Evaluation of alternative bases to TMAH for tissue extraction of ENMs from tissues prior to spICP-MS analysis

Abstract

Engineered nanomaterials (ENMs) are used in various consumer and industrial products, including human and biological systems for diagnostic and therapeutic purposes. Evaluating the size or number of ENMs contained within a biological tissue to evaluate material performance or toxicity requires an extraction procedure which breaks down tissue while leaving the target ENMs intact. Existing alkaline digestion procedures use tetramethylammonium hydroxide (TMAH) to liberate ENMs from tissues prior to spICP-MS analysis. TMAH is not an ideal extractant as it poses risks to analysts. Therefore, this work evaluates the alternative extractants tetrapropylammonium hydroxide (TPAH) and tetrabutylammonium hydroxide (TBAH) relative to existing TMAH (20%) for 100 nm Au and Ag ENMs from ground beef tissue. Of these alternatives, TPAH (20%) was preferrable to TBAH (12%) extraction based on ENM recovery for Au and Ag ENMs. Mass recoveries of Au ENMs were 99.3 ± 6.2%, 107.6% ± 4.92%, and 90.3 ± 5.43%, while Ag ENM recoveries were 100.5 ± 9.34%, 74.7 ± 4.90%, and 72.2 ± 5.48% after 24-hours for TMAH, TPAH, and TBAH. Extended monitoring of ENM recovery for all QAHs showed that Au ENMs could be held for 48 hours in concentrated TMAH and TPAH while Ag ENMs could be held for 24 or 72 hours in TMAH or TPAH. Acceptable extraction time was defined as the timepoint where particle mass and number recovery were both greater than or equal to 100 ± 25%. TPAH digestion was shown to minimize transformations to the target ENMs during extraction relative to TMAH. Overall, this work indicates that TPAH extraction is preferrable to TMAH by exhibiting similar ENM extraction efficacy, reducing risks to analysts, and minimizing transformations to ENMs during digestion. Further, sample extraction time information is a step towards establishing standard alkaline ENM tissue extraction protocols.