Volumetric determination of iron (III) with hydroxylamine as a reducing agent
A new volumetric method has now been developed for the determination of iron(III) through reduction to iron(II) with excess of hydroxylamine. The reduction is completed at the temperature of the boiling water bath in 10 min, keeping the acidity at 0.2–0.5 N sulphuric acid. The mixture is cooled and treated with enough 1 ∶ 1 sulphuric acid to bring up the acidity to 6 N. It is then titrated with a standard solution of sodium vanadate, using N-phenyl anthranilic acid as inside indicator. Diphenyl benzidine, barium diphenyl sulphonate, or 1,10-phenanthroline cannot be used as indicators in this titration, because of the interference of the unreacted hydroxylamine.
The method has been found to be very precise, and convenient. It has also the advantage that it is subject to fewer interferences than the existing methods.
Available from: Qin-Hong Hu
- "We used a reducing agent, 0.1 M NH 2 OH·HCl, and boiling condition  "
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ABSTRACT: A simple, sensitive, and selective headspace gas-chromatographic method has been developed for measuring hydroxylamine (HA) in a variety of sample matrices including pharmaceutical formulations. This procedure relies on converting HA into nitrous oxide (N2O), which is a single-step reaction that is carried out directly in a heated headspace vial. The gaseous products are then analyzed by headspace capillary gas chromatography. Several detection strategies were evaluated and electron capture provided the best sensitivity (4 parts-per-billion (ppb)) while the mass selective and thermal conductivity values were higher (14 ppb and 1.4 parts-per-million (ppm), respectively). The method's linear dynamic range spans two to four decades with a run-to-run precision that was better than 5% R.S.D. (n=7). The reagent concentrations (oxidant, buffer) strongly impact the N2O signal and the greatest response was obtained for solutions that contained equimolar amounts of reactants. HA was efficiently (98%) recovered from a sample matrix that contained only the active pharmaceutical ingredient (API) but the recovery was lower (83%) when excipients were present.
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ABSTRACT: A spectrophotometric flow injection method is proposed for the determination of formaldehyde (HCHO) in wastewater. The condensation of HCHO with hydroxylamine sulfate produces formaldoxime. In this reaction hydroxylamine decreases in proportion to the concentration of HCHO. Residual hydroxylamine reduces the iron(III)-1,10-phenanthroline (phen) complex to a red iron(II)-phen complex (λmax = 0 nm). Therefore, the decrease in hydroxylamine can be monitored by measuring the decrease in the absorbance at 510 nm. Consequently, HCHO can be determined indirectly. A standard/sample solution containing HCHO is injected into a water carrier solution so that a negative FIA peak can be obtained. Under the optimized experimental conditions, HCHO in an aqueous solution was determined over the concentration range of 0.25 ~ 1.0 mg L-1. The limit of detection (S/N = 3) was 20 μgL-1 HCHO. The relative standard deviation values (n = 4) were 2.03, 0.80 and 0.27% for the responses at 0.25, 0.50 and 1.00 mg L-1. The sampling throughput was 15 samples h-1. Analytical results for 5 wastewater samples were obtained with no significant difference between the proposed method and an official method.
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