Physicians who treated the victims of the Tokyo attack ran extensive tests to look for signs of sarin in blood, urine and other medical samples. The tests, as well as others developed by the military, have become standards for chemical weapons inspectors looking for evidence that sarin has been used.
Sarin itself reacts easily with water and so it breaks down when it meets rain, moisture in the air or sweat. The agent’s fragility in water led hospital staff in Syria to uses hoses to drench rooms where they received victims after chemical attacks. For the same reason, sarin does not hang around for long in the environment, or in people.
Laboratories can test for the substance, but more often will find breakdown products. The first substance sarin degrades into is isopropyl methylphosphonic acid (IMPA), which is generally regarded as proof positive for sarin. However, IMPA itself breaks down, into methylphosphonic acid (MPA). Finding MPA in blood or urine is not a smoking gun for sarin: it can come from other organophosphates. Knowing which one matters.
The UN inspectors found concrete evidence that sarin was used with lethal effect in Ghouta on the outskirts of Damascus on Aug. 21. The team plans to go back soon, to visit Khan al-Assal, Sheik Maqsood and Saraqueb, before submitting a final report. That will end another grim chapter in the story of sarin and open a new one focused on destroying the weapon.