JEOL USA Blog

Tags

accurate mass AccuTOF-DART Additive Manufacturing Aerospace ambient ionization Analysis atmospheric pressure interface Batteries Chromatography CID collision-induced dissociation cone voltage Cryo-EM DART DART-MS Deformulation Direct Analysis in Real Time direct write double bond equivalents ebeam EDS Electron Beam Powder Bed Fusion elemental composition even-electron ions fragment ions fragmentation GC-Alpha GC-HRTOFMS GC-MS/MS GCxGC-HRTOFMS General Gulf Coast Conference Image Contest in-source CID isomers isotope measurements isotope patterns lithography mass spectrometer mass spectrometers mass spectrometry Materials molecular weight msFineAnalysis AI MXene NMR Upgrade Nuclear Magnetic Resonance odd-electron ions Pesticide Analysis Petrochemical Analysis Petroleum Pittcon Pyrolysis-GC-MS Pyrolyzate SEM SEM-EDS semiconductor TD DART-MS Thermal Desorption time-of-flight unsaturation

How DART mass spectrometry uncovers elemental compositions

Learn how accurate mass information from DART-MS provides information about the elemental composition of a molecule

JEOL USA last year

https://www.jeolusa.com/PRODUCTS/Mass-Spectrometers/AccuTOF-DART

2 MIN READ

If we have accurate mass data, DART-MS can tell us more than the molecular weight of a molecule. Let’s see how to determine the elemental composition from accurate-mass DART-MS data.

Note: The next few articles focus on the interpretation of accurate-mass spectra. Although I am using a DART-MS example, the information here applies to any data from an accurate-mass mass spectrometer, such as the JEOL AccuTOF GC-Alpha. We’ll come back to DART-MS shortly.

Elemental composition determination from an accurate mass

The first step in determining an elemental composition from an accurate mass is to specify a set of elements that might be present and set some limits on the minimum and maximum number of each element that might be present. We’ll use the caffeine example from the previous posts. Let’s assume that we know that we don’t know that the compound is caffeine, but that the compound only contains carbon, hydrogen, nitrogen and oxygen. Because accurate mass measurements are not always exactly correct, let us also assume that the measured m/z is 195.0899 instead of the exact calculated value of 195.0882. We can set the element limits based on the maximum number of each element that could give a molecular weight less than 195.

Element	Symbol	Maximum
Carbon	C	16
Hydrogen	H	34
Oxygen	O	12
Nitrogen	N	14

Next, we specify an error tolerance of 5 millimass units (5 mmu) for the accurate mass measurement. That’s 0.005 u, a bit wider than the error we expect, but wide enough that we won’t miss any possible compositions. Software then calculates the weight (actually, the m/z) for all possible combinations of the elements within the specified limits and only reports those elemental compositions that have a calculated m/z within 5 mmu. There are nine compositions that fit those constraints.

Calc. m/z	mmu	DBE	Composition
195.085512	-4.39	6.5	C₄ H₇ N₁₀
195.08552	-4.38	1	C₅ H₁₃ O₅ N₃
195.086856	-3.04	6	C₆ H₉ O₁ N₇
195.086863	-3.04	0.5	C₇ H₁₅ O₆
195.088199	-1.7	5.5	C₈ H₁₁ O₂ N₄
195.089543	-0.36	5	C₁₀ H₁₃ O₃ N₁
195.092223	2.32	9.5	C₁₃ H₁₁ N₂
195.094065	4.17	2	H₉ O₂ N₁₁

Here’s a summary of the process:

Elemental composition determination from an accurate mass

What does DBE mean, and how do we know that the correct elemental composition for the m/z 195.0899 peak is C₈H₁₁N₄O₂ instead of one of the other 8 compositions? Stay tuned for the next piece in this series!

Accurate mass information obtained with DART-MS can be used with to determine the elemental composition of molecules. You can read more about how elemental compositions are determined from accurate-mass data here. To learn more about JEOL mass spectrometers and the AccuTOF-DART system, please visit us here.