Evaluation of the stability and the encapsulation efficiency of W1/O/W2 multiple emulsions by electrochemical determination
A facile and accurate electrochemical approach was developed to evaluate the stability of water-in-oil-in-water (W1/O/W2) multiple emulsions and the encapsulation efficiency (EE) for water-soluble active ingredient by W1/O/W2 emulsions. In the present work, vitamin B6, a kind of electroactive and water-soluble substance was used as the marker encapsulated in the internal aqueous phase (W1). The encapsulation efficiency for vitamin B6 and the stability of the W1/O/W2 emulsions could be evaluated through electrochemical oxidation of vitamin B6 in the external aqueous phase (W2), rather than in W1, where vitamin B6 isolated by oil membrane. The effects of the electrolyte and electrochemical measurement process on the stability of W1/O/W2 emulsions were investigated. Optical microscope images showed that W1/O/W2 emulsions could be dispersed in the electrolytes solution and stable in electrochemical process. The linear relationships between the peaks current in CV curves and the vitamin B6 concentration ranged from 9.0 μmol/L to 2.5 mmol/L with a detection limit (S/N = 3) of 2.0 μmol/L. It was testified that only vitamin B6 in the external aqueous phase in W1/O/W2 emulsions could be oxidized electrochemically. The instability of W1/O/W2 emulsions could be monitored through an increase of the peak current due to vitamin B6 leaking from W1 to W2. When the total amount of vitamin B6 was 1.5 wt %, the EE of vitamin B6 was 86.9 ± 0.59%, and decreased to 72.2 ± 0.43% after two weeks.