WO2012025374A1

WO2012025374A1 - Method and device for the online determination of the isotopic ratio of chlorine, bromine or sulfur in an organic sample

Info

Publication number: WO2012025374A1
Application number: PCT/EP2011/063687
Authority: WO
Inventors: Matthias Gehre; Martin Seidel; Kristina Hitzfeld; Hans H. Richnow
Original assignee: Helmholtz-Zentrum Für Umweltforschung Gmbh - Ufz
Priority date: 2010-08-12
Filing date: 2011-08-09
Publication date: 2012-03-01
Also published as: DE102010039275A1; DE102010039275B4

Abstract

The present invention relates to an on-line method for measuring the isotopic ratio of chlorine, bromine or sulfur in an organic sample in a compound-specific manner and to a device for carrying out the method. The method comprises separating the sample in a gas chromatograph (1), converting said sample in a catalytic reactor (2) connected to the gas chromatograph into hydrogen chloride gas, hydrogen bromide gas or hydrogen sulphide gas and verifying same in a mass spectrometer (3).

Description

Method and apparatus for the online determination of the isotopic ratio of chlorine, bromine or sulfur in an organic sample

The present invention relates to a method for the compound-specific measurement of the isotopic ratio of chlorine, bromine or sulfur in an organic sample and to an apparatus for carrying out the method.

The method is based on a gas chromatographic separation of the sample, conversion of this in a connected to the gas chromatograph high-temperature furnace in chlorine, bromine or hydrogen sulfide gas and their detection in the mass spectrometer. The inventive method for determining the quantitative isotopic composition of chlorine, bromine or sulfur in a compound of the organic sample is an online measurement that is specific for each compound in the mixture, so for example between different chlorine and / or bromine compounds in can distinguish a mixture. The method according to the invention is easy to handle and comparable in terms of accuracy and sensitivity to offline methods. Since it is significantly less expensive, only a fraction of the time is required for the measurements.

Online methods are known for the isotope ratio measurement of elements such as hydrogen, carbon, nitrogen and oxygen. For chlorine, with its two stable isotopes ³⁵ CI and ³⁷ CI, bromine with its two stable isotopes ⁷⁹ Br and ⁸¹ Br, and sulfur with its three stable isotopes ³² S, ³³ S, and ³⁴ S, there have been no adequate methods in the last decade used and improved offline methods that produce accurate results but are disadvantageous in terms of implementation. Thus, the method of Holt et al. (Anal Chem.1997, 69, 2727-2733) and their modifications various elaborate offline steps to extract, enrich and convert to be determined organic chlorine compounds in methyl chloride, which is measured by DI-IRMS (dual inlet isotope ratio mass spectrometry) , With this established method For example, it is possible to determine the total isotopic chlorine isotope ratio, but not the isotope ratio in the individual organic chlorine compounds involved.

The established method of thermal ionization mass spectrometry (TIMS) involves an offline conversion into CsCl for the determination of chloroisotopes and, moreover, has high requirements for sample purity (see Holmstrand et al., Anal. Chem. 2004, 76, 2336-2342).

An apparatus-simple method for detecting chlorine isotope in an organic compound is described by Aeppli et al (Anal. Chem. 2010, 82, 420-426), which provides for the coupling of a gas chromatograph to a quadrupole mass spectrometer. A disadvantage of this method is the immense computational effort to determine the connection-specific isotope ratios over the complete spectrum from the frequencies of the individual peaks. Each data run must be processed manually or the calculation scheme has to be redeveloped for each substance.

The object of the present invention was to provide an improved method and an associated apparatus for the connection-specific quantitative determination of the isotopic ratio of chlorine, bromine or sulfur in an organic sample, which has the necessary accuracy of measurement and sensitivity. In particular, the method should be simple to carry out and labor-intensive offline steps avoid The object of the invention is achieved by the method specified in claim 1 and the apparatus according to claim 5. The dependent claims indicate advantageous embodiments.

According to the invention, the sample by means of hydrogen as make-up gas in a catalytic reactor 2, which contains or consists of Al ₂ 0 ₃ as a catalyst, at temperatures of 800-1500 ° C, preferably at about> 1300 ° C, to Anaiysengas, namely converted to HCl, HBr or H ₂ S, and carbon. It takes place in the In the high-temperature furnace 2 used according to the invention, complete conversion of the organic halogen or sulfur compounds to hydrogen chloride gas, hydrogen bromide gas or hydrogen sulfide gas takes place and at the preferred temperatures of 1300 to 1500 ° C. according to the invention, the analysis gas at the end of the reactor 2 is anhydrous.

First, the organic sample, which may be liquid or gaseous, a single compound or a compound mixture is introduced by means of sample introduction system 4 in a carrier gas. Helium is preferably used as the carrier gas according to the invention. In order to ensure a connection-specific analysis, the sample to be examined is then separated in a gas chromatograph 1. Hydrogen is then metered directly into sample stream 8 as a make-up gas before it enters reactor 2, in which, while maintaining the separation, the on-line conversion to HCl, HBr or H ₂ S takes place. The analysis gas is then analyzed by mass spectrometer 3. The mass spectrometer is set to record the m / z values (mass-to-charge ratio) of the isotopes to be determined. The measured values are preferably processed by means of software. Instead of mass spectrometry, laser spectroscopy can also be used to analyze the analysis gas.

According to the invention, the mass fraction 36 ( ¹ H ³⁵ CI) and 38 (H ³⁷ CI) are used to determine the isotopic ratio ³⁷ Cl / ³⁵ CI by mass spectrometry on HCl, and the mass traces 80 ( ¹ H ⁷⁹ Br) and 82 ^ H ^ in the HBr Br) the isotopic ratio ⁸ Br / ⁷⁹ Br. The negligible error of the determination of ¹ H is accepted, since the natural frequency of ³⁵ CI to ³⁷ CI with about 75% to 25% and of ⁷⁹ Br to ⁸ Br with 51% to 49% is much higher. The isotopic ratio ³⁴ S / ³² S is determined on mass traces 34 ( ¹ H ¹ H ³² S) and 36 (HH ³ S) on H ₂ S. The natural abundance of sulfur isotopes ³² S to ³⁴ S is about 95% to 4.2%.

The stated isotope ratios (δ) of chlorine, bromine or sulfur can, preferably with a computerized measurement program, according to the stand ardformel 5 = (R _sa / R _st - 1) ^■ 1000 (% ₀ )

be calculated, where

R _{sa is} the measured isotope ratio of the sample and

R _{si is} the isotope ratio of the IAEA reference material. The measuring program integrates the individual peaks and performs a background correction. The resulting isotope ratio represents a relative value to the [AEA reference material.

If it is desired to compare the results directly with an international standard (eg for chlorine with the SMOC), the respective reference gas HCl, HBr or H ₂ S can be calibrated with a reference material WS with known isotopic value 5WS_PS against a primary standard. After measuring the unknown sample X against WS, the isotope ratio of the unknown sample δχ-ps against the primary standard in per thousand is determined according to the following equation (compare Coplen, TB et al., Nature (London), 1983, 302, 236-238): δχ-ps ⁼ δχ-ws ⁺ ÖWS-PS + (Öx-ws ^■ ÖWS-PS) / 1000.

Any mass spectrometer suitable for isotope ratio measurement can be used for the method according to the invention. In a high temporal resolution, it has to measure between 2 to 8 defined masses in a timely manner and transfer the data to the connected PC. According to the invention, a quadrupole mass spectrometer or an IRMS (isotope ratio mass spectrometer) is preferably used. The present invention also provides a device which is set up for carrying out the method according to the invention and the use of this device in the method according to the invention.

The core of the device according to the invention is the catalytic reactor 2, which is preferably designed as a tube. It may consist entirely of Al ₂ O ₃ or be lined with it. Its inner diameter is in a preferred Embodiment 0.5 - 1 mrn and its outer diameter is preferably about 1, 6 mm.

The reactor 2 is connected via the line 8 with the gas chromatograph 1 and via the line 8a with the mass spectrometer 3, in the furnace chamber 7 of the gas chromatograph a line 9 for the necessary hydrogen supply to the sample stream in line 8 is arranged according to the invention for the conversion of the sample in the catalytic reactor 2 in HCl, HBr or H ₂ S is needed. The hydrogen is mixed into the sample stream 8 as a make-up gas during the entire measuring time. Downstream of the hydrogen supply 9 and before the reactor 2, a fixed splitter (fixed flux divider) 10 is arranged. This splitter 10 reduces the amount of sample to be reacted in the reactor 2. According to the invention, the split device 10 is preferably a throttle capillary. The GC separation column and the lines 8, 8a, 9, 11, 12, 14 and 15 represent capillaries in a preferred embodiment of the invention.

The split device 10 is connected to the line for the backwash 11. In order to prevent any solvent present from the sample stream 8 from entering the reactor 2, by opening the valve 12a with carrier gas which is identical to the carrier gas of the sample stream, the line 11 is backwashed via the simultaneously opened valve 11a, ie. H. the valves 11a and 12a are always connected in parallel. Backflushing protects the reactor during solvent elution or between measurements. In a preferred embodiment of the invention, all valves of the device (9a, 11a, 12a, 14a, and 15a) are computer controlled via a circuit.

The direct coupling of the gas chromatograph 1, reactor 2 and mass spectrometer 3 takes place with an open split 13, ie via an open coupling (open to the atmosphere), whereby no overpressure can build up. Thus, at all changeable conditions in GC and catalytic reactor, a steady gas flow into the ion source of the MS is ensured. The device according to the invention is preferably designed so that the sample flow in 0.8-1.2 ml / min, is slightly reduced at the fixed flow divider 10 and the analysis gas impinges on the ion source of the MS at about 0.4 ml / min, the remainder being discharged via the open split 13 ,

In a preferred embodiment of the invention, the apparatus comprises an external reference gas supply 14, which is supplied either to the analysis gas 8a, the sample stream 8, or preferably into the ion source of the mass spectrometer.

Thus, a more accurate feedback of the measured values relative to a reference value is possible. The coupling of the reference gas supply 14 takes place via an open split, to which an inert gas, for example helium, is supplied as protective gas against air.

Since in the reaction 2 carbon is formed in the catalytic reactor, which deposits in the reactor 2, it is provided in a preferred embodiment of the invention to purify the reactor 2 after one or more measurements by oxidation with oxygen. For this purpose, an oxygen supply 15 is arranged between reactor 2 and carrier gas feed 12. By supplying oxygen by opening the valve 15a and simultaneously opening the valve 12a of the carrier gas supply 12 can be carried out at the same time open valve 11a of the backwash 11, the cleaning. The supply of carrier gas to the oxygen stream serves to prevent the penetration of oxygen into the mass spectrometer.

Figure 1 shows the device according to the invention in a preferred embodiment, wherein the reference numerals have the meaning given in the reference list.

The invention is explained in more detail below using the example of the determination of the isotope ratio of ³⁷ Cl / ³⁵ Ci. embodiment

2 μ! of a sample mixture of cis-DCE, TCE and TCA (di-, tri- and tetrachloroethene) in pentane as solvent is added to the split / splitless injector of the gas chromatograph (HP 6890, Agilent) by means of an autosampler (CTC AS 200) with a 10μ! Syringe injected. On the GC column (ZB1 Phenomenex, 60mx0.32rnmx1pm), the 3 substances are separated from the solvent and with each other by means of a temperature program in GC (5 ° C) - 10 min-250 ° C (5 min) Backflush hidden (this does not occupy the reactor with unnecessary carbon) and after switching to the Straigth mode (backflush off, reactor to mass spectrometer directly coupled via open split), the three individual components are directly in the reactor with the addition of H ₂ to HCL The conversion to HCl according to the general formula (I) takes place to 100%, which was found in background measurements.

C _x H _y Cl _z + H ₂ ^{T = mo} ° ^{c> Al} i °> _{x C (s)} + z HCl ₍ i)

The following chromatogram clearly shows the separation of the sample mixture of the three chloroethenes and three reference gas peaks.

0 4 6 8 10 12

retention time At the mass spectrometer, the frequencies of the masses 36 (H ³⁵ CI) and 38 ( ¹ H ³⁷ CI) are registered via the interceptor (here 1 SEV, or Faraday Cup or two interceptors, one for each mass) and the time course results in two integrals as surfaces. These are shared with each other via a software and set in relation to the reference gas (HCl from a compressed gas cylinder, Linde), which is switched on via the valve 14a at the beginning of the measurement three times for 40 seconds (while backflush is turned on).

With the formula:

the isotope value is calculated from the relative distance of the R ³⁷ ratios (R ³⁷ = area 37 / area35) between sample and standard (here reference gas first).

About the formula: δ Champl SMOC ~

the result is adjusted to the international Cl scale

With this technique, reproducible isotope ratios are possible during a CSIA. The standard deviation is in the range of 1 ⁰ ₀ o-

The individual results of the chloroisotopic ratios show different ³⁷ CI contents. On the basis of the different ³⁷ CI contents, it is possible to determine, for example, the origin of the chemicals or the processes in which they are formed. References

1 gas chromatograph

2 catalytic reactor

3 mass spectrometers

4 sample application system

5 GC separation column

6 Heating device for the catalytic reactor

7 Oven space of the gas chromatograph

8 Transport line for the sample stream

8a Transport line for the analysis gas

9 line for hydrogen supply

9a valve

10 split device

11 Backwash pipe 11a Valve

12 line for carrier gas supply

12a valve

13 open split

14 line for reference gas supply

14a valve

15 line for oxygen supply

15a valve

Claims

claims

1. A method for online determination of the isotopic ratio of chlorine, bromine or sulfur in an organic sample,

characterized in that

the sample is introduced into a carrier gas which does not comprise any of the elements mentioned, and the sample stream is passed through a gas chromatograph (1) into a catalytic reactor (2) directly coupled thereto and the analysis gas produced in the reactor is injected into a mass spectrometer (3) directly coupled to the latter. is transported to determine the isotope ratio,

wherein in the gas chromatograph (1) the connection-specific separation of the sample takes place, then hydrogen gas is added to the compound-specific sample stream before it enters the catalytic reactor (2), in the catalytic reactor (2) comprising alumina as a catalyst, the compound-specific sample at 800- 1500 ° C is reacted by means of hydrogen completely to the analysis gas and carbon, wherein the Anaiysengas hydrogen chloride gas, hydrogen bromide gas or hydrogen sulfide, and from the recorded mass spectrum of the mass spectrometer (3) passing gas analysis the frequencies of the respective isotopes and from the isotopic behaviors of chlorine, bromine or sulfur! be determined.

2. The method according to claim 1, characterized in that the reaction of the sample in the catalytic reactor 2 at 1300 - 1500 ° C takes place.

3. The method according to claim 1 or 2, characterized in that the frequencies of the respective isotopes and the Isotopenverhit are determined by means of a computerized measurement program.

4. The method according to any one of claims 1-3, characterized in that the analysis gas is analyzed by means of a quadrupole mass spectrometer or an isotope ratio mass spectrometer.

5. Device for the online determination of the isotopic ratio of chlorine, bromine or sulfur in an organic sample,

comprising a sample introduction system (4) for introducing the sample into a carrier gas, a gas chromatograph (1) with GC separation column (5) for connection-specific separation of the sample, a catalytic reactor (2) with heating device (6) for converting the sample to the analysis gas, wherein the inlet of the catalytic reactor (2) in the furnace chamber (7) of the gas chromatograph (1) is arranged and the output of the catalytic reactor (2) outside the furnace chamber (7), and further comprising a mass spectrometer (3) for determining the isotope ratio chlorine, bromine or sulfur in the analysis gas,

wherein the gas chromatograph (1), catalytic reactor (2) and mass spectrometer (3) are directly connected to one another via a transport line (8 and 8a),

the device further comprises in the furnace chamber (7) of the gas chromatograph (1), arranged between GC separation column (5) and catalytic reactor (2), a hydrogen supply (9) to the sample stream (8), a split device (10) for quantitative limitation the sample stream (8) into the reactor (2) and a backwash (11) to protect the reactor (2) from solvent in the case of liquid samples, the split device (10) being connected to the backwash (11),

the apparatus further comprises a carrier gas supply (12) communicating with the backwash (11) between the catalytic reactor (2) and the mass spectrometer (3), and an open split device (open coupling) (13) between the latter and the mass spectrometer (3) Ensuring a uniform flow of the analysis gas in the mass spectrometer (3) is arranged.

6. Apparatus according to claim 5, characterized in that it comprises a reference gas supply (14) which leads either to the transport line of the analysis gas (8a), to the transport line of the sample stream (8) or in the ion source of the mass spectrometer (3).

7. Apparatus according to claim 5 or 6, characterized

in that for purifying the catalytic reactor (2) of residues, in particular carbon, between the catalytic reactor (2) and carrier gas feed (12), an oxygen feed (15) communicating with the backwash (11) and the carrier gas feed (12) is arranged.