Evaluation of the stability and the encapsulation efficiency of W₁/O/W₂ multiple emulsions by electrochemical determination

Abstract

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.

Graphical Abstract

Keywords:

• Multiple emulsions
• electrochemical detection
• encapsulation efficiency
• vitamin B6

Acknowledgments

We gratefully acknowledge the financial support from the Key Laboratory of Synthetic and Biological Colloids, Ministry of Education, Jiangnan University (Grant No. JDSJ2018-13).