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ASSOCIATED CONTENT

Supporting Information for

Development and validation of an universal interface for

compound-specific stable isotope analysis of chlorine

(37Cl/35Cl) by GC-HTC-MS/IRMS

Julian Renpenning, Kristina L. Hitzfeld, Tetyana Gilevska, Ivonne Nijenhuis, Matthias Gehre*

and Hans-Hermann Richnow

1Department for Isotope Biogeochemistry, Helmholtz-Centre for Environmental Research –

UFZ, Permoserstrasse 15, D-04318 Leipzig, Germany

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Content

Figure S1: Evaluation of ethylene conversion at 500-1500°C with and without reactant gas (H2),

monitored via ion trap MS.

Figure S2: Evaluation of benzene conversion at 500-1500°C with and without reactant gas (H2),

monitored via ion trap MS.

Figure S3: Evaluation of the conversion quality of trichloroethene (TCE) at 1300°C and1500°C,

as well asat optimized conditions (Flow 0.4 ml/min, H2 0.1 ml/min, HTC at 1450-1500°C). The

HTC quality was monitored via ion trap MS.

Figure S4: Evaluation of the conversion quality of trichloroethene (TCE) at 1300°C vs 1500°C

by taking in account the hydrocarbon by-product formation (A) and the HCl formation (B). The

abundance of products was monitored via ion trap MS.

Figure S5: Evaluation of the conversion efficiency of different chlorinated hydrocarbons,

demonstrated for chlorinated compounds. The corresponding mass spectra were monitored for

non-converted (black) and converted (red) compound at 1500°C.

Figure S6: Determination of chlorine isotope composition of several chlorinated reference

compound via GC-HTC-IRMS. Normalization of measured chlorine isotope composition was

done using TCE reference 2 and 6. True isotope composition δ37

ClSMOC(‰) is given on the y-

axis (determined off-line via DI-IRMS). Measured isotope composition δ37

Clraw(‰) (on-line via

GC-HTC-IRMS) is plotted at the x-axis.

Figure S7: Sensitivity and linearity of GC-HTC-IRMS using TCE as model compound. (A)

Concentration of Cl on column vs. peak intensities m/z 36 (blue) and δ37

Cl vaues (red) (n=5).

δ37

Cl isotope composition is presented as raw data (A) and corrected (B).

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Figure S8: Water-air background of GC-HTC at 1500°C w/o reactant gas H2. Background

monitored via ion trap MS

Figure S9: Characterization of water (m/z 18) formation from oxygen (m/z 32) during HTC by

considering conversion temperature in combination with reactant gas (H2) concentration (left)

and carbon availability in HTC reactor (right). The range of product formation (m/z 18 [H2O],

m/z 28 [CO]) was monitored via ion trap MS and given as relative abundance.

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Figure S1: Evaluation of ethylene conversion at 500-1500°C with and without reactant gas (H2),

monitored via ion trap MS.

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Figure S2: Evaluation of benzene conversion at 500-1500°C with and without reactant gas (H2),

monitored via ion trap MS.

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Figure S3: Evaluation of the conversion quality of trichloroethene (TCE) at 1300°C and1500°C,

as well as at optimized conditions (Flow 0.4 ml/min, H2 0.1 ml/min, HTC at 1450-1500°C). The

HTC quality was monitored via ion trap MS.

Figure S4: Evaluation of the conversion quality of trichloroethene (TCE) at 1300°C vs 1500°C

by taking in account the hydrocarbon by-product formation (A) and the HCl formation (B). The

abundance of products was monitored via ion trap MS.

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Figure S5: Evaluation of the conversion efficiency of different chlorinated hydrocarbons,

demonstrated for chlorinated compounds. The corresponding mass spectra were monitored for

non-converted (black) and converted (red) compound at 1500°C.

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Figure S6: Determination of chlorine isotope composition of several chlorinated reference

compound via GC-HTC-IRMS. Normalization of measured chlorine isotope composition was

done using TCE reference 2 and 6. True isotope composition δ37

ClSMOC(‰) is given on the y-

axis (determined off-line via DI-IRMS). Measured isotope composition δ37

Clraw(‰) (on-line via

GC-HTC-IRMS) is plotted at the x-axis.

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Figure S7: Sensitivity and linearity of GC-HTC-IRMS using TCE as model compound. (A)

Concentration of Cl on column vs. peak intensities m/z 36 (blue) and δ37

Cl vaues (red) (n=5).

δ37

Cl isotope composition is presented as raw data (A) and corrected (B).

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Formation of water during HTC

Formation of water (m/z 18) was observed in the background, most probably enhanced by

availability of hydrogen as reactant for the conversion. Water is suspected to condense in the

non-heated parts of the transfer-lines, and therefore, generate a trap for hydrochloric acid and

memory effects during chlorine isotope analysis.18

For optimization of the HTC to improve

chlorine isotope analysis a reduction of water was intended to reduce the potential memory due

to condensation of water in the system.

Oxygen is known to react during HTC to either CO or H2O if carbon or hydrogen as reactants are

available, respectively.7,31

Though oxygen was completely excluded from our instrumental

system, traces of oxygen were still present. We monitored the background at different conditions

in order to understand the underlying reaction dynamics. Remarkably, H2O was observed to

replace CO as main product as soon as hydrogen as reactant gas was available during HTC

(Figure S8). The increase of conversion temperature to 1500°C had a minor effect on H2O

formation. To provide additional carbon during HTC the reactor was purged with methane via

back flush. Deposits of carbon in the HTC reactor tube were shown to enhance conversion of O2

to CO and reduce the amount of H2O (Figure S9). Still, H2O remained the main background

product. Preferential conversion of O2 to H2O is most probably related to high availability of H2

as reactant in our setup (H2 ~ 20%). Though formation of H2O may be reduced by reduction of

hydrogen availability, H2 is also required for conversion of chlorine to HCl, especially for higher

chlorinated compounds. Therefore, H2 limitation may result in isotope fractionation effects

during conversion. However, monitored H2O background levels were observed to remain stable

and not significantly interfered with chlorine isotope measurements. Therefore, no further

measures to reduce H2O levels were undertaken.

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Figure S8: Water-air background of GC-HTC at 1500°C w/o reactant gas H2. Background

monitored via ion trap MS.

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Figure S9: Characterization of water (m/z 18) formation from oxygen (m/z 32) during HTC by

considering conversion temperature in combination with reactant gas (H2) concentration (left)

and carbon availability in HTC reactor (right). The range of product formation (m/z 18 [H2O],

m/z 28 [CO]) was monitored via ion trap MS and given as relative abundance.

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Definition related to isotope analysis

‘Continuous-flow’ IRMS:

General term for analytical devices with a continuous flow delivery of an analyte to MS in a gas

phase. This includes analytical devices as for instance GC-MS, GC-IRMS, EA-IRMS (Brenna et

al. 1997).

Off-line methods:

Off-Line Sample Preparation for dual inlet analysis (DI-IRMS). Chemical conversion of analyte

in sealed quartz tubes into appropriate compound for analysis. Approaches relying on offline

sample preparation are labour-intensive, slow, and typically require large sample sizes, but can

achieve high accuracy (Elsner et al. 2012).

On-line methods:

Modern techniques with chemical conversion ‘on the fly’. Analytical device combines

separation, conversion and MS analysis in one run, as for instance GC-C-IRMS for carbon or

GC-HTC-IRMS for hydrogen isotope analysis. Continuous flow, or “online” methods, in

contrast, are relatively fast, economical, and enable analysis of small samples (Elsner et al.

2012).