Evaluation of Methods for Trace Zinc Determination

Abstract

b Methods for determination of microgram quantities of zinc are experimentally evaluated. The preferred method uses bis(2-hydroxyethy1)dithiocarbamate (diethanoldithiocarbamate) masking with dithizone extraction and a single color method; 30 pg. of zinc are determined with an accuracy of 99.0 =t 1.8% (for duplicate samples with 95% confidence limits) in the presence of a tenfold excess of each of the following: cadmium, cobalt, copper, mercury, nickel, lead, iron, manganese, chromium, and tin. Because zinc is a common contaminator of reagents, the true efficiency of zinc separation procedures is proved with zinc-65. Radiozinc also elucidates the difference in behavior of diethyldithiocarbamate and diethanoldithiocarbamate as masking agents in dithizone extractions. The use of Zincon for zinc determinations is not recommended unless a limited number of impurities are present.HIS WORK compares and evaluates T methods for the determination of microgram quantities of zinc in the presence of an excess of a Ride range of metallic impurities. The chemical behavior of these methods is elucidated where helpful. The methods considered were limited to those adaptable to the determination of 1 to 100 pg. of Zn in solution with concentrations as low as 0.1 p.p.m. and to those with good accuracy (relative error less than 10%). Determinations without separations did not meet these limitations and the only suitable separations were dithizone extractions in the presence of various masking agents, anion elchange resin elution with hydrocliloric acid, and certain sulfide precipitations.Since Zn is a very common contaminator of reagents and of water, it is not knomn whether many separation procedures are truly efficient or if they merely give reproducible distribution of zinc in the various steps. For this reason several separation procedures have been tested with radiozinc to determine the total loss of Zn in a determination and to locate operations which might be particularly susceptible to error due t o incomplete separation.

Antibacterial activity in human amniotic fluid: dependence on divalent cations

“…The concentration of calcium in amniotic fluid at term is between 1.5 and 3.0 mmol/l, and that of magnesium between 0-5 and 2.0 mmol/l (Johnell & Nilsson 1971;Goodlin 1972). EDTA chelates magnesium and calcium from solution, o-phenanthroline chelates all group IIb cations, while dithizone at neutral p H is relatively specific for zinc (Margerum & Santacana 1960). In our studies, high-molecular-weight (6-lysin) antibacterial activity was reduced after cation chelation with EDTA, but not with o-phenanthroline or dithizone.…”

“…The activity was restored by zinc but not by addition of manganese, cobalt, magnesium or calcium at sub-physiological concentrations (1.5-3.0 pmol/l). EDTA chelates magnesium and calcium from solution, o-phenanthroline chelates all group IIb cations, while dithizone at neutral p H is relatively specific for zinc (Margerum & Santacana 1960). EDTA chelates magnesium and calcium from solution, o-phenanthroline chelates all group IIb cations, while dithizone at neutral p H is relatively specific for zinc (Margerum & Santacana 1960).…”

Extraction

“…A dithizone method for Bi and Pb in Cu alloys was developed (486). In the dithizone determination of Zn, masking of impurities with bis-(2hvdroxyethyl) dithiocarbamate was found superior to use of diethyldithiocarbamate (301). Dithizone was found suitable for determining trace amounts of Cd in uranyl nitrate (138) and for traces of Co in the presence of larger amounts of Cu(II), Fe(II), Ag(I), and Zn (448).…”

Determinação polarografica do zinco em plantas, após a sua separação em resina trocadora de íons

“…Um exame dos trabalhos publicados sôbre os métodos de determinação do zinco em quantidades relativamente baixas, evi¬ dencia que uma das maiores dificuldades encontradas reside na se¬ paração do citado elemento de seus interferentes (MARGERUM & SANTACANA, 1960).…”