The determination of oxalic acid, oxamic acid, and oxamide in a drug substance by ion-exclusion chromatography

Determination of ferric iron chelators by high-performance liquid chromatography using luminol chemiluminescence detection

Iron is an essential element for higher plants, and its acquisition and transportation is one of the greatest limiting factors for plant growth because of its low solubility in normal soil pHs. Higher plants biosynthesize ferric iron [Fe(III)] chelator (FIC), which solubilizes the iron and transports it to the rhizosphere. A high-performance liquid chromatography (HPLC) post-column method has been developed for the analysis of FICs using the luminol/H2O2 system for chemiluminescence (CL) detection. A size-exclusion column was the most suited in terms of column efficiency and CL detection efficiency. Mixing of the luminol with H2O2 in a post-column reaction was feasible, and a two-pump system was used to separately deliver the luminol and H2O2 solutions. The luminol and H2O2 concentrations were optimized using Fe(III)-EDTA and Fe(III)-citrate (Cit) solutions as analytes. A strong CL intensity was obtained for Fe(III)-Cit when EDTA was added to the luminol solution, probably because of an exchange of Cit with EDTA after separation on the HPLC column; CL efficiency was much higher for Fe(III)-EDTA than for Fe(III)-Cit with the luminol/H2O2 system. The present method can detect minute levels of Fe(III)-FICs; the detection limits of Fe(III)-EDTA, Fe(III)-Cit and Fe(III)-nicotianamine were 0.77, 2.3 and 1.1pmol, respectively.

Graphene-supported PtPd Bimetallic Gathered Nanocrystals for Non-enzymatic Sensing of Oxalic Acid

A novel non-enzymatic oxalic acid (OA) sensor was developed using a nanocrystal PtPd loaded reduced graphene nanosheets (PtPdNCs/RGO)-modified electrode. PtPdNCs/RGO were successfully achieved by a facile, one-step and template-free method, in which PtPd nanoparticles with 100 nm-scale were assembled from polyhedral PtPd nanocrystals of various shapes and dispersed on the graphene nanosheets. Resulting PtPdNCs/RGO were characterized and used for PtPdNCs/RGO-modified electrodes. Electrochemical oxidation of OA on the modified electrode was investigated by cyclic voltammetry and differential pulse voltammetry (DPV). Well-defined peaks of OA oxidation could be obtained using an electrode that indicated its high electrochemical activity. The concentration of OA and the current responses could be obtained in the ranges of 0.5 - 10 and 10 - 35 mM with correlation coefficients of 0.9994 and 0.9952; the detection limit (S/N = 3) was found to be 0.05 mM. The modified electrode presented good characteristics in terms of both stability and reproducibility, promising its applicability in practical analysis.

High-performance liquid chromatography method for ferric iron chelators using a post-column reaction with Calcein Blue

Iron (Fe) is an essential element for higher plants, which take it up from the soil at the root surface and transport it to shoots through the xylem. Fe(III) chelators, such as organic acids and phytosiderophores, play important roles in the acquisition and transportation of Fe(III). Therefore, a selective and sensitive method for analyzing Fe(III) chelators is required to study the many Fe-related physiological mechanisms in plants. A novel analytical approach employing a high-performance liquid chromatography post-column method with fluorescence detection was developed to separate and detect Fe(III) chelators. This method takes advantage of the quenching of the fluorescence of Calcein Blue (CB) that occurs with the formation of an Fe(III)-CB complex and the dequenching that occurs with the release of CB as a result of competition for Fe(III) between CB and an Fe(III) chelator. This simple experimental method does not require complicated pretreatments and can selectively detect Fe(III) chelators according to their Fe(III)-chelating ability. The detection limit for citric acid using this method was 72pmol. Furthermore, this method can also detect unknown Fe(III) chelators that exhibit a high affinity for Fe(III). The method was evaluated with xylem sap of barley, which was shown to contain several Fe(III) chelators.

A novel ion-pair RP-HPLC method for determination of five components in compound α-ketoacid tablets

A sensitive and reliable ion-pair reversed-phase high-performance liquid chromatographic (RP-HPLC) method has been developed and validated for the simultaneous determination of D,L-α-hydroxymethionine calcium (HMACa), D,L-α-ketoisoleucine calcium (KILCa), α-ketovaline calcium (KVCa), α-ketoleucine calcium (KLCa) and α-ketophenylalanine calcium (KPACa) in the compound α-ketoacid tablets using tetrabutylammonium hydroxide as an ion-pair reagent. The analytes were separated on a C(18) column (250 mm × 4.6 mm, 5 μm) with the mobile phase of methanol-potassium dihydrogen phosphate buffer (pH 3.0; 50mM) (37:63, v/v) at a flow rate of 0.6 mL min(-1). The UV detection wavelength was set at 210 nm. Good linearity with correlation coefficients larger than 0.9990 (n=6) for all analytes were achieved. The average recoveries were within the range of 99.6-100.9%, and the RSDs of the results were within the acceptable limit of 2.0%, which showed that this method was accurate and precise. The limits of detection were 10.44, 5.94, 3.44, 3.60 and 1.63 ng mL(-1), and the limits of quantification were 34.80, 19.80, 10.32, 12.00 and 5.44 ng mL(-1) for HMACa, KILCa, KVCa, KLCa and KPACa, respectively. The method is simple and accurate for quality control of the compound α-ketoacid tablets.

Pharmacokinetics and metabolism of UK-383,367 in rats and dogs: A rationale for long-lived plasma radioactivity

UK-383,367 (5-{(1R)-4-cyclohexyl-1-[2-(hydroxyamino)-2-oxoethyl]butyl}-1,2,4-oxadiazole-3-carboxamide) is a novel procollagen C-proteinase inhibitor evaluated for the treatment of post-surgical dermal scarring. It is extensively metabolized in rat and dog absorption, distribution, metabolism and excretion studies, and a metabolic pathway for UK-383,367 was determined. A long-lived metabolite was identified in dog plasma. Data indicate that this metabolite results from the oxadiazole ring-cleavage-producing oxamic acid, oxamide and oxalic acid. Ion exclusion chromatography was used to identify these polar metabolites, which were unretained on a standard reversed-phase high-performance liquid chromatography system. The oxamide metabolite was identified as the long-lived radioactivity, which was observed in dog plasma.

Cathodic adsorptive stripping voltammetric determination of muscle relaxant: gallamine triethiodide (flaxedil)

A sensitive and simple voltammetric method of analysis is developed for the determination of trace amounts of gallamine triethiode in phosphate media. This method is based on controlled adsorptive preconcentration of the relaxant onto a Hanging Mercury Drop Electrode (HMDE) whereby mercurous iodide salt(s) are formed. The technique used is Cathodic Linear Sweep Stripping Voltammetry (CLSSV). The adsorptive response was evaluated with respect to preconcentration time and potential. As little as 3 x 10(-9) mol dm(-3) i.e. 2.7 ppb flaxedil (proconcentration time 300 seconds) can be determined successfully. The application of this method was tested in the determination of flaxedil in pharmaceutical preparation (ampoules).

Hydrophilic interaction chromatography using amino and silica columns for the determination of polar pharmaceuticals and impurities

Hydrophilic interaction chromatography (HILIC) is described as a useful alternative to reversed-phase chromatography for applications involving polar compounds. In the HILIC mode, an aqueous-organic mobile phase is used with a polar stationary phase to provide normal-phase retention behavior. Silica and amino columns with aqueous-acetonitrile mobile phases offer potential for use in the HILIC mode. An examination of the retention and separation of several pyrimidines, purines, and amides on silica and amino columns from three manufacturers revealed that mobile phases should contain a buffer or acid for pH control to achieve similar and reproducible results among columns from different sources. Amino columns may also be used in an anion-exchange mode, which provides an advantage for some applications. In some cases, silica can provide different selectivity and better separation than an amino column. Example applications include: low-molecular-mass organic acids and amides as impurities in non-polar drug substances, 5-fluorouracil in 5-fluorocytosine, guanine in acyclovir, and different selectivity for polar basic compounds compared to an ion-pairing system.