Enzymatic hydrolysis as a sample pre-treatment for titanium dioxide nanoparticles assessment in surimi (crab sticks) by single particle ICP-MS.

A reliable sample pre-treatment based on enzymatic hydrolysis has been fully optimized and validated for TiO2 NPs isolation and determination/characterization in surimi (crab sticks). Efficient extractions have been found when using a pancreatin/lipase mixture at pH 7.4 and 37 °C for 12 h under continuous stirring. The proposed sample pre-treatment procedure has been found not to change TiO2 NPs size distribution, therefore guaranteeing TiO2 NPs integrity. TiO2 NPs determination (TiO2 NPs concentration) and TiO2 NPs characterization (size distribution) were assessed by single-particle inductively coupled plasma mass spectrometry (sp-ICP-MS) working with dwell times in the microsecond range (high frequency of data acquisition). Method validation was performed for TiO2 NPs concentrations and TiO2 NPs sizes. Good repeatability (25% and 8% for TiO2 NPs concentration and TiO2 NPs most frequent size), and sensitivity (limit of detection of 5.28 × 105 NPs g-1for TiO2 NPs concentrations, and 31.3-37.1 nm for TiO2 NPs size) were obtained. Accuracy, calculated through analytical recovery was adequate. Recoveries for TiO2 NPs standards of 50 and 100 nm were 108 ± 5 and 105 ± 4%, respectively. The proposed methodology was applied to several surimi samples for assessing TiO2 NPs concentrations and size distribution. Some surimi samples were found to contain TiO2 NPs (concentrations from 1.40 × 107 to 1.19 × 109 NPs g-1). TiO2 NPs size distributions were very different among the samples, and some of them showed wide size ranges (the most frequent size varied from 53.8 to 62.1 nm; whereas, the mean size values were within the 73.4-217.5 nm range).