Preservatives

Experimental Section
Instrument and Reagent
Instrument ：TriSepTM-2010GV capillary electrochromatography
(Shanghai Unimicro Technologies co.，Ltd.) UV Detector, High Pump, HW Workstation.
Back-pressure Restrictor ：2000 psi
Reagent ：Acetonitrile (HPLC); Redistilled Water; Phosphate
Sample ：Methyl4-hydroxybenzoate, Ethyl4-hydroxybenzoate, Propyl4-hydroxybenzoate
The method of solution confect ：Take fitting samples, use mobile phase dissolve, before used, filtrated 0.22m filter
Chromatography Conditions
Capillary column：100 m ID packed with 3m ODS, overall length 32 cm, effective length 20 cm
Mobile Phase ： Actonitrile/ Phosphate buffer (PH3.5) =35/65(V/V),
5 mM(after mixing)
Pump flow rate ： 0.02 ml/min; When injecting, the pump flow rate is 0.2 ml/min
Back-presure ：2000 psi
Detection ：254 nm
Temperature：Room temperature

Figure 1 (0kv)
1. Methyl4-hydroxybenzoate 2. Ethyl4-hydroxybenzoate 3. Propyl4-hydroxybenzoate

Figure 2 (-10kv)
1. Methyl4-hydroxybenzoate 2. Ethyl4-hydroxybenzoate 3. Propyl4-hydroxybenzoate