GERSTEL Solutions No 10 Asparagus on the Menu

Metabolomics I

Asparagus on the menu

Efficient detection of Sulfur-Containing Metabolites of Asparagus in Urine by SBSE-GCxGC-TOFMS.

onsumption of asparagus has been known to matograph equipped with a LECO dual-jet ther- Ccause a distinct odor in the urine of humans. mal modulator between the primary and secon- This odor can be present in urine in as little as 10 dary columns and a LECO Pegasus IV Time- to 15 minutes after consumption. The compound of-Flight Mass Spectrometer (TOFMS) as a that is unique to asparagus and is responsible for detector. The primary analytical column was a the odor is asparagusic acid. Subjects who consu- GERSTEL-MACH LTM10.0m x 0.18mmID med asparagusic acid, without consuming aspa- x 0.20 μm df Rtx-5. The secondary column was ragus, produced the characteristic odor associ- a 1.00 m x 0.10 mm ID x 0.10 μm df DB-17ms ated with asparagus consumption. The aspara- and was housed in the GC oven. The modula- gusic acid is metabolized to S-methyl thioesters tor temperature offset for this study was +30 °C. and ultimately to methanethiol, dimethyl sulfide, Helium was used as the carrier gas at a constant dimethyl disulfide, dimethyl sulfone, and dime- flow of 1.5 mL/minute. The transfer line to the thyl sulfoxide. Traditionally, samples are prepa- TOFMS consisted of the last 20 cm of the ana- red using heated solvent extraction over periods lytical column and was kept at 280 °C. For the as long as 48 hours. Our goal was to eliminate one-dimensional study, the modulator was tur- the use of potentially hazardous solvents and ned off and the GC oven was maintained iso- reduce overall extraction time through the use thermally at 280 °C. of GERSTEL‘s Twister Stir Bar Sorption Ext- Urine samples of approximately 250 mL were raction (SBSE). collected prior to consumption of asparagus and approximately 90 to 120 minutes after consump- Instruments and Methods tion of asparagus. The samples were immediately placed in 250 mL amber glass bottles, each con- In this study, measurements were made with a taining a 10 mm x 0.5 mm GERSTEL Twister LECO Pegasus 4D GCxGC-TOFMS system. and extracted on a stir plate at 800 rpm. Upon This system consists of an Agilent 6890 gas chro- completion of the extraction, the stir bar was

Figure 1: Overlay of pre- (blue) and post-asparagus (red) traces in 1D.

Figure 3: Peak True and Library Spec- tra for S-methyl 2-propenethioate.

10 GERSTEL Solutions Worldwide – March 2010 Figure 2: Contour plots of pre-asparagus urine (A) and post-asparagus urine (B). Relevant compounds not present in the pre- asparagus sample are highlighted in the post- asparagus sample.

removed, rinsed with DI water, and placed in a present in the pre-asparagus sample, but present GERSTEL Thermal Desorption Unit (TDU) in the post-asparagus sample include S-methyl tube for analysis. propene thioate and 1,4- bis(methylthio)-butane. The tube containing the stir bar was loaded In the GCxGC-TOFMS analysis of pre-aspa- into the TDU. The TDU was then heated, and ragus and post-asparagus samples, contour plots the analytes were desorbed from the stir bar. The are shown in Figure 2. The target compounds analytes were then cryo-trapped in the GERS- in this analysis are sulfur-containing metaboli- TEL Cooled Injection System (CIS). The CIS tes of asparagusic acid. S-methyl thioesters are 4 was then heated to desorb the analytes onto listed as being one of the primary metabolites. the GC column. S-methyl 2-propenethioate had retention times The TDU was operated in splitless mode. Its of 205 seconds in the first dimension and 1.7 initial temperature was 30 °C and was held at seconds in the second dimension. Its peak true this temperature for an equilibration time of 120 and library spectra are shown in Figure 3. seconds. It was then heated to 280 °C at a rate of 700 °C /minute and held at this temperature for Conclusions 120 seconds. The CIS 4 was cooled to a tempe- rature of -120 °C. It was heated to 280 °C at a This study has shown an improvement in not rate of 12 °C /second and held for 120 seconds. only overall analysis time, but in decreased complexity of sample preparation, as well as eli- Results mination of extraction solvents. The automated nature of the GERSTEL MPS 2–TDU–CIS4 In this study, the urine samples were not deri- system decreases the amount of manual work vatized. Analytes of interest in the post-aspa- necessary for each analysis by allowing for au- ragus samples are sulfurcontaining compounds tomation of the process. The use of GCxGC- not present in the pre-asparagus urine samples. TOFMS also allows for better resolution In Figure 1, the 1D traces of pre-asparagus and of analyte peaks and decreased coelu- post-asparagus samples are overlaid to highlight tions. Any remaining coelutions can be their differences. resolved through True Signal Some of the most prominent peaks, visible in Deconvolution, made possible by red, include A) acetone, B) acetic anhydride, C) the high-speed, fullrange spect- 4-heptanone, D) 5-methyl- 2-(1-methylethyl)- ra available from the LECO cyclohexanone and E) 1-(1,5-dimethyl-4- Pegasus TOFMS. hexenyl)-4-methyl benzene. Trace peaks not

For more information

Pete Stevens, LECO Corporation, Saint Joseph, Michigan USA, Phone: 800-292-6141, Fax: 269-982- 8977, [email protected], www.leco.com

GERSTEL Solutions Worldwide – March 2010 11