A SIMPLE CO2 EXTRACTION METHOD FOR RADIOCARBON ANALYSES OF DISSOLVED INORGANIC CARBON IN WATER SAMPLES WITHOUT A CARRIER GAS

ABSTRACT We developed a simple and cost-effective method for extracting carbon from dissolved inorganic carbon (DIC) in water samples without a carrier gas. This method only slightly modifies the existing vacuum line for CO2 purification in radiocarbon research laboratories by connecting several reservoirs and traps. The procedure consists of repeated cycles of CO2 extraction from water into the headspace of the reaction container, expansion of the extracted gas into the vacuum line, and cryogenic trapping of CO2. High CO2 yield (∼98%) was obtained from a variety of water samples with a wide range of DIC concentrations (0.4–100 mmol·L−1, in the case of 1.2 mgC). The δ13C fractionation depended on the CO2 yield, while the 14C concentration was constant within the error range, regardless of the CO2 yield. The average δ13C discrepancy between the results of this method and direct analyses made using the GC-IRMS was 0.02 ± 0.06‰. The standard deviations (1σ) in fraction of modern carbon (F14C) ranged from 0.0002 to 0.0004 for waters below 0.01 of F14C, and below 0.8% of F14C values for waters above 0.1. We conclude that this method is useful for effectively extracting CO2 from DIC in water and yields accurate 14C data.

A multi-location peak parking approach for calculation of second dimensional retention indices for improved volatile compound identification with cryogen-free comprehensive heart-cut two-dimensional gas chromatography

Comprehensive heart-cut multidimensional gas chromatography (CH/C MDGC) without a cryogenic trapping device was developed with an approach for calculation of first and second dimensional retention indices (1I and 2I).

Volatile selenium fluxes from selenium-contaminated sediments in an Australian coastal lake

Environmental context Methylation of sedimentary selenium to volatile dimethylselenide is a natural remediation process for contaminated aquatic systems. We present flux estimates for the loss of dimethylselenide from sediments of an anthropogenically affected lake and observe a 6-fold difference between late autumn–early winter and summer. The loss of dimethylselenide represents a significant sediment loss vector, of the same order as the diffusive loss flux for inorganic selenium across the sediment–water interface. Abstract Overflows from ash dams associated with the operation of coal-fired power stations in Lake Macquarie, NSW, Australia, have been a historical source of selenium to the lake. Although dissolved selenium concentrations have been marginally elevated, sediments are the major sink. Methylation of sedimentary selenium to volatile dimethylselenide (DMSe) is known to be a natural remediation process. Sediments from north of Wyee Bay and the Vales Point Power Station were the subject of field sampling and monitoring to determine the extent to which selenium is being lost to the atmosphere as DMSe. Flux estimates were obtained by trapping volatile selenium species using benthic domes, followed by analysis in the field using a fully automated cryogenic trapping system with atomic fluorescence detection. The detection limit of the system was 0.1ngL–1 for DMSe and 1ngL–1 for dimethyl diselenide (DMDSe). Measurements in both summer and late autumn–early winter showed a distinct seasonal difference, with a higher summer DMSe flux of 53±25ng Se m–2h–1 (±s.d.) compared with 8±5ng Se m–2h–1 in late autumn–early winter. No DMDSe was detected. These fluxes are similar to those measured in Europe and North America, and represent an annual loss of 1.3kg of selenium per year from the nearby lake area. Lake-wide this would represent a significant loss to the atmosphere.

A dynamic plant chamber system with downstream reaction chamber to study the effects of pollution on biogenic emissions

A system of two dynamic plant chambers and a downstream reaction chamber has been set up to investigate the emission of biogenic volatile organic compounds (BVOC) and possible effects from pollutants such as ozone. The system can be used to compare BVOC emissions from two sets of differently treated plants, or to study the photochemistry of real plant emissions under polluted conditions without exposing the plants to pollutants. The main analytical tool is a proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS) which allows online monitoring of biogenic emissions and chemical degradation products. The identification of BVOCs and their oxidation products is aided by cryogenic trapping and subsequent in situ gas chromatographic analysis. The data presented in the paper demonstrates the good performance of the setup.

A Study on Trapping CO2 Using Molecular Sieve for 14C AMS Sample Preparation

At the Seoul National University accelerator mass spectrometry (AMS) laboratory, we are planning to develop an automated sample preparation system for higher throughput of radiocarbon dating. This system will consist of several sections, including a combustion line, CO2 trap, graphitization system, and so on. We usually collect CO2 by cryogenic trapping. However, since handling liquid nitrogen is expected to be rather difficult, we are interested in replacing the cryogenic method with the molecular sieve method for the collection of CO2. In this study, we compare the performance of the cryogenic trapping method and molecular sieve method. Zeolite 13X is used as a molecular sieve, and as test samples we use the oxalic acid standard (NIST SRM 4990C), high-purity graphite powder, and archaeological charcoals. The pMC values and the radiocarbon ages (BP) obtained from samples prepared by the above 2 methods are very similar. We especially focused on the memory effect of the molecular sieve, meaning the CO2 contamination from a previous sample, which can cause errors in age determination. To reduce this effect, we flowed He gas through a zeolite container for several minutes at a high temperature before the CO2 was introduced. By the adding this step, we have obtained more reliable results.