Enhancement by Copper(II) of the voltammetric signal of vitamin B2 applied to its determination in breakfast cereals.

Addition of copper(II) to breakfast cereal samples was shown to significantly enhance the analytical signal obtained by electrochemical reduction of vitamin B(2) using linear sweep voltammetry on disposable carbon electrodes. The enhancement was observed only when dissolved oxygen was present. In model solutions the analytical signal was linear in the concentration range 6-150 ng/mL with a calculated limit of detection of 5 ng/mL (S/N = 3). This compared favorably with earlier work using a similar measurement approach--but in the absence of copper--in which the limit of detection was calculated to be 900 ng/mL. The effects of potential interferents commonly found in cereals were examined. In addition to signal attenuation by both sugar and starch (already reported), folic acid was found to increase (+6%) and iron to decrease (-11%) the analytical signal when present in the maximum concentration ratios, with respect to vitamin B(2), that are normally found in breakfast cereals. Nevertheless, the simplicity of the approach was potentially attractive for near-line quality control applications in manufacturing. The utility of the measurement approach was demonstrated by the addition of excess copper(II) sulfate to determine vitamin B(2) in aqueous extracts of breakfast cereals. The results agreed well with those provided by the cereal manufacturer who used an established HPLC method.

Hexacyanoferrate(III) as a mediator in the determination of total iron in potable waters as iron(II)-1,10-phenanthroline at a single-use screen-printed carbon sensor device.

Hexacyanoferrate(III) was used as a mediator in the determination of total iron, as iron(II)-1,10-phenanthroline, at a screen-printed carbon sensor device. Pre-reduction of iron(III) at -0.2V versus Ag/AgCl (1M KCl) in the presence of hexacyanoferrate(II) and 1,10-phenanthroline (pH 3.5-4.5), to iron(II)-1,10-phenanthroline, was complete at the unmodified carbon electrode surface. Total iron was then determined voltammetrically by oxidation of the iron(II)-1,10-phenanthroline at +0.82V, with a detection limit of 10microg l(-1). In potable waters, iron is present in hydrolysed form, and it was found necessary to change the pH to 2.5-2.7 in order to reduce the iron(III) within 30s. A voltammetric response was not found at lower pH values owing to the non-formation of the iron(II)-1,10-phenanthroline complex below pH 2.5. Attempts to incorporate all the relevant reagents (1,10-phenanthroline, potassium hexacyanoferrate(III), potassium hydrogen sulphate, sodium acetate, and potassium chloride) into a modifying coated PVA film were partially successful. The coated electrode behaved very satisfactorily with freshly-prepared iron(II) and iron(III) solutions but with hydrolysed iron, the iron(III) signal was only 85% that of iron(II).

Disposable sensor for measurement of vitamin B(2) in nutritional premix, cereal, and milk powder.

Methodologies for the determination of vitamin B(2) in food matrixes and a premix using simple sample conditioning steps coupled with a convenient and cheap electrochemical sensing device are presented. Electrochemical analysis based on differential pulse voltammetry (DPV) coupled to carbon electrodes gave a well-defined reduction peak at -0.42 V versus a Ag/AgCl quasi-reference electrode. Using a straightforward sample preparation step, vitamin B(2) can be measured successfully in a nutritional premix and food products. Standard additions of riboflavin were used to confirm the analyte concentrations and to provide precision data.