Chromatography Forum

Hello everybody,

Now i'm going to analyse Fenobucarb ( a herbicide compound),

But i have a funny question in making mobile phase :
In a document i have " The mobile phase was comprised of 87% of water, 13% of acetonitrile,and 0.1% of acetic acid."

And i make this mobile phase by getting 87ml H2O, 13 ml ACN and 0.1 ml acetic acid. All products belong Merck, HPLC grade.

Is it right solution ?

Thank you for your reply !

I should think it's in weight ratio.

Thanks thohry

May someone give me any solution ?

Thanks !

Would it be reasonable to try the solution you made and see if it works? If the separation is not what you want, adjustement to thohry's mixture would be somethign to try? But, the two mixtures should be fairly similar to each other.

Beyond that, the best idea is to try to track down the author of the document or someone who has used the procedure sucessfully.

hi,
you may use 2 mobile phase: mobile phase A: Water containing 0.1 % Acetic acid and Mobile phase B: Acetonitrile containing 0.1 % acetic acid. Then you may use 87:13 composition (final acetic acid is always 0.1 %) or different composition until you get good resolution. Therefore you don't need to prepare new mobile phases for every step. just inject your std and see what you get.

Ayhan

I hope you do not have isocratic pump

Ayhan

brightsun´s question is not funny, but the label of % is. Most likely the authors meant mL, not %. They could have also meant to have used g. Any attempt to justify the use of % here is bound to fail.
This is a typical example of sloppy reporting.

My best guess would be a some point the analyst made a water:acn (87:13 v/v) isocratic mobile phase tried it but got crappy results and decided to add a bit of acid to improve things

It probably succeeded and writing water: ACN:HAc (87:13:0.1v/v/v) is virtually equivalent 86.9: 13.0: 0.1 v/v/v (where the components add up to 100)

Thank you for all !

I think they use gradient pump.

Firstly, they mix 87% Methanol and 23% H2O in one bottle (A). The another bottle contains CH3COOH (B). After that, they use gradient pump with component : 99.9% A and 0.1% B

I think that.

If my way is not okay, i will try making all your suggestions.

Thanks !

Thank you for all !

I think they use gradient pump.

Firstly, they mix 87% Methanol and 23% H2O in one bottle (A). The another bottle contains CH3COOH (B). After that, they use gradient pump with component : 99.9% A and 0.1% B

I think that.

If my way is not okay, i will try making all your suggestions.

Thanks !

Certainly not. Precission of mixing 99.9/0.1% in gradient pump will be wery bad not speaking of damage made to the pump by the acid.

It was most likely meant 87:13:0.1v/v/v as suggested by JGK.

Taking into account decrease of volume after mixing 87 ml Methanol and 23 ml of Water addition of acid might even make it again 100 ml.

On the other hand I think in most cases you will not see substantial difference when using mixtures of 99.9+0.1 or 100+0.1 ml

Thanks Rolandas Plausinaitis !

I agree with the others who think it's by volume. This just shows why these types of instructions absolutely need to be written so they're definitive and not open to interpretation. Besides, automated HPLC mixing valves mix by volume.