GC-High-Resolution Time-of-Flight MS: AccuTOF-GCX Plus GC-MS
The high-resolution TOF mass spectrometer provided the greatest amount of information. High-resolution accurate mass data were acquired for electron ionisation (EI) and soft ionisation (PI and FI) measurements. Chromatographic deconvolution using the accurate mass information finds even low-level components that are not chromatographically resolved. The EI data provide fragmentation that can be searched against the mass spectral databases, and the soft ionisation data provide information to determine the elemental composition of the intact molecule.
Despite a relatively fast GC oven program, over 300 compounds in each sample were detected by the JEOL msFineAnalysis software chromatographic deconvolution function. Electron ionisation (EI) mass spectra were searched against the NIST 2020 Mass Spectral Database. The exact masses and isotope data for the molecular ions in the photoionisation (PI) mass spectra and field ionisation (FI) mass spectra provided elemental composition information to complement the database search results. Including the elemental composition for fragment ions in the EI mass spectra provided a comprehensive report with detailed information about each compound.
Ethyl hexanoate (aroma described as ‘sweet fruity pineapple waxy green banana’ [6]). elutes at 9.14 minutes. The EI mass spectrum for ethyl hexanoate does not show a molecular ion, but a molecular ion is present in the FI mass spectrum that is used to confirm the molecular weight and elemental composition.
The detailed view for ethyl hexanoate identification (Figure 7) summarises the database search results from the EI mass spectrum, elemental composition determination from exact mass and isotope data in the FI mass spectrum, and fragment ion coverage from accurate mass information in the EI mass spectrum. Similar results were obtained by using the combination EI/PI ion source.
Figure 8 Chromatographic deconvolution and comprehensive identification of trace components in the Ensamble mezcal. The anethole peak (0.14% relative height) is selected and highlighted in blue.
Conclusion
The AccuTOF-DART permitted extremely rapid analysis with 8- 12 replicates of each beverage measured within a total analysis time of 2 minutes. Differences in the chemical composition of the headspace vapour were identified by accurate mass and isotope data combined with chemometric analysis using Mass Mountaineer software. If the goal is to identify the source of a specific sample or to simply to distinguish the different beverages, the AccuTOF-DART provided the fastest and simplest solution. A ‘fingerprint’ spectrum of volatile aroma compounds could be used to identify the origin of an unknown sample. In addition, the AccuTOF-DART was somewhat more sensitive than GC-MS for certain compound classes, such as the substituted phenols that contribute to the smoky flavour of mezcal. Although not shown here, it is also possible to use the AccuTOF-DART to rapidly determine the alcohol-by-volume composition in beverages [7].
If the goal is to determine the identity and/or relative abundance of specific compounds including isomers, the Q1500 GC system provided a powerful and cost-effective solution. The JMS- Q1500GC single quadrupole mass spectrometer with SpectralWorks’ AnalyzerPro XD software easily identified differences between aroma profiles with chromatographic separation and mass spectral identification of isomeric compounds such as 2-methyl-1-butanol and 3-methyl-1- butanol. Compounds were identified by database search and GC retention indices, and statistical analysis revealed compound-dependent differences between classes.
Figure 7. Detailed summary of ethyl hexanoate data from both EI and FI mass spectra.
Both PI and FI soft ionisation methods show molecular ions that are weak or absent in the EI mass spectra, but field ionisation generally shows a higher abundance for the molecular ion and less fragmentation than the photoionisation. FI is operated with a cold combination EI/FI ion source, and EI is operated with a heated ion source. A benefit of the combination EI/PI source is that photoionisation can be carried out with the ion source heater on, so switching between EI and PI does not require heating or cooling the source.
Although some compounds are not fully separated by one-dimensional chromatography, they were separated by the msFineAnalysis program. Figure 8 shows the msFineAnalysis chromatographic deconvolution of these compounds in the GC-EIHRMS data (top chromatogram) and the GC-FIHRMS data (bottom chromatogram). The table at the bottom of the figure shows compounds highlighted in light blue that are identified with a high degree of confidence. Compounds with multiple isomers are marked in yellow and compounds with uncertain compositions in white. The deconvolved peaks for phenol are highlighted in both the EI and FI chromatograms.
The AccuTOF-GCX Plus with msFineAnalysis version 2 software provided the most complete analysis of samples. Electron ionisation (EI) mass spectra and photoionisation (PI) mass spectra or field ionisation (FI) mass spectra were easily measured for each beverage by using the combination EI/PI or combination EI/FI ion sources. The integrated report from msFineAnalysis combined information about molecular ion composition from the PI data with database search results from the EI data with accurate mass and isotope data obtained for molecular ions and fragments. Field ionisation (FI) mass spectra measured with the combination EI/FI ion source generally showed more abundant molecular ions and less fragmentation than the PI mass spectra. However, the combination EI/PI source permitted alternating EI and PI analysis for each sample without changing the ion source temperature.
References
1. R. B. Cody, A. J. Dane. Soft Ionization of Saturated Hydrocarbons, Alcohols and Nonpolar Compounds by Negative-Ion Direct Analysis in Real-Time Mass Spectrometry. Journal of The American Society for Mass Spectrometry, 2013, 24, 329. 2. R. B. Cody, A. J. Dane. Alternative mass reference standards for direct analysis in real time mass spectrometry. Rapid Communications in Mass Spectrometry, 2016, 30, 1206. 3. I. W. González-Robles, D. J. Cook. The impact of maturation on concentrations of key odour active compounds which determine the aroma of tequila. Journal of the Institute of Brewing, 2016, 122, 369. 4.
http://www.thegoodscentscompany.com/data/
rw1059521.html 5.
http://www.thegoodscentscompany.com/data/
rw1014671.html 6.
http://www.thegoodscentscompany.com/data/
rw1004811.html 7. Sisco, E.; Robinson, E. L. Determination of ethanol concentration in alcoholic beverages by direct analysis in real time mass spectrometry (DART-MS); Forensic Chemistry 2020, 18, 10021
Raman Technology Sensor Acquisition Advances Bioprocessing Capabilities
Merck has enhanced its advanced bioprocess portfolio through the acquisition of Resolution Spectra Systems, a Meylan, France-based leader in bioprocess analytical monitoring. The company offers Raman spectroscopy analysis through its GMP-ready instrumentation and software. Financial details of the acquisition were not disclosed.
“This acquisition supports our vision of delivering intensified, connected and continuous bioprocessing,” said Andrew Bulpin, head of Process Solutions, Life Science, at Merck. “Raman measurement technology, coupled with the software to analyse and manage the generated data, allows us to offer unique and integrated solutions to help our customers optimise their bioprocesses.”
Christophe Bonneville, co-founder of Resolution Spectra Systems, added: “This acquisition validates our common strategy to support Process Analytical Technology implementation as a key element of biopharmaceutical industry digitalisation.”
Resolution Spectra Systems specialises in bioprocessing monitoring sensors based on Raman technology, which: provides real-time monitoring and process control; measures broad range of bioprocessing parameters, including glucose, lactate, viable cell density and other process-related impurities; monitors all parameters simultaneously with a single probe.
This acquisition supports Merck’s recently launched Bio4C™ Software Suite, a first-of-its-kind ecosystem that combines process control, analytics and plant-level automation. The Bio4C™ Software Suite is the latest component of Merck’s expanding BioContinuum™ Platform, which allows for the convergence of intensified process and digital technologies to advance process speed, quality and flexibility, while reducing cost.
Raman technology’s bioprocess monitoring sensors complement the ‘collect’ dimension of the Bio4C™ Software Suite, as it provides real-time process analytics across multiple critical process parameters via in-line measurement. By combining these Raman technology sensors with the software to manage the data that they provide, Merck is able to offer unique and integrated bioprocessing capabilities. The acquisition of Resolution Spectra Systems enhances Merck’s ability to provide advanced process analytical technologies across its bioprocess portfolio, another critical step toward enabling the biomanufacturing facility of the future.
More information online:
ilmt.co/PL/ZJPm 52638pr@reply-direct.com
INTERNATIONAL LABMATE - SEPTEMBER 2020
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