Determination of sorbic acid in urine by gas chromatography–mass spectrometry

• Published in: Journal of Chromatography A 1999-06, Vol.847 (1), p.127-133
• Main Authors: Renner, Thomas, Baer-Koetzle, Michaela, Scherer, Gerhard
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Aged; Analysis; Biological and medical sciences; Biomarkers - urine; Chemical and industrial products toxicology. Toxic occupational diseases; Gas Chromatography-Mass Spectrometry - methods; General pharmacology; Humans; Investigative techniques, diagnostic techniques (general aspects); Medical sciences; Middle Aged; Miscellaneous. Technology; Muconic acid; Pathology. Cytology. Biochemistry. Spectrometry. Miscellaneous investigative techniques; Pharmacology. Drug treatments; Sorbic acid; Sorbic Acid - analysis; Toxicology; Various organic compounds
• ISSN: 0021-9673
• DOI: 10.1016/S0021-9673(98)01035-8

The average daily uptake of the common food preservative sorbic acid is estimated to range from 0.01 to 1.1 mg kg −1. Sorbic acid mainly is metabolised to carbon dioxide. Minor amounts are converted to trans, trans-muconic acid (ttMA) as well as excreted unchanged into the urine. Since urinary ttMA is a biomarker for the occupational and environmental exposure to benzene, there is an additional need for monitoring the uptake of sorbic acid, particularly at low, environmental benzene exposure levels. For this purpose, a simple, robust and rapid method for the determination of sorbic acid in urine at trace levels was developed. After addition of 10 ml of water and 5 ml of 8 M hydrochloric acid to 10 ml of the thawed urine, the sample was water steam distilled using an automated distillation device. A total of 100 ml of the distillate were solid-phase extracted. After washing, the sorbic acid was eluted with 4 ml methanol. The eluate was reduced under a stream of nitrogen to a volume of 300 μl. After addition of 500 μl boron trifluoride in methanol and incubation for 1 h at 60°C, the resulting sorbic acid methyl ester was extracted three times with 1 ml heptane. To the combined heptane layers, sorbic acid ethyl ester was added as an internal standard. After reducing to a volume of 100 μl in a stream of nitrogen, the final analysis was performed by GC–MS using the fragment ions m/ z 126 for the analyte and m/ z 140 for the internal standard. The limit of detection was 0.7 ng ml −1 urine and the R.S.D. of 69 duplicate determinations was 7.5%. In a controlled, experimental study and in a field study, we were able to show that urinary sorbic acid is a marker for the dietary uptake of sorbic acid and that sorbic acid is converted to ttMA. On average, 0.1% of the dietary sorbic acid is excreted unchanged into the urine. Excretion is complete within 24 h. We found that, on average, 0.23% of the oral dose of sorbic acid is excreted as urinary ttMA. There was a significant correlation between urinary excretions of sorbic acid and ttMA ( r=0.74, n=69). We conclude that urinary sorbic acid can be used to correct the urinary ttMA level in order to determine the portion related to benzene exposure. This appears to be necessary particularly at low, environmental benzene levels.