determination of some compounds

the_dreamer · Mon Mar 28, 2005 10:59 pm

Hi all (first serious post teehee)

For a school-project we have to do some analysis of a given sample (aquaeous-solution) on the following compounds:

Ethanol, Acetone, THF (tetrahydrofuran), Toluene, MTBE(Methyl-tert-butylether), iron and chrome

Biggest problem is we have no idea wich of these compounds are present in our given sample and in what concentrations.

So my main Q. :

Does anybody know a determination-technique for these compounds and a method for a rough approximation of their concentration (before we'll work on the GC, HPLC & AAS determinations for each of these compounds)

Many thanx: The_Dreamer

(ps excuse my poor english)

(BTW: only apparatus we have available are HPLC, AAS and GC)

Vitriodor · Tue Mar 29, 2005 5:35 am

In order to determine residual solvents in an aqueous solution one could use head space analysis or solid phase micro extraction, coupled to a GC(/MS). Both sample preparation techniques have been developed for this purpose (although SPME also can be used for less volatile materials) and tell you what sovents are in your sample and in which relative ratios.

If you don´t have these techniques available you could put a small drop of your aqueous solution in a GC vial, wait for a while so that the air above your is saturated with the volatiles and than only sample the air in the vial. Be careful not to inject the water itself and do a blank injection before, without rinsing the needle afterwards.

Depending on the concentration of the solvents it may also be possible to get some hints with infrared spectroscopy (if available). Look for specific bands of the solvents you mentioned.

Iron and chrome concentrations should be determined with AAS. Maybe an element specific precipitation reaction can give you an indication about the presence and concentration prior to analysis? For iron for instance you could use NaOH which will give a brown color. With K4Fe(CN)6 you will get a blue precipitate. For chrome there will be similar tricks.

Vit

the_dreamer · Wed Mar 30, 2005 8:23 pm

^ lol, apparently out of the 5 solvents that 'could have been' in our sample we only got 1 spike when running the sample through GC, looked something like this:

the_dreamer · Sat Apr 02, 2005 7:00 am

So it actually was acetone. And the little bumb was probably ethanol, but too small to give an aqurate reading.

Another lesson learned in the wonderfull world of chemistry Smile