4,7-phenanthroline-5,6-dione: A new labelling reagent for liquid chromatographic analysis of amino acids

Chromatography of amino acids and short peptides. New advances

The newest results in the application of various chromatographic methods (gas-liquid chromatography, liquid chromatographic techniques, electrically driven systems) for the separation and quantitative determination of amino acids and short peptides in pure state and in complicated matrices are compiled. The results are concisely described and critically evaluated. The future trends of the chromatographic analysis of amino acids and short peptides are briefly discussed.

2,7-Dimethyl-3,8-dinitrodipyrazolo[1,5-a:1′,5′-d]pyrazine-4,9-dione: A new labelling reagent for liquid chromatographic analysis of amino acids

The use of 2,7-dimethyl-3,8-dinitrodipyrazolo[1,5-a:1',5'-d]pyrazine-4,9-dione as pre-column reagent for LC analysis of amino acids is proposed. The compound reacts (30 min at 68 degrees C in presence of 0.04 M triethylamine in a dimethylsulfoxide-water mixture) with primary and secondary amino function and the stable resulting adducts can be chromatographed under reversed-phase conditions and detected at lambda=280 nm. The derivatization conditions were optimized by a series of experiments. The effect of temperature, triethylamine concentration and reagent on the reaction was investigated. The yield of the glycine derivative was found to be quantitative at a reagent amino acid molar ratio of about 6 by comparison with an authentic specimen of synthesized glycine adduct. Application of the method to quality control of commercially available oral polyaminoacid formulations is described.

Phanquinone as a suitable derivatization reagent in micellar electrokinetic chromatography and HPLC analysis of amino acids

Phanquinone (chemically: 4,7-phenanthroline-5,6-dione) was applied as an original precolumn derivatization reagent for amino acids followed by separation using MEKC with UV detection (240 nm). The derivatization reaction was carried out at 68 degrees C in the presence of aqueous phosphate buffer (pH 8.0) and it was found to be complete after 30 min. Twelve derivatized standard amino acids were separated in about 22 min under MEKC conditions using sodium cholate (250 mM) as the surfactant in phosphate buffer (20 mM, pH 9.0). The developed method was validated for the analysis of D,L-phosphoserine (D,L-p-Ser) and L-glutamine (L-Gln); good linearity (r > 0.999) was achieved in the calibration range of 0.25-2.5 micromol/mL. The sensitivity of the MEKC method (LOD 0.1 micromol/mL; LOQ 0.25 micromol/mL, RSD% <5.0%, n = 3) was found to be adequate for quantitation of amino acids in pharmaceuticals. Quantitative applications of the validated MEKC method were carried out by the analysis of commercially available oral polyaminoacid formulations (tablets and extemporaneous solutions) containing L-Gln and D,L-p-Ser; the obtained results were found to be in agreement with those from a validated reference RP-HPLC method.

LC determination of leuprolide component amino acids in injectable solution by phanquinone pre-column derivatization labelling procedure

A sensitive LC method for the determination of leuprolide acetate component amino acids in injectable solution with fluorogenic pre-column derivatization has been developed. The derivatization reaction with phanquinone was optimised by a series of experiments. Histidine, arginine, serine, tryptophan, glutamic acid, tyrosine, methionine, isoleucine, leucine and phenylalanine were separated on a reversed-phase ODS column using as eluent a binary mixture of triethylammonium phosphate buffer-methanol, under gradient elution conditions. The derivatives were eluted in 30 min with good reproducibility. The hydrolysis reaction of the peptide was carried out at reflux with 12 N hydrochloric acid for 2 h 30 min. The intra-day accuracy of the entire procedure (hydrolysis, derivatization, LC separation) ranged from 80.5 to 109.5% of the nominal concentration of leuprolide acetate and the precision (%R.S.D.) was less than 5.8%; the inter-day accuracy was in the range 81.5-107.2% and corresponding R.S.D. values were less than 4.6%. The detection limits (signal-to-noise ratio=3) for the adducts are 30-800 fmol.

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.