Surfactant-assisted dispersive liquid-liquid microextraction and centrifugal ultrafiltration as potential extraction procedures for silver and titanium dioxide nanoparticles from human urine

Inorganic nanoparticles (NPs) hold great promise in nanomedicine, cosmetics, the food industry and other human-related sectors, raising concerns about their safety and effects on biological systems. Urine shows great potential as a biological compartment for biomonitoring, but the presence of NPs in urine (basal levels) is expected to be very low and requires advanced instrumentation as well as sample pretreatment. This study reports on the use of single particle inductively coupled plasma mass spectrometry (spICP-MS) as a tool for the assessment of silver nanoparticles (AgNPs) and titanium dioxide nanoparticles (TiO2NPs) in urine, previously extracted/preconcentrated by two different approaches: surfactant-assisted dispersive liquid-liquid micro- extraction (SADLLME) and centrifugal ultrafiltration (UF). Optimal experimental conditions for SADLLME were: 10 mL urine, 1.0 mL surfactant/extractant mixture, vortexing at 2000 rpm for 30 s and a final centrifugation step at 3500 rpm for 10 min. Centrifugal ultrafiltration (molecular weight cut-off (MWCO) of 30 kDa, 5000xg, 25 min, 1 rinsing cycle with 1.0 % (v/v) glycerol) showed improved results for NP preconcentration using up to 30 mL of urine. An improved limit of detection (number concentration) was achieved with UF (3.1 x 102 and 2.9 x 102 particle mL-1 for TiO2NPs and AgNPs, respectively), while the analytical recovery of both methods was similar for TiO2NPs (in the range of 77-97 % for SADLLME and between 74 and 99 % for UF) and from 81 to 88 %, and from 90 to 115 % for AgNPs when using SADLLME and UF, respectively.