Ion Chromatography Using an Electrochemical Detector: Response to Non-Electroactive Anions

Abstract

The effect of non electroactive anions on the response of glassy carbon electrode used as an electrochemical detector in an ionic chromatographic system with dual column has been investigated and a method to eliminate this anomalous behaviour has been proposed. The results showed that the response of the electrode observed for non electroactive anions is related to the drop in pH of the eluent during the elution of anions.     

The Simultaneous Assay of Naproxen and Salicylic Acid in Serum Using High Pressure Liquid Chromatography

Abstract

A rapid, sensitive, reverse-phase high pressure liquid chromatographic assay was developed for the simultaneous determination of naproxen and salicylic acid. These compounds are extracted from serum and then separated on a reverse-phase column using an acidified methanol eluent. Utilization of a flow-through fluorescence detector in series with a variable wavelength micro-UV detector enhances the sensitivity of the assay. Application of the assay to therapeutic levels of the drugs in human serum is demonstrated.     

High-Performance Liquid Chromatographic Determination of Acetazolamide in Human Plasma

Abstract

A simple, rapid and specific HPLC method has been developed to determine acetazolamide concentrations in human plasma. The assay procedure requires only 250 μl of sample with direct injection of the organic supernatant after protein precipitation with acetonitrile. Chlorothiazide was used as an internal standard. A reversed-phase C₁₈ μBondapak column was employed for the chromatographic separation. The eluent was monitored at 265 nm using a UV variable wavelength detector. The retention times for acetazolamide (ACZ) and chlorothiazide (CTZ) were 6 and 8 min respectively. A linear relationship (r).995) was obtained over the 1-20 μg/ml concentration range. The limit of sensitivity for ACZ was 0.5 μg/ml, with greater than 85% recovery of ACZ and internal standard. The method was applied to human plasma samples obtained after administration of a 250 mg acetazolamide tablet.     

Specific High-Performance Liquid Chromatographic Determinatioin of Ampicillin in Bulks,Injectables, Capsules,and Oral Suspensions by Reverse-Phase Ion-Pair Chromatography

Abstract

A rapid, specific, stability-indicating high-performance liquid chromatographic (HPLC) method has been developed for the assay of Ampicillin in Ampicillin Trihydrate bulk, capsules and oral suspensions and Sodium Ampicillin bulk and injectables. The assay is specific for Ampicillin in the presence of possible contaminants; Penicillin V, Phenylglycine, and 6-Aminopenicillanic Acid (6-APA); the degradation product, Penicilloic Acid of Ampicillin; and all excipients present in the formulations assayed. Ampicillin, Ampicillin formulations, and formulation excipient blends were force-degraded to further demonstrate specificity.

The assay is precise, accurate, linear over the range 50% to 125% of expected Ampicillin sample level, and stability-indicating toward the described thermal, acid, base, aqueous, and light degradations.

The procedure employs an ion-pairing eluent with UV detection at 254 nm. Ampicillin Trihydrate and Sodium Ampicillin bulk are stable in assay diluent for six hours allowing the use of automatic HPLC injectors for unattended analysis. One set of HPLC parameters can assay bulks and formulations.     

Quantitative Determination of Tabersonine and Methoxytabersonine by Reversed-Phase High-Performance Liquid Chromatography

Abstract

A method for the quantitative determination of tabersonine and methoxytabersonine by reversed-phase high-performance liquid chromatography has been developed based on employing amine modifiers of the mobile phase as silanol group masking agents. Thus peak tailing is reduced and peak shapes are improved. The effect of pH of the eluent and the type of the organic modifier upon the overall separation has been examined. A mobile phase optimization procedure has been carried out for selecting the most favorable eluent mixture. The accuracy and precision achieved by the quantitative analysis are satisfactory.     

Determination of Metronidazole Benzoate in Liquid Preparations by Reversed Phase HPLC

Abstract

Despite the availability of several commercial suspension formulations of metronidazole benzoate, there is no official method for its analysis. The conventional analytical method requires extensive extraction following each extraction with evaporation then non-aqueous titration with perchloric acid. The method is time-consuming and is not stability-indicating. This proposed HPLC methodology has the advantages of being fast since it requires no chemical manipulation. The assay is stability-indicating being capable of separating the hydrolysis products (metronidazole and benzoic acid) and the common impurity (2-methyl-5-nitroimidazole) from metronidazole benzoate. The method is also specific as it is free of interferences from excipients. The proposed HPLC method was verified for linearity, accuracy and precision and was applied successfully to several commercial suspensions.     

Retention in Reversed-Phase Ion-Pair Chromatography of Amines On Alkyl-Bonded Phases

Abstract

Reversed phase ion-pair chromatography of phenethylamine derivatives (noradrenaline, adrenaline, dopamine, synephrine, tyramine and pholedrine) and lower alkylamines has been performed with octyl sulfate as counter ion in an aqueous eluent with a low content of 1-pentanol. LiChrosorb RP-18 was used as the solid phase. The retention of lithium and potassium in the system has also been studied.

On the basis of adsorption and retention studies a model for the chromatographic behaviour of the amines is proposed that includes interaction with two sites with different binding ability in the stationary phase. The adsorption capacity of the sites has been calculated as well as adsorption constants for the octyl sulfate ion pairs.     

Chromatographic Separation of Synthetic Isoflavones on Stannic Molybdate Papers

Abstract

Chromatographic separation of 24 synthetic isoflavones on stannic molybdate papers has been described. Various analytically and biochemically important separations, such as separation of isomers and that of having same molecular weights have been achieved. Out of different solvent systems used aqueous methanol was found to be the best eluent.     

Determination of Bitrex,Quassia Powder and Sucrose Octaacetate Next to Diethyl Phthalate and Camphor in Specially Denatured Alcohols by Liquid Chromatografhy

Abstract

A HPLC method for determination of the bitter principles, bitrex, quassia and sucrose octaacetate, next to other ingredients in Specially Denatured Alcohol formulations is described. The method is based on evaporation of a sample, extraction of the residue with hexane and analysis of the extracted residue on a Cyano-type column with acetonitrile-water used as the eluent. Baseline separation of compounds and satisfactory quantitation has been achieved. Samples without pretreatment can occasionally be analysed with slight modifications of the procedure.     

Ion-Pair Liquid Chromatography of Alkylanilines

Abstract

The optimization of ion-pair liquid chromatography of structural isomers of carbon number two alkyl anilines has been studied.

The shorter alkyl cha in bonded silica gel demonstrated the stereo selectivity. the alkyl chain length of ion-pair reagent ruled the equilibration of ion-pair formation. the longer chain of ion-pair reagent formed hydrophobic ion-pair and the shorter chain could not form ion-pair, and ionized solute formed ion-pair with polar ion which was a component of eluent. Three ethylanilines and six xylidines mixture was separated on an octadecyl-bonded silica gel column using an eluent containing methanol/water mixture with sodium 1-dodecanesul-fonate.     

Determination of Bile Acids In Pharmaceutical Dosage Forms By Hplc

Abstract

A rapid reversed-phase high-performance liquid chromatographic assay was developed for chenodeoxycholic acid and ursodeoxycholic acid in commercially available capsule and tablet formulations. A Supelcosil LC-18-DB column with UV detection at 210 nm and a methanol-acetate buffer eluent were used. Individual dosage forms were disintegrated in the mobile phase and an aliquot of the resulting suspension was filtered for the HPLC analysis. Recovery of the drugs from spiked placebo preparations was quantitative. the method was tested for linearity and specificity and was found to be simple, accurate and reproducible.     

Gel Chromatography of Metal Acetylacetonates in Organic Solvents

Abstract

Tris (acetylacetonato)cobalt(III) and tris(acetylacetonato)-chromium(III) have been eluted by gel chromatography through styrene-divinylbenzene copolymer gel using an organic solvent as an eluent. Elution counts of these chelates in these solvents reflect some mutual interactions between metal chelate, gel and solvent. When benzene or chloroform was used as an eluent, sieving effect seems to be dominant for the separation of these chelates. Discussions were done in relation to solubility parameters of the solvent, the complex and the gel.     

Determination of Trialkyl and Triaryl Phosphates by Narrow-bore Liquid Chromatography with On-line Thermionic Detection

Abstract

The potential of a previously reported on-line reversed-phase liquid chromatography-thermionic detector (LC–TID) system has been further evaluated. Several trialkyl (trimethyl to tri-octyl) and triaryl (triphenyl and tri-o-cresyl) phosphates were chosen as model compounds. LC was done on an alkyl-bonded silica column with methanol-water (80:20) at a flow-rate of 35—70μ/min as eluent. The band broadening in the interface-TID unit increased with decreasing volatility of the compounds and for the relatively non-volatile compounds, the band broadening decreased with increasing eluent flow-rate.

For most of the test compounds, detection limits of 40–100pg were obtained. As an illustration of the high selectivity of the LC[sbnd]TID system, the trace-level determination of two aryl phosphates in sediment samples is reported.     

Evaluation of the Use of Lithium Nitrate as a Test Substance for the Determination of the Hold-Up Time of a Reversed-Phase Packing

Abstract

The use of lithium nitrate as a test substance for the determination of the hold-up time on μ Bondapak C18 columns has been evaluated by comparison with the hold-up time calculated with the homologous series of n-alcohols. The influence of charge exclusion effects on the retention time of lithium nitrate is investigated. The addition of phosphoric acid to the eluent appears to be an effective method to reduce charge exclusion effects. The existence of deviations from linearity are demonstrated for the homologous series of n-alcohols in eluents with a low methanol content.     

Determination of Propylthiouracil in Human Breast Milk by Direct Injection High Performance Liquid Chromatography

Abstract

A high-performance liquid chromatographic(HPLC) method was developed for the assay of propylthiouracil in human breast milk. After filtration with membran filter(Molcut II), the eluent was injected into a liquid chromatogaph equipped with C₁₈ precolumn and analytical column in series according to column switching techniques. This method is sufficiently sensitive for most pharmacokinetic studies in human breast milk. The concentration of propylthiouracil was linear over the 50 – 5000ng/ml range. The recovery and the coefficient of variation was 92.0 – 100.6% and 1.6 – 2.9%, respectivery. This assay has the advantages of specificity, simplicity and reproducibility for the measurement of propylthiouracil in human breast milk.     

Adsorption of Tetralkyl Ammonium Ions on Reversed-Phase HPLC Columns

Abstract

A systematic study of the influence of several chromatographic parameters upon adsorption of tetralkyl ammonium ions on reversed-phases has been made. Results show that organic solvent content in mobile phase, tetralkyl ammonium hydrophobicity and tetralkyl ammonium concentration in eluent are the most influent variables. A mathematical expression to calculate the adsorbed ion concentration for different combinations of these variables is deduced. Results from this study can be applied in Ion Pair Reversed-Phase Chromatography to calculate column equilibration times, for setting gradient elution separation methods and for the study of retention mechanisms.     

Effects of Counter Ions in Ion-Pair Liquid Chromatography of Hydrophobic Amines on Non-Polar Bonded Phases

Abstract

The retention behaviour of alprenolol and related hydrophobic amines in ion-pair adsorption systems has been examined with particular emphasis on the influence of different mono-and divalent counter ions (dihydrogenphosphate, bromide, perchlorate, dimethylcyclohexyl sulphate, sulphate and ethylenediaminetetraacetate). N,N-dimethyloctylamine (DMOA) and 1-pentanol were used as modifiers in the aqueous eluent and LiChrosorb RP-8 as stationary phase.

The retention is evaluated according to a two-site adsorption model and equilibrium constants are given for ion pair adsorption of DMOA. The retention of alprenolol has been evaluated in terms of ion exchange with DMOA and the ion-exchange constants are shown to be of the same magnitude and independent of the nature of the counter ion used. The ion-pair adsorption and the ion-exchange approaches are analogous expressions for the distribution process governing the retention.     

Separations of Threo-Erythro Aminoalcohols by Preparative HPLC

Abstract

A liquid chromatographic method which enables the separation of the threo/erythro diastereoisomers obtained from the reduction of Wellbutrin^TM brand bupropion using a ternary eluent system is described. This has been achieved on a preparative scale.     

Reversed Phase High Performance Liquid Chromatography with Cetrimide Containing Eluents

Abstract

A radially compressed column, packed with micro particle, reversed phase (C 18) material, was used to study HPLC with cetrimide containing eluents. The amount of cetrimide adsorbed onto the stationary phase was measured; not the number of available adsorption sites, but rather the presence of micelles in the eluent appears to be the limiting factor for the uptake of cetrimide from the eluent.

The capacity factors, κ′, of several - mainly acidic - compounds were determined in this system, with varying pH and cetrimide concentration of the eluent (methanol-water, 50% w/w). The results obtained upon changing the pH of the eluent can not all be explained with an ion-exchange (or ion-pair) model.

Upon increasing the cetrimide concentration, maximum values in κ′ are reached at about the critical micelle concentration (cmc) of cetrimide in the eluent. The results of conductimetric experiments suggested, that the decrease of κ′ at cetrimide concentrations above this CMC, observed for most of the compounds, can be explained by partitioning of the solutes between the micelles and the bulk of the mobile phase. From these experiments it was also clear that ion-pair formation between cetrimide and solutes is possible.