GB2304189A

GB2304189A - Preparing samples for analysis

Info

Publication number: GB2304189A
Application number: GB9615984A
Authority: GB
Inventors: Zachary D Sharp; Thure E Cerling
Original assignee: Finnigan MAT GmbH
Current assignee: Finnigan MAT GmbH
Priority date: 1995-08-11
Filing date: 1996-07-30
Publication date: 1997-03-12
Also published as: GB9615984D0; DE19529717A1

Description

2304189 Process and apparatus f or the preparation of an inorganic or

organic sample for isotope ratio analysis DescriDtion:

The invention relates to a process for the 5 preparation of an inorganic or organic sample or for the provision of, preferably, C02 from such a sample for isotope ratio analysis of certain carbon and/or oxygen isotopes. The invention furthermore relates to an apparatus particularly for carrying out the said process.

The main area of application of the invention is isotope ratio analysis, in particular determination of carbon or oxygen isotopes from an inorganic or organic sample. Conventional processes operate, for example, using a so-called elemental analyser. A combustion oven and a gas chromatograph are integrated into these. Gases produced in the combustion are subjected to time separation from one another, emerge successively and can subsequently be analysed. The analysis preferably takes place using a mass spectrometer. Accordingly the analysis gases are also ionised.

The present invention now relates to a process and an apparatus for the provision of a gaseous sample for subsequent separation of individual components and analysis thereof which is subsequent thereto in turn.

The process according to the invention has the following features:

a) the organic sample is exposed to a stream of carrier gas, in particular stream of helium, b) laser illumination impinges on the sample, in particular until vaporization and/or decomposition of the sample or of parts of the sample, the resulting products (sample gases) are conveyed with the stream of carrier gas to an analysis and/or separation unit.

The combination of stream of carrier gas and laser makes it possible to provide, simply, at low cost and, in particular, rapidly, a gaseous sample which was c) is solid or liquid before exposure to the laser. Tests have revealed a high accuracy and reproducibility of the process according to the invention. This applies particularly when helium is used as stream of carrier gas and in conjunction with a C02 laser. It is thus possible to carry out an isotope ratio.analysis on carbonates with a quality not hitherto achieved.

The generated sample gases are subsequently separated, advantageously together with the stream of carrier gas, from impurities by chromatography and subjected to analysis by mass spectrometry. The sample gases are normally compared with a reference gas during the analysis. According to another feature of the invention, the reference gas is supplied to the sample gases in the region of a so-called open coupling (a plurality of reference gases is also possible). This principle is described, for example, in our own DE-A 43 33 208. Also to be found therein are further details of the principle of isotope ratio analysis using a gas chromatograph and a mass spectrometer (IRM GCMS or GC-IRMS).

The sample is preferably exposed to the laser illumination in the region of a chamber. The chamber has a volume of about 0.5 to 10 ml. A stream of from 1 to 500 ml of carrier gas per minute flows through the chamber.

The apparatus according to the invention is particularly suitable for carrying out the process described above and has the following features:

a) a chamber is provided for receiving the sample, through which a stream of carrier gas, in particular a stream of helium, can be passed via a supply line and a corresponding outlet, b) a unit (laser) for generating laser illumination, by which laser illumination can be impinged on the sample in the chamber to generate a sample gas, is assigned to the chamber.

Other features of the invention can be found in the claims. The described technique can be combined with other known techniques or procedures. Thus, for example, a concentration of the sample gases carried by the stream of carrier gas can be carried out. For example, the sample gas can be frozen out in a cold trap with liquid nitrogen and subsequently conveyed in concentrated form to a downstream gas chromatograph.

One embodiment of.the invention is explained in detail hereinafter. The single figure shows the design in principle of an apparatus for carrying out the process according to the invention.

To analyse a plate-shaped sample 10, an apparatus comprising, inter alia, an infrared laser 11, sample chamber 12, chromatography column 13, open coupling 14, mass spectrometer 15 and a line system connecting each of them is provided. The chamber 12 is tubular in shape and has an O-ring 16 as substantially gas-tight termination on the plate-shaped sample 10 on which the chamber 12, which is open at the bottom, stands. An upper end of the chamber 12 has a lasertransparent window, a ZnSe window when a C02 laser with 20 a wavelength of 10. 6 gm, is used. The laser 11 is arranged so that illumination of the sample 10 through the window 17 is possible. When another laser is used, in particular a (more precise) UV laser, the material of the window must be adapted appropriately. 25 The sample 10 lies on a stage 18 which can be moved in the X and Y directions by stepping motors which are not shown in detail. This makes it possible to move the sample relative to the laser beam. Alternatively, the laser itself can be arranged so that its location can be changed. When the stage 18 is moved, either the sample 10 is conveyed along slidingly under the O-ring 16 or else the chamber 12 is also moved. In the latter case, the maximum movement is then limited by the size of the window 17.

The chamber 12 is connected to an appropriat e line system for supplying carrier gas and for the emer gence of sample gases - An inlet line 19 and an outlet line 20 are depicted in the figure and are connected to a six-way valve. The gas is supplied in the lower region is of the chamber, that in to say near the sample 10. Accordingly, the gas outlet Is located near the window 17. The chamber volume ia about 2 al. The stream of carrier gas, In particular a stream of helium, is about 5 50 ml per minute.

The valve 21 in the figure is of such a form that a stream of helium in passed through the chamber 12 towards the downstream chromatography column 13. In another position, the chamber 12 and the units 13 to 15 downstream of the valve 21 are flushed.

The colimm 13 can be arranged upstream of a unit, which in not shown in detail, for concentrating the sample gas, for example in conjunction with a cold trap containing liquid nitrogen.

The sample 10 is analyaed in the following manner:

The stage 18 and, with it, the sample 10 are displaced in the X and Y directions at a previously defined location. The sample itself is, for example, a carbonate- or phosphate-containing material. A stream of helium is passed through the chamber 12. The laser 11 is activated briefly or pulse-wise. The combustion products (sample gases) produced from the sample 10 are passed with the stream of helium from the chamber into the chromatography column 13 and there subjected to time separation in a conventional way.

The gases emerging from the column 13 are conveyed via the open coupling 14 without pressure to the mass spectrometer 15 for the analysis. At the same time, a reference gas is supplied in the region of the open coupling 14. On analysis of C021 the reference gas is a C02 gas with a standard isotope ratio. The reference gas is supplied through a reference gas line from an appropriate tank (not shown) and through a pressure regulator 23.

in situ analysis of a sample is possible with the process described and the apparatus shown. Lengthy pretreatment is unnecessary. In particular, analysis of 13C and 180 can be carried out relatively rapidly and with high accuracy and reproducibility.

Smaller samples can likewise be easily analysed. For example, in place of the plate-shaped sample 10, it is possible to provide a cover plate (not shown) onto which sample material in laid. The cha er 12 can also be closable or closed, and contain the sample (in a small amount).

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Claims

Claims:

1. Process for the preparation of an inorganic or organic sample or for the provision of, preferably, C02 from such a sample for isotope ratio analysis of certain carbon and/or oxygen isotopes with the following features: a) the sample is exposed to a stream of carrier gas, in particular a stream of helium, b) laser illumination impinges on the sample, in particular until vaporization and/or decomposition of the sample or of parts of the sample, c) the resulting products (sample gases) are conveyed with the stream of carrier gas to an analysis and/or separation unit.

is

2. Process according to Claim 1, characterized in that an IR laser, in particular a C02 laser, is used.

3. Process a ccording to Claim 1 or 2, characterized in that the resulting products are separated together with the stream of carrier gas by chromatography, and in that preferably a concentration of the sample gas takes place before carrying out the separation by chromatography.

4. Process according to one or more of Claims 1 to 3, characterized in that the resulting products, in particular COV are subjected, where appropriate after previous separation by chromatography, to analysis by mass spectrometry.

5. Process according to one or more of Claims 1 to 4, characterized in that the resulting products, in particular COV are subjected, where appropriate after previous separation by chromatography, to analysis alternately with a reference gas via an open coupling.

6. Process according to one or more of Claims 1 to 5, characterized in that the laser reaction takes place in the region of a chamber with a chamber volume of from 0.5 to 10 ml, preferably 2 ml, in particular with a stream of from 1 to 500 ml of carrier gas per minute, preferably 50 ml per minute, through the chamber.

b)

7. Apparatus for the preparation of an organic sample or for the provision of, preferably, C02 from an inorganic or organic sample for isotope ratio analysis of certain carbon and/or oxygen isotopes with the following features:

a) a chamber is provided for receiving the sample, through which a stream of carrier gas, in particular a stream of helium, can be passed via a supply line and a corresponding outlet, a unit (laser) for generating laser illumination, by which laser illumination can be impinged on the sample in the chamber to generate a sample gas, is assigned to the chamber.

S. Apparatus according to Claim 7, characterized in that the laser unit is located outside the chamber, and the chamber has a light- or emission-transparent window for entry of the laser illumination.

9. Apparatus according to Claim 8, characterized in that the window consists of a ZnSe compound, in particu- lar when a C02 laser is used.

10. Apparatus according to one or more of Claims 7 to 9, characterized in that an IR laser, in particular a C02 laser, is provided.

11. Apparatus according to one or more of Claims 7 to 25 10, characterized in that a gas chromatograph or a chromatography column is downstream of the chamber.

12. Apparatus according to one or more of Claims 7 to 11, characterized in that an open coupling for supplying reference gas is downstream of the chamber, in particular of the chromatography column or of the gas chromatograph.

13. Apparatus according to one or more of Claims 7 to 12, characterized in that a mass spectrometer is provided for analysis of the sample gas which is, in particular, mixed with carrier gas.