Potential-time curves have been carried out in CuSO 4 -H 2 SO 4 electrolytes to establish the effect of various impurities and additives on the stability of the protective PbO 2 layer formed on Pb-Ca-Sn alloys used in copper electrowinning. The most important effects are those of guar and Fe(III). Acting separately, they tend to stabilise the protective layer, whereas Co(II) and Mn(II) do not. The effect of Fe(III) can be explained by its strong oxidising power; the effect of guar, by its ability to form a protective barrier of organic molecules adsorbed on the PbO 2 layer. The effects of both guar and Fe(III) are diminished by the presence of other species in solution: reducing species diminish the effect of ferric ions and guar is degraded by oxidising species.
A derivative spectrofluorimetric method for simultaneous determination of enrofloxacin (EFX) and ciprofloxacin (CFX) in cow milk was developed. The sample preparation was based on rotating disk sorptive extraction (RDSE) using Oasis HLB® as extraction phase and followed by desorption of the analytes with methanol. The final extracts were evaluated by derivative spectrofluorimetry. An analyte-free cow milk was used as blank sample which was spiked with a known amount of analytes for the study of variables. The sample was treated with trichloroacetic acid in order to precipitate proteins. Furthermore, the extraction was carried out in the presence of Mc Ilvaine-EDTA 0.3M buffer to avoid any type of interference from the calcium ion. The variables involved in the RDSE process were pH and extraction time. Spectral variables were also optimized and analytical signals were evaluated at 417nm and 438nm for EFX and CFX, respectively. The limit of detection (LOD) and limit of quantification (LOQ) were 2.98-9.04 µg • L-1 and 2.56-7.75 µg • L-1 , for EFX and CFX respectively. The precision levels, expressed as relative standard deviation, for EFX and CFX were 3.2% and 3.0%, respectively. The recoveries were between 98.8% to 100.5%. Commercial milks were analyzed and both antibiotics shown concentrations below to LOD in the batches analyzed. Finally, the proposed method offers advantages in terms of simplicity, efficiency and cost. Besides being friendly with the environment.
SIn this work are presented two methods for the simultaneous determination of 17α-ethinylestradiol (EEL) and chlormadinone acetate (CMA) by second order derivative spectrophotometry.The first analytical method proposed is based in the dissolution and extraction of both drugs in acetonitrile. The solution was directly evaluated by second order derivative spectrophotometry with a smoothing factor of 8,000 and a scale factor of 10,000. The determination of EEL and CMA was carried out to 296,6 and 291.8 nm, respectively. The detection limits (3.3 σ criterion) for EEL and CMA were 6.9 × 10 -7 and 9.8 × 10 -8 mol / L, respectively. Furthermore, a study of the effect of the excipients containing in the pharmaceutical formulation was included. Polyvidone presents greater tendency to produce interference, but its spectral bands are located between 215 and 240 nm, so these bands do not interferes spectrally in the simultaneous determination of EEL and CMA. Both drugs were extracted from the pharmaceutical formulation with acetonitrile, obtaining a good recovery relative to the nominal content.The second method is a screening method and was applied in fortified drinking water. In this method, drugs were extracted in chloroform, which was then removed with N 2 and the residue was redissolved in acetonitrile. Due to the difference in the procedure in relation to the pharmaceutical formulation a new analytical parameters were obtained. For EEL this parameters were very similar to those obtained directly in solution, however these were higher for CMA, which could be attributed to that under these conditions was found a higher standard deviation of the blank. Recoveries of fortified samples were 81.8 ± 1.5% and 101.1 ± 0.73% for EEL and CMA, respectively.
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