"There's also no trace of any such substance on the clothes or bodies of the injured victims," she told a press conference.
Pornthip, head of the Central Institute of Forensic Science, conducted the inspection to assist the National Human Rights Commission. It focused on whether tear gas could blow off people's limbs, and if not, why so many protesters lost legs, arms and fingers during Tuesday's bloody clashes.
The deaths and serious injuries raised questions about whether police used lethal force - and not only tear gas - to disperse PAD demonstrators.
While Pornthip was inspecting the scene of Tuesday's events in front of the Metropolitan Police Bureau, many injured victims showed up to tell her what happened to them on that day. They also allowed Pornthip's team to examine their wounds.
National artist Naowarat Pongpaiboon also called on Pornthip to give justice to fellow artist Chingchai Udomkij, who lost a hand in the violence.
"It's impossible for such an artist to carry bombs," Naowarat said in response to police suggestions that some victims had inadvertently harmed themselves from carrying bombs.
Pornthip said the cause of Chingchai's injuries had yet to be determined.
"Our team has used a GT200 substance detector and found no substance used in making bombs. We've already checked the clash scenes and the bodies and clothing of the injured victims," she said.
However, she said the detector had collected chemicals from the scenes and victims that could be used for comparisons later.
Pornthip said the Royal Thai Police would next week show how the different types of tear gas worked.
"Then we can collect the chemicals from their demonstration and compare them with what we found at the clash scenes," she added.
Meanwhile, Pol Lance Corporal Nattawoot Jantorn - the policeman caught aiming his gun at an unidentified target on Tuesday in a video clip - yesterday came out to tell his side of the story.
"I just wanted to puncture a tyre in the pickup that ran over another policeman," Nattawoot said.
Photos and the video of his actions have been posted on the Internet, attracting widespread condemnation against the police.
Police earlier maintained no policemen had carried arms to control the PAD crowds.
"No, there was no PAD demonstrator at the scene when I drew my gun, only the pickup and a policemen," Nattawoot told a press conference.
He also explained he was not a riot policeman and was thus allowed to carry a gun.
"I was driving a bus carrying special equipment, and I had a gun to protect the equipment," Nattawoot said.
He said he ended up not firing his weapon.
"An examination of my gun will prove what I say," the 22yearold said.
Nattawoot said he had already submitted a report on what he was doing in the video to his supervisor.