calibration HPLC non linéaire

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I am developing an HPLC method for anions / cations with a Poroshell Hillic column and a DEDL detector.

On the sulphate analysis, the resolutions are excellent but the calibration shows a nonlinear curve, is this possible and normal?

hello, if you are french customer you can create a ticket on this mail Customercare_france@agilent.com. I m looking for details for this method.  

Hello, 

when you talk about "sulfates" you mean SO₄^2- 

DEDL is a non-linear detector, values must be reported in log. Can you give us more details about your method and calibration. 

Bonjour Karine fr,

Oui la calibration est faite avec Na2SO4 5, 10,15, 20, 35, 50 ppm.

Tampon 100 mM acétate d'ammonium/acide acétique pH3

Gradient avec 91% éthanol 9% tampon

30°C 0,4 ml/min

Nébuliseur 70°C Evaporateur 90°C gaz 0,9

what software are you using ? if you need a linear response, can you use a calibration curve with log of response and log of mass ?

translation : calibration is on anion Na2SO4 for 5, 10, 15, 20, 35, 50 ppm

mobile phase is 100 mM ammonium acetate, acetic acid buffer pH3 / gradient with 91% ethanol 9% buffer 

oven temperature 30°C / flow 0.4 ml/min 

nebulizer 70°C 

evaporator 90°C 

gas flow 0.9 ml/min