Molecular parameters and retention characteristics of unsubstituted polyaromatic hydrocarbons in HPLC

Summary The present research studies the possibility of using the correlation dependence between molecular parameters of unsubstituted polyaromatic hydrocarbons (PAH) and their retention in reversed-phase liquid chromatography to optimize the conditions for the separation and identification of unknown peaks on the chromatograms of multicomponent mixtures. A linear correlation equation, that takes the number and environment of the carbon atom in the PAH molecule into account as well as the differences in the specific interactions of isomeric molecules with polar eluent, has been proposed. The adequacy of the proposed PAH retention model was verified by comparing the calculated retention values with the experimental data. The possibility of identifying unsubstituted PAH according to the number of carbon atoms of various types and according to the values of the molecules lengths (calculated on the basis of the retention of these substances under different eluent compositions) was exemplified by various chromatographic systems (reversed phase-eluent-PAH molecules).     

Evaluation of polycyclic aromatic hydrocarbons in gasoline by HPLC and GC-MS

Summary In this paper the evaluation of polycyclic aromatic hydrocarbons (PAHs) in gasoline is described. A procedure involving a double extraction of samples with N-methylpirrolidone-water-phosphoric acid and with cyclohexane has been used followed by HPLC-DAD and GC-MS. The results obtained show that all gasoline samples contain PAHs with two to six rings and no substantial difference was noticed between leaded and unleaded gasoline. The benzo(a)-pyrene content ranged between 1.0–2.0 mg L⁻¹, a comparatively high concentration for a dangerous compound.     

HPLC determination of the aromatic fraction of gasoline

Summary This work reports a rapid and easy procedure for the analysis of the aromatic fraction in gasoline. No sample pretreatment is required, since the gasoline is diluted in methanol and directly injected into a liquid chromatograph. A spectrophotometer detector and a spectrofluorimeter detector are used in series. The procedure has been applied to a large number of Italian and European refined gasoline samples.Dedicated to Prof. Dr. A. Liberti on the occasion of his 70th birthday.     

HPLC on pentalfuoroanilinopropyl silica gel

Summary The preparation of a new pentafluoroanilino-phase for HPLC is described. The retention times (t_r) of about twenty aromatic hydrocarbons have been determinated. It has been shown that the aromatics were eluted according to the number of rings. The influence of water content in the mobile phase is commented.     

Survey of concentration of polycyclic aromatic hydrocarbons in lake balaton by HPLC with fluorescence detection

Summary Concentrations of polycyclic aromatic hydrocarbons (PAHs) were determined in water and sediment samples at 15 sites in Lake Balaton during three sampling campaigns in 1996. PAHs were concentrated from water samples by solid phase extraction. Sediment samples were extracted with acetone in an ultrasonic bath then cleaned by solid phase extraction. The total concentration of PAHs ranged from 30–360 ng g⁻¹ and from 170–720 ng L⁻¹ in sediment and water samples, respectively. Spatial and temporal variations of the concentration of PAHs were also investigated. Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997.     

Quantitative analysis of mebeverine in dosage forms by HPLC

Summary A simple and rapid, high performance liquid chromatographic (HPLC) procedure for determination of mebeverine in dosage forms (tablet and liquid) is described. Reversed-Phase chromatography was carried out using a mobile phase containing 0.05 M ammonium acetate buffer and acetonitrile, [(45%, v/v) pH 5.2] with UV-detection (263 nm). Replicate regression analyses of three standard plots in the concentration range of 0.5–10 mcg mL⁻¹ obtained on three different days gave a correlation coefficient >0.9995 and the coefficient of variation of the slopes <2.2%. The assay was precise within day and between days as indicated by ANOVA test. The recoveries from 10 replicate tablets of two commercial mebeverine brands and liquid were in order 99.3, 100.5 and 100.1% of the label amount and their coefficient of variations were 1.41, 0.89 and 0.69%, respectively. The limit of quantitation of mebeverine was 5 ng mL⁻¹.     

Separation of urea and other polar compounds by HPLC

Summary Urea, glycolic and aminoxyacetic acid amides are the polar metabolites of 2-acetyl-3-phenyl-tetrahydro-1,2,4-oxadiazin-5-one (RGH 4615). They cannot be separated on octadecyl-, cyanosilyl- or amino-phase columns, but silica, used with C₃-C₄ alcohol and water mixtures as the eluent permits their separation. Besides refractive index detection and on-line radioactivity measurement the metabolic formation of¹⁴C-urea was proved by enzymatic cleavage into¹⁴CO₂.     

The use of large polycyclic aromatic hydrocarbons to study retention in non-aqueous reversed-phase HPLC

Summary Elution strengths of 11 common HPLC solvents on a polymeric C₁₈ phase were compared using a marker set of polycyclic aromatic hydrocarbons. Naphthalene, pyrene, benzo[ghi]perylene, and three larger naphthologues of 8, 10, and 12 rings (constituting a naphthalene zigzag series) were chosen because they span the solvent strength range up to and including the strongest solvents, tetrahydrofuran (THF) and chlorobenzene. Four pairs of similarly shaped isomers were used to probe solvent selectivity. With the exception of THF, HPLC solvent strength correlated with observed red shifts of fluorescence band maxima in each solvent. For THF, the pure solvent and blended mixtures behaved quite differently.     

Quantitative determination of lansoprazole in human serum by HPLC

Summary Lansoprazole is a new inhibitor of gastric proton secretion. An HPLC method for the quantitative determination of lansoprazole in serum is described. The method consists of liquid-liquid extraction and enrichment of the analyte and subsequent reverse-phase liquid chromatography with UV detection. The method is specific, sensitive and practical. It has been applied to serum from healthy volunteers. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

Simultaneous assay of platelet and plasma catecholamines by HPLC with coulometric detection

Summary Platelets and monoaminergic neurons share many morphological, biochemical, and pharmacological properties. In addition to its similarities to serotonergic nerve endings, the platelet has also been considered a good model for the study of the noradrenergic function, since it can selectively take up, store, and release norepinephrine (NE).In this study platelet and plasma levels of free catecholamines (CA) in 20 healthy subjects have been determined by HPLC with a reversed phase (C₁₈) ionpairing system equipped with a coulometric detector. Direct correlation was observed between platelet and plasma levels of NE. A positive correlation was also found between the age of the sujects and both platelet and plasma NE levels.While showing that the peripheral noradrenergic hyperactivity of the elderly is also reflected in platelet NE content, this study also demonstrates that simultaneous assay of platelet and plasma CAs can be a useful tool for an integrated and more complete evaluation of sympathetic nervous system activity.     

Modified polystyrene,stationary phases for the separation of different aromatic hydrocarbon types by HPLC

Summary One possible method of characterizing chemicall-modified stationary phases is to describe their chromatographic properties. In this study we investigated several chemically-modifiedpolystyrene-divinylbenzene packings for the separation of nitroarenes, polycyclic aromatic hydrocarbons and aminosubstituted aromatic hydrocarbons. Chromatography was carried out on commercially available polymer stationary phases, for example C-18 or vinylpyridine modified polystyrene. In addition, a chemically-immobilized polymer packing was prepared by introducing nitrogroups, which were established by elemental analysis and infrared spectroscopy.     

Polypyrrole-coated silica as a new stationary phase for liquid chromatography

Summary Polypyrrole chloride and polypyrrole dodecylsulfate coated-silica packing materials have been synthesized. Reverse-phase chromtographuy was employed to characterise both packings. A series of test compounds with known properties was used as molecular probes. They included benzene and derivatives, basic drugs, and polyaromatic hydrocarbons. A commericial C₁₈ column was also used for the purpose of comparison in some cases.     

Resolution of enantiomers by HPLC on cellulose derivatives

Summary Various polysaccharide derivatives, particularly cellulose derivatives, were synthesized and used as chiral stationary phases for optical resolution by HPLC after being adsorbed on macroporous silica gel. Cellulose triacetate (CTA-II), which was synthesized under homogeneous conditions, showed a chiral recognition ability for many racemates. Other cellulose derivatives such as cellulose tribenzoate (OB), cellulose-trisphenylcarbamate (OC), cellulose tribenzyl ether (OE), and cellulose tricinnamate (OK) also showed unique chiral recognition. Among other polysaccharide derivatives, curdlan triacetate was also exhibited an effective chiral recognition. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

Use of a keeper to enhance the recovery of volatile polycyclic aromatic hydrocarbons in HPLC analysis

Summary The recorveries of volatile polycyclic aromatic hydrocarbons in HPLC analysis may be enhanced if a long-chain alcohol, e.g. 1-hexanol or 1-octanol, is used as keeper in the solvent-evaporation step. Even under the harsh conditions of the vacuum-concentrator centrifuge, recoveries of more than 90% were achieved for 14 of the 15 PAH tested. The use of liquid-liquid extraction (LLE) eliminates the problem of adsorption of highly condensed aromatics by the wall of the sampling bottle. The combination of LLE with vacuum-controlled rotary evaporation and use of a keeper yielded overall recoveries between 50 and 130%, for most substances close to 100%, from tap water spiked with trace concentrations. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

Quantitation of cortico-steroids as common adulterants in local drugs by HPLC

Summary A sensitive and specific method for quantitation of the steroids betamethasone, prednisolone and cortisone acetate commonly used as adulterants in locally produced herb extracts and in certain homeopathic drugs is described. Reverse-phase liquid chromatography with UV detection has been used.     

Quantitation of 1,2 and 1,4-naphthoquinone in phthalic anhydride by HPLC

Summary A simple method of analysis of the 1,2 and 1,4 isomers of naphthoquinone in crude phthalic anhydride has been developed. The sample was first dissolved in water at 60°C to quantitatively hydrolyse the anhydride to phthalic acid.Analysis of the aqueous solution by reversed-phase HPLC using 7525 methanol:water mobile phase resulted in excellent resolution between the phthalic acid and the naphthoquinones and enabled quantitative measurement of each of the naphthoquinones to 0.1 % in crude phthalic anhydride.     

Determination of grepafloxacin in plasma samples by HPLC: Application to clinical pharmacokinetic studies

Summary A sensitive HPLC assay for the determination of grepafloxacin (GRE) in biological samples is described. Sample preparations were carried out by adding phosphate buffer (pH 7.4, 0.1M), followed by extraction with trichloromethane. GRE and the internal standard, enrofloxacin (ENR), were separated on a reversed-phase column using an aqueous phosphate solution-acetonitrile (78∶22) mobile phase. The concentrations of ENR and GRE eluting of the column with retention times of 2.55, and 4.90 min, respectively were monitored by fluorescence atλ _ex 338 andλ _em 425 nm. The method was shown to be linear from 5 to 4000 ng mL⁻¹. The detection and quantitation limits were 5 and 10 ng mL⁻¹, respectively. Mean recovery was determined as 90%. Inter- and intra-assay precisions were 3.0% and 3.5% respectively. The method was applied to the determination of GRE in plasma samples collected during clinical pharmacokinetic studies.