In what circumstances HPLC assay is more than 100%

[kumaresan]

In what circumstances HPLC assay is more than 100%

[josebenjamin]

Dear Friend,

If you are getting values close to 100%, such as 101%, then it could be that just some experimental errors are being accumulated and the values turn out higher than expected. Most assay techniques by HPLC have standard deviations close to 1%.

If your values are much higher than 100%, such as 110%, then the reason very likely is that your standard and your samples are not the same. In other words the purity of your standard is less than 100%, or lower than stated in the certificate of analysis.

A common situation that causes high assay values is when the standard has a higher water content than the samples. Obviously the water in those cases could be just accumulated moisture or crystallization water.

Good luck,

josebenjamin

[ravenwork]

The possibilities here are numerous. You should really specify the type of assay and the calibration method involved. I used to work for a bulk pharmaceutical company that just used the area percent for a rough measure of purity. That method at least had the advantage of never yielding a purity above 100%.

One significant possibility that comes to mind is an unresolved impurity.

ravenwork

[bert]

Most assay techniques by HPLC have standard deviations close to 1%.

Not in bio-analysis So, kumaresan, as ravenwork asked, please specify.

Regards Bert

[DR]

If you're weighing standard by difference, and spill a bit during the transfer,

If you qualify a very good in-house standard against a marginal, old USP lot (100%, by definition),

If your standard has shed some water since it was last tested,

you introduce a high bias.

If you have a batch of product that was slightly overcharged with X, you have a high result.

(I had to say something different - I thought I was channeling Jeff Foxworthy for a minute there).

[kumaresan]

thanks benjamin, actully i got assay around 106%. I confirmed the moisture also

[LCFlo]

I know a story of a substance which could contain up to 10% impurities (Dequalinium chloride). But a high purity standard is available. When you have bad separation (co-elution) it might be possible that the sum of the areas (analyte plus impurities) is higher than the area of the standard.

Florian

[josebenjamin]

Dear Kumaresan,

I am glad my comments were of help. The situation you found is very commmon. Over the years I found it at least 10 times.

Once you know the water contents of samples and standrds, then you can correct your calculations as required.

Good luck,

josebenjamin