Determination of methanol in juices by Gas Chromatography

Hi everybody!!

Right now I'm trying to determine the content of methanol in juice drinks by gas chromatography. More concretely I'm studying how degrades the Velcorin (DMDC) in juices, and how this antimicrobial produces methanol by hydrolisis in the juices.

So, for studying how is increasing the content of methanol, I need to determine the concentration in the drink every 40 min, so every 40 min I inject a sample to the chromatograph.

The problem is the concentration of sugars in the drink, which obturates the column of the chromatograph and makes dirty the glass liner. So, due to this, when I start the experiment I get a lot of bad determinations, with no sense (lower concentrations, no peaks or a lot of interferences in the chromatograms...).

I have tried to solve this cutting the column every day I start an experiment, but it's not enough, I can't get solid results and see how is increasing the content of methanol.

I have tried also to make it by Static Headspace, but I haven't got good results too: bad chromatograms with no peaks and no sensibility by the method.

Before inject the sample I centrifugue it (11000 rpm during 5 min), and then pressed through a 0,45 um porus.

I have thought in make it by Dynamic Headspace, because I have read that is a better way to analyse dirty samples.

I don't know what else can I try...

I'm a little bit desperate... If you could give me some advice, it would be great!!!

Thanks in advance to everybody!!!!

Hi,

You cannot inject the sample containing water directly into GC as you know now...

To check for methanol content using GC, you will need to do a solvent extraction first. I think the retention time between diethyl ether and methanol is not too close? (any analytical experts can confirm?)

Anyway, one very common solvent to use for extraction is ether. Since methanol can dissolve in ether, but not water soluble components, you can do an extraction with ether, centrifuge, and inject the ether component into GC.

The best companies in the world that bottle fruit juices and drinks, to stabilize these products, use the DMDC 242 Dimethyl And the best cold stabilizer that can exist in the world today. Clearly, a machine is used to dispense the product at the final stage of bottling, dosing without this machine, it would be tremendously difficult.

 

Best Greetings
Stefano Mento

Hello Mr pau_borras,

you can distill out the methanol from the diluted juices, centrifugation  and analyse by gas chromotograph

                                                                                    Regards

                                                                                           Sushil