7. A mass spectrometer identifies various molecules within a sample by measuring

Question

7. A mass spectrometer identifies various molecules within a sample by measuring their charge-to-mass ratio. The sample is ionized and positive ions are accelerated from rest through a potential difference AV, where they enter a region of uniform magnetic field (B = 0.25 T). The ionized molecules travel in circular trajectories, which will pass through a hole to the detector if the G trajectory has the correct size (d = 5.5 cm). Determine the accelerating potential, AV, which corresponds to the detection of the following ions (note: 1 Da 1 u) Atomic Masses 12 WN 12.0000u 14.0031u 15.9949u Detector b) CO+ c) If you wanted to detect cyanide, CN, what changes would you need to make to the setup of the spectrometer?

Explanation / Answer

a) N2+

let V is the required potential diffrence.

we know,

radius of orbit, r = m*v/(B*q)

diamater, d = 2*r

= 2*m*v/(B*q)

= 2*sqrt(2*m*KE)/(B*q)

d = 2*sqrt(2*m*q*V)/(B*q)

d^2 = 4*2*m*q*V/(B^2*q^2)

V = d^2*q*B^2/(8*m)

= 0.055^2*1.6*10^-19*0.25^2/(8*2*14*1.66*10^-27)

= 81.4 V

b) CO+

V = d^2*q*B^2/(8*m)

= 0.055^2*1.6*10^-19*0.25^2/(8*2*28*1.66*10^-27)

= 40.7 V

c) detecter should be shifted to upward or magnetic field direction should be pointed inward.

Related Questions

Navigate

• Browse (All)
• Browse 7
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.