Trace element determination in soy sauce: A novel total reflection X-ray fluorescence procedure and comparison with inductively coupled plasma\u2013mass spectrometry

Soy sauce is a widespread food commodity very common in East and Southeast Asia. It features a complex matrix, including a highly saline matrix (NaCl up to 15%) and a relevant organic component, typically around 15%. Methods for trace element determination in this matrix have been scarcely reported and no procedure has been proposed including Total Reflection X-Ray Fluorescence (TXRF). Aim of the present paper is to setup a TXRF method requiring minimum sample treatment and suitable for process control and risk assessment related to soy sauce consumption. Accordingly, a digestion (HNO3/H2O2) plus dilution (1:5 w/w) procedure was developed, applied to six soy samples from the Chinese market and the results compared to Inductively Coupled Plasma\u2013Mass Spectrometry data. As a result, the procedure was fully validated for the six elements that could be compared: Cu, Fe, Mn, Rb, Sr and Zn. A dilution only procedure was also assessed showing, on average, a 125% bias only. Accordingly, sample digestion yields highly accurate data, whereas a simple 1:5 dilution may be perfectly suited for most purposes. Regarding detection capabilities, the limits of detection are typically below 0.5 mg/kg for both digested + diluted and diluted only samples. The reported procedures are accordingly fit for purpose in quality assurance/quality control procedures and risk assessment related to soy sauce consumption

Phase Evolution in Synthesis of Manganese Ferrite Nanoparticles

Physico-chemical equilibria that influence oxide powders’ precipitation from an aqueous solution can be substantially altered when the process is carried out in a microemulsion system. To obtain nanosizedMnFe2O4 and gain information about the physico- chemical characteristics of products, Mn21 and Fe31 metal ions were induced to precipitate in a toluene/water/sodium dodecylbenzenesulfonate microemulsion system. Portions of the precipitated powder were differently treated, both in solution and in the solid state, and the role of restricted aqueous domains in the obtained materials was investigated. X-ray diffraction profile-fitting methods and chemical analysis were applied to characterize the powder particles. Samples obtained from the selected microemulsion were identified as nanosized mixed hydroxide compounds. A low metal content and a limited matter exchange among aqueous nanodroplets appear to inhibit hydroxide to oxide transformation inside the selected micellar system. A calcination process of precipitated powder was required to obtain a manganese ferrite compound