Chromatography Forum

Hey guys, I am trying to figure out my options for analyzing methanol in biodiesel. As per this method http://las.perkinelmer.com/content/Appl ... diesel.pdf

Does anyone here have experience with headspace analyzers? Are there any used ones that are robust or have known issues? I am trying to find a used 7694.

Currently I only have one HP5890 gc with on column injection and FID. I use agilent's db5ht column for free and total glycerol. We can't currently afford a headspace analyzer, so I am also on the lookout for in process methods to do a quick and dirty analysis. What about a PTV backflush system? Are there any that are compatible with the 5890? I wish i could inject the biodiesel mix onto my column and just slow down the temp ramp program, but I don't want all the heavy ends gunking up the column, although i do have a guard installed. Problem is I won't be to load enough sample on the column for the methanol peak to detectable. ( Can only inject 5 uL)

Any advice is appreciated, thanks.

Your cheapest but not inaccurate technique is to use SPME.

A syringe, the proper fiber, and vials are all you need. It need not be automated but can be done manually.

Call Supelco and ask for technical assistance. They have a CD with methods and it should be no problem to reach extremely low levels accurately.

Almost any HS unit can do methanol but a thin film 5% phenyl column is not the column of choice.

Perkin Elmer and Tekmar also make good HS analyzers beside the Agilent unit you mentioned and there are others with smaller market share but nevertheless are useful.

Good luck,

Rod

This is great thank you. The only aspect I am worried about is how long it will take for the methanol to absorb onto the fibers, and how well it will do so. As in our sample matrix there is sometimes a high amount of soap (sodium salts of any free fatty acids), and the sample can be quite viscous. however i did find one paper on the extraction of methanol from caustic viscous industrial waste, similar to what our glycerin byproduct looks like, so this gives me hope! I think i can centrifuge out the soap too in any case...Thanks again!!