Suspect screening workflow comparison for the analysis of organic xenobiotics in environmental water samples

Suspect screening techniques are able to determine a broader range of compounds than traditional target analysis. However, the performance of the suspect techniques relies on the procedures implemented for peak annotation and for this, the list of potential candidates is clearly a limiting factor. In order to study this effect on the number of compounds annotated in environmental water samples, a method was validated in terms of absolute recoveries, limits of quantification and identification, as well as the peak picking capability of the software (Compound Discoverer 2.1) using a target list of 178 xenobiotics. Four suspect screening workflows using different suspect lists were compared: (i) the Stoffident list, (ii) all the NORMAN lists, (iii) suspects containing C, H, O, N, S, P, F or Cl in their molecular formula with more than 10 references in Chemspider and (iv) the mzCloud library. The results were compared in terms of the number of annotated compounds at each confidence level. The same 8 compounds (atenolol, caffeine, caprolactam, carbendazim, cotinine, diclofenac, propyphenazone and trimetoprim) were annotated at the highest confidence level using the four workflows. Remarkable differences were observed for lower confidence levels but only 4 features were annotated at different levels by the four workflows. While the third approach provided the highest number of annotated features, the workflow based on the mzCloud library rendered satisfactory results with a simpler approach. Finally, this latter approach was extended to the analysis of organic xenobiotics in different environmental water samples.

SEM-EDX linear scanning: a new tool for morpho-compositional analysis of growth bands in urinary stones

The genesis and growth of calculi are imprinted in their structure, so the pathogenesis of lithiasis could potentially be read via proper analytical techniques. In this study, electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) is used to obtain a description of the morphology and compositional structure of a single bladder stone. This technique establishes the chemical and crystalline architecture of the urolith to assess the effect of the chemical environment on its growth. Scanning electron microscopy-backscattered electrons (SEM-BSE) images clearly show that the stone has a multilayered structure. These layers and Liesegang ring-like structures are characterized by one predominant chemical component but also by slighter compositional changes. The mean crystalline components are determined by X-ray diffraction (DRX), infrared spectroscopy (FT-IR), and Raman analysis (RMN). Elemental analysis along a radial trajectory of the calculus by EDX linear scanning (EDX-LS) also reveals the compositional structure of the layers and the spatial distribution of the main chemical components. EDX-LS data processing reveals concentration profiles that clearly show morpho-compositional growth bands, which correspond to precipitation waves and urinary concentration peaks. The width of the growth bands is independent of the radial position, layer, and element analyzed. We conclude that the bands observed are a consequence of slight changes in the biochemical composition of the urine and consequently reflect a short-term biological cycle of the renal system. This non-specific growth rate suggests that stone formation is a kinetically controlled phenomenon in which promoters of crystal cluster aggregation may have played a key role.

Changes in solution color during phenol oxidation by Fenton reagent

Fenton reaction is a highly effective treatment for degrading phenolic compounds in an aqueous solution. However, during phenol oxidation, the oxidized water takes on a dark brown color associated with increased toxicity. Then, although phenol can be completely removed, if the oxidation process is not carried out properly, the final wastewater will be brown in color and have higher toxicity, two parameters in which legislation imposes restrictions. This paper analyzes the development of the dark color observed in the solution under oxidation treatment and formulates a reaction mechanism to explain the color generation. The experiments were carried out following the batch-wise procedure, but with the solution pH being kept constant throughout the reaction at its optimum value for phenol removal, i.e., pH 3.0. It is checked experimentally that color is formed at the beginning of the reaction in less than five minutes, and follows the kinetic-path of a reaction intermediate. During the first steps of the reaction phenol is degraded to dihydroxylated rings (catechol, resorcinol, and hydroquinone). These aromatic intermediates generate higher colored compounds such as ortho- and parabenzoquinone. On the other hand the dihydroxylated rings can react with their own quinones to generate charge-transfer complexes (quinhydrone), compounds which take on a dark color at low concentrations. Moreover, when iron reacts with hydrogen peroxide, ferric ions are generated that can be coordinated to benzene rings to produce colored metal complexes. The observed color of the solution is not a fortuitous result depending on trace components of low significance, but depends directly on the main reaction intermediates, so it is concluded that observed color depends on the level of oxidation reached. The maximum color observable during oxidation treatment (A(o)) depends only on initial phenol concentration and not on oxidant or catalyst doses.

Cooperative biosorption of copper on calcium alginate enclosing iminodiacetic type resin

Composite gels of calcium alginate containing iminodiacetic type resin were prepared as a chemical analogue of biological tissues and membrane such as the cell wall. This chemical model was applied in copper biosorption from synthetic aqueous solutions. Experimental data on the composite were compared to those obtained for the biopolymer and the iminodiacetic-type resin separately and fitted into the ion exchange equilibrium model proposed in this work, which basically assumes that metal retention is the sum of the metal loaded onto the biopolymer and onto the resin. This model is tested with experimental data on copper biosorption on composite gels, including the equilibrium expressions of all the ionic species that are present in the system, the fraction of metal enclosed in the gel fluid, the gel volume variation, and the Donnan equilibrium theory. Another simplified model that only requires one equilibrium constant for each metal in the resin is shown to fit the results of the experiment fairly well, but it proves necessary to include an empirical parameter n into the equilibrium equation of copper in the resin to obtain the best fit of experimental data.

Ion exchange selectivities of calcium alginate gels for heavy metals

An equilibrium model has been proposed and verified, based on the conditions in the gel phase and Donnan equilibrium theory, for the analysis of the experimental data on the recovery of lead, copper, cadmium, cobalt, nickel and zinc from synthetic, nonmetallic aqueous solutions on calcium alginate gels. This equilibrium model considers that the system behaves as an ion-exchange process between the calcium in the gels and the divalent metals in solution, and that the metallic portion enclosed in gel fluid is supposed an important quantitative contribution to the total amount of metal uptake by gels. According to the equilibrium constants calculated, it is deduced that the selectivity order is: Pb > Cu > Cd > Ni > Zn > Co.