These questions are in regards to molecular and atomic mass spectrometry: Consid

Question

These questions are in regards to molecular and atomic mass spectrometry:

Consider the electron ionization source, what do you think would be the effect of decreasing the voltage between the filament and the target? What effect would using an unheated filament have?

Which method of ionization would you suggest foreach of the following samples? Explain your reasoning.

(a) ethanol

(b) naphthalene

(c) copper metal shavings

If we want the mean free path for an ethanol molecule in a CI chamber to be 0.098 mm, what pressure would be required in the chamber?

Explanation / Answer

a) We know that KE=1/2 mV2= e*V=106*10^-19*22300 Thus velocity v=2KE/m=2*1.6*10^-19*22300/6.8*10-27=1.014*10^11 m/sec

b) 1/2 mV2=e*V thus V=1/2 mV2/e=68*10^-8*0.5*4.2*4.2*10^ V=37.485 kV

For ethanol, proton transfer soft ionisation method is used as in doing so the OH of OH2+ cleaves and thereby produces ethyl cation.

For naphthalene photoionisation may be used as naphthalene undergo sublimation readily so phonton can ionise it with very less energy.

For cupper metal shavings electrolysis may be usedfor ionisation as cupper is agood conductor of electricity.

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