Digestion Coupled with Programmed Thermal Analysis for Quantification of Multiwall Carbon Nanotubes in Plant Tissues

Abstract

The rapidly growing application of carbon nanotubes (CNTs) for industry and consumer products will inevitably lead to their accumulation in the environment. Protection of food safety from contamination by CNTs and best-practice management of agricultural application of CNTs require quantification of CNTs in agricultural plants. Herein, a novel method of digestion coupled with programmed thermal analysis (PTA) was developed for quantitative analysis of multiwall CNTs (MWCNTs) in plant (lettuce) tissues. MWCNT-bound carbon was linearly correlated with elemental carbon (EC) detected by PTA, including EC1 (58.5%) (evolved at 580 °C) and EC2 (41.5%) (evolved at 740 °C), corresponding to less stable and stable carbon, respectively. The background plant materials could interfere with EC quantification of CNTs, as a substantial fraction of the plant biomass was charred during the thermal analysis. Sequential digestion with concentrated nitric acid (HNO3) and sulfuric acid (H2SO4) effectively minimized the interference caused by the lettuce tissues, reducing the background EC generated from leaf tissues to 10.73 ± 10.26 μg of C/g. Via the coupling of digestion with PTA, a detection limit of 64.9 μg of CNT-C/g of plant tissues was achieved. This method can be applied for unambiguous quantification of CNTs in plant tissues at low concentrations and provide critical information for evaluating the risk of exposure to CNTs through crops and optimizing applications of CNTs in agriculture.