Ümmihan T. Yilmaz

Determination of Melamine by Differential Pulse Polarography/Application to Milk and Milk Powder

Melamine made headlines in September 2008 because it was found to be the contaminant responsible for the deaths of several infants and making many more sick. Determination of trace melamine is very important. Therefore, in this work a novel, sensitive and reliable method was developed using differential pulse polarography. The most suitable buffer system was found to be Britton–Robinson (B–R) buffer, pH 11.2. The melamine peak in this medium appeared at about −50 mV, it responded well to standard additions and high reproducibility was obtained. The calibration graph was linear in the concentration range of melamine from 1.0 to 66.4 μM with a correlation coefficient of 0.999. The limit of detection (LOD) and limit of quantification (LOQ) were obtained as 0.3 and 1.0 μM, respectively. The current was characterized as being adsorption-controlled process. The proposed method was successfully applied to the determination of melamine in spiked milk and milk powder. The linear dynamic ranges observed for melamine concentration in milk and milk powder samples were between 1–58 and 10–57 μM, respectively. The sufficiently good recoveries and low standard deviations for the data reflect the high accuracy and precision of proposed differential pulse polarographic method.

Interference between selenium and some trace elements during polarographic studies and its elimination

When selenite was added into solutions of some ions such as copper, lead, cadmium, zinc, chromium and arsenic their DPP peak decreased. This kind of interference was observed in all acids and in wide range of pH values, causing at least 50% error when both ions (the ion present and selenite) were in similar quantities. It was found that this interference was not taking place at pH 8.5 in the presence of large amounts of selenite. A synthetic sample containing these elements in 10(-5)M in the presence of 50 times selenite has been analyzed at pH 8.5 without any interference. The detection limit in this medium was 3 x 10(-7)M for cadmium and lead, 1 x 10(-6)M for copper and zinc and it was 3 x 10(-7)M for selenite.

Determination of Gallic acid by differential pulse polarography: Application to fruit juices

Phenolic compounds possess antioxidant, antitumor, antimutagenic, antibacterial and anticarcinogenic properties. Gallic acid (2,3,4-trihydroxybenzoic acid) is a natural phenolic compound; therefore, determination of trace gallic acid is very important. In this work, a novel, sensitive and reliable method was developed using differential pulse polarography. The most suitable buffer system was found to be Britton-Robinson (B-R) buffer, pH 10.0. The gallic acid peak in this medium appeared at about −160 mV, it responded well to standard additions, and high reproducibility was obtained. The calibration graph was linear in the concentration range of gallic acid from 1.0–50.0 μM with a correlation coefficient of 0.999. The limit of detection (LOD) and limit of quantification (LOQ) were obtained as 0.3 and 1.0 μM, respectively. The proposed method was successfully applied to the determination of gallic acid in fruit juices. The influences of some other commonly found inorganic and organic salts on the determination were also examined. Some interferiences were eliminated by using complexing agents, e.g. EDTA.