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 TiO ₂ 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 TiO ₂ NPs size distribution, therefore guaranteeing TiO ₂ NPs integrity. TiO ₂ NPs determination (TiO ₂ NPs concentration) and TiO ₂ 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 TiO ₂ NPs concentrations and TiO ₂ NPs sizes. Good repeatability (25% and 8% for TiO ₂ NPs concentration and TiO ₂ NPs most frequent size), and sensitivity (limit of detection of 5.28 × 10 ⁵ NPs g ^-1 for TiO ₂ NPs concentrations, and 31.3-37.1 nm for TiO ₂ NPs size) were obtained. Accuracy, calculated through analytical recovery was adequate. Recoveries for TiO ₂ 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 TiO ₂ NPs concentrations and size distribution. Some surimi samples were found to contain TiO ₂ NPs (concentrations from 1.40 × 10 ⁷ to 1.19 × 10 ⁹ NPs g ^-1 ). TiO ₂ 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).
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