[135223395]

Chlorinated hydrocarbons in soil can be analyzed by pyrolysis GC or by LC-MS. Why is pyrolysis GC preferred?

Help me, plzzzzz

[enahs]

This question is very broad and the instrumentation specifics are very broad too.

In order to see something by MS, you need to ionize it, yes/no/maybe?

Is it easy to ionize, lets say chloroform by typical LC-MS methods?

Also, what is the reactivity of chlorinated hydrocarbons? Could that cause some issues in LC method?

[135223395]

Here is my teacher's hints, don't know what to do.

Rather than answer the question for you, let me ask some questions that will lead you to the answer.

What is the boiling point of 2,4-D and related compounds?
What is the solubility of 2,4-D and related compounds in common solvents?
How polar is 2,4-D?  Is it a compound that would work well on normal phase LC?  Reverse-phase LC?
If you can vaporize 2,4-D, what would a good GC column be?  At what temperature would it run?
What interferents would pyrolysis eliminate?  What interferents would be unaffected?  Which would be enhanced?
What interferents would solvent extraction eliminate?  What interferents would be unaffected?  Which would be enhanced?
What detector would be best for the molecule in each system?  What is the likely detection limit?  What about selectivity?
Now, given the totality of the evidence, what are the chemical and physical reasons for choosing one method over the other?

[enahs]

Well, I think your teacher is saying to do 2,4-D in the GC, but, I do (and many other people) do 2,4-D via LC-MS all the time. Its quite easy and works very well.


Your teacher is clearly looking for a specific answer, and since I do not know your teacher and what you covered it is kinda hard to tell what he/she wants.
The truth is, there are so many different variations of GC and LC setups, and there are many different things you would be wanting to optimizing for when analyzing that this question is just super broad and kind of poor, at least how you are presenting it. At least, in my opinion.

[Toxophilus]

Have you considered Headspace SPME (solid phase micro extraction) with GCMS? A soil sample is put into a 20 ml headspace bottle and septum sealed. This is then incubated at an eleveted tempertaure and the headspace is sampled using a SPME fibre. The fibre is then thermally desorbed in the GCMS injector port.