Chromatography Forum

I want to determined 2,4 hexadine in benzene matrix. The commercially available of hexadine consist of three isomers. Two of isomers are very close to other non aromatics of benzene. I found that the best separation is in low temperature and lowest temperature possible in our GC is 28 C◦ . Suppose one isomer appear at 13.24 and nearest non aromatic appear at 13.39. Also second isomer appears at 14.157 while a big non aromatic peak appears at 14.00. These two pair of peak has different properties. In case of low column flow (1.2 ml/min and initial pressure 28 psi) first pair has best separation but second pair not good separate. By increasing column flow second pair will be separate but first pair converts to one peak. We are using Varian CP-3800 and it has an option for pressure programming. I tried to combine two above fact. That mean use a program with low pressure until end of first two pairs and increasing pressure (column flow as result) in order to separation of second peaks. But it wasn’t successful. Is any idea for better results? As recommended by basic method we are using two columns in series for this test. One CP-WAX 52 CB 60 m 0.32 followed by one CP SIL 8 CB 30 m 0.25.

Using a 3 column Backflush heartcut application, should separate them cleanly.

A short polar column to move BZ from HDs, backflush BZ and cyclo and heavier alkanes, a long non-polar column to move lighter alkanes ahead of HDs, sending them to vent, but cutting the HDs onto a long polar column to move olefins and medium alkanes ahead of HDs.

Adjustments of each column length or film thickness may be necessary.

Good luck,

Rod

mr3573,

Are you literally using two columns connected to each other? If so, the separation you gain on one could easily be lost on the second (to the same compounds or to different compounds.) Much better to use a valve to make a cut from first to second (or, as Rodney suggests, a heartcut is even better.) Considering the temperatures you are working at, a switching valve would be a relatively easy thing to implement.

Best regards,

AICMM

Dear chromatographer1

sorry for question but what means HDs ?

HDs = hexadiene isomers

Rod