Chromatography Forum

Can someone explain in lay man terms what is difference between free base and salt form reference standards?

Can someone explain in lay man terms what is difference between free base and salt form reference standards?

One example is Diquat (herbicide) it has an organic part but is commonly used as a salt Diquat Dibromide.

When put into water it disassociates into Diquat and Bromide, so the HPLC sees only the Diquat portion. But there is about 40% difference in the molecular weight of Diquat and Diquat Dibromide, so if you simply weight up the salt to make a calibration standard, then your concentration must be corrected to Diquat or make sure it is reported as Diquat Dibromide. We have failed blind performance samples before because someone reported the salt concentration as the free base concentration so we were about 40% higher than the accepted value.

Always check your standard certificates to see if the concentration given is for the base or acid form or the salt.

I believe that we used salt standards such as sodium lactate when assaying for lactic acid in products. We just corrected for this in the software to report as percent lactic acid.

Let's take the example of a common drug, like aspirin.

Free Base (Acetylsalicylic Acid): This is the basic form of aspirin, without any added ions. It has a neutral charge.
Chemical structure: CH3COOC6H4COOH
Salt Form (Aspirin Hydrochloride):
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Aspirin hydrochloride is the salt form of aspirin, created by reacting acetylsalicylic acid with hydrochloric acid.
Chemical structure: CH3COOC6H4COOH + HCl → CH3COOC6H4COO- + H3O+

There are often major solubility differences between salt and free base forms (oxycodone vs. oxycodone HCl, for example) - which explains why salts are sometimes preferred for standard use even when a label claim is in terms of base.

Aspirin hydrochloride is the salt form of aspirin, created by reacting acetylsalicylic acid with hydrochloric acid.
Chemical structure: CH3COOC6H4COOH + HCl → CH3COOC6H4COO- + H3O+

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The salt form is a version of the compound that has been combined with another chemical (like an acid) to form a salt. This is often done to stabilize the compound, make it easier to handle, or help it dissolve better in certain solvents (like water). Salt forms are typically more stable than free bases and can be easier to store and work with. Dino Game Offline