Question: I have two unknown peaks on my GC (both with the same MW or rather highest M/Z ratio peak = 98) and I am trying to confirm their identity. 

**Unknown-1**

[![Unknown-1](https://i.stack.imgur.com/TsPcF.png)](https://i.stack.imgur.com/TsPcF.png)

**Unknown-2**

[![enter image description here](https://i.stack.imgur.com/dbzvc.png)](https://i.stack.imgur.com/dbzvc.png)

Based on the expected chemistry I have identified two potential candidate molecules from a library of GCMS spectra (see images below; just click on the images please if you cannot read the smaller font numbers). 

**Compound-A**

[![enter image description here](https://i.stack.imgur.com/ItbGJ.png)](https://i.stack.imgur.com/ItbGJ.png)

**Compound-B**
[![enter image description here](https://i.stack.imgur.com/X3oZr.png)](https://i.stack.imgur.com/X3oZr.png)

Is it safe to think these are matches or not really? The MS was run in EI+ mode. 

* Unknown-1 is Compund-B?
* Unknown-2 is Compound-A?

Both likely? Neither likely? Any one likely?

Is having the same set of M/z fragments good enough (e.g. 98-83-55 similar between Unknown-1 & Compound-B) or ought the abundance ratios also match mostly?

Answer: 
It depends. Bread has moth small molecules (like 2-Acetyl-1-pyrroline). These molecules will just pushed aside by the blade. You have hydrogen bond network between water molecules. You break those. Bread has large polymers like starch. Knife breaks those. 

A cleaner system to study is a polyethylene. You can freeze it in N2, break under inert atmosphere and study by EPR spectroscopy. You will find free radicals at the breaking point. This is because it costs less energy to break a bond then to move one molecule relative to others.
Essentially, what you are doing with an everyday knife is wedging your way through the substance. You are pushing aside the particles within the substance. In this instance, bread; you are pushing apart the different particles, requiring you to break the inter molecular forces that held them together.