Stepwise complexometric determination of calcium and magnesium in the presence of a high manganese and iron content using potassium hexacyanoferrate(II) as a masking agent

Abstract

A critical study has been made on the masking of manganese and iron by their precipitation as Fe,[Fe(CN),] and Mn,[Fe(CN),J with K4[Fe(CN),] in the presence of ascorbic acid and potassium chloride for the complexometric titration of calcium plus magnesium with EDTA a t p H 10. The optimum acid concentration and temperature for the selective and quantitative precipitation of Mn (I I) and Fe( I I) liexacyanoferrates (I I), which are granular and nonadsorbant metallochromic indicators, are found to be 1-2.5 N hydrochloric acid and 25-50 O C , respectively. I n a solution with an acidity of lower than 1 N, the hesacyanoferrates(I1) of Mn(I1) and Fe(I1) coprecipitate calcium and magnesium hexacyanoferrates(I1). At 70 O C , the amount of coprecipitation increases. Up to 08.75 and 19.60 mg of manganese and iron, respectively, can be successfully inaslced in coiiiplesonietric titration. For the titration of calcium alone at pH 12, the interference of manganese and iron has been overcome by osidising Mn(I1) -TEA to Mn(II1) -TEA, which is stable against EDTA titration with air bubbling. Iron forms a quantitative Fe -TEA complex almost instantaneously at pH 12. A simple procedure has been devised for the titration of Ca + Mg with EDTA after masking manganese and iron with K,[Fe(CS),], a non-toxic reagent. For calcium, TEA alone is used for masking both manganese and iron.

An air-assisted liquid–liquid extraction using a dual-valve sequential injection manifold (DV-SIA): Determination of copper

“…However, its application in analytical chemistry is less widely used. We found a few interesting examples in the literature: Dasgupta et al used air bubbling to overcome the interference of high manganese content based on the oxidation of Mn(II)-TEA to Mn(III)-TEA during the titration of calcium at pH 12; 1 Idowu et al used ambient air to generate ozone in a gas-phase chemiluminescence-based analyser for waterborne arsenic; 2 Pereira et al reported methods for the determination of Mn and Ni in lake and marine sediment slurries by GFAAS, in which slurries were kept homogeneous by air bubbling with an aquarium pump; 3 Camou et al described a portable sensor for measuring benzene in water based on bubbling extraction and UV spectroscopy detection. 4 Air has also been widely used in flow-based systems for segmentation or as a carrier.…”