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BACKGROUND Tracing the source of polycyclic aromatic hydrocarbons (PAHs) by the compound-specific carbon isotope is becoming increasingly popular. For precise carbon isotope analysis, a pretreatment process is required to reduce co-outflow and unresolved complex mixture (UCM). Some existing studies require more instrumentation, such as high-performance liquid chromatography (HPLC). In addition, little attention has been paid to PAHs with a ring number less than 3. OBJECTIVES To establish a good separation method of 16 PAHs for meeting the requirements of compound-specific carbon isotope analysis. METHODS The effects of solid phase extraction (SPE) cartridges with amino and silica fillers were compared, and 10 eluent solvents were used on the separation, purification and enrichment effects of PAHs. Gas chromatography (GC) was used to test the separation and purification effect, and gas chromatography-isotope ratio mass spectrometry (GC-IRMS) was used to analyze compound-specific carbon isotopes. RESULTS More than 20% of the naphthalene and acenaphthene in the amino cartridge cannot be completely separated from the alkanes and unresolved peaks. The silica gel SPE cartridge has better impurity removal and separation effects than the amino cartridge. Choosing 1000mg/6mL silica gel SPE cartridge, using 6mL n-pentane to elute UCM and alkanes, and 5mL n-pentane-dichloromethane (70:30, V/V) to elute PAHs, and GC to conduct a preliminary inspection of the separation and purification effect, and GC-IRMS for individual carbon isotope analysis. The recovery of 16 kinds of PAHs was 79%-128%, the relative standard deviation was 2%-13% (1σ, n=6), and the analysis accuracy of the single carbon isotope ratio (δ13C) was 0.1‰-0.75‰. CONCLUSIONS The method greatly reduces the interferences of co-outflow and UCM to compound-specific carbon isotope analysis of PAHs, especially the low cyclic PAHs. No significant carbon isotope fractionation of PAHs is observed during purification, which satisfies compound-specific carbon isotope analysis requirements.

BACKGROUND Before analyzing the carbon isotopes of n-alkanes by gas chromatography-gas isotope mass spectrometry (GC-IRMS), it is necessary to pre-separate and enrich n-alkanes and isoparaffins in saturated hydrocarbon samples. Whether the carbon isotope fractionation of n-alkanes occurs is the key for the high-precision analysis of the carbon isotope ratio. OBJECTIVES To determine isotopic fractionation characteristics for n-alkanes during column chromatography and molecular sieve separation. METHODS Saturated hydrocarbon components were extracted with a 500mg/3mL SPE silica gel column using 2mL n-pentane. After separating by a 5Å molecular sieve and extracting by a mixture solvent of cyclohexane and n-pentane, n-alkanes were concentrated and analyzed by gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). RESULTS During column chromatographic separation, the carbon isotope ratio of most n-alkanes differed from -0.2‰ to 0.2‰. When n-alkanes was not completely complexed by 5Å molecular sieve, the uncomplexed alkane carbon isotope was about 0.7‰ heavier, and weak carbon isotope fractionation occured, but it did not affect the eluted n-alkanes carbon isotope ratio. Eluted with cyclohexane-n-pentane mixed solvent, the carbon isotope values before and after the elution differed from-0.2‰ to 0.5‰, and eluted in the same way for the second time, the difference between the eluted n-alkanes carbon isotope and simulate sample was between -0.3‰ and 0.2‰. Analyzing the carbon isotope ratios of n-alkanes with different recoveries (>20%), the difference between carbon isotopes of n-alkanes before and after pretreatment was within 0.3‰. It was found that when the recovery was as low as 20%, the carbon isotope ratios did not undergo significant fractionation. CONCLUSIONS The column chromatography-5Å molecular sieve adsorption and mixed solvent elution method is suitable for the analysis of carbon isotope ratios of normal alkanes, which yields a recovery greater than 20%.

BACKGROUND Heavy metal elements in sediment can migrate in an active state under natural action, which has potential bioavailability and potential regional ecological risks. The use of near-infrared spectroscopy (NIRS) technology to study the response mechanism of samples of different matrices can provide a non-destructive and rapid analysis method for evaluating the active state of heavy metals and provide a basis for ecological risk research. OBJECTIVES To reveal the characteristics of active metal elements in lagoonal wetland sediment and evaluate their ecological risk. METHODS Sediment core and soil samples near by the drilling site were analyzed using both spectral and chemical method. NIR spectra of dry-freezed sample were collected by infrared spectrometer with integrating sphere. Based on the near infrared spectroscopy analysis technique, near infrared spectrum were collected by the integrating device within range of 4000-10000cm-1 (1000-2500nm), at the resolution of 2cm-1. Meanwhile the chemical mobile fractions of heavy metal elements were extracted from soil and sediment samples by diluted nitric acid, the dissolved concentrations of Co, Ni, Cu, Zn, Cd, Pb were determined by inductively coupled plasma-mass spectrometry (ICP-MS). With both chemical and spectral predicted value, the partial least squares regression prediction model had been developed and applied to determine mobile fraction of Co, Ni, Cu, Zn, Cd and Pb. RESULTS Area of absorption peaks at 7290-6390cm-1 and 4683-4000cm-1 related to O-H strentching along with AlAl-OH and Al(Mg)-OH bending indirectly indicate the active content of heavy metals. Spectral prediction results show that the changes in the active components of Co, Ni, Cu, Zn, Cd and Pb in the sediments of the Qilihai in the past 100 years corresponded to the three obvious changes from 1934 to 1948, 1956 to 1963, and 1976 to the present. The temperature increase also corresponded to large-scale human disturbances such as the construction of the Qilihai Reservoir in 1980. CONCLUSIONS The total and mobile fractions of Co, Ni, Cu, Zn, Cd and Pb in Qilihai sediments were lower than the ecological risk threshold specified in the national standard. The ecological risk of heavy metals released from wetlands towards nearby villages and farmland in the Qilihai catchment area was extremely low.

The efficient electroreduction reaction of nitrate (NO3−RR) at low concentrations to ammonia is energetically favorable for ammonia production and environmentally essential to treat water contamination. Copper-based conjugated molecule electrocatalysts for the NO3−RR are advantageous in terms of their customizable Cu-coordinative micro-environment and facile preparation; however, they easily agglomerate due to their large π-conjugating system, which severely lowers the active site density and increases the internal resistance. This study demonstrates that Ti3C2Tx MXenes are promising supports to disperse and anchor a molecular catalyst (copper phthalocyanine, CuPc) to construct a CuPc@MXene electrocatalyst in order to significantly promote NO3−RR performance. 10% CuPc@MXene achieved higher ammonia selectivity (94.0%) and higher nitrate conversion (90.5%) compared to those of unsupported CuPc, and retained high ammonia selectivity (∼80%) after seven recycling tests. The combination of online differential electrochemical mass spectroscopy (DEMS) and density functional theory (DFT) calculations has showed that CuPc molecules are able to inhibit the hydrogen evolution reaction and effectively convert nitrate into ammonia through the ONH reaction pathway. The results showed that the MXene support is applicable to many metal phthalocyanines (MPcs, M = Fe, Co, Ni), demonstrating its potential in other electrochemical catalysis applications. [ABSTRACT FROM AUTHOR]