Time of flight(t tof ) of monovalent proteins (P + ) with molarmass 31000 amu wa

Question

Time of flight(ttof) of monovalent proteins (P+) with molarmass 31000 amu was measured to be 400 s in 1 m long mass spectrometer(MALDI-TOF, see pic) with positive high voltage (+HV) repeller and extractor (0 V). The distance between repeller and extractor is 5 cm.

a) What would time of flight (s) of divalent proteins(P2+) be at same conditions?

b) What is the voltage between the repeller and extractor?

c) what would time of flight(s) be for monovalent proteins(P+) from the repeller to the extractor? (answer: 40 s, show calculations)

Explanation / Answer

a) time of flight (s) of divalent proteins(P2+) at same conditions =   200 s

     as, applied force will be doubled , so time is halfed .

b)    the voltage between the repeller and extractor    = 200 V

c)    time of flight(s) for monovalent proteins(P+) from the repeller to the extractor :-

   speed =   1/(400 * 10-6)

                =   2500 m/sec

   =>   time of flight(s)   =   0.05 * 2/2500

                                         = 40    s

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