Abstract:Travertine and tufa can be used as a high-resolution record for reconstructing the paleoclimate and paleoenvironment. It is not clear whether travertine is able to preserve the radionuclides for the reconstruction of modern human nuclear events. In this study, we developed and compared two sample preparation methods for the determination of 129I and 127I in travertine samples using direct acid dissolution and pyrolysis combustion. The analytical results of the levels of 129I and 127I as well as the 129I/127I ratios in travertine are presented here for the first time, and the hydrodynamic influence on the levels and distribution of iodine isotopes are discussed. It was found that the concentration of 127I in travertine was low in the winter but high in the summer. This temporal variation of 127I is likely related to the level and species of iodine in the water supply by mixing geothermal water with rainfall, as well as the amount of iodine-containing impurity. The 129I level clearly suggests that the Baishuitai travertine is endogenic and slightly affected by the amount of rainfall and biological impurities. The results of this study show that endogenic travertine can be used in reconstructing the influence of human nuclear activity with high resolution, and also imply that hypergenic tufa has great potential for such studies. Both archives have implications on the mechanism used for iodine incorporation into carbonate in the natural environment.

Abstract:Silicon dioxide (SiO2) occurs as both crystallized quartz and amorphous quartz, and their oxygen isotope is widely used to trace the source of hydrothermal fluids, to reconstruct paleotemperature of oceans and to provide genetic constraints on petrogenetic studies. Precise and accurate oxygen isotope analysis, therefore, is fundamental for the application of oxygen isotope study. Secondary Ion Mass Spectrometry (SIMS) is capable of obtaining oxygen isotope information at micron levels, but precise and accurate SIMS isotopic microanalysis requires high quality reference materials to correct instrumental mass fractionation and to monitor data quality. In this study, we report two reference materials, a natural crystallized quartz (Qinghu-Qtz) from Qinghu quartz monzonite (Guangdong, P.R. China) and a fused amorphous quartz (Glass-Qtz). Multiple SIMS analyses suggest that both Qinghu-Qtz and Glass-Qtz are homogeneous in terms of oxygen isotope composition at ca. 20 μm level, with a two-standard deviation of 0.50 ‰ (N = 1083) and 0.22 ‰ (N = 283), respectively. In comparison, the widely utilized NBS-28 quartz reference material, designed for bulk analysis, is less homogeneous at micro levels. The δ18OVSMOW values of the two reference materials were obtained by conventional fluorination isotope ratio mass spectrometry (IRMS) and the recommended δ18OVSMOW values were 8.49 ± 0.20 ‰ (Qinghu-Qtz, 2 SD, N = 12) and 1.68 ± 0.08 ‰ (Glass-Qtz, 2 SD, N = 10).

Abstract:By use of dual atomic absorption lines with a two-element hollow cathode lamp, a simple method was developed for air/acetylene flame temperature measurement. The results are comparable to literature values with a peak temperature at about 2400 K. The spatial temperature variation of a fuel-rich flame was investigated, and it was found that the tendency for variation conformed to the flame combustion process. The proposed method was compared to the traditional dual-line atomic absorption method of indium and showed a similar tendency of temperature variation. The proposed instrumental setup is simple, which uses a Cu/Fe two-element hollow cathode lamp, a handheld charge coupled device detector, an optical fiber and a computer. Due to its simplicity, non-contact and portability, this technique is promising for flame temperature characterization of various kinds of flames or electrothermal atomizers.

Abstract:Comparison of Three Sequential Extraction Methods for the Determination of Iron, Manganese, and Thallium in Asphaltite Samples

Abstract:Lead (Pb) is a non-essential but extremely noxious metallic element, which is important for the assessment of environmental pollution. A simple and high throughput method involving fast heat extraction slurry sampling electrothermal atomic absorption spectrometry (HESS-GFAAS) was developed to detect trace Pb content in geological standard reference materials (SRMs). Compared with the traditional digestion method, the HESS-GFAAS method greatly reduces the time of sample pretreatment. The HESS-GFAAS technique improved Pb recovery and precision compared to conventional slurry sampling techniques. This optimized HESS-GFAAS procedure was performed as follows: first, the sample was added into 1 mL HNO3, 1 mL HCl and 1 mL HF, followed by heating for 30 min at 120 ℃ on a heating block; Next, dilute the solution with 50 mL water, and finally, the solution was introduced into a graphite tube with Pd(NO3)2-NH4H2PO4 as the mixed matrix modifier and analyzed by the GFAAS with a Pb electrodeless discharge lamp (EDL). To eliminate the interface of the geological sample matrix, the method of additions calibrate was used for Pb determination in geological samples. The results for 20 of these materials were in good agreement with the reference values. The characteristic mass and limit of detection for Pb based on the integrated absorbance for a 0.2% (m/v) sample were 14.8 ± 0.8 pg and 0.035 mg kg-1, respectively. The accuracy (96.05–102.4% recovery) and precision (0.13–2.07%) of this procedure are illustrate by the results obtained for the 20 geological reference materials. The proposed method shows great potential for the determination of trace Pb in geological samples.

Abstract:A rapid analysis of methylmercury (MetHg) in fish samples is reported by using stannous chloride reduction and direct sampling electrothermal vaporization atomic absorption spectrometry (ETV-AAS). After the simple reduction reaction using 10% SnCl2 (w:v), Hg2+ was changed to volatile Hg0 and vaporized from the analyte extraction solution. Then, the residual Hg species was determined with the direct sampling Hg analyzer without requiring chromatographic separation. Since the dominating organic Hg in fish tissues is mostly MetHg (methylmercury), the measured alkyl Hg residue can therefore be considered to be MetHg+ for rapid screening. The LOD (detection limit) of the proposed method reached 0.6 μg/kg of MetHg with 0.4% - 6.3% RSD (relative standard deviation). No significant difference (P > 0.05) was found between the proposed method and the liquid chromatographic atomic fluorescence spectrometry (LC-AFS) method or certified values of reference materials, which proves the accuracy of the MetHg analysis in real marine and freshwater fish samples. The total testing time for one aliquot, including instrumental analysis (~3 min) and sample preparation, can be performed within 100 min. Considering the possible EtHg (ethylmercury) existence in most fish samples, it is suggested that this proposed method be used for future rapid screening analysis, which no doubt also offers considerable applicable potential for fast mercury speciation analysis to protect food safety.