Fault phenomenon:
Negative peak
possible reason:
(1) Column failure
(2) When using a refractive index detector, the refractive index of the sample is smaller than the refractive index of the mobile phase solvent.
(3) The mobile phase used is not pure
(4) Injection failure
(5) When using a UV detector, the solvent used to dissolve the sample is not miscible with the mobile phase solvent or the pH of the two solvents is different. When the solvent flows through the detection cell, the light is refracted at the two mutually insoluble interfaces, so that the photocell receives light of different intensities, and the light intensity is weakened, so that the negative peak is also lower than the reference.
Method of exclusion:
(1) Check and replace the column
(2) If you want to get a positive peak, you can change the polarity of the detector or recorder.
(3) use a pure mobile phase
(4) Using the injection valve, confirm that there are no air bubbles in the sample loop during the injection
(5) The solvent should be dissolved in a solvent that is compatible with the mobile phase solvent, preferably using a mobile phase as a sample solvent.
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