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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 (OVA-MP) 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 tha 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.

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