Any methods to do melamine testing by GC-FID?

[Hurricane]

I tried last week and had no success...even though it seems everything should have been quite simple. The melamine standard (1mg/mL) was in a 50:50 water:ACN matrix and I did two extractions with an equal volume of toluene to extract the melamine. I derivatized the extracted standard in ~20% v/v of BSTFA (bis-trimethylsilyl-trifluoroacetamide) + 0.1% TMCS (trimethylchlorosilane) @ 70 degrees for 15 mins but had no success getting a signal on our GC-FID using a DB-5 column. I could not find anything on Pubmed or Google search where anyone has used GC-FID method for melamine analysis. Almost everything is either GC or LC with MS detection. Has anyone had any success, have suggestions, or know of any papers where melamine was analyzed using GC-FID? I have access to HPLC but am limited to UV detection. Thanks!

[Carvone]

Hi Hurricane,

First, I am not sure there would be a strong FID signal given for melamine. From what I know of FID, the signal strength is increased by an abundance of -C-C- bonds and to a lesser extent -C-H bonds. Melamine has only three carbon molecules and they are all attached to nitrogens. I know that -C-OH or -C=O bonds give very little signal in FID and would think also -C-N- bonds would also give a weaker signal. Possibly with derivatization the signal strength will be increased.

Second, Melamine has a BP of 557.5 C and a Log P of -1.37 so on a DB-5 column, this would mean an estimated 2670 for a Kovats Retention Index, which is quite high, and depending on your starting temperature and ramp program, 15 minutes may not be long enough for the melamine to go through your column, even if it were detected. The derivatization should help to make the compound more volatile but I do not know how much it would affect the retention index.

Hope this helps some,
Carvone

[Carvone]

Hi Hurricane,

I also checked a GC derivatization guide and it said that the reactivity for silylation is in the order of:

alcohol > phenol > carboxyl > amine > amide

So it could be possible the derivatization is not very efficient meaning your sensitivity will be greatly decreased. Combined with low FID detector sensitivity, it could be why you are not detecting anything.

The derivatization guide also recommended 60 C for silylation to avoid degradation 10-15 minutes, but said longer times were better than higher temperatures.

[krickos]

Hi

These links might be helpful:

http://www.sigmaaldrich.com/analytical- ... elamine-gc

and

http://www.fda.gov/Food/ScienceResearch ... 200,top=50'