Hello all... I m looking for a method for assay DMAE (deanol bitartrate)- dimethylaminoethanol bitartrate in aqueous samples (cosmetic product) using GC- MS mass spectrum HP- 5 ms U.I 0.25 (5%-phenyl)- methyl- polysiloxane- PDMS Column or HPLC- DAD . any idea? tks everybody...(+34)- 655 87 82 35
Mr. Winkler,
Please, consider the content of the following discussion and the reference section, shown therein.
[1https://www.researchgate.net/post/LCMS_method_development]
It is not just an idea, but only, currently, available absolute method for quantification by mass spectrometry, worldwide.
You are looking at an organic salt. When in aqueous solution, the DMAE does not “know” what its counterion is. Likewise, the bitartrate does not know what it was associated with in the solid form.
So, the first question is, what do you want to measure? Is it the amount of DMAE, the amount of bitartrate or do you need to know the amounts of both? That is, a solution of 1 mM deanol bitartrate and 1 mM NaCl looks identical to 1 mM deanol hydrochloride and 1 mM sodium bitartrate.
First, let’s look at DMAE. DMEA is a small molecule with a relatively high boiling point of 133 C. It has no chromophore, so it will not be easily detected with a DAD (unless you derivatize it). It is also an alcohol. Alcohols tend to tail significantly in GC. To eliminate this problem, they are often derivatized. Check your lab procedures to see whether you have standard procedures for derivatizing small alcohols like pentanol or butanol. If so, those methods are likely to derivatize DMAE. Note that you will need to evaporate all the water from your sample before derivatization.
Of course, if you have to derivatize for GC, you can also derivatize for HPLC and use a dye that is easily detected. I would suggest a hydroxyl-reactive dye like N-methylisatoic anhydride, FITC or an acyl nitrile. As with GC, the samples need to be dry to derivatize them.
Now to the bitartrate. Bitartrate is the name given to tartaric acid with one ionized carboxylic acid. Start with a solution of pure tartaric acid in water and titrate against sodium hydroxide and you with start to form both bitartrate and tartrate (the dianion). The ratio of the uncharged tartaric acid, the anion bitartrate and the dianion tartrate depend upon the pH. See the attached curves. For example, at pH 3.8, the amount of tartaric acid (uncharged) is 7.1%, the amount of bitartrate is 84.4% and the amount of doubly negatively charged tartrate is 8.6%. Change the pH of the solution and the ratio of tartaric acid:bitartrate:tartrate changes. So, depending upon the pH of the solution, you may have wildly different values. The total amount of all the tartrate species (neutral, anionic and dianionic) will be constant. So, what do you want? The total amount of tartrate species?
Tartrate (and bitartrate and tartaric acid) absorb a little more UV light but not very much. You could go with GC/MS but there are some problems. First, acids usually need to be derivatized for GC. Since tartaric acid has both carboxylic acid groups and hydroxyl groups, you will need an agent to derivatize all four positions. You can find the tetra-TMS derivative of tartaric acid in PubChem (https://pubchem.ncbi.nlm.nih.gov/compound/519591). That suggests that you could get a reasonable mass spectrum.
You could also consider derivatizing the tartaric acid so that it could be detected with your DAD. The Molecular Probes catalog has multiple reactive dyes that might work.
In the end, you will be able to determine how much DMAE is present, how much “tartrate species” are present and, by measuring the pH of your sample, how much of the tartrate is in the bitartrate form.
Hello Joe Joe Olechno ., tks for the answer. My product is an Dermal Filler (Aqueous matrix) with DMAE/ Deanol bi- tartrate 0.3 %., and my target is DMAE Assay (0.3%)..I have a signal by GC- MSD target: 58.xx Cap. Col HP- 5 inlet: 250º MSD 300º oven ramp: 70 º 6 min to 200º 4 min rate: 15º/min . Solvent- diluent CH3OH msd. I ran an DMAE raw material solution/CH3OH but the problem is the signal type., tailing... the Alcohol derivtarization is the best option, I understand... so, maybe the HP- 5 Column (mid. polarity: Phenyl 5%) is not indicated for this method. What do you think about that?
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