# What is mass spectroscopy?

Oct 5, 2017

Mass spectroscopy is a method to find a molecule weight.

#### Explanation:

I'm not so familiar, sorry...

[Step 1] Molecules are ionized and crashes into fragments.
[Step2] Then, the ions are accelerated and induced into magnetic field.
[Step3] In the magnetic field, the ions are affected by Lorentz force $F \left(N\right)$ and their obrit is bended.

$F = q \left(v \times B\right)$ ($q \left(C\right)$ the charge of ion: $v \left(m \text{/} s\right)$: velocity of ion, $\times$: cross product, $B \left(T\right)$: magnetic flux density).

And of course...
$F = m a$ (m($k g$): mass of ion, a(m"/"s^2): acceleration) and you can conclude:
$a = \frac{q \left(v \times B\right)}{m}$

The point is that $\textcolor{red}{\text{orbit of lighter ions or fractions are bended}}$
$\textcolor{red}{\text{more easily than that of hevier ions.}}$
Acceleration rate $a$ is proportional to $\frac{q}{m}$.

[Step4] Sort ions or fractions by $\frac{m}{q}$(i.e. the reciprocal of $\frac{q}{m}$) and record the relative abundance of ions. This is how you can find a mass of the molecule or mass of fragments. This is a mass spectrum for 1-phenyl-1-butanone(${C}_{6} {H}_{5} C O {C}_{3} {H}_{7}$). Cited from http://www2.odn.ne.jp/had26900/topics_&_items2/about_MS1.htm

What you can find from the result…
148: The mass of the whole molecule, and this is exactly the same as ${C}_{6} {H}_{5} C O {C}_{3} {H}_{7}$.
77: The mass is same as the phenyl group, ${C}_{6} {H}_{5} -$. This implies that the molecule might have benzene ring.
105: $105 - 77 = 28$ is the mass of carbonyl group($- C O -$). Thus we can expect the molecule to have ${C}_{6} {H}_{5} C O -$ group.