Chemical Weapons Convention.
The United States signed the Convention on January 13, 1993, seven days before the end of President George H. W. Bush's term.
It came into force the first year of President Clinton's second term. The UK and USA memberships in the Organization for the Prohibition of Chemical Weapons came into effect the same day, April 29, 1997. They are listed by number on the OPCW website; these numbers do not reflect the order of signature.
The Organization for the Prohibition of Chemical Weapons is NOT a United Nations Agency, but operates as an independent organization in the Hague, the Netherlands. It has 189 member countries, at last count on the OPCW website. Syria is NOT one of the members.