Carbon Material Can Pull Toxic Compounds Out Of Complex Samples

Toxic compounds, such as flame retardants and pesticides, can be difficult to detect in complex samples like blood, urine, or river water because they often occur at very low concentrations, mixed with many biological materials. Now, using two types of carbon—mesoporous carbon tubes and graphene sheets—researchers have developed a quick and inexpensive way to enrich the concentration of toxic small molecules in such samples for analysis. In blood, for example, the presence of proteins, cellular debris, or other large molecules often makes it difficult to isolate or identify the hazardous compounds an individual may have been exposed to—many of which have a low molecular weight. Current methods for screening blood for toxic chemicals have multiple steps that require expensive equipment and may require days to complete. To speed up the screening process, Qian Liu of the Chinese Academy of Sciences, in Beijing, and his colleagues tested four commercially available tubular mesoporous forms of carbon and silica for their ability to act as molecular sieves. The mesoporous materials are particles made of bundles of nanotubes, with aligned channels, 4 to 7 nm in diameter. The researchers used them to concentrate small molecules—known hazardous chemicals such as bisphenol S and cetyltrimethylammonium bromide—out of mixtures containing large molecules, either bovine serum albumin protein or humic acid. When the researchers mixed these particles into a liquid sample, the small molecules entered and adsorbed to the tube walls while the larger molecules were excluded. Liu and colleagues then recovered the mesoporous materials and extracted the compounds collected within. They deposited the compounds onto sheets of graphene for detection using matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) mass spectrometry. Out of the four mesoporous materials tested, a form of carbon with a pore size of about 6.5 nm was the most efficient at enriching small molecules. To validate the technique with real samples, Liu and his coauthors tested human serum, urine, and river water spiked with known concentrations of the contaminants. They also screened serum samples from 30 workers in a perfluorochemical plant in Wuhan, China, and from five healthy athletes in Beijing. The researchers detected high levels of perfluorochemicals in the workers’ blood, but not in the athletes’. The entire process to detect hazardous chemicals by this method required only three to four hours. The method concentrates the toxic substances, improving sensitivity, while also reducing interference from salts and other contaminants. “We can solve two problems at once,” says Liu. The method allows the team to detect contaminants at concentrations as low as a few parts per trillion, he adds. This new approach to separate molecules is promising and may have many practical applications, according to I. H. (Mel) Suffet of the University of California, Los Angeles. He says the chemical nature of mesoporous carbon may factor into its effectiveness as a molecular sieve, since silica with a similar pore size did not filter as well. “Why only this material filters effectively and not the others is not clear,” he says, an important question for future work. “There are not many other methods available that can screen for small molecules so simply,” says Sheng Dai of Oak Ridge National Laboratory. “This can potentially be used even in rural areas to test workers in mining or chemical industries, who are often the most vulnerable to hazardous environments.”

Chemical & Engineering News, 24 June 2015 ; ;