The development and incorporation of engineered nanomaterials (ENMs) in consumer and industrial products will inevitably expose environmental and human receptors to some form of ENMs. Some beneficial ENM applications, such as drug delivery, place ENMs directly in biological tissues. Evaluating the fate and toxicity or the effectiveness of ENMs used in beneficial applications requires robust extraction and analytical procedures. Analysis of ENMs in environmental or biological media is generally conducted using single particle inductively coupled plasma mass spectrometry (spICP-MS). Sample digestion prior to spICP-MS analysis often utilizes tetramethylammonium hydroxide (TMAH) However, TMA is a known neurotoxin which limits its use in many laboratories. Further, the sample holding time of ENMs under alkaline conditions is untested. Here, tetrabutylammonium hydroxide (TBAH) and tetrapropylammonium hydroxide (TPAH) are evaluated as alternatives to TMAH. Both bases are structurally similar to TMAH but have no reported neurotoxic effects. Commercially available 100 nm Au and Ag ENMs were evenly mixed independently into a standard tissue (ground beef) at a nominal concentration of 10 mg/kg. Tissues samples were digested using TBAH (20%), TPAH (12%), or TMAH (20%) at a 20:1 solvent to tissue ratio. Au and Ag ENM were analyzed from digested tissue samples using spICP-MS and ICP-MS. The 24-hour recovery of ENMs from digested tissue samples ranged from 53.5% to 90.6% on a particle number basis and 83.4% to 114.5% on a particle mass basis relative to aqueous control experiments. Aggregates of Au and Ag ENMs greater than 100 nm were observed in size distributions measured using spICP-MS from all bases tested. Digestion time beyond 24 hours up to 60 days indicated a negative trend in particle mass and particle number recovery over time. Au and Ag ENM loss attributed to aggregate formation and dissolution. Overall, these results indicate that TBAH or TPAH can replicate and potentially replace 24-hour TMAH digestion. However, care must be taken to dilute and analyze ENMs from digestion reactors within 48 hours to prevent changing ENM distributions during tissue digestion.

Evaluation of alternatives to tetramethylammonium hydroxide (TMAH) digestion for nanomaterial analysis in biological tissues using spICP-MS

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ACS Fall 2022

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