Development and Optimization of a Procedure for the Determination of Indium-Tin Oxide Particle Size and Concentration in Cellular Media

Abstract

Indium-tin oxide (ITO) is a solid mixture often comprised of approximately 90% indium oxide and 10% tin oxide by weight. ITO is employed as a transparent conductive coating for flat panel, liquid crystal, and plasma displays and is typically deposited after sintering as a thin film on a substrate through a variety of processes. Unfortunately, there have been published reports of workers who have been adversely impacted through exposure to this compound. When these reports are coupled with the industrial utility of ITO, future toxicological investigations are likely. Comprehensive characterization of ITO test materials would be an essential component of these studies. Ideally, characterization would include assessment of ITO particle size as administered during dosing because this physicochemical parameter can significantly impact solubility. The objective of this task was to develop, optimize, and apply a dynamic light scattering (DLS) sample preparation and measurement protocol for determination of particle size for a suite of sintered/non-sintered ITO samples prepared in cellular growth media at nominal 0.3 mg/mL doses. Sonication time was evaluated from 15 to 90 minutes over a 24-hour, continuous DLS measurement period. Resulting suspensions from samples subjected to 30 minute sonication times were stable with respect to hydrodynamic particle size between 10 and 24 hours after sonication. Throughout the 24-hour DLS measurement period, suspension aliquots were analyzed by inductively coupled plasma mass spectrometry to determine indium concentration. The developed protocol enabled investigators to use ITO suspensions of known hydrodynamic particle size and concentration in their in vitro cellular study.

Keywords:

• Dynamic light scattering
• Indium-tin oxide
• Inductively coupled plasma mass spectrometry
• Physicochemical characterization

Notes

^a Primary particle size is provided, if known, by the product manufacturer; secondary size is provided in parenthesis as measured by the milling vendor using laser scattering.

^b Not applicable; information not provided by product vendor.

^a Time sample subjected to sonication procedure.

^b Time after sonication that aliquot was removed for ICP-MS indium determination.

^c Percentage of nominal indium concentration from initial preparation.

^a Mean particle size as determined immediately after sonication (n = 3).

^b Mean particle size as determined 18 hours after sonication (n = 3).

^c Sample was polydisperse, making DLS measurement difficult.

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