Determination of free and total zinc using 2-[(5-bromo-2-pyridylazo)]- 5-diethylaminophenol in mixed surfactant medium

Abstract

A simple and sensitive spectrophotometric method for chemical fractionation and determination of zinc in cosmetics and pharmaceuticals is described based on the formation or red coloured species of Zn(II) with 2-[(5-bromo-2-pyridylazo)]-5-diethylaminophenol (5-Br-PADAP) and mixed surfactants (TX-100 and Brij-35) in the <i style="mso-bidi-font-style:normal">p</i>H range 8.2- 10.5. The red coloured Zn(II)-5-Br-PADAP-(TX-100+Brij-35) complex in aqueous medium shows maximum absorbance at 550 mm with molar

absorptivity of 1.60<img src='/image/spc_char/cross.gif' border=0>10⁵ dm³ mol^-1 cm^-l. The detection limit or the method is 6 ng Zn(II)/cm² and obeys Beer's law up to 0.4 µg Zn(II)/cm² in aqueous phase. Relative standard deviation for ten determinations for solution containing 0.2 µg Zn(II)/cm² is 1.5%. The validity of the method has been satisfactorily examined for the determination of zinc (free and total) in cosmetics and pharmaceutical formulating samples manufactured in India, with RSD value from actual analyte content ranging between 2.1 and 2.7% for cosmetics and between 1.9 and 2.8 % for pharmaceutical formulations.

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