1. Measuring the Mass of
an Electron by LC/TOF-
MS
A Study of “Twin Ions”Imma Ferrer & E. Michael Thurman
Department of Analytical Chemistry, University of Almerıa,
Anal. Chem. 2005, 77, 3394-3400
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2. This Paper Discusses………
 The use of LC/MS ion trap to show the formation of fragment
ions of the same nominal mass in positive and negative ion and
their pathway
 The use of LC/TOF-MS to measure the accurate mass of
fragment ions and the importance of including the mass of the
electron in ion fragmentation studies
 Recent advances in continuous mass calibration allow the
measurement of the electron to one significant figure using
LC/TOF-MS, when combined with the analysis of the NSAID
solution
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3. How small is an electron?
• Mass : 9.1093829×10−31 kg / 0.00055 u
• Charge : −1.602176565×10−19 C
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4. Twin Ions
 Same fragment ion (nominal mass) formed in either positive or
negative ion electrospray for a suite of analyte
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5. What is NSAID?
 Non steroidal anti inflammatory drugs
 Analgesic and antipyretic effects
 In higher doses anti inflammatory
 Non narcotic
 E.g : Aspirin , Ibuprofen ,Naproxen, Diclofenac
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6. LC / MS Ion Trap Method
• Column : Reverse phase (C8)
• Column temperature : 25 °C
• Mobile phase
 A - acetonitrile
 B - 0.1% formic acid.
• Linear gradient flow :50 - 100% A in 10 min further maintained for 2
min
• The flow rate :0.6 mL /min
• Injection volume :50 uL
• Maximum ion accumulation
time : 200 ms
• Capillary voltage :3200 V
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7. LC/TOF-MS Method
• Same LC parameters
• Electrospray interfaced
• Positive ion mode
• Capillary Voltage : 4000 V
• Gas temperature : 300 °C
• A second orthogonal sprayer with a reference solution was
used as a continuous calibration in positive ion (121.0509 &
922.0098 m/z)
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8. Results & Discussion
Full scan in-source CID spectra of NSAIDs. 8

9. Inductive (i) cleavage of ibuprofen [M + H]+ or [M - H]-
to form the twin ions in either positive or negative ion electrospray
Results & Discussion
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10. Chemical structures of NSAIDs and twin ion examples by MS/MS.
Results & Discussion
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11. Results & Discussion
Accuracy of CO2 and HCOOH Neutral Losses
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12. Accurate mass spectra of ibuprofen in both positive and negative ion
Results & Discussion
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13. Results & Discussion
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14. Calculation of Electron Mass from the Difference of the
Twin Ions Based on Each Chromatographic Run
(Negative - Positive) Containing Ibuprofen, Diclofenac,
and Naproxen Using Hand
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15. Resolution in Positive and Negative Ion Electrospray
for LC/TOF-MS
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16. Finally…….
 It is now possible to reach accuracy values of 1 ppm regularly for small
molecules (which is 0.2 mmu for a mass of m/z 200) using LC/TOF-MS.
 The maximum calculated mass precision for the Agilent TOF used in this
study was 0.4 ppm based on the m/z 161 ion using a resolution of 5 000
and an ion intensity of 105 (20 000 ions)
 Similar calculations for the m/z 185 ion and m/z 250 ion gave maximum
precision values of 0.2 and 0.3 ppm, respectively
 The combination of twin information and routine accuracy of <1 ppm
makes it possible to measure electron mass to one significant figure.
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