Speciation and Determination of Low Concentration of Iron in Beer Samples by Cloud Point Extraction

A laboratory experiment is described in which students determine the concentration and speciation of iron in beer samples using cloud point extraction and absorbance spectroscopy. The basis of determination is the complexation between iron and 2-(5-bromo-2- pyridylazo)-5-diethylaminophenol (5-Br-PADAP) as a colorimetric reagent in an aqueous micellar solution followed by cloud point extraction for preconcentration. Total iron and Fe(II) were determined with and without addition of ascorbic acid as a reducing agent, respectively. The determination of iron concentration in real beer samples using cloud point extraction provides an opportunity for students to become familiar with preconcentration, complexation chemistry, masking agents, and the speciation of an analyte. Students also gain hands-on experience with adapting methods from scientific literature, using absorbance spectroscopy, and exploring quality control techniques, such as method detection limits and spike recovery.