Reason for negative peak after main peak in RP HPLC

[satyabrata.kundu]

Request for the reason .

[skunked_once]

Please supply more information such as column, mobile phase, detector type, flow rate, analyte in order to receive an explanation.

[Gerhard Kratz]

In addition to skunked_once please let us know if your sample is in the same solvent diluted than you mobile phase. If your target compound is less retarded than the solvent you dissolved the sample it can cause a change in the refractive index in the flow cell. That can cause a positive or negative Peak. But we need more information.

[paul_b]

Another common reason for a negative peak is the use of the 'background subtract' wavelength (most commonly set up on Agilent / HP systems and called the reference wavelength). If the eluting species absorbs strongly at that wavelength and relatively poorly at your recorded wavelength you will see a negative peak. This one is easy to check - just re-run the sample with the reference turned off.