A silica–titania sensor material prepared by cetylpyridinium chloride assisted sol–gel synthesis for solid phase spectrophotometric and visual test determination of propyl gallate in food samples
A silica–titania xerogel obtained by cetylpyridinium chloride (CPC) assisted synthesis has been used as a new sensor material for solid phase spectrophotometric and visual test determination of propyl gallate. The increase in CPC concentration (from 0 to 2.4 × 10−4 mol L−1) in sol during the sol–gel process has led to the increase of the BET surface area (from 453 to 703 m2 g−1) and average pore diameter (from 18.5 to 25.6 Å) of the dry xerogels. The interaction of these xerogels with propyl gallate has been investigated and the reaction conditions have been chosen. The fastest reaction of xerogel incorporated titanium(IV) with propyl gallate and the greatest equilibrium constant of this complex forming reaction have been observed for the xerogel with the maximal BET surface and pore diameter. This xerogel has been selected for solid phase spectrophotometric determination of propyl gallate (analytical range 2.0 × 10−7 mol L−1 to 4.0 × 10−6 mol L−1, LOD 7.1 × 10−8 mol L−1) and visual test determination in the range of 5.0 × 10−5 mol L−1 to 1.0 × 10−3 mol L−1. The parameters of test determination are: positive predictive value 89.5%, negative predictive value 95.0%, and reliability 92.3%. Both spectrophotometric and visual test procedures have been successfully applied to the analysis of refined vegetable oils and cookies.