Reagents and Sampling
All chemicals were purchased from E. Merck, Darmstadt,
Germany, and were of analytical reagent grade. All solutions
2146 Food Anal. Methods (2014) 7:2145–2152
were prepared using doubly distilled water. A stock solution
of 2×10−3 M 3H2NA was prepared by dissolving its appropriate
amount in 250mL ofmethanol.A stock solution of Al3+
with concentration of 1×10−3 M was prepared from
Al(NO3)3• 9H2O. The working solutions of Al3+ and
3H2NAwith concentration of 1×10−4 M were made by diluting
the above solution in water and 50 % methanol, respectively.
The following buffered solutions with concentrations
of 0.1Mwere prepared: hydrochloric acid/potassium chloride
(pH 1–2), formic acid/sodium formate (pH 2–4), acetic
acid/sodium acetate (pH 4–6), and hydrochloric acid/Tris
(hydroxymethylaminomethane) (pH 6–8). Finally, the acetic
acid/sodium acetate buffer (pH 4.5) was used for the Al3+
determinations. All products used for sampling were stored
according to the manufacturer's instructions. The experimental
samples were directly obtained from their packaging of the
products to avoid extraneous contamination.
Procedures
Determination of Al-3H2NA Complex Formation Constant
By using the buffer of acetic/acetate and stock or diluted
solutions of Al3+ and 3H2NA, a series of solutions (25 mL)
were prepared in which the concentration of 3H2NA was
varied in the range of 1.0×10−7–2.4×10−5 M while the concentration
of Al3+, pH, ionic strength, and methanol content