Single-use optical sensor for the determination of iron in water and white wines

A new method, based on the use of a disposable sensor, for the determination of Fe(II) in waters and wines is proposed. The sensor is formed by an inert rectangular strip of polyester (Mylar) and a circular film (6 mm in diameter) adhered on its surface. This film, which contains the required reagents for the fixation of the analyte by means of a complexation reaction, forms the sensing zone of the sensor. When the sensor is introduced in an acidified (pH 2.5) sample solution containing between 4.0 and 300.0 micrograms/L of Fe(II), a violet-red colour develops in the initially colourless sensing zone. The linear range of the method depends on the equilibration time of the sensor with the sample solution. Thus, when the equilibration time was 5 min, the linear range was 41.0-300.0 micrograms/L, while for 60 min the range was 4.0-50.0 micrograms/L. Detection and quantification limits were 12.0 and 41.0 micrograms/L, respectively, for an equilibration time of 5 min. The precision of the method, expressed as relative standard deviation of ten samples of 100.0 micrograms/L of Fe(II), was 4.9%. Interferences produced by other species usually present in waters or wines have been studied. Cu(II) and Co(II) interfered seriously at concentration levels higher than 100.0 and 150.0 micrograms/L, respectively. The method was applied to the determination of Fe(II) in different types of waters and wines, using atomic absorption spectrometry as a reference method.