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Time-of-flight mass spectrometry (TOFMS) is a method of mass spectrometry in which an ion's mass-to-charge ratio is determined via a time measurement. Ions are accelerated by an electric field of known strength.〔Stephens, W. E., (A Pulsed Mass Spectrometer with Time Dispersion ) ''Phys. Rev.'', 1946, ''69'', 691.〕 This acceleration results in an ion having the same kinetic energy as any other ion that has the same charge. The velocity of the ion depends on the mass-to-charge ratio. The time that it subsequently takes for the particle to reach a detector at a known distance is measured. This time will depend on the mass-to-charge ratio of the particle (heavier particles reach lower speeds). From this time and the known experimental parameters one can find the mass-to-charge ratio of the ion. == Theory == The potential energy of a charged particle in an electric field is related to the charge of the particle and to the strength of the electric field: where ''E''p is potential energy, ''q'' is the charge of the particle, and ''U'' is the electric potential difference (also known as voltage). When the charged particle is accelerated into time-of-flight tube by the voltage ''U'', its potential energy is converted to kinetic energy. The kinetic energy of any mass is: In effect, the potential energy is converted to kinetic energy, meaning that equations () and () are equal The velocity of the charged particle after acceleration will not change since it moves in a field-free time-of-flight tube. The velocity of the particle can be determined in a time-of-flight tube since the length of the path (''d'') of the flight of the ion is known and the time of the flight of the ion (''t'') can be measured using a transient digitizer or time to digital converter. Thus, and we substitute the value of ''v'' in () into (). Rearranging () so that the flight time is expressed by everything else: \frac\,|}} Taking the square root of the time \sqrt}\,|}} These factors for the time of flight have been grouped purposely. |}} Note that the mass had to be converted from daltons (Da) to kilograms (kg) to make it possible to evaluate the equation in the proper units. The final value should be in seconds: : which is about 28 microseconds. If there were a singly charged tryptic peptide ion with 4000 Da mass, and it is four times larger than the 1000 Da mass, it would take twice the time, or about 56 microseconds to traverse the flight tube, since time is proportional to the square root of the mass-to-charge ratio. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Time-of-flight mass spectrometry」の詳細全文を読む スポンサード リンク
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