[Dolphinsiu]

My book says that sometimes we are difficult to distinguish isomer from mass spectrum. With the use of authentic cpds, we distinguish them easily.

But what is authentic cpds??What is the corresponding examples??

[AWK]

Isomers show often different intensities of ions with the same m/e
Authentic means known

[Dolphinsiu]

Thank you! It seems I have made the question complex! Actually it is simpler!

[alphahydroxy]

an authentic compound is simply a sample of a compound which you know the correct material.

For example if you had made say, alanine, you could  compare (using various techniques) the compound you made with an authentic[/b] sample of alanine you had bought, and you would be able to tell that you have indeed made alanine.

For enantiomers you could do the same thing - e.g. you have made one enantiomer of serine, and you have bought or made one enantiomer that you know is S, then you can compare these via chiral GC (for instance) to be sure which one you have made.