The ex-Russian spy and his daughter were hit with an attack that used 50-100 grams of Novichok, the head of the OPCW has said.
Vladimir Uglev identified the poison that hospitalized former double agent Sergei Skripal as Novichok.
Chapman was part of a spy swap deal with the U.S. which saw Sergei Skripal handed over.
The man who may have invented the poison that took down Sergey Skripal has said he supports the British government's stance on Russia.
Sergei Skripal is “improving rapidly,” while his daughter can now look forward to leaving hospital.
Meanwhile, Russia's foreign minister accused the U.K. of arm-twisting other countries to "demonize Russia."
Russia's top diplomat argued that U.S. military presence in Syria was illegal and rebutted accusations over the poisoning of an ex-Soviet spy.
State Department spokeswoman Heather Nauert said Russia was like a beast with "long arms" and "lots of tentacles."
The tests come as Russian President Vladimir Putin revealed new nuclear missiles and Moscow's relationship with the West took another major blow.
At least 20 countries expelled 139 suspected Russian spies in solidarity with the United Kingdom.
At least 20 countries have kicked out more than 130 Russian diplomats, believed to be covert intelligence officers.
The U.S., Germany, France, other EU countries and Ukraine have all announced they are expelling Russian diplomats.
Four countries bordering Russia reportedly called in Moscow's top diplomats on their territory as the EU decided its response to spy poisoning scandal.
Sergei Skripal and his daughter are being kept heavily sedated and are still unable to communicate two weeks after they were poisoned.
The foreign ministers of both countries took aim at each other.
Russian Foreign Minister Sergey Lavrov says Moscow will "soon" expel British diplomats in a tit-for-tat response.
The Kremlin may have ordered a hit on an ex-Russian spy in the U.K. But some point to a scarier prospect—that Moscow’s death squads did it on their own.
Investigators did not identify which nerve agent was used on the pair, but the best-known nerve agents are sarin and VX.