Testing the resistance of single- and multi-walled carbon nanotubes to chemothermal oxidation used to isolate soots from environmental samples.

Quantification of natural and engineered carbon nanotubes (CNT) in the environment is urgently needed to study their occurrence and fate and to enable a proper risk assessment. Currently, such methods are lacking. Here, we tested the resistance of 15 structurally different CNTs to chemothermal oxidation at 375 degrees C (CTO-375), a method used to isolate soots from environmental samples. Depending on their structure, CNTs survived CTO-375 in proportions ranging from 26 to 93%. Standard addition of CNTs to soil and sediment yielded recoveries between 66 and 171%, demonstrating the capability of CTO-375 to isolate CNTs from complex environmental matrices. These data of pure and added CNTs correspond to recoveries obtained with "ordinary" soots under similar experimental conditions. Hence, soot fractions commonly isolated with CTO-375 from environmental matrices most probably encompass CNTs. Future work should attempt to enhance the method's selectivity, i.e., its capability to separate CNTs from other forms of soot.