Impurities at 1 minute

[Sunjay]

Dear All,

I would like to know if it is right to add the peaks at 1, 2 minutes (in HPLC) in total impurities, if no such peak is there in blank or placebo.

Regards

[Kostas Petritis]

I would say yes as impurities can be polar compounds that can be eluted very early in chromatography (assuming reverse phase chromatographic conditions). The fact that you do not see these compounds in blank or placebo reinforces the likelihood of these being impurities of your compound of interest...

[danko]

I would very much agree with Kostas and I’d like to add some thoughts too.
Peaks eluting at 1, 2 min hence most probably at void volume, are not that easy to quantitate. They tend to be very narrow which demands higher sampling rate of the detector. It doesn’t need to be a problem now-a-day with modern detectors, but it is rarely considered by the users, so narrow peaks are seldom defined correctly (15 – 20 sampling points per peak)
Another problem I have experienced with early eluting peaks is that they tend to be very high and in combination with their sharpness it is very difficult to see if they are off scale.
I guess the right approach here is to optimize the method in order to retain and potentially separate early eluting peaks which will facilitate their quantitation greatly. Maybe in this situation it’s worth trying stationary phase with embedded polar groups.

Best Regards

[HW Mueller]

Is UV detection assumed here? With all the possibilities of refractivie index, scattering, etc., effects up front, it would be advantageous to have a wizzard to do the quantitation?

[tom jupille]

I'll elaborate on HW Mueller's comment: attempting quantitation on any peak eluting at or near t0 is unwise. Your system is in a state of "dis-equilibrium". In general, you should have a k' of at least 1 (i.e., retention time of at least twice t0) for good quantitation.

[JM]

One should be careful about the "placebo " supplied by Formulators, Some of them, the placebo is just a mix of ingredients and they do not bother to process that mix through the same process as of formulation with drugs. Some specific points are,

1. No additions of buffer, pH modifiers in placebo.
2. No compression cycle ( including solvents used) followed for placebo tablets.
3.No use of gases
4. Reaction between placebo components with drug.

While doing method development for impurities , we always ask for placebo produced with same process except addition of API.

JM