[Tzushca]

Hello,

I am trying to do some quantitation for a hydrochloide salt of a substance and the reference I found on the market is the non hydrochloride substance.

The problem is that when I do the calibration curve with the non hydrochloride and read the sample, the result is ten times more than it should be.

Is this due to the fact that one is a hydrochloride and one is not?

[chenbeier]

Which compound is it. How is the preparation. Without HCl the compound is probably alkaline .

[Arkcon]

That's no problem.  Often the standard is one chemical form, and the analyate is another chemical form.  You will have to calculate taking the different molecular weights into account, but many software packages are even designed to do that for you.  As chenbeier: reports, you will have to be sure both forms can be analyzed by your procedure in the same way.

[Tzushca]

Thanks for the answers.

Few more details:
1. The reference being a non hydrochloride it contains dextrin for stabilization.
2. The sample is extracted from capsules.
3. Solvent for both samples is water.

[chenbeier]

What do get if you add some hydrochloric to your standard.

[Tzushca]

Regarding the method, it is an HPTLC densitometric one. I tried adding HCl to the standard but it wont leave start.

The thing that I didn't took in consideration is the molar mass difference. The reference is 356.25 and the sample is 390.7 (with the chloride).

How can I use this to apply some sort of correction?

[Arkcon]

Thanks for the answers.

Few more details:
1. The reference being a non hydrochloride it contains dextrin for stabilization.
2. The sample is extracted from capsules.
3. Solvent for both samples is water.

Good.   The free base standard that you have is at a certain purity, you'll have to know that so you account for the dextrin.

The capsules also have other things there, make sure you're getting all the analtyte.

Fortunately, they're both soluble and chromatograph-able.  That works out well.

I don't know

The thing that I didn't took in consideration is the molar mass difference. The reference is 356.25 and the sample is 390.7 (with the chloride).

How can I use this to apply some sort of correction?

Maybe you have the option hidden somewhere in your densitometry software, or scanning software (radio-label counter?  fluorescence counter?  Anything like that?)

If you, you have to use ... math.   

OK.  What you could visualize is that the sample in capsules is "adulterated" with a known number of
equivalents of Cl (exactly one HCl molecule, if you count the MW)  So you take your densitometry number, and apply your ratio.  When you're done, the amount in your capsules should become less.  That's how you know you're doing it correctly.

[Tzushca]

Arkcon what ratio are you referring at and how to find it?

The software doesn't offer the possibility to correct via molar mass.

[Arkcon]

I gave you some hints, and you can also consult Analytical chemistry textbooks, this is a common problem, that has to be done, and done correctly.

Method development, from all steps: from sample prep, method development, verification and validation will cost upwards of USD $100,000.  You don't need that.  However, just this important step, done for you, and checked, and typed out, well, I'll do that for you once the check clears.