Determination of Sulfur Compounds in Water Samples by Ion Chromatography Dynamic Reaction Cell Inductively Coupled Plasma Mass Spectrometry

Simultaneous measurement of aqueous redox-sensitive elements and their species across the soil-water interface

The redox-sensitive elements, such as iron, manganese, sulfur, phosphorus, and arsenic, shift their speciation every millimeter (mm) across the soil-water interface in the flooded soil environments. Monitoring of element speciation at this high-resolution (HR) within the SWI is still difficult. The key challenge lies in obtaining sufficient porewater samples at specific locations along the soil gradient for downstream analysis. Here with an optimized inductively coupled plasma mass spectrometry (ICP-MS) method and a HR porewater sampler, we demonstrate mm-scale element profiles mapping across the SWI in paddy soils. High-concentrations of iron and manganese (> 10 mg/L) were measured by ICP-MS in an extended dynamic range mode to avoid signal overflow. The iron profile along the SWI generated by the ICP-MS method showed no significant difference (p < 0.05) compared to that measured independently using a colorimetric method. Furthermore, four arsenic (arsenite, arsenate, monomethylarsonic and dimethylarsinic acid), two phosphorus (phosphite and phosphate) and two sulfur (sulfide and sulfate) species were separated in 10 min by ion chromatography -ICP-MS with the NH₄HCO₃ mobile phase. We verified the technique using paddy soils collected from the field, and present the mm-scale profiles of iron, manganese, and arsenic, phosphorus, sulfur species (relative standard deviation < 8%). The technique developed in this study will significantly promote the measurement throughput in limited samples (e.g. 100 μL) collected by HR samplers, which would greatly facilitate redox-sensitive elements biogeochemical cycling in saturated soils.

Measurement of sulfur in environmental samples using the interference standard method with an O2 -pressurized reaction cell and a single-quadrupole inductively coupled plasma mass spectrometer

RATIONALE

Precise and accurate analysis of trace sulfur in environmental samples is essential to understand its biogeochemical cycle. Yet it remains a challenging analytical task for single-quadrupole inductively coupled plasma mass spectrometry (ICP-MS) instrumentation because of the presence of significant isobaric interferences.

METHODS

We evaluated the effect that different instrumental parameters have on the formation of SO⁺ species, and show that, under our instrumental configuration, it is not possible to fully remove all spectral interferences. Consequently, our instrumental optimization is focused on minimizing their contribution while obtaining the best possible sensitivity. We assessed the performance of the interference standard (IFS) method, where the signal corresponding to the SO⁺ ions formed in the ICP is normalized to that of ³⁶ Ar⁺ .

RESULTS

We found that, by pressurizing the cell with O₂ , there is a significant improvement in sensitivity and detection limits, associated with a more effective production and focalization of SO⁺ ions. Moreover, by applying the systematics of the IFS with pure O₂ injected into the cell (IFS-O₂ ) we observed a significant improvement in accuracy and detection limits, making this the method of choice for the quantification of trace sulfur in environmental samples by ICP-MS.

CONCLUSIONS

The method described here represents an effective and affordable alternative for the accurate and precise determination of sulfur using single-quadrupole ICP-MS in environmental samples, with LODs and LOQs comparable with those obtained with more expensive instrumentation.

Atomistic Insights into the Stability of Pt Single-Atom Electrocatalysts

Single-atom catalysts (SACs) have quickly emerged as a new class of catalytic materials. When confronted with classical carbon-supported nanoparticulated catalysts (Pt/C), SACs are often claimed to have superior electrocatalytic properties, e.g., stability. In this study, we critically assess this statement by investigating S-doped carbon-supported Pt SACs as a representative example of noble-metal-based SACs. We use a set of complementary techniques, which includes online inductively coupled plasma mass spectrometry (online ICP-MS), identical location transmission electron microscopy (IL-TEM), and X-ray photoelectron spectroscopy (XPS). It is shown by online ICP-MS that the dissolution behavior of as-synthesized Pt SACs is significantly different from that of metallic Pt/C. Moreover, Pt SACs are, indeed, confirmed to be more stable toward Pt dissolution. When cycled to potentials of up to 1.5 V_RHE, however, the dissolution profiles of Pt SACs and Pt/C become similar. IL-TEM and XPS show that this transition is due to morphological and chemical changes caused by cycling. The latter, in turn, is a consequence of the relatively poor stability of S ligands. As monitored by online ICP-MS and XPS, significant amounts of sulfur leave the catalyst during oxidation. Hence, in case catalysts with improved stability in the anodic potential region are desired, more robust supports and ligands must be developed.

Anion-Specific Sulfur Isotope Analysis by Liquid Chromatography Coupled to Multicollector ICPMS

An accurate method has been developed to measure, in a single analytical run, δ³⁴S in sulfite, sulfate and thiosulfate in water samples by liquid chromatography combined with multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). The method is based on the anionic exchange separation of sulfur species prior to their online isotope ratio determination by MC-ICPMS. Mass bias correction was accomplished by a novel approach based on the addition of an internal sulfur-containing standard to the sample. This innovative approach was compared to the sample-standard bracketing procedure. On-column isotopic fractionation was observed and therefore corrected by external calibration. Isotopic ratios were calculated by linear regression slope (LRS), an advantageous method for transient signals, leading to a combined uncertainty of δ³⁴S below 0.25‰ and a reproducibility below 0.5‰ for the injection of 1 μg of S. The method was successfully applied to the measurement of δ³⁴S in synthetic solutions and environmental water samples. Matrix effects leading to δ³⁴S overestimation were observed for sulfate in some samples with high sodium/sulfate mass ratios. The developed analytical procedure simplifies the δ³⁴S analysis of liquid environmental samples since preparation steps are no longer required and allows the analysis of several sulfur-containing species in a single run.

Preparation and characterization of γ-Fe2O3 nanoparticles and investigation of its adsorption performance for sulfide, sulfite and thiosulfate from aqueous solutions using ultrasonic assisted method: Modeling and optimization

Maghemite nanoparticles, as an adsorbent, was used for the removal of sulfur species including sulfide, sulfite and thiosulfate from waste water samples by ultrasonic-assisted adsorption method. The characterization of the prepared nanoparticles was carried out by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction and BET technique. The nanoparticles well dispersed in the water. The adsorbent was easily separated magnetically from the solution after loading with adsorbate. According to central composite design, the best experimental conditions including initial pH, the dosage of adsorbent and sonication time were obtained for sulfide, sulfite and thiosulfate. After optimization of the parameters, the removal of analytes in these conditions lead to the highest analytes removal efficiency (above 98%). The adsorption capacity was evaluated using different adsorption isotherm models. The maximum predicted adsorption capacities for sulfide, sulfite and thiosulfate were obtained as 148.5, 122.5 and 119.6mgg^-1, respectively. Then, desorption process of the adsorbed thiosulfate was also investigated using sodium hydroxide solution as the solvent and the other conditions affect to desorption were optimized.