sciencehabit writes "The Boston marathon bombers Tamerlan and Dzhokhar Tsarnaev reportedly purchased several pounds of black powder explosive before the bombing. Used in fireworks and bullets, the explosive substance is both deadly and widely available. It's also very hard to detect. Now, researchers have modified one bomb-sniffing device to accurately spot very small amounts of black powder, an advance that could make us safer from future attacks. What has prevented detection of black powder by IMS in the past, however, is that sulfur and oxygen -- which composes 20% of air—hit the detector at almost the same time. A strong oxygen signal can thus mask a small amount of sulfur, like what a bombmaker's dirty fingers might leave on a luggage strap. A group led by chemist Haiyang Li at the Dalian Institute of Chemical Physics in China modified an IMS to eliminate the oxygen signal. 'We have tested the sensitivity of TR-IMS, and its limit of detection of black powder can reach as low as 0.05 nanograms,' Li says."