous compounds, for example by liquid chromatography.

In order to illustrate the performance of the invention, FIG. 5 shows two spectra of europium Eu and europium hydroxide EuOH obtained from prepared samples, one according to the prior art (CTA continuous line). ), and the other according to an exemplary method according to the invention (discontinuous line Ci) using an example of a cathode having a tip. Both spectra are obtained by mass spectrometry.

On the abscissae are presented the values m / z that is to say "mass on load" (here z = 1). The ordinates show the intensities of the signals (peaks) picked up by the mass spectrometer in arbitrary units (u.a.).

The higher the intensity of the signals, the easier it is to identify the peaks of the spectra, because it is easier to distinguish these signals from the noise.

It should be noted in FIG. 5 that the intensities obtained for a sample prepared according to the method of the invention using a cathode having a peak are nearly four times higher than the intensities obtained for a sample prepared according to the method of the prior art.

Claims

claims

1. A device (1) for preparing a sample from a liquid comprising analytes, comprising:

- a glow discharge lamp comprising a cathode (2) and an anode (3), between which a glow discharge (5) can be formed,

the device (1) being characterized in that it further comprises an injector (4) having an inlet (40) and an outlet (41);

the inlet (40) being adapted to receive the liquid and a nebulizing gas, so that the injector (4) forms a nebulizer for distributing the aerosolized liquid directly on the cathode (2), the outlet ( 41) being directed to the cathode (2) and adapted to distribute the liquid directly on the surface of the cathode (2), so that the analytes can interact with the glow discharge (5) to form the sample.

2. Device (1) according to claim 1, wherein the cathode (2) is a cylinder having a longitudinal axis (A-A) and comprising:

a base (21) at one end of the cylinder having a center (21A) through which the longitudinal axis (A-A) passes;

- a free end (22) opposite the base (21) having an oblique portion (222) defined by an oblique plane (P) relative to the longitudinal axis (A-A);

- a shaft (23) extending parallel to the longitudinal axis (A-A) between the base (21) and the free end (22);

- a central recess (24) inside the barrel (23) and extending parallel to the longitudinal axis (AA) from the oblique plane (P); the free end (22) having an edge (220) peripheral to the recess (24), the edge defining a point (221) of glow discharge primer at the point of the edge (220) whose projection ( 22A) on the longitudinal axis (AA) is furthest from the center (21A) of the base;

and wherein the outlet of the injector (3) is arranged to deposit the upstream liquid droplets (6) of the glow discharge primer (221).

3. Device (1) according to claim 2, wherein the oblique plane (P) forms an acute angle (a) with the longitudinal axis (A-A); the angle (a) being between 40 ° and 60 °.

4. Device (1) according to one of claims 2 or 3, wherein the shaft (23) comprises a bore (25) housing the injector (4) extending from the base (21) and opening into the recess (24).

5. Device (1) according to claim 4, wherein the bore (25) through the shaft (23) has a longitudinal axis of bore forming an angle (β) between 20 ° and 30 ° with the axis longitudinal cylinder (AA).

6. Method of producing a sample by discharge using the device (1) according to one of claims 1 to 5, characterized in that it comprises the step of:

injecting (E2) at least once a liquid comprising analytes directly onto the surface of the cathode (2) using a nebulizer.

The method of claim 6, further comprising the step of:

after the injection (E2) of the liquid, forming (E4) a glow discharge (5) between the cathode (2), optionally the tip (221) of the glow discharge primer of the cathode (2), and an anode (3) for ionizing the analytes injected on the cathode (2).

The method of claim 7, further comprising the step of sending (E5) the ionized analytes to an assay device.

9. Method according to one of claims 6 to 8, further comprising between the injection (E2) of the liquid and the formation (E4) of the glow discharge, the step of:

injecting (E3) a plasmagene gas between the cathode (2) and the anode (3) in order to supply the glow discharge (5) and possibly to facilitate desolvation of the analytes.

10. Method according to one of claims 6 to 9, wherein the step of injecting (E2) the liquid is repeated more than once in order to concentrate the analytes.