HPLC Method for sodium acetate anydrous determination

[DSP007]

70,72+28,28? Hu stole the one percent ?!
Ratio Na/ac =23/(12*2+6*1+16*2+23)= 2,7/7,3 .


You product not dissolve in wather ? OK! Push whith wather , filtrate without glass filter and "separate the wheat from the chaff" (c ,Biblia)
For determination of chaff (sodium acetate) you will use:
1) Potentiometry - pH as quantity buffer salt and pX Na as quantity sodium ione.
From small calibration "pH curvee unlinear" and need use calibration which real sodium acetate solution.
2) GC - as I said. Ethylacetat good see on a FID and in PEG-20M (5% on diatome or 50m *0.32 capillare FFAP it good separated whith alcohol. Should controlled ethanol - in alcohol etithylacetate is standart admixe)
3) If "many more acetate admix " - you may use gravimetry => if you evaporated (boiled) wather and weight sodium acetate trihydrate ( unevaporated liquid, kristallysing on a cold and vary small soluble in absolut ethanole )

[tom jupille]

Okay, let's back up a bit.

I do not mean to be harsh, but some of the questions you are asking suggest that you do not have much experience or background in chemistry. There is nothing wrong with that (we all had to start somewhere), but it's hard to give relevant advice without knowing the skill level of the person we are giving advice to.

Can you give us some background on your experience (both in general chemistry and in chromatography), what sort of product you are dealing with, and what sort of analytical techniques you have available.

If it will make you feel more comfortable, you can e-mail me privately.

[alemaggot]

No no! There is no problem to write in forum! Thanks Tom!

So. I'm twenty years. I'm a chemist. I'm not graduate. I'm using HPLC from about 3 years. But my knowledge about chromatography and general chemistry is little, unfortunately. At school I was study too little. Now I repent!

Recently I try to increase my knowledge, but the way (as you seen) it's very long.

I'm work in pharmaceutical world. In my laboratory I've: HPLC with UV detector, GC with FID detector, potentiometric titraor, unit Karl fischer, IR and UV spectrophotometry.

Do you want know more?

[tom jupille]

That helps quite a bit.

If you are working with pharmaceuticals, you should be using validated methods. These may be "compendial" methods that come from the EP (European Pharmacopeia), USP (United States Pharmacopeia) or they may be methods developed by your company and submitted to the appropriate regulatory agencies. Talk to your supervisor and ask him or her what validated methods you have on file and follow one of those. If you have no validate method for this, then, in my opinion, your management is being unreasonable in expecting an inexperienced person to develop and validate one -- especially if they do not provide the necessary tools (like an ion chromatography system!)

Okay, if you have to do it anyway, here are the basics:
Sodium acetate is a salt, typically formed from acetic acid and sodium hydroxide. In aqueous solution, it does not exist as a molecule, but dissociates into separate sodium ions (Na+) and acetate ions (CH3COO-). You can analyze for either one (or both). If there is no other source of sodium in your sample (i.e., if all of the sodium comes from sodium acetate), then an ion-selective electrode might be the easiest approach. Ion chromatography would also work, but you either need a dedicated IC system or you need a fair amount of experience in order to adapt an HPLC system for the purpose.

Acetate (acetic acid) is somewhat easier. If you acidify a solution of sodium acetate, the resulting acetic acid can be analyzed by GC (for example: http://www.ncbi.nlm.nih.gov/pubmed/1274853).

Sodium acetate is highly water-soluble, so even if your formulation does not dissolve, you should be able to extract it and get the sodium acetate into the aqueous solution.

[DSP007]

Well. Clearly, it means nearly colleagues.
Something that says dear... not dear, regard Tom - quite rightly refer to the leader (cheef) of the lab (not the "you supervisor") http://demiart.ru/forum/uploads5/post-5 ... 547303.jpg and the boss for help in the creation , validation and approval procedures. Boss is not a wolf , and not eat. This however does not negate the need to study your fundamental basis of science. Boss will not last forever, and deaths. Therefore, as Lenin said, "need each day teach myself, teach myself again, and again to teach myself" (c).
You need to create a foundation, now as the Bible says - your not built house on sand, the house built on the sand will not stand ( (с). Take any old (pre-1980) university general chemistry textbook and read. If something does not understand - ask and we are always happy to explain.

[alemaggot]

Thank you very much guys! You're fantastic

I will offer to you a cup of beer

I will propose to my boss the method "ion-selective electrode" and GC Method. About the last... I've see the link that you've post Tom and I've read "GC conditions are described for the suppression of "ghosting" and "tailing" caused by adsorption phenomena associated with the GC behavior of organic acids". I've serch in the site, but I can't find it. I don't understand where I can found this things... Can you help me?

Thanks and good evening!

[tom jupille]

There is a citation to the original journal article near the top of the PubMed summary. It is:
Am Ind Hyg Assoc J. 1976 May;37(5):268-73. You will have to contact a library to get a copy of it.

Down at the bottom of the PubMed page, there are links to learn how to use the service effectively.

[alemaggot]

Tom on the site there is write that the volume isn't avaible.

Do you know where I can find it in other site?

Thanks!

[tom jupille]

Unfortunately, I don't. If you were in the US, I would say a university library, or contact the Association that publishes the journal. That said, once you know it can be done, do a Google search on "acetic acid" + GC and you will find many additional references.

[alemaggot]

I've search more information on forum and on internet.

Acetic acid have a less reply. His boiling point is 118°C. I'll use Dimethylformamide as solvent (bp 153°C). The column that I'll use is OVI G43 (30m * 0,53 id * 3 um film) or a column with less film thickness. I'll must try.

If the reply of compound it's very less I'll try also with addition of inorganic salt for change the liquid/gas equilibrium.

On the forum I read that acetic acid "eat" the stationary fase of column very quickly. It's real?

[DSP007]

1) Acetic acid can boils at 118 C. But you have a sodium acetate. From which to extract the free acetic acid by adding a strong acid - sulfuric or hydrochloric.
2) It depends on the phase. Cross-link metilsiloksanes completely resistant to hydrolysis in the presence of water, acetic acid. And how you have it there? 10 mg / g in product or 1 mg / ml rinse water?

[alemaggot]

1)Ok... But If I use that strong acids I don't cause problem at gc system with them strong vapour?

2) I don't understand your question. You want know how many sodium acetate I have in my solution?

Thank you

[tom jupille]

DSP007's replies are often cryptic. They are originally written in Russion and translated via something like Google, which often does not work well with scientific or technical material.

As far as column stability is concerned, your best resource would probably be the supplier (your local salesperson or distributor should be able to help).

[alemaggot]

Today I ask to my supplier information about my column. He said that my column resiste without problem with acetic acid. Perfect!

In last few days I've made some tests with GC. I must modify the oven ramp, but I'm fairly confident for conclude the test in next week.

But the problem for the "acetic acid" extraction from my analyte is not resolved. We are sure that if I inject the powder into headspace vial with DMF, I can't see acetic acid?

[DSP007]

Once again. In the future, take the time to self-learning. Theoretical chemistry.

1) You work with sodium acetate. It is not volatile.
2) To get a free acetic acid - it should displace the sodium salt of a strong acid - as a variant of sulfuric acid.
3) However, DMF as solvent for this purpose will not do. With respect to sulfuric acid, DMF is the base (alkaline).

Simply pour in your wash water with sulfuric acid. By 10 ml -2-3 drops H2SO4. And analyze it without dilution. Acetic acid by vapor-phase analysis, you'll see from about 1 mg / ml.
And if it smallest - you need to think about. "Do I need to look ?". Several times wash product with water and forget about the water-soluble impurities "as a nightmare".