Question

An ion is accelerated into the 1.33 m flight tube of a linear time-of-flight (TOF) mass spectrometer with an acceleration voltage of 25.0 kV. It takes the ion 81.1 microseconds to reach the detector. What is the m/z of the ion? ( Dont forget to convert units!)

Answer 1

Answer – We are given, length of the flight tube, d = 1.33 m

acceleration voltage V = 25.0 kV , time, t = 81.1 microseconds

we know the formula for Time-of-flight mass spectrometry –

t² = d²/2V * m/z

We need time in s, V in volt so we need to convert the respective units

We know

1 µs = 1.0*10^-6 s

So, 81.1 µs = ?

= 8.11*10^-5 s

Now we need to convert kV to V

We know

1 kV = 1000 V

So, 25 kV = ?

= 25000 V

Now we need to plug the values in to the formula

t² = d²/2V * m/z

(8.11*10^-5 s)² = (1.33 m)² / 2*25000 V * m/z

6.57*10^-9 = 3.54*10^-5 * m/z

So, m/z = 6.57*10^-9 / 3.54*10^-5

               = 1.86*10^-4 Da/C

OR

We know,

1 Da = 1.66*10^-27 kg

m/z = 1.86*10^-4 Da *1.66*10^-27 kg /C

        = 3.086*10^-31 kg/C