A method for determination of [Fe3+]/[Fe2+] ratio in superparamagnetic iron oxide

Abstract Superparamagnetic iron oxide nanoparticles (SPION), as a kind of nanophase materials, are widely used in biomedical application, such as magnetic resonance imaging (MRI), drug delivery, and magnetic field assisted therapy. The magnetic property of SPION has close connection with its crystal structure, namely it is related to the ratio of Fe 3+ and Fe 2+ which form the SPION. So a simple way to determine the content of the Fe 3+ and Fe 2+ is important for researching the property of SPION. This review covers a method for determination of the Fe 3+ and Fe 2+ ratio in SPION by UV–vis spectrophotometry based the reaction of Fe 2+ and 1,10-phenanthroline. The standard curve of Fe with R 2  = 0.9999 is used for determination the content of Fe 2+ and total iron with 2.5 mL 0.01% (w/v) SPION digested by HCl, pH = 4.30 HOAc-NaAc buffer 10 mL, 0.01% (w/v) 1,10-phenanthroline 5 mL and 10% (w/v) ascorbic acid 1 mL for total iron determine independently. But the presence of Fe 3+ interfere with obtaining the actual value of Fe 2+ (the error close to 9%). We designed a calibration curve to eliminate the error by devising a series of solution of different ratio of [Fe 3+ ]/[Fe 2+ ], and obtain the calibration curve. Through the calibration curve, the error between the measured value and the actual value can be reduced to 0.4%. The R 2 of linearity of the method is 0.99441 and 0.99929 for Fe 2+ and total iron respectively. The error of accuracy of recovery and precision of inter-day and intra-day are both lower than 2%, which can prove the reliability of the determination method.