A rapid reverse phase liquid chromatographic method was developed for the determination of levodopa and levodopa-carbidopa in tablets and capsules. The method also separates these drugs from 3-(3,4,6- trihydroxyphenyl)alanine and methoxytyrosine, impurities of levodopa, and from methyldopa and 3-O-methylcarbidopa, impurities of carbidopa. The mobile phase was 3% acetic acid and the detection wavelength was 280 nm. The method was linear over the concentration range 0.05-0.40 mg levodopa/mL, 0.01-0.06 mg carbidopa/mL, 0.9- 12.8 μg 3-(3,4,6-trihydroxyphenyl)alanine/mL, 0.7-3.1 μg methyldopa/ mL, 5-20 μg methoxytyrosine/mL, and 0.5-3.3 μg 3-O-methylcarbidopa/ mL. Mean recoveries (%) for spiked commercial tablets were: levodopa 100.3, carbidopa 100.4, 3-(3,4,6-trihydroxyphenyl) alanine 99.1, methoxytyrosine 100.0, methyldopa 100.0, and 3-O-methylcarbidopa 99.4.
A simple and rapid reverse-phase liquid chromatographic method was developed for the qualitative and quantitative analysis of 13 cephalosporin compounds. A mixture of cefaclor, cefadroxil, cefamandole nafate, cefamandole sodium, cefazolin, cefoperazone, cefotaxime, cefoxitin, ceftizoxime, cephalothin, cephalexin, cephapirin, and cephradine was resolved into its components in raw material and dosage form samples by using a Clg column, a methanol-water-acetic acid (30 + 70 + 0.1) mobile phase, and a UV detector set at 254 nm. The proposed method is suited both for the determination of cephalosporins in a wide variety of commercial dosage forms and for the investigation of related compounds and other impurities in samples of 7 of the cephalosporins
A liquid chromatographic method for the determination of levodopa in tablets and capsules and levodopa-carbidopa in tablets was collaboratively studied by 6 laboratories. Collaborators were supplied with duplicate powdered composites of levodopa (1 synthetic formulation, 1 commercial tablet, and 1 commercial capsule) and levodopa- carbidopa (1 synthetic formulation and 2 commercial tablets), along with individual levodopa-carbidopa tablets for content uniformity determinations. The repeatability coefficient of variation (CV„) and reproducibility coefficient of variation (CV„) for levodopa single component were 0.48 and 0.87%; for levodopa in combination, 0.50 and 0.90%; and for carbidopa, 0.77 and 1.20%, respectively. Overall, the recovery values for levodopa and carbidopa from synthetic formulations simulating tablets were 100.4 and 99.5%, respectively .The pooled CVD„ and CVDX values for the individual tablet assays were 2.07 and 2.30% for levodopa, and 1.80 and 2.24% for carbidopa, respectively. The method has been adopted official first action for determination of the active ingredients in levodopa tablets and capsules and in levodopa-carbidopa tablets and for content uniformity testing in the combination dosage form.
A liquid chromatographic (LC) method, using a reverse phase C18 column, an acetic acid-methanol-water mobile phase, and detection at 280 nm, was developed for the determination of methyldopa in tablets and oral suspensions and combinations of methyldopa with hydrochlorothiazide or chlorothiazide in tablets. A mixture of these 3 drugs was resolved in <8 min. Detector responses were linear for the following amounts (mg/mL) of drug injected: methyldopa 0.031-0.393, chlorothiazide 0.019-0.114, and hydrochlorothiazide 0.004-0.083. Recoveries from commercial dosage forms ranged from 99.1 to 100.9% for methyldopa, 99.2-100.4% for chlorothiazide, and 100.0-101.2% for hydrochlorothiazide. Replicate injections of methyldopa, chlorothiazide, and hydrochlorothiazide standard preparations alone or in combination gave overall relative standard deviations of <1.6% (n = 10). The results for methyldopa tablets by the proposed method were in agreement with those obtained by the USP XX method. The LC method detected as little as 0.6 μg 3-O-methylmethyldopa/mL and 0.5 μg 4-amino-6- chloro-l,3-benzenedisulfonamide/mL, which are sometimes found as contaminants of methyldopa and thiazides, respectively, and resolved methyldopa from its methyldopa glucose adduct, a substance found in methyldopa oral suspensions.
A liquid chromatographic method using a reversed- phase C18 column and octanesulfonic acid sodium salt-methanol as the mobile phase was developed for the simultaneous determination of phenobarbi- tal, scopolamine, and hyoscyamine in tablets. The mixture of the 3 drugs was resolved in <8 min. Detector responses were linear for 10 μL injections of the following: scopolamine hydrobromide, 8.25-206.3 μg/mL; hyoscyamine sulfate, 15.01-750.76 μg/mL; and phenobarbital, 250-751 μg/mL. Recoveries from tablets were 100.8% for scopolamine hydrobromide, 100.1% for hyoscyamine sulfate, and 100.3% for phenobarbital. Replicate injections of scopolamine hydrobromide, hyoscyamine sulfate, and phenobarbital gave an overall relative standard deviation of <1.0% (n = 10). The method detected as little as 3.3 ng scopolamine hydrobromide.
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