Janina Szaran

Achievement of carbon isotope equilibrium in the system HCO3− (solution)-CO2(gas)

The magnitude of stable carbon isotope fractionation between dissolved bicarbonate and gaseous carbon dioxide as a function of isotope exchange time was measured in the temperature range 7 to 70°C at an initial partial pressure of CO2 of 26.7 kPa and from 7 to 60°C at a total initial pressure P(CO2 + H2O vapour) of 28 kPa. Isotope equilibrium was also examined at a temperature of 53.5°C and at an initial pressure of carbon dioxide that varied from 13.3 to 118.7 kPa. The permil fractionation, ϵ13C, as a function of exchange time, t, is given by the formula ϵ13C = ϵ∞13C(1 − e−tτ) where the carbon fractionation at isotopic equilibrium, ϵ∞13C, and relaxation time, τ, are calculated from the experimental data. It has been found that the relaxation time in a given experimental apparatus depends on two variables: (1) temperature and (2) the initial pressure. The ϵ∞13C value as a function of temperature is well described by the equation: ϵ∞13C = −(0.0954±0.0027) T[°C] + (10.41 ± 0.12). The relaxation time as a function of absolute temperature at a total initial pressure of 28 kPa is given by the equation: τ[hours] = (350 ± 35) T−12 − (18 ± 2), and as a function of the total initial pressure, P (in kPa), at temperature 53.5°C is well represented by the following dependence: τ[hours] = (0.03054 ± 0.00097)P.

Carbon isotope fractionation between dissolved and gaseous carbon dioxide

Abstract Fractionation of the stable carbon isotopes between dissolved and gaseous carbon dioxide has been measured at temperature 25°C by two methods. In the first method the open system conditions and different methods of CO 2 sampling were arranged. In the second method—the closed system conditions and CO 2 gas extraction were used. The results obtained by these methods are very consistent. Gaseous CO 2 is enriched in heavy isotope 13 C by 1.03±0.02 permil in comparison to dissolved carbon dioxide.

Experimental determination of carbon isotope equilibrium fractionation between dissolved carbonate and carbon dioxide

By mixing aliquots of pure Na2CO3 and CO2, solutions with precisely known molal fractions of CO3=, HCO3−, and dissolved CO2 were prepared. The apparent fractionation factor between gaseous CO2 and total carbon in the solution was determined mass spectrometrically from which the CO3= − CO2 fractionation factor was calculated taking into account the known fraction of HCO3− and respective isotope fractionation. Although the measurements have been made for a rather narrow temperature range, from 4 to 80°C, a theoretical curve was fitted through the experimental points, and thereby, tge isotopic partition function ratio of 13CO3= and 12CO3= molecules has been obtained for an extended temperature range. The results obtained for CO3=−CO2 isotope fractionation are significantly lower than those for HCO3−−CO2 exchange (with 103(α − 1) = 5.0 ± 0.2 at 25°C and cross-over point at about 63°C).

Use of Cu2O – NaPO3 mixtures for SO2 extraction from BaSO4 for sulfur isotope analysis

In earlier papers, we described a laboratory method to extract sulfur dioxide from sulfates for S/S isotope analysis using NaPO3 [1–3]. In paper [3] the method was significantly improved by use of copper boats and V2O5 in addition to NaPO3. The only drawback of this improved approach is a toxicity of the V2O5. Therefore, in this study, we replaced it successfully by cuprous oxide. Moreover, analytical grade Cu2O is much cheaper than V2O5.

EXPERIMENTAL INVESTIGATION OF SULPHUR ISOTOPIC FRACTIONATION BETWEEN DISSOLVED AND GASEOUS H2S

Abstract In this study sulphur isotope fractionation between undissociated dissolved H 2 S and H 2 S gas has been investigated experimentally. Such measurements were carried out at temperatures of 11°, 20° and 30°C. The experiment was performed at pH = 5, at which H 2 S remains nearly totally undissociated. The experimental conditions were as follows: (1) an aliquot of distilled water was saturated with H 2 S at a pressure of 1 atm; (2) the system containing gaseous and dissolved H 2 S was kept at constant temperature for a certain time; and (3) the gas phase was separated from the solution prior to sulphur extraction from both phases, which was prepared in the form of SO 2 gas for isotopic analysis. The results obtained show that dissolved undissociated H 2 S is enriched in the heavy isotope with respect to gaseous hydrogen sulphide in the temperature range 11–30°C. In this temperature range the permil fractionation obeys the following formula: Δ 34 S = + (2.75 ± 0.15) − (56 ± 7) · 10 −3 t (°C) The fractionation factor, α, can be calculated from the following expression: α = 1 + 0.001Δ 34 S

Sulfur Isotopic Composition of H2S and SO4 2− from Mineral Springs in the Polish Carpathians

Abstract A number of springs in Carpathian Mts. contain dissolved H2S and SO4 2- in concentrations above 10 mg/dm3. In this study we have investigated the sulfur isotope composition (δ34S) of the dissolved sulfur species in the springs from the flysch area in the Carpathian Mts. along the tectonic dislocation. It is believed that some of these springs may carry a major fraction of dissolved sulfur species of extremely deep sulfur (of mantle origin), which is subjected to SO4 2-—H2S isotope exchange at high temperatures. The original isotopic compositions may be modified by reduction/oxidation at low temperatures and by admixture of sulfur from other sources. In order to distinguish the sulfur of mantle origin we investigated δ34S of dissolved sulfide and sulfate and on the basis of known concentrations we calculated δ34S of total dissolved sulfur. The isotope fractionation between sulfate and sulfide helped to distinguish the sulfur origin. Evaluating the sulfur isotope exchange, we selected 4 springs which likely have only weakly disturbed sulfur of mantle origin.

A Modified Technique for the Preparation of SO2 from Sulphates and Sulphides for Sulphur Isotope Analyses

Abstract A modified technique for the conversion of sulphates and sulphides to SO2 with the mixture of V2O5—SiO2 for sulphur isotopic analyses is described. This technique is more suitable for routine analysis of large number of samples. Modification of the reaction vessel and using manifold inlet system allows to analyse up to 24 samples every day. The modified technique assures the complete yield of SO2, consistent oxygen isotope composition of the SO2 gas and reproducibility of δ34S measurements being within 0.10‰. It is observed, however, oxygen in SO2 produced from sulphides differs in δ18O with respect to that produced from sulphates.

Seasonal Variations of δ13C Values and CO2 Concentration in the Air During Vegetation Growth

Abstract The 24-hour variations of carbon isotopic composition and carbon dioxide concentration in the air over a meadow (51.9°N, 22.29°E) were investigated in different seasons. The amplitude of air CO2 concentration varied from about 350 ppm in May (1990) to 23ppm in February (1992) whilst the corresponding amplitude for δ13C varied from 10.7 to 1.2‰, respectively. δ13C values and CO2 concentrations are strongly correlated for air samples collected in May, June and October. Calculated values of δ13C of carbon dioxide released by plant and soil respiration are in the limits -28.0 to -25.2‰. The results are an excellent example of the influence of vegetation activity on atmospheric carbon dioxide.