2023, 44(3):123-130. DOI: 10.46770/AS.2023.113
Abstract:Lead-tin solder is a useful piece of evidence from a crime scene and may be examined for information related to the construction or source of an improvised explosive device (IED). A technique based on electrothermal vaporization into inductively coupled plasma optical emission spectrometry was improved for the direct quantification of trace and major elements in solder (Ag, As, Bi, Cr, Fe, Sb, Sn). NIST 1728, a tin-alloy certified reference material, was used for external calibration and achieve a direct, fully solid-sampling procedure using only 0.5–3.0 mg of sample. Point-by-point internal standardization with Ar 404.442 nm was performed to compensate for sample loading effects on the plasma, and a background correction technique was introduced to improve the overall efficiency of analysis. As solder was observed to change composition during some mock scenarios of IED preparation, which limits how solder can be examined in forensics, different soldering conditions (temperature, solder size, cleaning of the soldering tip or not between subsequent samples) were studied using a Fe-tip soldering device. Statistical analyses including Student’s t-tests and a one-way analysis of variance revealed that none of these conditions resulted in contamination of the melted solder sample, hence confirming the viability of the mock procedure used to replicate IED soldering in research. A new qualitative discrimination method is introduced and demonstrated in a blind trial for matching and discriminating lead-tin solders. This method represents an improvement from past research and has potential for use in evaluating other forensic evidence involving ferrous-alloys.
2023, 44(3):131-141. DOI: 10.46770/AS.2023.141
Abstract:Secondary ion mass spectrometry (SIMS) for sulfur isotope analysis in chalcopyrite is an essential technique with exceptional spatial resolution, which enables precise constraints on mineralization mechanisms. However, the scarcity of matrix-matched chalcopyrite reference materials (RM) for SIMS hinders its accuracy and reliability. This study introduces a large-grained natural chalcopyrite RM (IGSD) for precise sulfur isotope analysis (δ34S) using SIMS and laser ablation multicollector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS). Petrographic examination and electron microprobe analysis (EMPA) results confirm the homogeneity of major elements in the IGSD chalcopyrite grains. The results of in situ analysis at four SIMS laboratories and one LA-MC-ICPMS laboratory and bulk analysis confirm the homogeneity of the S isotope composition in the IGSD chalcopyrite grains. The in situ analysis result is consistent with the result of isotope ratio mass spectroscopy (IRMS), which falls within the same range of uncertainty. This supports the suitability of the IGSD chalcopyrite RM for in situ S isotope analysis. The recommended δ34S value of the IGSD chalcopyrite RM, based on IRMS, is 4.21 ± 0.23‰ (2SD, n = 30).
2023, 44(3):142-152. DOI: 10.46770/AS.2023.079
Abstract:Mass-independent chromium (Cr) isotope ratios measurements have been widely used in dating early solar system events and tracing the genetic relationships between different solar system, as well as terrestrial materials. Current analytical techniques need relatively large sample sizes, and this limits the application of Cr isotopes on precious mission return samples and some Cr-poor samples (e.g., BCR-2 with Cr contents of ~15 ppm). This paper reports a novel analytical method for mass-independent Cr isotopic ratios measurements using a Thermal Ionization Mass Spectrometer (TIMS) operated in total evaporation (TE) mode. A three-step cation column (AG 50W-X12 resin, 200?400 mesh) chemistry is used to purify Cr in various samples, including chondrites, basalts and peridotites, and the Cr yield is better than 92%. Residual organics from column resins is detrimental to Cr ionization on filaments, we demonstrate that this can be effectively removed by treating samples with H2O2 at 40 OC on hotplate. Single Cr measurements on rhenium filaments consume 15 to 20 ng of Cr and sustain 52Cr of ~10V for 10 to 20 minutes. Generally, for one sample of 200 ng Cr, 10?15 ng repeated measurements can be made and 2-standard error precisions of ~ 0.05 and ~ 0.10 for ε53Cr and ε54Cr*, respectively can be achieved. The reproducibility (the 2-standard deviation) for ε53Cr and ε54Cr is 0.05 and 0.07, respectively, tested by multiple measurements for DTS-2b (USGS dunite) and NWA 7734 (ordinary chondrite). Concentration and doping test (mainly for Fe) have also been conducted. These tests show that the Fe/Cr must be < 5 % and the measured 56Fe/52Cr<1 ‰ in order to achieve accurate ε54Cr. Finally, the ε53Cr and ε54Cr values measured by normal method on TIMS are systematically higher than those measured by total evaporation method on TIMS, which is potentially caused by non-kinetic mass-dependent fractionation during Cr evaporation and ionization on TIMS. The TE method could reduce this effect that may cause inaccurate mass-independent Cr isotope data on TIMS.
2023, 44(3):153-159. DOI: 10.46770/AS.2023.086
Abstract:Fe-Ni@ACC nanocomposite was synthesized by hydrothermal method and characterized using scanning electron microscope (SEM) and Fourier-transform infrared spectroscopy (FT-IR). Fe-Ni@ACC was used as adsorbent for magnetic dispersive micro solid-phase extraction (M-D-μSPE) procedure for separation and preconcentration of trace level of copper at trace levels before its determination by microsampling flame atomic absorption spectrometry (FAAS). The effects of various parameters such as pH, amount of adsorbent, eluent type and eluent volume, and sample volume on the recoveries of copper on Fe-Ni@ACC were optimized. The presented method is accurate, inexpensive and environmentally friendly and due to magnetic properties of the adsorbent, the separation process is very simple and fast. The method presents limit of detection (LOD)(3s/m) of 0.69 μg L?1, limit of quantification (LOQ)(10s/m) of 2.29 μg L?1, preconcentration factor of 40 and relative standard deviation (RSD %) (s/x) 1,18%. The accuracy of the method was confirmed by the analysis of TMDA-53.3 fortified water and TMDA-64.2 fortified water certified reference materials and addition-recovery tests to real samples. The present M-D-μSPE method was successfully applied to determination of copper level of tap water, cigarette, human hairs and black teas samples.
2023, 44(3):160-168. DOI: 10.46770/AS.2023.102
Abstract:The miscellaneous materials, including gangue, plastic, and wood commonly present in coal. These miscellaneous materials affect the reliability of coal analysis using laser-induced breakdown spectroscopy in power plants, but have significantly distinct spectral characteristics from coal. Hence, this paper proposes a step-by-step classification method to screening the false spectra of miscellaneous materials. The first step aims to identify the plastic and wood spectra by determining the existence of specific characteristic spectral lines using the standard deviation (SD) values. The spectral lines Si Ι 288.16 nm with the SD value of more than 850 counts and Li Ι 670.78nm with SD value of more than 1750 counts were used as the distinguishing markers. The classification accuracy of first step was 100%. Due to the high similarity between gangue and coal, the second step utilized the random forest (RF) classification model to identify the gangue spectra. The number of trees and random variables in the RF model was optimized. The accuracy of classification model without and with the proposed step-by-step method was 98.30 and 99.96%, respectively. To assess the necessity of spectra classification, a set of calorific value analysis was performed by adding false spectra of different proportions, which were compared with analysis after removing the false spectra. The root mean square error of prediction (RMSEP) was 0.42 MJ kg-1 (after removing), compared with 0.50 MJ kg-1 (mixing with 10% gangue spectra), 0.56 MJ kg-1 (mixing with 20% gangue spectra) and 0.57 MJ kg-1 (mixing with 30% gangue spectra). The results demonstrated that the proposed step-by-step classification method could effectively identify the spectra of coal and miscellaneous materials and improve the accuracy of coal analysis.
2023, 44(3):169-177. DOI: 10.46770/AS.2023.115
Abstract:X-ray fluorescence method was proposed for a determination of major elements in samples of snow cover solid phase collected in the urban areas of the Irkutsk region near aluminum smelter and combined heat and power plant. The limitation of the analyzed sample mass, which in some cases does not exceed 50 mg, as well as the features of the elemental composition (high Al and low Si contents) require a special methodological approach to quantitative elemental analysis. Due to the lack of matrix-matched certified reference materials, the calibration set includes certified reference materials of igneous and sedimentary rocks as well as aluminum ore samples. Results of X-ray fluorescence method were compared with the results obtained by reference methods including atomic absorption, atomic emission and spectrophotometry methods. It showed that it is necessary to use samples of snow cover solid phase analyzed by reference methods as a calibration set for X-ray fluorescence analysis, which ensures the quantitative determination of major elements (Na, Mg, Al, Si, P, K, Ca, Ti, Mn and Fe). These elements are important for environmental pollution investigation. Al was discovered as a main pollutant produced by aluminum smelter, Si, Ca, Ti, Mn, and Fe - by combined heat and power plant.
2023, 44(3):178-190. DOI: 10.46770/AS.2023.117
Abstract:This review's main purpose is to provide a succinct overview of recent developments in the field of volatile organic compounds (VOCs) detection based on Laser-induced breakdown spectroscopy (LIBS). VOCs are important air pollutants, which have great harm to the environment and human body. It is of great significance to realize the rapid detection of VOCs in the atmospheric environment. LIBS is a novel atomic emission spectroscopy technology, which can achieve the rapid in-situ detection of substances and shows great potential in the online monitoring of atmospheric VOCs. To illustrate the development and difficulties of LIBS technology in atmospheric VOCs detection, some typical cases for various aspects of are listed, including the detection of harmful elements in VOCs, source tracing of VOCs, the identification of isomers, and the detection of VOCs in living environment.