Background
Salicylic acid (SA) is present in the serum of people who have not taken
salicylate drugs. Now we have examined the urine of these subjects and found that it
contains SA and salicyluric acid (SU). We have established the identities of these
phenolic acids and determined their concentrations.
Methods and Results
The acidic hydrophobic compounds of urine were separated using
high-performance liquid chromatography (HPLC) and were detected and quantified
electrochemically. Two approaches were used to establish the identity of SA and SU.
First, the retention times (Rt) of the substances extracted and those of
SA and SU were compared under two sets of chromatographic conditions; the
Rt of the compounds suspected to be SA and SU and those of the
authentic substances were very similar under both sets of conditions. Second, the
unknown substances, isolated by HPLC, were treated with acetyl chloride in methanol
and compared with the methyl esters of SA and SU by using gas chromatography-mass
spectrometry; the unknown compounds after esterification had very similar mass
spectra and gas chromatographic Rt to those of methyl salicylate and
methyl salicylurate. The median (n = 10) urinary concentration of SA
was 0·56 μmol/L (range 0·07-0·89 μmol/L) and that of SU was 3·20 μmol/L (range
1·32-6·54 μmol/L). SA and its major urinary metabolite, SU, were found in the urine
of all of the 10 people examined.
