Pre-concentration of trace Mn from dairy products through a pH-induced tautomerization/charge transfer complexation before spectrophotometric analysis

In this study, a new method was developed for extraction and pre-concentration of trace Mn in dairy products before analysis. The method is based on the pH-induced charge transfer complexation and extraction of Mn from the matrix at pH 6.0. Their free Mn (II) and total Mn levels were detected at 269 nm by UV spectrophotometry. For total Mn, the method was validated by analysis of two certified milk samples. The results were in good agreement with the certified values, and the precision was lower than 7.0%. After a pre-concentration of 62.5-fold, the limits of detection were 0.40/0.62 and 0.42/0.69 mu g L-1 in linear range of 1-125 mu g L-1 by calibration curves prepared in solvent and sample extracts. From comparison of the slopes, a matrix effect was not observed. After pre-treatment by the ultrasound and microwave, free Mn (II) and total Mn levels of dairy products were found to be in the range of 90-285, 155-350 and 153-345 mu g kg-1.