Quantifying Low Concentration of active by HPLC

[VJ]

we are working on a liquid dosage form in which active drug concentration is 2.5ug/ml. We have tried inecting a neat sample into the HPLC, DAD Detector but area count of impurities are very small so it is hard to detect and quantify impurities. we have tried several wave lengths to maximise the sensitivity of impurities but we can not. Is there any other way to maximise the sensitivity of impurities? pLEASE HELP..

FYI.
we can quantify impurites in the API with better sensitivity but we can not quantify impurities in the Finished product with 2.5ug/ml concentration.

[tom jupille]

If the dosage form is in a weak solvent such as water, you can inject a larger volume (I'm assuming reversed-phase chromatography). You will have to experiment to determine how high you can go; at some point overloading of your API will cause problems.