Simultaneous Determination of Hydrochlorothiazide and Losartan Potassium in Osmotic Pump Tablets by Microemulsion Liquid Chromatography.

A rapid and efficient oil-in-water microemulsion liquid chromatographic (MELC) method has been optimized and validated for the determination of hydrochlorothiazide (HCT) and losartan potassium (LOP) in osmotic pump tablets. Samples were injected into a C18 (150 mm × 4.6 mm ID, 5 µm particle size) analytical column, which was maintained at 30°C. The most effective MELC system had a mobile phase consisting of 95% (v/v) of 3.0% (w/w) SDS, 6.0% (w/w) n-butanol, 0.8% (w/w) n-octane, 90.2% (w/w) water and 5% (v/v) acetonitrile (pH 5). The flow rate was 1.0 mL min(-1) and UV detection was performed at 265 nm. Linearity ranged from 2.5 to 12.5 µg mL(-1) for HCT and 10.0-60.0 µg mL(-1) for LOP (r > 0.999 for both drugs). The proposed method was rapid, precise (RSDs < 1.4%) and accurate (98.9% recovery for HCT and 101% recovery for LOP). It is applicable to simultaneous determination of HCT and LOP in osmotic pump tablets.

Determination of drug lipophilicity by phosphatidylcholine-modified microemulsion high-performance liquid chromatography.

A new biomembrane-mimetic liquid chromatographic method using a C8 stationary phase and phosphatidylcholine-modified (PC-modified) microemulsion mobile phase was used to estimate unionized and ionized drugs lipophilicity expressed as an n-octanol/water partition coefficient (logP and logD). The introduction of PC into sodium dodecyl sulfate (SDS) microemulsion yielded a good correlation between logk and logD (R(2)=0.8). The optimal composition of the PC-modified microemulsion liquid chromatography (PC-modified MELC) mobile phase was 0.2% PC-3.0% SDS-6.0% n-butanol-0.8% ethyl acetate-90.0% water (pH 7.0) for neutral and ionized molecules. The interactions between the analytes and system described by this chromatographic method is more similar to biological membrane than the n-octanol/water partition system. The result in this paper suggests that PC-modified MELC can serve as a possible alternative to the shake-flask method for high-throughput unionized and ionized drugs lipophilicity determination and simulation of biological processes.

Optimization of liquid chromatographic method for the separation of nine hydrophilic and hydrophobic components in Salviae miltiorrhizae Radix et Rhizoma (Danshen) using microemulsion as eluent.

In this study, we have proposed and developed a novel, environmental-friendly and simple method for separation of nine hydrophilic and hydrophobic components in Danshen using microemulsion liquid chromatography. The proposed method was optimized via the preliminary screening experiment and the experimental design. The following factors were investigated in preliminary screening experiment: pH of mobile phase, column type, the nature of surfactant, the nature of oil phase and additives. In order to simultaneously optimize resolution and analysis time, the chromatographic optimization function (COF) was adopted to evaluate chromatograms. The central composite design (CCD) was used to create the matrix of experiments for mapping the chromatographic response surface. Finally, the COF values were fitted into a second order polynomial model and the response surface methodology (RSM) was employed to find the optimal eluent constituents. The reliability of the established model was confirmed by the good agreement obtained between experimental data and predictive values. Based on the results from the preliminary screening experiment and the CCD optimization, the optimal mobile phase was identified as a solution consisting of 6.68% (w/w) polyoxyethylene lauryl ether (Brij35), 0.84% (w/w) cyclohexane, 6.92% (w/w) n-butanol, 85.56% (w/w) phosphate buffer (pH 6.60) and 8mM cetyltrimethyl ammonium bromide (CTAB).

[Simultaneous determination of five cold medicine ingredients in paracetamol triprolidine hydrochloride and pseudoephedrine hydrochloride tablets by pH/organic solvent double-gradient high performance liquid chromatography].

A pH/organic solvent double-gradient mode in reversed-phase high performance liquid chromatography (HPLC) has been established as a new approach to the simultaneous determination of acetaminophen, caffeine, salicylamide, pseudoephedrine hydrochloride and triprolidine hydrochloride in paracetamol triprolidine hydrochloride and pseudoephedrine hydrochloride tablets. Through the optimization of the organic solvent gradient mode and pH/organic solvent double-gradient mode, the optimum double-gradient HPLC system of the five cold medicine ingredients has been built. The determination was carried out on a Diamonsiol C18 column (250 mm x 4.6 mm, 5 microm). The mobile phase consisted of methanol, 0.05 mol/L ammonium acetate solution and 0.08 mol/L acetic acid solution. The column temperature was set at 30 degrees C. The flow rate was 1.0 mL/min. The sample was measured at multiple wavelengths: 0-6 min, 280 nm; 6-7 min, 257 nm; 7-14 min, 280 nm; 14 min, 233 nm. The separation of the five cold medicine ingredients in the tablets was achieved in 25.5 min. The linear ranges of acetaminophen, pseudoephedrine hydrochloride, caffeine, salicylamide and triprolidine hydrochloride were 0.055 -0.998 g/L, 0.053-0.946 g/L, 0.007-0.129 g/L, 0.035-0.622 g/L and 0.002-0.039 g/L, respectively, with their correlation coefficients greater than 0.999 0. The detection limits (S/N = 3) were 0.09, 6, 0.02, 0.128 and 0.02 mg/L, respectively. Their mean recoveries were 97.9%-102.8%. The advantage of the method is the simultaneous determination of acidic, neutral and basic compounds. It also can improve the column efficiency of the analyte, compress the half-peak width and reduce the trailing. The optimized and validated method can be used for the simultaneous determination of the five cold medicine ingredients in the tablets.