Dichloromethane Evaporative Behavior during the Solidifying Process of Ovalbumin-Loaded Poly (DL Lactic-co-Glycolic Acid) Microparticles
JIIN-LONG CHEN1, MING-KUNG YEH2 AND CHIAO-HSI CHIANG1*
1. School of Pharmacy, National Defense Medical Center, Neihu, P.O. BOX 90048-508, Taipei City 114, Taiwan, R.O.C.
2. Department of Clinical Pharmacy, Tri-Service General Hospital, National Defense Medical Center, National Defense University, Taipei City 114, Taiwan, R.O.C.
(Received: February 13, 2004; Accepted: July 23, 2004)
ABSTRACT
The purpose of this study is to develop an analytical method for determining the evaporative behavior of dichloromethane (DCM) during the solidifying process of poly(DL lactic-co-glycolic acid) (PLGA) in the preparation of ovalbumin-loaded microparticle (OVAMP) with double emulsion solvent extraction method. The time courses of DCM levels in the external phase and total mixture were determined by a gas chromatography (GC) method combined a headspace sampler. Samples were spiked with an internal standard carbon tetrachloride, prior to mixing with a large volume of chloroform. The retention times of carbon tetrachloride, DCM and chloroform were 2.6, 2.8 and 3.3 min, respectively. The analytical method had a minimum quantitative concentration of DCM 7.3 mM and good linearity from 7.5 to 75 mM with coefficient of variations 1.2~3.9%. Four formulations containing NaCl (0~5%) and urea, an osmotic agent to adjust osmolarity at 1240 mOsm/kg, were investigated. The disappearance of DCM levels in total mixtures of four formulations were described as a function of time by zero-order (0~15 min) and first-order (after 15 min) kinetics. During the initial 15 min, these formulations had almost identical zero-order rate constants, 2.30~2.63 mmole/min. After 15 min, formulation with 5% NaCl (F4) showed a significant lower value of rate constant (0.193 min-1) in comparison with other formulations using the lower amounts of NaCl (0.288~0.367 min-1). It indicated that the surface characteristic of the F4 OVA-MP was different from other formulations by forming a crust-like structure to inhibit the efflux of DCM from the inner layer. In conclusion, we established a rapid and convenient GC approach without the need for sample pre-treatment for determining DCM levels during the solidifying process of microparticles. The analytical method could be applied to further assess the relationship between DCM level and formulation factors of drug-loaded microparticles.
Key words: PLGA, gas chromatography, salt effect, dichloromethane evaporation