Analytical methods for SiO₂ and other inorganic oxides in titanium dioxide or certain silicates for food additive specifications

Abstract

An analytical method has been developed for the detection of SiO₂ and other oxides in titanium dioxide and certain silicates used in food additives using inductively coupled plasma (ICP) atomic emission spectrometry without hydrofluoric acid. SiO₂ and other oxides in titanium dioxide or certain silicates were resolved by alkali fusion with KOH and boric acid and then dissolved in dilute hydrochloric acid as a test solution for ICP. The recovery of SiO₂ and Al₂O₃ added at 0.1 and 1.0%, respectively, in TiO₂ was 88–104%; coefficient of variation was <4%. The limit of determination of SiO₂ and Al₂O₃ was about 0.08%, and the accuracy of the ICP method was better than that of the Joint FAO/WHO Expert Committee on Food Additives (JECFA) test method. The recovery of SiO₂ and other oxides in silicates was 95–107% with a coefficient of variation of <4%. Using energy dispersive X-ray fluorescence spectrometry (EDX) with fundamental parameter determination, the content of SiO₂ and other oxide in titanium dioxide and silicate showed good agreement with the ICP results. ICP with alkali fusion proved suitable as a test method for SiO₂, Al₂O₃ and other oxides in titanium dioxide and certain silicates, and EDX proves useful for screening such impurities in titanium dioxide and componential analysis of certain silicates.

Keywords:

• metals analysis, ICP
• method validation
• screening assays
• colours
• metals
• aluminium