Toxicity and fate assessments are key elements in the evaluation of the environmental, health and safety risks of engineered nanomaterials (ENMs). While significant efforts and resources have been devoted to the toxicological evaluation of many ENMs, and in particular nanoscale TiO2 [1-4], obtaining conclusive and reproducible results remains a challenge . This can be traced in part to the lack of standardized dispersion protocols and the inconsistent application of dispersion procedures in relevant biological and environmental matrices [6, 7].
This protocol was developed and validated using National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 1898, which consists of an industrially relevant and widely studied commercial TiO2 nanomaterial with a production history dating back several decades [3, 8-10]. The protocol provides a validated method for the preparation of aTiO2 nanoparticle dispersion in high purity de-ionized water, as a stock preparation compatible with biological and environmental matrices. Furthermore, this protocol can be used in combination with matrix-specific protocols for the preparation of dispersions in more complex biological or environmental media. Matrix-specific protocols are currently under preparation and will be issued in the near future.
While the procedures detailed in this document focus on the dispersion of SRM 1898 in high purity water, it is believed that the adopted characterization, validation and optimization approaches can be more generally applied to the preparation of aqueous dispersions for a wide range of ENMs that are available in the dry powder form. For this reason, and to allow for a broader applicability of this work, experimental details and discussions regarding the characterization, validation and process optimization adopted for the development of the dispersion method are offered as appendices to this protocol.
 SRM 1898 was in production as of the publication of this protocol, with a target date for release in 2011. The NIST SRM inventory can be accessed at http://www.nist.gov/srm/.