A promazine derivative-oriented chemical sensor for ultra-sensitive chromium determination

The study reports a simple and highly selective spectrofluorometric method for trace determination and speciation of chromium(iii & vi) species in water using 10-(3-dimethylaminopropyl) phenothiazine hydrochloride, namely, promazine hydrochloride (PMH) as a fluorescence tagging reagent.

The control and optimization of the curing process of epoxy coatings: a case of poly(glycidoxy siloxane) resins

Coatings from poly(glycidoxy siloxane) resins were developed and their mechanical properties examined. Three different resins with varying numbers of methyl siloxane and glycidyl siloxane units were tested. Crystallinity was found to be a very important indicator of the mechanical properties of coatings, as the parameters such as cupping and hardness were linearly dependent on the degree of crystallinity of coatings. The method involving the spectrophotometric determination of unbounded amine curing agent was successfully applied as a way of optimizing the curing process both for expected mechanical properties and for ecological aspect. It was found that the resin with 50 methyl siloxane and 25 glycidyl siloxane units was the most appropriate for technological use because of the preferred mechanical properties and stability of technological parameters. Interestingly, this type of resin was characterized by the lowest degree of crystallinity. The curing conditions leading to the optimal product corresponded to 30 min of curing at 120°C or 20 min at 140°C. Under such conditions, the amount of released unbounded amine was the lowest. It was also found that poly(glycidoxy) siloxane resins may be ecologically valuable since the release of amine from this type of resins is smaller than that from a typical epoxy resin.

Application of alizarin colorimetric measurements for quantification of amine extraction by model food simulants from epoxy polymer

A simple and straightforward method has been proposed for quantification of residual amine in cured epoxy resin. Non-bounded triethylenetetramine was extracted from epoxy polymer and determined via spectrophotometry using alizarin chromophore. Four solvents commonly used as food simulants, namely water, 95% ethanol, 10% ethanol and 3% acetic acid were examined. Released amine induces changes in the absorption spectrum of alizarin, by decreasing the intensity of the maximum at 430 nm band and mutually increasing the 527 nm band. These changes were proportional to the amounts of amine concentration in samples. The statistical significance of obtained calibration curves was validated. Among studied solvents, the highest amine release was observed for water solution and 3% acetic acid, that is approximately 7% w/w. The maximal amount of residual amine extracted with 95% ethanol was about 1.25%, while for 10% ethanol this amount was 2%. The effect of aging of the samples and exposure to artificial sunlight were also examined. The proposed method has been proven to be fast, low cost and directly applicable for analysis of typical epoxy resins.

Solid phase extraction and determination of Cr(III) by spectrophotometry using cefaclor as a complexing reagent and FAAS

The present study reports on the application of modified groundnut shell as a new, easily prepared, and stable sorbent for the extraction of trace amount of Cr(III) in aqueous solution. 2-Hydroxybenzaldiminoglycine was immobilized on groundnut shells in alkaline medium and then used as a solid phase for the column preconcentration of Cr(III). The elution was carried out with 3 mL of 2 mol L(-1) HCl. The amount of eluted Cr(III) was determined by spectrophotometry using cefaclor as a complexing reagent and by flame atomic absorption spectrometry (FAAS). Different experimental variables such as pH, amount of solid sorbent, volume and concentration of eluent, sample and eluent flow rate, and interference of other metal ions on the retention of Cr(III) were studied. Under the optimized conditions, the calibration curves were found to be linear over the concentration range of 13-104 and 10-75 μg L(-1) with a detection limit of 3.64 and 1.24 μg L(-1) for spectrophotometric method and FAAS, respectively. An enrichment factor of 200 and RSD of ±1.19-1.49 % for five successive determinations of 25 μg L(-1) were achieved. The column preconcentration was successfully applied to the analysis of tap water and underground water samples.

Methacrylate copolymers with pendant piperazinedione-sensing motifs as fluorescent chemosensory materials for the detection of Cr(VI) in aqueous media

A fluorogenic sensory film, or dense membrane, capable of detecting Cr(VI), Fe(III), and Hg(II) in water was prepared. The film was prepared by a bulk radical polymerization of different comonomers, one of which contained a piperazinedione motif as sensory fluorophore. The film exhibited gel-like behavior and was highly tractable, even after being swollen in water. The sensing conditions were chosen to overcome interference from iron and mercury cations, giving rise to a material with a detection limit of 1 ppb for Cr(VI).

Chemical speciation of chromium(III) and (VI) using phosphonium cation impregnated polyurethane foams prior to their spectrometric determination

Fast and selective sorptions of Cr(VI) species from aqueous media onto tetraphenylphosphonium bromide (TPP(+) · Br(-)) physically immobilized polyurethane foams (PUFs) sorbent were achieved. Based on the Scatchard model of binding sites of the PUFs and Langmuir and Dubinin-Radushkevich (D-R) adsorption models of Cr(VI) retention onto TPP(+) · Br(-) immobilized PUFs, a dual retention mechanism involving absorption related to "weak-base anion ion exchange" and an added component for "surface adsorption" was proposed. Thus, the TPP(+) · Br(-) loaded PUFs were successfully packed in column mode for preconcentration of trace and ultra trace concentrations of Cr(VI) as halochromates [CrO(3)C](-)(aq) from aqueous HCl media. The retained [CrOCl(3)](-)(aq) species were recovered with NaOH (1.0 mol L(-1)) and analyzed by flame atomic absorption spectrometry. Cr(III) species after oxidation to Cr(VI) with H(2)O(2) in aqueous KOH (1.0 mol L(-1)) were also retained and could be recovered by the proposed method. The limits of detection (LOD) and quantification (LOQ) of Cr(VI) were 0.04 and 0.13 µg L(-1), respectively. The chemical speciation of Cr(III, VI) species in various water samples at trace and ultra trace levels were carried out by TPP(+) · Br(-) loaded PUFs packed column. The enhancement factor and sensitivity factor of [CrO(3)C](-)(aq) sorption were 80.0 and 30.0, respectively.