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The first element legislated adopting chemical speciation was chromium (Cr) for differentiation between the highly toxic Cr(VI) from the micronutrient Cr(III). Therefore, this work aimed to develop a new analytical method through the coupling of High-Performance Liquid Chromatography with Diode-Array Detection (HPLC-DAD) with inductively coupled plasma mass spectrometry (ICP-MS) to obtain molecular and elemental information simultaneously from a single sample injection. In the first step, a low-cost flow split made of acrylic was developed aiming at optimally directing the sample to the detectors, enabling the HPLC-DAD/ICP-MS coupling. After the extraction of Certified Reference Materials (CRM of natural water NIST1640a and sugar cane leaf agro FC_012017), the recoveries determined by ICP-MS were 99.7% and 85.4%, respectively. Then, the method of HPLC-DAD/ICP-MS was applied for real samples of the CRMs. The presence of possible biomolecules associated with Cr(III) and Cr(VI) species was evaluated, with the simultaneous response detection of molecular (DAD) and elementary (ICP-MS) detectors. Potential biomolecules were observed during the monitoring of Cr(VI) and Cr(III) in sugar cane leaves, water samples and a supplement of Cr picolinate. Finally, the article also discusses the potential of the technique applied to biomolecules containing other associated elements and the need of more bioanalytical methods to understand the presence of trace elements in biomolecules.

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We report a detailed investigation of the interaction of Cr(NN)33+ with bovine serum albumin (BSA), an important protein for the transport of drugs in blood plasma which allows us to understand further the role of Cr(NN)33+ as a sensitizer in photodynamic therapy (PDT). Chromium(III) complexes, Cr(5Cl-phen)33+, Cr(5Me-phen)33+ and Cr(5Ph-phen)33+ (where Cl = chlorine, Me = methyl and Ph = phenyl are substituents in position 5 of the phen = 1,10-phenanthroline bidentate ligand), were used for the present study. The interactions of BSA with Cr(NN)33+ were assessed employing fluorescence spectroscopy and UV-Vis absorption spectroscopy; in addition electrochemical experiments carried out at a liquid/liquid interface gave insight into the relative hydrophobicities of the complexes. We found that chromium complexes bind strongly with bovine serum albumins (BSA) with intrinsic binding constants, Kb, of (3.33 ± 0.08) × 105 M-1, (5.92 ± 0.08) × 105 M-1 and (1.64 ± 0.05) × 105 M-1 at 300.3 K. Analysis of the thermodynamic parameters ΔG, ΔH, and ΔS indicated that hydrophobic interactions played a major role in all the BSA-Cr(NN)33+ association processes. The binding distances and transfer efficiencies for BSA binding reactions were calculated according to the Förster theory of non-radiation energy transfer giving distance (r) of 2.63 nm, 2.94 nm and 3.00 nm for 5Clphen, 5Mephen and 5Ph phenanthroline complexes, respectively. All these experimental results indicate that Cr(NN)33+ binds to serum albumins, by which these proteins could act as carriers of this complex for further applications in PDT.

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Experimental data of adsorption of Cr(III) from aqueous solutions using a Colombian bentonite were acquired. The adsorbent material was characterized by XRF, XRD, and nitrogen physisorption. The effect dataset of pH, agitation speed, contact time and adsorbent amount on the removal of Cr(III) from an aqueous solution, using sodium bentonite was reported. A complete factorial design 32 with two replicates was used to estimate the influence of the adsorbent amount (0.50, 0.75 and 1.00 g) and pH (2.0, 3.0 and 4.0) on Cr(III) removal. Experimental dataset was evaluated with Design Expert® software using the response surface methodology (RSM) in order to obtain the interaction between the processed variables and the response. The optimal conditions for Cr(III) removal from aqueous solution of 50 mg/l were as follows: pH of 3.5, and the bentonite amount equals 0.96 g, keeping constant the contact time at 60 min and stirring speed at 250 rpm. The equilibrium isotherms at 25, 30 and 35 °C were fitted by means of the Langmuir and Freundlich models, and the respective parameters of such models were obtained. The maximum adsorption capacity of sodium bentonite to Cr(III) removal was between 6.44 ± 0.11 and 6.79 ± 0.21 mg/g in the temperature range from 25 to 35 °C. According to the experimental data acquired, sodium bentonite is an effective adsorbent for the Cr(III) removal from aqueous solutions, with the advantage of being a natural, abundant and low-cost material.

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We analyzed the effect of pH on Cr(III) accumulation, biomass production, and phenolic profile of Salvinia rotundifolia and Salvinia minima plants grown in the presence of increasing concentrations of CrCl3 . Biomass accumulation, metal tolerance index, and photosynthetic pigment contents indicate that Salvinia rotundifolia seems to be more tolerant of Cr(III) than S. minima at different pHs. Increased metal accumulation by Salvinia species under increasing pH could be explained by changes of the protonation status of cell wall functional groups because both the highest and the lowest pH values used in the present study were outside of the levels at which Cr(III) species start to precipitate. The metal translocation factor indicates that in buffered conditions S. rotundifolia tend to retain more Cr(III) in lacinias than S. minima, probably through the involvement of insoluble phenolics. The results of the present study could be useful to the management of solution pH to maximize the removal of Cr(III) by aquatic plants. Environ Toxicol Chem 2019;38:167-176. © 2018 SETAC.

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Photocatalytic degradation of 4-chloro-2-methylphenoxyacetic acid (MCPA) in aqueous solution using Cr(III)-doped TiO2 under UV and visible light was investigated. The semiconductor material was synthesized by a microwave-assisted sol-gel method with Cr(III) doping contents of 0.02, 0.04, and 0.06 wt%. The catalyst was characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), nitrogen physisorption, UV-Vis diffuse reflectance spectroscopy (DRS), and atomic absorption spectroscopy (AAS). The photocatalytic activity for the photodegradation of MCPA was followed by reversed-phase high-performance liquid chromatography (HPLC) and total organic carbon (TOC) analysis. The intermediates formed during degradation were identified using gas chromatography-mass spectrometry (GC-MS). Chloride ion evolution was measured by ion chromatography. Characterization results showed that Cr(III)-doped TiO2 materials possessed a small crystalline size, high surface area, and mesoporous structure. UV-Vis DRS showed enhanced absorption in the visible region as a function of the Cr(III) concentration. The Cr(III)-doped TiO2 catalyst with 0.04 wt% of Cr(III) was more active than bare TiO2 for the degradation of MCPA under both UV and visible light. The intermediates identified during MCPA degradation were 4-chloro-2-methylphenol (CMP), 2-(4-hydroxy-2-methylphenoxy) acetic acid (HMPA), and 2-hydroxybuta-1,3-diene-1,4-diyl-bis (oxy)dimethanol (HBDM); the formation of these intermediates depended on the radiation source.

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The natural mordenite from Palmarito de Cauto deposit (PZ), Cuba, was studied in this work as an ion exchanger to remove Cr(3+) cations from alkaline aqueous solutions at different pH and chromium concentrations. The mordenite stability under cyclic treatment processes with alkaline solutions and its capacity to decrease the pH of the solutions was also analyzed. It was shown that PZ removes Cr(3+) ions from alkaline solutions, and it happens independently of the starting chromium concentration and the pH of the exchange solution used. This material has an important neutralizing effect on alkaline solutions, expressed in a significant pH decrease from the early stages of the treatments. For solutions with initial pH equal to 11, it decreases to a value of around seven. The stability of this material is not affected significantly after continuous cyclic treatment with NaOH solution, which shows that mordenite, in particular from Palmarito de Cauto deposit, has high stability in alkaline solutions. The results are important as they suggest that natural zeolites may be of interest in treatments of alkaline industrial waste effluents.

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