Asparagus has long been known for its distinctive odor in human urine. The chemical responsible for this odor, which can arise just 10 to 15 minutes after consumption, is asparagusic acid and appears to be unique to asparagus. After consumption, the acid is metabolized to sulfur-containing thioesters, ultimately resulting in the metabolites methanethiol, dimethyl sulfide, dimethyl disulfide, dimethyl sulfone, and dimethyl sulfoxide.
Traditional methods for isolating and detecting these metabolites, as well as many other aromatic compounds, have involved heated solvent extraction, which requires the use of hazardous solvents and takes up to 48 hours. In addition, the sample preparation procedure requires a number of manual steps, which can lead to unacceptable data variability. Finally, co-elutions, smaller phase quantity, and other process steps can reduce detection sensitivity.
Can an automated system eliminate the use of solvents, reduce manual processes and provide results faster? That’s what we were seeking to find out during a recent study conducted with LECO Corp. Using our Twister Stir Bar Sorption Extraction (SBSE), researchers ran urine samples before consumption and between 90 and 120 minutes after consumption of asparagus. Samples were simply placed in glass bottles (each of which each contained a Twister) and extracted on a stir plate, then placed in a thermal desorption unit for analysis by Time of Flight Mass Spectrometry (TOFMS). No other extraction process, including solvent use, is necessary. The analytical system consisted of a gas chromatograph, a dual-jet thermal modulator between the primary and secondary columns, and TOFMS as detector.
Results revealed asparagusic acid metabolites in post-asparagus consumption samples (and did not find metabolites in pre-consumption samples). The study showed that the automated MPS 2-TDU-CIS4 system, coupled with SBSE, resulted in:
TOFMS analysis allowed for more sensitive detection and better analyte peak resolution. In addition to finding targeted compounds like sulfur-containing metabolites of asparagusic acid, a very complete picture of analytes was developed, including dimethyl sulfone, dimethyl trisulfide, and S-methyl 2-propenethioate.
Learn more about this technique, including contour plots of pre-asparagus and post-asparagus urine, peak spectra for key analytes detected, and details on the gas chromatography, thermal modulators and TOFMS system used, in our article, “Metabolomics I: Asparagus on the menu.”
After reading the details of this experiment, we’re available for an in-depth conversation about saving labor, time, and solvent use in your metabolomics and aromatic compounds studies. Just reach out.