HPLC Method for sodium acetate anydrous determination

[alemaggot]

Hi everybody!

I tell you sorry for my bad english!

I've got a problem with the analysis cited in the topic title. I must do a quantitative determination. I've try to use a non polar column (licrhosphere C18 250 * 4,6 * 5um) and the compound dosen't be reteined. It elute about on the dead volume of cloumn. This cause a many inegration problem. There is a wide contamination of blanck peak (water). Mobile phase is 100% water ( I know that this is dangerous for the column life) with sodium eptansolphonate.
Then I've try to use a polar column (alltima NH2 150 * 4.6 * 5um), but also with this column the component dosen't reteined. Mobile phase is composed by 90% by acetonitrile and 10% by acqueos buffer.

How can I do to make my component to be retentied?

Than you very much!

[tom jupille]

What pH is your buffer?

[alemaggot]

In the session 90% Acetonitrile 10% buffer, the buffer composition was: weight 20mg of potassium dihrygenophospate in 100 ml of water. (major concentration with 900ml of acetoniitrile precipitate salt). The pH value was not determinated.

In other session I try with pH 2.5. But the result was egual: component wasn't reteined.

[tom jupille]

Do a series of experiments at pH 2.5, with decreasing ACN
90%, 80%, . . . etc. down to 10%.

[alemaggot]

What column advise you? Reverse or normal phase?

How many gram of salt in 1 liter of buffer solution? I use KH2PO4?

If I work at pH 2.5 what is the improvement for my retention?

[DSP007]

I do not understand one. Nafiga (why, but dirty) for to determine the anhydrous sodium acetate need use HPLC?
More appropriate methods (flame photometry for sodium and GC or anhydrous titrometer for acetic acid) does not permit faith or object properties?

[HW Mueller]

abcmoal, try
http://www.liv.ac.uk/buffers/buffercalc.html

[tom jupille]

Code: Select all

What column advise you? Reverse or normal phase?

You said you were using a C18 column. That is reversed-phase. I was making a suggestion for you based on that column.

In reversed-phase, retention is controlled by the ratio of organic solvent to aqueous buffer, with more organic solvent = less retention. Your first try was 90% organic, and you got no retention. Therefore, the thing to do is to try decreasing the amount of organic solvent.

[alemaggot]

I do not understand one. Nafiga (why, but dirty) for to determine the anhydrous sodium acetate need use HPLC?
More appropriate methods (flame photometry for sodium and GC or anhydrous titrometer for acetic acid) does not permit faith or object properties?

I've learned a new word

However sodium acetate is impurity into my product! I must separate my product from impurity. In your method this is possible?

[alemaggot]

abcmoal, try
http://www.liv.ac.uk/buffers/buffercalc.html

Thank you very much!

[alemaggot]

Code: Select all

What column advise you? Reverse or normal phase?

You said you were using a C18 column. That is reversed-phase. I was making a suggestion for you based on that column.

In reversed-phase, retention is controlled by the ratio of organic solvent to aqueous buffer, with more organic solvent = less retention. Your first try was 90% organic, and you got no retention. Therefore, the thing to do is to try decreasing the amount of organic solvent.

No no Tom. The session with 90% organic was by with polar column! In reverse phase mode I've used 100% buffer solution! Without organic the component wasn't however reteined!

I can't write corret to made me understood. Sorry sorry

Now... For sodium acetate is preferable normal phase or reveresed phase? This is the problem.

Thank you so much guys for the help!

[tom jupille]

I apologize for misreading the initial post!

Best way would probably be ion exchange. Go to one of the ion chromatogaphy suppliers (Dionex, Metrohm, etc.) and get their recommendation.

For example:
http://pdf.directindustry.com/pdf/dione ... -_171.html

http://www.kf-titration.us/Applications ... pplication

[alemaggot]

I search in internet information about ionpac as11 sell by dionex.

in the manual there is write: "The ionpac as11 anion-exchange column provides fast profiling of inorganic anions and organic acid anions". If I dissociate sodium acetate I obtain Na+ and CH3COO-, correct? Then acetate anion be determinated, but the sodium? I do my assay only on CH3COO- peaks?

Also the detector use by dionex for column test is "suppressed conducivity, ASRS-Ultra 4mm, Autosuppression recycle mode". What is this detector? In my HPLC system my detector is a normal UV detector. I can see the same peaks?

[DSP007]

Many different ways - you need to know that for the product.
If this is (for exampl)e 70% acetic acid - it is sufficient to measure the pH of its water solution - acetate buffers are stable pH and the ratio of acid and salt can be determined by normogramme C mM/mL acetate/pH, or C mM/ml Na/pX Na ( Na selective electrode).
If it is substancies- sodium lactate (for example)- you can use gas chromatography ethyl esters after mixing with sulfuric acid and alcohol.
Ion and ion-pair chromatography, too, have a right to exist. For ion-pair chromatography with RP -18 can be used (for example ) tributilammonium ​​buffer. But it is not robust (not reliable) method. Especially considering the fact, that UV sees acetic acid only below 210 nm, the redox-detector sees her only at a potential of more than +1,5 V, a mass spectrometer will have to periodically clean from sediments acetate salts.

As they say - it everywhere wedge (in the sense - everywhere possible problems)

[alemaggot]

On the Merck index I found:

Sodium acetate - C2H3NaO2 - C 29.28 % ; H 3,69 %, Na 28,03 %, O 39,01 %. Then... 70,72 is acetic acid and 28,28 is sodium. It's corret this?

I can't use the first method you've write. My product, where I must determinate the % of sodium acetate, is insouble in water!

But the GC method.. mmm... I've FID as detector. Acetic acid have a low respound on this detector. It's high ionization potential, right?
Sorry but I can't understand this part of your post: "gas chromatography ethyl esters after mixing with sulfuric acid and alcohol". How must I do?

Thank you