The recent attacks, near Damascus, appear to have involved Sarin.
Sarin has extreme potency as a nerve agent and production and stockpiling of sarin was outlawed by the Chemical Weapons Convention of 1993 where it is classified as a Schedule 1 substance.
As at 21st May 2009, Syria had not signed or acceded to the Chemical Weapons Convention - see OPCW - though Syria was a party to the 1925 Geneva Gas Protocol. There is some authority that the use of chemical weaponry is unlawful under customary international law.
Law and Lawyers 31st August - House of Commons debate on Syria 29th August
Organisation for the Prohibition of Chemical Weapons
OPCW 31st August - UN Investigation Team return to The Hague from Syria
UN Office for Disarmament Affairs - Chemical Weapons
UN Office for Disarmament Affairs
Statement of Foreign Secretary (William Hague) 23rd August 2013.
Sales of chemicals to Syria:
The Guardian 2nd September - Chemical export licences for Syria - just another UK deal with a dictator
Update --- Syria and the Chemical Weapons Convention:
Syria is to accede to the Chemical Weapons Convention - HERE.
Update --- Syria acceded to the Chemical Weapons Convention on 14th September 2013
The Director-General of the Organisation for the Prohibition of Chemical Weapons (OPCW), Ambassador Ahmet Üzümcü, has welcomed the agreement on chemical weapons in Syria that was announced today following talks held in Geneva...14 September 2013
The Director-General of the OPCW Ambassador Ahmet Üzümcü received a letter on 12 September sent by the Syrian Foreign Minister, Mr Walid al-Muallem, informing him of the decision by the Syrian Government to join the Chemical...13 September 2013