Does anyone know why I am getting negative dip in the diluent at the same rt of active?. My mobile phase is 10mM ammonium acetate and 1-propanol (90:10) and diluent is water.
column is acclaim surfactan plus 150x 4.6 mm , 3um.
Your mobile phase contains a salt which can be a source of positive charge that is read by the electrometric sensor in the CAD detector. This gives the signal of your background which is set to zero at the begining of each run. When diluent (water) is injecteted it "dilutes" locally the charge of the mobile phase and makes the detecor signal drop down.
Thank you and is there any solution for it ? . How can I improve it ? . Even using water as mobile phase also gives negative dip.
Srikanth Voruganti: Samples should be dissolved (fully) in the mobile phase before injecting (not in water).
Make sure your sample is retained on the column and not eluted at Tzero, has a good K prime, the baseline is stable and the detector has been cleaned. Your "neg" dip at the the Rt of sample implies you have NO retention and no Chromatography taking place. Your method may be invalid. You will have to provide your actual method and Rt of peak(s) to be sure. As this is your first time using HPLC (and esp with an advanced detector such as a CAD) please work with a professional chromatographer on-site for best results.
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