This is a question about time of flight (TOF) mass spectrometry.
Give the equation, including state symbols, for the formation of Si+\text{Si}^+Si+ ions from Si\text{Si}Si atoms by electron impact.
A sample of silicon is analysed by TOF mass spectrometry. The sample is ionised using electron impact. The ions are accelerated to have a kinetic energy (KEKEKE) of 2.50×10−18 J2.50 \times 10^{-18}\text{ J}2.50×10−18 J. An ion takes 1.35×10−4 s1.35 \times 10^{-4}\text{ s}1.35×10−4 s to travel along a 140.0 cm140.0\text{ cm}140.0 cm flight tube.
KE=12mv2 KE = \frac{1}{2}mv^2 KE=21mv2where m=mass (kg)m = \text{mass (kg)}m=mass (kg) and v=speed (m s−1)v = \text{speed (m s}^{-1}\text{)}v=speed (m s−1). Use the information given to deduce the mass number of this ion. The Avogadro constant, L=6.022×1023 mol−1L = 6.022 \times 10^{23}\text{ mol}^{-1}L=6.022×1023 mol−1.
Explain how the ions are detected in the TOF mass spectrometer. State how the relative abundance of the ions is determined.
A sample of silicon contains three isotopes, 28Si^{28}\text{Si}28Si, 29Si^{29}\text{Si}29Si and 30Si^{30}\text{Si}30Si. 85%85\%85% of the sample is 28Si^{28}\text{Si}28Si. The other isotopes are in a 2:32:32:3 ratio of 29Si:30Si^{29}\text{Si} : ^{30}\text{Si}29Si:30Si. Calculate the percentage abundance of 30Si^{30}\text{Si}30Si in this sample. Use your answer to deduce the relative atomic mass (ArA_rAr) of the sample. Give your answer to 1 decimal place.
Electrospray ionisation is used instead of electron impact for the ionisation of a large polypeptide in a mass spectrometry experiment. Suggest why.
