Adding high-resolution mass spectrometry improves the world and even protects a whiskey’s brand
Writing this article in southwest Ohio, only a couple hours of driving from the renowned Kentucky Bourbon Trail, I can appreciate the value of improving whiskey with gas chromatography (GC) plus high-resolution accurate-mass (HRAM) mass spectrometry. Around Kentucky, bourbon is serious business. As Kentucky Congressman John Yarmuth once noted: “Kentucky has always said you can’t really make bourbon outside of Kentucky because it’s a combination of the barrels and the limestone-fed springs that give us the water. That’s our story, and we’re sticking to it.”
Some of today’s technology makes it possible to analyze bourbon and other whiskeys more completely than ever. The GC-Orbitrap MS can be used to “comprehensively characterize the chemical constituents and identify markers to allow differentiation of whiskeys, not only from different sources, but whiskeys matured in different types of barrels, and whiskeys manufactured at the same distillery, but in different years,” says Richard Fussell, global marketing manager for the food and beverage market in the chromatography and mass spectrometry business at Thermo Fisher Scientific (Waltham, Mass.). “These findings open up new possibilities for brand protection and in the fight against global food and beverage fraud.”
Chromatography with HRMS can also be used in other applications. “The combination of multidimensional chromatography with high-resolution mass spectrometry has allowed us to analyze truly complex mixtures,” such as crude oil and samples from environmental and metabolomics studies,” says Robert “Chip” Cody, product manager at JEOL (Peabody, Mass.). “Multidimensional chromatography has been developed for both gas and liquid chromatography, but we have focused our efforts on comprehensive two-dimensional chromatography (GC×GC) combined with high-resolution time-of-flight mass spectrometry (HRTOFMS).”
The depth of information obtained from GC/HRMS arises from multiple dimensions. “I think of mass defect—the exact mass obtained from high-resolution mass spectrometers—as a fifth dimension of information,” says Cody. This follows boiling point and polarity from GC, plus nominal mass and abundance. “In fact, there are additional dimensions of information in the GC×GC/HRTOFMS data,” notes Cody, “such as isotopic data, including exact isotopic masses and abundances.”
More power for petroleum
“GC×GC/HRTOFMS is a very good method for petroleum analysis,” Cody says. “This can be done with a reflectron TOF [mass spectrometer] because species—such as SH4/C3 doublets with exact masses that differ by only 0.0034— that would otherwise require ultrahigh mass resolving power have different retention times on GC×GC.” It can be used with various sources: electron ionization (EI), field ionization (FI) and photoionization (PI).
Cody and his colleagues analyzed diesel fuel and crude oil samples using GC×GC/HRTOFMS with field ionization. “This allows us to create a comprehensive analysis profile for a petroleum sample, because fragment ions that complicate the data analysis are eliminated in field ionization,” Cody says.
His team also used GC×GC/HRTOFMS with photoionization to identify biomarkers in crude oil samples. Cody explains, “Because photoionization causes much less fragmentation than EI, but more fragmentation than FI, we can identify families of biomarkers by looking for common fragment ions.”
Chromatography plus high-resolution accurate mass (HRAM) mass spectrometry can be used to analyze many samples, including crude oil. (Image courtesy of the U.S. Department of Energy.)
At the University of Vienna (Austria), biochemist Wolfram Weckwerth and his colleagues used a JEOL GC/MS platform with a combined EI/FI source to analyze biodiesel.1 According to Weckwerth, “This allows you to measure pseudo-molecular precursor ions of the fatty acids, which simplifies the identification process, especially of the number of double bonds.” As he and his colleagues wrote: “The proposed workflow provides a convenient strategy to analyze algae and other plant crop systems with respect to their capacity for third-generation biodiesel and high-quality bioproducts for nutrition such as [polyunsaturated fatty acids].”
This U.S. FDA chemist prepares to test produce for pesticides, which can be performed with GC-HRAM with electron ionization. (Image courtesy of U.S. Food and Drug Administration.)
Concerns about food contaminants in a wide range of complex sample matrices continue to drive the need for higher-resolution analyses. The analysis of contaminants also extends through a range of environmental sample matrices, such as soil and water.
GC/HRAM with EI can be used for “routine and simultaneous targeted and nontargeted quantitative analysis of pesticide residues in feed and food,” says Fussell. “The fact that the most abundant ions of almost 600 pesticides are in the range of 100–250 m/z puts them exactly within the range of the optimal resolving power of the Orbitrap MS.” He adds that “this technology could become the approach of choice for the routine analysis of residues and contaminants in the near future.”
Cody and his colleagues at JEOL “used exact-mass data with a computational trick—Kendrick mass defect analysis—to identify chlorinated and brominated environmental contaminants in a dust sample from an electronics recycling facility.”2 This work came from collaboration between JEOL USA, the Ministry of the Environment and Climate Change (Ontario, Canada), Zoex (Houston, Texas)—manufacturer of the GC×GC thermal modulator system—and GCImage (Lincoln, Neb.)—developer of GC×GC data analysis software.
Advances in the technology determine who can use it and what can be learned from the results. “High-resolution time-of-flight mass spectrometers have continued to evolve, becoming faster, more sensitive and more versatile,” Cody explains. “Our AccuTOF GCx mass spectrometer is JEOL’s fourth-generation high-resolution time-of-flight mass spectrometer for both GC/ MS and comprehensive two-dimensional gas chromatography, GC×GC, combined with mass spectrometry.”
In addition to improved sensitivity and resolving power, the AccuTOF GCx can use various sources: EI, FI and field desorption (FI/FD), PI and positive- and negative-ion chemical ionization. “The soft ionization methods—FI and PI—are particularly helpful for complex mixture analysis because they produce abundant molecular ions with little or no fragmentation,” Cody says. “This makes it easier to interpret the data from complex data sets, like GC×GC/ HRTOFMS.”
In July 2016, Thermo Fisher Scientific launched the Thermo Scientific Exactive GC Orbitrap GC-MS system, which, according to Fussell, is “designed to provide robust and sensitive performance for use in routine laboratories that demand repetitive high performance, day in day out.” He notes that it provides “simple, full-scan, generic electron ionization, an incredible resolving power of 60,000 at m/z 200, mass accuracy less than 1 ppm, wide dynamic linear range and parts-per-trillion-level sensitivity.” The key advance in GC/MS is deeper data. Scientists can quickly acquire large amounts of information about a wide range of samples, from crude oil to Kentucky whiskey. That’s today’s GC/MS story, but we’re sure that it will continue to evolve.
- Furuhashi, T.; Nakamura, T. et al. Biodiesel and poly-unsaturated fatty acids production from algae and crop plants—a rapid and comprehensive workflow for lipid analysis. Biotech. J. 2016; doi: 10.1002/ biot.201400197.
- Ubukata, M.; Jobst, K.L. et al. Non-targeted analysis of electronics waste by comprehensive two-dimensional gas chromatography combined with high-resolution mass spectrometry: using accurate mass information and mass defect analysis to explore the data. J. Chromatogr. A 2015; doi: 10.1016/j. chroma.2015.03.050.
Mike May is a freelance writer and editor living in Florida. He can be reached at [email protected].