Arsenazo III is usually used in the determination of calcium in serum,has been used to evaluate calcium transport in permeabilized cells,has also been used for the spectrophotometric determination of uranium and thorium.
Arsenazo III reacts with more than 30 metal ions to give coloured complexes.
So far it has been utilized for the determination and detection of about 25 metal
ions (including 16 rare earth metals). The majority of the analytical procedures
are spectrophotometric.
The absorption spectra of the metal complexes of Arsenazo III possess two
maxima at about 610 and 665 nm. Since the absorption of the reagent is very low
at 665 nm, but is considerable at 610 nm, the extinction of the complexes at 665
nm is utilized for analytical purposes. At this wavelength the molar extinction
coefficients of the complexes lie in the range 5 x 104—1.3 x 105. This explains the
extremely high analytical sensitivity of the reagent. (Under optimum conditions
the sensitivity may reach 0.01 γ/ml.).
The main advantage of Arsenazo III over Arsenazo I lies in the considerably
higher stabilities of the complexes of the former. This makes possible the analytical
utilization of the reagent in strong mineral acidic media. It gives complexes with
tri- and tetravalent metal ions in acidic media where hydrolysis and the consequent
formation of polynuclear species do not interfere with the analytically
utilized reaction. Those metals whose complexes form only in solutions of higher
pH do not interfere with the analytical determination of the metal ions giving
complexes in strongly acidic media (thorium, zirconium, uranium, plutonium,
neptunium, etc.). This is the reason of the relatively high analytical selectivity of
Arsenazo III.
Trace amounts of zirconium can be enriched before determination by coprecipitation
with titanium hydroxide. The titanium hydroxide precipitate containing
the zirconium content of the sample is dissolved in 6 M hydrochloric acid
solution and the zirconium determined photometrically with Arsenazo III.
Thousand-fold amounts of titanium do not interfere with the determination of
zirconium. The absorption maximum of the zirconium complex of Arsenazo III
is at 665 nm.
Spectrophotometric reagent for U, Th, Zr and other metals.Indicator for the precipitation titration of SO4 with Ba.
