Ultrasound assisted enzymatic hydrolysis for isolating titanium dioxide nanoparticles from bivalve mollusk before sp-ICP-MS

Abstract

Applicability of single-particle inductively coupled plasma mass spectrometry (sp-ICP-MS) using dwell times equal to or shorter than 100 μs has been tested for assessing titanium dioxide nanoparticles (TiO₂ NPs) in bivalve mollusks. TiO₂ NPs isolation from fresh mollusk tissues was achieved by ultrasound assisted enzymatic hydrolysis procedure using a pancreatin/lipase mixture. Optimum extraction conditions imply ultrasonication (60% amplitude) for 10 min, and 7.5 mL of a solution containing 3.0 g L^-1of pancreatin and lipase (pH 7.4). The developed method was found to be repeatable (repeatability of 17% for the over-all procedure, TiO₂ NPs concentration of 5.33 × 10⁷ ± 8.89 × 10⁶, n = 11), showing a limit of detection of 5.28 × 10⁶ NPs g^-1, and a limit of detection in size of 24.4-30.4 nm, based on the 3σ criteria, and on the 3σ/5 σ criteria, respectively. The analytical recovery within the 90-99% range (use of TiO₂ NPs standards of 50 nm at 7 and 14 μg L^-1 as Ti). Several bivalve mollusks (clams, cockles, mussels, razor clams, oysters and variegated scallops) were analyzed for total titanium (ICP-MS after microwave assisted acid digestion), and for TiO₂ NPs by the proposed method. TiO₂ NPs concentrations were within the 2.36 × 10⁷-1.25 × 10⁸ NPs g^-1 range, and the most frequent sizes were from 50 to 70 nm.

Keywords: Bivalve mollusk; Enzymatic hydrolysis; Titanium dioxide nanoparticles; Ultrasonic probe; sp-ICP-MS.