Monitoring metal catalyst content of carbon nanotubes during purification using X-ray fluorescence*

There have been many studies that suggest that catalyst metals in carbon nanotubes (CNTs) may pose a health threat. As there are several potential applications of CNTs in medicine, it is important to be able to quantitatively determine the amount of catalyst contained in a CNT sample. The relative catalyst content of carbon nanotube samples synthesized via arc-discharge has been determined at various stages of the purification process using X-ray fluorescence (XRF) analysis. Purification was achieved by immersing samples in heated nitric acid. The intensities of the nickel K$\alpha $ X-rays were studied to determine the relative catalyst content in the samples. Scanning electron microscopy (SEM) images of purified nanotubes have been compared to the images of a sample that has been irradiated by 0--15keV bremsstrahlung in order to determine if the XRF analysis of the nanotubes is in any way destructive. No obvious structural defects were observed as the result of irradiation.