Method to be use for Glycerine and Diethylene glycol analysi

[lingo_belle]

hi,

have to inject glycerine and diethylene glycol for GC analysis. In fact, just wanted to know the estimated retention time thus was instructed to ignore the derivitization. However, I always encounter a error that refers that my primary pressure is out of range. I'm using Shimadzu GC2010 with column of carbowax, (WCOT Fused Silica 50m X 0.53mm ID, coating: CP-Wax 52Cb, DF =2.0.)
Was told that this error was due to incorrect settings of the method. What method should I used/develop to get the retention time of the two compounds. kindly enlightened!

thx
belle

[chromatographer1]

Glycerine will take forever and a day to elute on your column.

Diethylene glycol will only take a very long time.

You might want to try a shorter column ( 5 meters ? )and perhaps a 0.5 micron film if you insist on using Carbowax.

Did you try Supelco technical service?

How to Contact Supelco

USA only:
Phone: 800-247-6628
or 814-359-3441
fax: 800-325-5052
email: techservice@sial.com

[Consumer Products Guy]

I have to inject glycerine and diethylene glycol for GC analysis. I was instructed to ignore the derivatization.

I have to ask why you were instructed NOT to derivatize for this assay? Is your supervisor knowledgeable or have pointy hair? Anyway, if you would like to assay without derivatization, I would suggest columns as those detailed in the USP assay for DEG and related amterials in glycerin, such as a 30 m x 0.53 mm i.d. x 3.0 mm SPB-624 (Supelco #25430) or Restek Rtx-624 (Restek #10971) capillary column. We use this routinely.

[AICMM]

lingo_belle,

Saying the same thing a different way than CPG and C1, you are putting a very polar compound on a very polar column. You might just cut a meter or two off of your current column and try that.

Best regards.

[lingo_belle]

Hi all,

thx for your prompt replies.
had contacted Supelco before, and they had informed that the column I'm using was suitable for analysis of glycol. Similar to what you all had been advising, they told me that the compound will probably tail on most columns.

According to my superior who hadn't used the machine for too long a time, due to budget and time constraint, have to use other's dept machine and that includes the column(which somehow had also restricted me to manipulate with the column.)

CPG, may I know what method do you use for analysing the glycerine. I meant abt the temperature(injector,column) pressure, column flow, linear velocity etc.

I'm sorry that I demanded so much but I guess I need this infomation to set up my test method asap for i'm really at my wits end.

thx again,
belle

[WK]

CPG,
I would be interested to know what derivatizing reagent you use.
Best Regards
WK

[lingo_belle]

hi WK,

From what I know, seems like MSTFA or BSTFA are the common type of derivatising agents that most used. CPG, your take?

thx
belle

[WK]

Hi lingo belle and CPG,
Is this suitable for determining DEG in glycerine?
WK

[chromatographer1]

Supelco told you correctly.

But the answer was for glycol, ETHYLENE GLYCOL, and DEG will elute but at a very high temperature. Glycerine is another matter on a Carbowax column.

CPG gave you a great answer.

To measure DEG in glycerine may be difficult unless you make the acetate derivative and then you can use the Carbowax column I believe.

The silylation derivative for DEG may be difficult to separate from the reagent. CPG may know much better than anyone as I believe he has done/is doing this type of analysis.

Bosses want results and sometimes the impossible. Check your facts and then inform them of the truth. They have to deal with the truth, that is why they get paid the big bucks.

To make the TMS derivative, MSTFA is a good reagent. But will DEG-TMS separate from it on a thick film non-polar column? Low temperature 40 held for 5 minutes then 4°C/min oven ramp.

DO NOT USE MSTFA on a Carbowax column ! I repeat, DO NOT.

Good luck,

Rod

[lingo_belle]

Maybe I didn't state clearly but my aim is not to measure DEG in glycerine. These are 2 different compounds that I wanted to analyse. E.g inject glycerine, find the retention time, inject DEG, find likewise.

Sorry for the confusion.

Rgds,
belle

[chromatographer1]

Belle,

I believe you now understand that glycerine on a carbowax column is not a good solution, in spite of your instructions from your boss.

So there are no conditions that I am aware of that allow a good analysis of glycerine on that column within the temperature limits of the phase.

CPG has offered an excellent solution to your needs. It is unfortunate you are not able to use that column. There is one detail missing from your description of the analysis: What are the other components of the solution you wish to inject on the column? You may very well damage or ruin the Cwax column if you inject inappropriate compounds onto it.

I hope you convince your boss to change his mind if he really wants an analysis that truly indicates the content of the sample.

best wishes,

Rod

[WK]

Sorry lingo belle,
I asked CPG about DEG in glycerine. Sorry for the confusion.
I wonder if the chromatogram CPG displays on 624 is underivatized or derivatized. Luckily I have wax and 624 in same GC oven!
best regards
WK

[Consumer Products Guy]

Yes, the chromatogram I posted is for underivatized DEG and glycerin. The set up is like in USP for glycerin monograph. This would work for DEG in glycerin -OR- DEG and glycerin.

When I do derivatize DEG and glycerin, I usually dissolve sample and standards in DMF and simply mix with BSTFA (containing 1% TMCS) to derivatize, instantaneous.

[WK]

Thanks CPG,
It works nicely on a 624 - I should really have tried that before - since its quite nasty on a wax type!
WK