STUDIES OF ENTRAPMENT EFFICIENCY OF
LIPOIC ACID INTO LIOTROPIC
NANOPARTICLES BY DIFFERENTS
METHODS OF ANALYSIS
CAMPOS, PATRÍCIA MAZUREKI; PRAÇA, FABÍOLA S. G.; BENTLEY, MARIA VITÓRIA L. B.
School of Pharmaceutical Sciences of Ribeirao Preto - University of Sao Paulo, Ribeirao Preto, Sao
Paulo, Brazil
[email protected]
Keywords: encapsulation, entrapment efficiency methods, liquid crystalline nanodispersion, lipoic
acid.
Purpose: To investigate the suitability of different entrapment efficiency (EE) methods, such as size
exclusion chromatography, filtration-ultracentrifugation and ultrafiltration to assess the lipoic acid´s
loading into liquid crystalline nanoparticles. Methods: Lipoic acid (LA) (100 µg/mL) was entrapped
into liquid crystalline nanodispersion, composed by monoolein, oleic acid and aqueous phase with
aqueous phase composed by 30 mM phosphate buffer solution (pH 7.2) plus surfactant polymer, and
liotropic nanodispersion sized around 189. 59 ± 14.09 nm was obtained as described before (Lopes,
L. B. et al 2006).The amount of LA encapsulated was determined by following methods (n=5): i) Size
exclusion chromatography method using a Sephadex LH-20 column (3 cm diameter, measuring 15.5
cm); samples (1.0 mL) eluted using purified water as mobile phase; turbid fractions from 7 to13
were collected; ii) Filtration-ultracentrifugation method, samples (3.0 mL) were filtrated using 0.8
µm membrane and ultracentrifugated at 100,000 x g, 20 °C, 15 min (Beckman XL-70); supernatant
were collected; iii) Ultrafiltration method using Amicon® Ultra (50 kDa mol. wt. cut-off); samples (0.6
mL) were added to filter unit followed by centrifugation (Centrifuge 5430R) at 7,000 x g, 25 °C, 20
min; ultrafiltrated were collected. All samples collected were assayed in HPLC with electrochemical
detector. EE was calculated from difference between the concentrations of LA quantified in
nanodispersion before and after the procedures. Results: EE assessed by size exclusion
chromatography, filtration-ultracentrifugation and ultrafiltration, presented an average of: 44.08 %
(±31.59); 32.19 % (±0.03) and 73.48 % (±9.4), respectively. The same samples of liquid crystalline
phase nanodispersion, presented different EE values for LA, because ultrafiltration prevents the
passage of nanoparticles and centrifugal force separates LA not entrapped. Conclusions:
Appropriate EE method is crucial for physicochemical characterization and high performance of
drug delivery system. A successful procedure was developed and applied for liquid crystalline
nanodispersion. Ultrafiltration was showed most adequate and reproducible method, considering the
soft characteristic of system. Acknowledgments: This work was supported by CAPES, CNPq and
Fapesp, Brazil.