The problem with LowOx column

[mole3737]

Dear all:

We use LowOx column to analyze oxygenates in light hydrocarbon stream, recently, I found that some ethers (ETBE, MTBE, DIPE) can not be separated anymore, they formed a very sharp peak. Does anyone has some experience with this problem?

[chromatographer1]

I have no experience, but based on the selectivity of the column I am not surprised. This is a good characteristic based on measuring oxygen containing impurities.

A simple second column should separate the single sharp peak into its components. An ideal situation for those of us who use multidimensional chromatography.

This sounds like a solution looking for a problem.

best wishes,

Rod

[mole3737]

Thank you, Rod.

I am confused, why this column can not resolve those ethers anymore.

[chromatographer1]

It is due to the selectivity of the column.

The hydrogen bonding attractions of the H-C and C-C bonds are almost non-existent in comparison to the strength of the attraction of the pi electrons of the oxygen with the phase.

Think of having a mixture of various sizes of necklaces of made of peas and iron ball bearings being separated with a plastic sieve (methyl silicone) in comparison of being separated with a magnetized iron screen (LowOx). All the necklaces would separate by size easily by the plastic sieve but the necklaces which contained an iron ball with tightly stick to the iron screen no matter what their size and would tend to only be released from the iron screen at the same time with a strong tap.

Sorry about the poor explanation, but I hope you can see the point I am trying so badly to make.

best wishes,

Rod

[AICMM]

mole3737,

The Lowox is an interesting beast. Extremely selective separations but I found it to be very picky. IF I had to guess, I would say you altered your flow or oven parameters somehow recently or you are getting it wet. If you formerly had good separations for ETBE and MTBE I would first make sure you have all the conditions you had before. Then I would bake for several hours AND I would add a water scrubber to your carrier line if you don't already have one.

I have found that running these as dual column configuration (pre-sep the heavies so they don't land on the Lowox) really helps with the RT stability.

Best regards,

AICMM