Determination of total iron in water and foods by dispersive liquid-liquid microextraction coupled with microvolume UV-vis spectrophotometry

A novel microvolume UV-vis spectrophotometry method was proposed for the rapid determination of total iron coupling with an efficient pretreatment method known as dispersive liquid-liquid microextraction (DLLME). The basis of the method is a quantitative colorimetric reaction between ferrous iron and 2-(5-bromo-2-pyridylazo)-5-(diethyl amino) phenol (5-Br-PADAP) after the reduction of Fe(III) to Fe(II) by using ascorbic acid as reducing agent. Parameters related to the efficiency of microextraction, such as pH, complexant concentration, the volume ratio of disperser solvent and extraction solvent were discussed and optimized in detail. Under the optimized conditions, the absorbance was in proportion to iron concentration in the range of 5-400 μg L−1 with a correlation coefficient (R) of 0.9993. The limit of detection (LOD) and limit of quantitation (LOQ) were 1.5 μg L−1 and 5.2 μg L−1, respectively. The relative standard deviation (RSD) for samples were 1.37- 4.42% (n = 3). Good recoveries of iron were obtained in the range of 95.4-103.2% in food samples, 96.9-103.6% in water samples and 98.8-102.3% in Certified Reference Material. The proposed method was rapid, reliable and high-selective for the determination of total iron in food and water samples.