Aqueous ferric chloride was added to a urine sample, and the formation of the iron complex turned the solution purple.
[2] This test was not specific to acetylsalicylic acid but would occur in the presence of any phenol or enol.
[citation needed] The current in vitro testing utilizes molecule specific methods of detecting salicylates.
Polarization allows the machine to detect the difference between antibody bound, and unbound fluorescein.
It is therefore possible to quantify the serum salicylate level through the signal strength—the amount of reflected light received.