What to do when there are no peaks, small peaks or negative peaks?
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First thing that should be checked is that the detector lamp is on. A loose or broken wire between the detector and the integrator could also be the source of the problem.
Make sure the pump is on or that the flow is towards the column and not going to your waste. The sample vial might be with wrong sample or the sample might have deteriorated.
Negative peaks appear when the sample solvent and mobile phase differ greatly in composition or the mobile phase might be more absorptive than sample components to the set UV wavelength.