Simultaneous analysis of Vitamins A and E in infant milk-based formulae by normal-phase high-performance liquid chromatography-diode array detection using a short narrow-bore column

A rapid, simple and reproducible normal-phase (NP) high-performance liquid chromatography (HPLC)-diode array detection (DAD) method for simultaneous qualitative and quantitative determination of Vitamin A (retinol acetate and retinol palmitate) and Vitamin E (alpha-tocopherol acetate, alpha-, gamma- and delta-tocopherols) in milk-based infant formulae was developed and validated. The preparation sample was based on protein precipitation and vitamin extraction with ethanol, followed by re-extraction with hexane, while the chromatographic method was based on the use of a short narrow-bore column (50 mm x 2.1 mm; 3 microm particle size), which afforded less solvent consumption and higher mass sensitivity. The method showed acceptable values for precision, recovery and sensitivity, and proved very simple for routine analysis work.

Determination of the hydrophobicity of local anesthetic agents

Hydrophobicity, a term used to describe a fundamental physicochemical property of local anesthetics, was in the past obtained by octanol/buffer partitioning. It has been suggested that the octanol method, despite its obvious advantages, also has some drawbacks. HPLC has become an attractive alternative for the measurement of hydrophobicity and has been applied to local anesthetics recently. However, the methods in current use for measuring the hydrophobicity of local anesthetics suffer from a number of limitations and remain obscure. This study introduces a new HPLC method for measuring the hydrophobicity of eight local anesthetics in current clinical use. Using a C(18) derivatized polystyrene-divinylbenzene stationary phase HPLC column, the log k'(w) values of local anesthetics were determined by measuring the capacity factor k'(i) in the process of chromatographic separation using a hydrophobic stationary phase and a hydrophilic mobile phase. A rapid reversed-phase HPLC method was developed to directly measure log k'(w) of eight local anesthetics. A high correlation between log k'(w) and hydrophobicity (log P(oct)) from the traditional shake-flask method was obtained for the local anesthetics, demonstrating the reliability of the method. The results reveal an improved method for measuring the hydrophobicity of the local anesthetic agents in the unionized form. This simple, sensitive and reproducible approach may serve as a valuable tool for describing the physicochemical properties of novel local anesthetics.

Reversed-phase liquid chromatography with microspherical octadecyl-zirconia bonded stationary phases

Microspherical zirconia particles were synthesized and surface modified with octadecylsilane compounds for reversed-phase high-performance liquid chromatography. Monomeric and "polymeric" octadecyl-zirconia bonded stationary phases were obtained by reacting the support with octadecyldimethylchlorosilane or octadecyltrichlorosilane, respectively. The surface coverage of the zirconia-based stationary phases with octadecyl functions was approximately the same as that of octadecyl-silica sorbents. These phases were evaluated in terms of reversed-phase chromatographic properties with non-polar, slightly polar and ionic species over a wide range of mobile phase composition and pH. Monomeric octadecyl-zirconia with end-capping exhibited some metallic interactions with both basic and acidic solutes, but these interactions were greatly reduced in the presence of competing agents (e.g., tartrate ions) in the mobile phase. The "polymeric" octadecyl-zirconia sorbents exhibited higher retention than the monomeric ones with the various solutes investigated, and their residual absorptivities toward acidic solutes were much lower. The retention of non-polar and slightly polar aromatic compounds was quasi-homoenergetic on both types of octadecyl-zirconia stationary phases. Stability studies conducted at extreme pH conditions (pH 2.0 and pH 12.0), have shown that "polymeric" octadecyl-zirconia sorbents are more stable than their monomeric counterparts. These stationary phases were quite useful in the separation of polycyclic aromatic hydrocarbons, alkylbenzene and phenyl alkylalcohol homologous series, oligosaccharides, dansyl-amino acids, peptides and proteins.

Chromatographic analysis of antituberculosis drugs in biological samples

Numerous chromatographic and non-chromatographic methods of analysis for anti-tuberculosis drugs and metabolites in biological tissues have been discussed in this review. Depending upon the analytical methodology selected, limits of detection range from microgram to picogram levels. A number of examples have been given of the correlation between different types of assay procedures. The metabolism and pharmacokinetics have been described along with some of the commonly associated problems of sample collection and storage.

Improved high-pressure liquid chromatographic method for the analysis of erythromycin in solid dosage forms

A stability-indicating high-pressure liquid chromatographic (HPLC) method for the assay of erythromycin in enteric film-coated tablets was developed. The method used a reversed-phase column at 70 degrees with a mobile phase of acetonitrile-methanol-0.2 M ammonium acetate-water (45:10:10:35) at pH 7.0. The column were evaluated for the analysis of erythromycin. The HPLC method was also applicable for the analysis of salts and esters of erythromycin. The linearity and precision of the HPLC assay method for erythromycin in the solid dosage form were examined by spiking erythromycin into a tablet placebo a 60-120% of the label. The recovery of erythromycin was 99.9% with a relative standard deviation of less than 1%. The correction factors to express the results of HPLC in terms of antimicrobial bioequivalency against Staphylococcus aureus TCC 6538P for erythromycins A, B, and C were determined to be 1.0, 0.92, and 0.48, respectively. Eight lots of tablets were assayed by the HPLC method, and the results, expressed in terms of erythromycin bioequivalency, showed no statistically significant difference from those of the microbiological assay method.

High-performance liquid chromatographic determination of hydrocortisone cypionate: method development and characterization of chromatographic behavior

A reversed-phase high-performance liquid chromatographic method for hydrocortisone cypionate bulk drug and oral solution was developed that avoids the use of a heated column as described in USP XX. A study of the effect of the organic modifier concentration on the capacity factor suggests that mixed partition and adsorption phenomena are responsible for the retention of several steroids when acetonitrile is used in the mobile phase. Evidence is presented that hydrogen bonding of the solute molecule with silane hydroxyl groups may be responsible for the adsorption.