Quinine in tonic water using is isocratic methods

[danw9]

Hi

Currently I'm trying to develop a method for quinine analysis but whatever I do I only get a 60% recovery. I only have a uv detector but I do have a column oven.

Thanks

[Gerhard Kratz]

I guess your column is a C18 reversed phase column. What sample preparation are you doing? It can be that you will see effects from interferences with other compounds like salicylic acid etc.!
If you get a chance to get a fluorescence detector, take it.
More details about your chromatography conditions will help.

[kubowicz.tomasz]

Hello

Do you need to separate quinine and quinidine?

Regards

Tomasz Kubowicz

[danw9]

I'm using a phenomonex C18 RP polar column, we use quinine hydrochlorite in the standard and convert that to quinine for the hplc. I make my standard to 60ppm as this is the answer im looking for on our samples but currently im getting 40ppm after converting my result to quinine sulphate. I run a degassed sample of either diet or full sugar tonic water.

[Peter Apps]

Is it the standard or the samples that gives you a result of 40 ppm (presumably mg/l) ?

If it is the standard, how do you do the calibration ?

If it is the sample, how do you know that it really contains 60 ppm ?

Peter

[danw9]

The standard contains 60 ppm. My samples come out at around 40ppm. They have to get sent away for analysis presently but want to bring it in house

[tom jupille]

The standard contains 60 ppm. My samples come out at around 40ppm.

Uhh, is it possible that your samples actually contain 40 ppm?

I'm not trying to be sarcastic here. How did you actually measure the recovery (spike a matrix blank? standard addition?)?

[HPLCaddict]

How do you perform the "conversion" of hydrochloride to sulfate?
Is it a mathematical conversion (i.e. are you converting the different molar weights in the calculation) or are you actually trying to "chemically" transform the salt?
If it is a mathematical conversion, I'd first check if there isn't some fault in the calibration introduced by some sort of mathematical quinine/quinine sulfate/quinine hydrochloride mixup.

[danw9]

The results we get from the external samples are always in and around 60 ppm as they should be. I run a blank and get no peaks. Only thing I can see that there is something in the tonic limiting detection where as a standard of just quinine comes off as the should. Its all mathematical conversion I've checked and double checked the calculation as that's what I first thought was the issue