The use of HPLC or High Pressure Liquid Chromatography is preferred to Titration analysis for e-liquids as they may have a significant amount of interfering substances (i.e. flavors) in their composition. The HPLC is a reliable method of analysis because it can affect rapid separation of components with high resolution and fast analysis time. 
The titration analysis is based upon a known chemical reaction with only one specific component (i.e.  Nicotine) dissolved in the e-liquid solution. Titration technique is prone to interferences as it is not selective to a specific compound, nor does it quantify if any degradation of the Nicotine has occurred.