Development and validation of a liquid chromatographic method for the determination of ascorbic acid, dehydroascorbic acid and acetaminophen in pharmaceuticals

A reversed-phase ion pair liquid chromatographic method (RP-LC) for the determination of dehydroascorbic acid (DHA) and ascorbic acid (AA) and also acetaminophen, which is combined in pharmaceuticals, is proposed and validated. AA and acetaminophen were analyzed directly, while DHA was determined after pre-column derivatization with 4,5-dimethyl-1,2-phenylenediamine (DMPD). The derivatization reaction was carried out under mild conditions (10min at ambient temperature) in the dark in sodium acetate buffer (80mM; pH 3.7) solution containing EDTA as metal scavenger. The chromatographic separations were performed on a Phenomenex Synergi 4u hydro-RP (150mmx4.6mm) under isocratic elution conditions, using cetyltrimethylammonium bromide (CTAB) as ion-pairing reagent in the mobile phase. Linear responses were observed for each compound. The intra-day precision (R.S.D.) was < or =1.40% and there was no significant difference between intra- and inter-day data. Recovery studies showed good results for all compounds (99.7-101.8%) with R.S.D. ranging from 0.56 to 1.82%. The limits of quantitation were about 40, 50 and 140pmol for acetaminophen, AA and DHA, respectively. The DHA impurity values found in dosage forms were < or =0.2% of AA.

Development and validation of a liquid chromatographic method for the determination of branched-chain amino acids in new dosage forms

A reversed-phase liquid chromatographic method (RP-LC) is proposed and validated for the analysis of branched-chain amino acids (l-leucine, l-isoleucine and l-valine) in new pharmaceutical formulations. The pre-column derivatization reaction of these amino acids with 2,4-dinitrofluorobenzene (DNFB) has been investigated considering the matrix effect. The compound reacts at 60 degrees C for 10 min at pH 9 with the amino function, in presence of cetyltrimethylammonium bromide (CTAB), to give adducts that have been separated on a RP amide C16 column and detected at lambda=360 nm. Linear responses were observed for each derivative. The intra-day precision (R.S.D.) was <or=2.22% and there was no significant difference between intra- and inter-day data. Recovery studies showed good results for all amino acids (98.9-100.9%) with R.S.D. ranging from 0.1% to 0.8%. The limit of quantitation was about 20 nmol/mL.

HPLC-fluorescence determination of amino acids in pharmaceuticals after pre-column derivatization with phanquinone

4,7-Phenanthroline-5,6-dione (phanquinone) was used as a fluorogenic labeling reagent in pre-column derivatization for the quality control of amino acids in pharmaceuticals. The amino acid adducts were efficiently separated by C12 RP high-performance liquid chromatography (HPLC) using a ternary mixture of triethylamine (TEA) phosphate buffer (pH 2.5, 0.05 M)-methanol- tetrahydrofuran (THF) as mobile phase by varying composition gradient elution and detected fluorometrically. The results obtained by the proposed method were compared statistically, by means of the Student's t-test and the variance ratio F-test, with those obtained by a rapid reference method, which involved o-phthaldialdehyde (OPA) as pre-column reagent; no significant difference was found. The stronger derivatization conditions (60 degrees C, pH 8, 60 min) required for the method with phanquinone are compensated by the major stability of derivatives and by the absence of fluorescent degradation products.