F.A. Maris

Comparison of high-performance liquid chromatographic methods for the analysis of basic drugs

Problems that are often encountered in the high-performance liquid chromatographic analysis of basic compounds are severe peak asymmetry and low separation efficiency. In attempting to solve these problems, one can become confused by the variety of suggestions given by specialists and by the numerous stationary phases available. In this work, the analysis of basic drugs was studied from two directions. In both approaches a set of 32 basic drugs was used, differing in basicity, polarity and number and type of nitrogen atoms. In the first approach the effect of mobile phase additives and buffers on the performance of a single column was determined. It was found that tertiary and quaternary amines can be applied successfully as silanol blockers. The latter proved to be aggressive towards silica-based stationary phases. Addition of triethylamine showed a remarkable improvement in peak shape in different columns. Other aspects, such as pKa, retention and amount injected, were systematically studied. In the second approach, eight different columns, specially recommended for the chromatography of basic drugs, were evaluated. The chromatographic results showed great variability. As far as peak shape as a function of pH is concerned, an electrostatically shielded stationary phase was most promising for the analysis of basic compounds. This column can even be used without buffers, which can be an advantage in liquid chromatography-mass spectrometry coupling. Because some results were inconsistent with published results, a third approach was to study three columns in more detail.

Important effect of food on the bioavailability of oral testosterone undecanoate.

Study Objective. To assess the effects of food on the bioavailability of testosterone undecanoate, testosterone, and 5a‐dihydrotestosterone (DHT) after administration of a new oral testosterone undecanoate formulation, Andriol Testocaps.

Comparison between positive, negative and chloride-enhanced negative chemical ionization of organophosphorus pesticides in on-line liquid chromatography—mass spectrometry

Positive and negative chemical ionization (PCI and NCI, respectively) have been used for the characterization of ten organophosphorus pesticides in on-line liquid chromatography-mass spectrometry (LC-MS). LC analyses were performed on a 20 cm X 0.7 mm I.D. C8-bonded phase using acetonitrile-water (70:30) or acetonitrile-water-chloroacetonitrile (69:30:1) as eluent. With PCI, molecular weight information was obtained with both eluents. For NCI considerable differences in the spectra were found using the two eluents. Without chloroacetonitrile the spectra were dominated by the functional group fragment and with chloroacetonitrile the base peak was [M - R]- with R being methyl or ethyl, while the spectra further contained the functional group ions. Special emphasis was devoted to the occurrence of chloride attachment at different source temperatures. With several compounds the [M + Cl]- ion was formed and its relative intensity strongly increased when the source temperature decreased. With NCI the sensitivity was about one order of magnitude better than with PCI. This advantage was partly lost when 1% of chloroacetonitrile was used in the eluent; on the other hand, complementary structural information was obtained. As an application, the determination of three organophosphorus pesticides in sediment is reported.

On-line trace enrichment for improved sensitivity in liquid chromatography with direct liquid introduction mass spectrometric detection

Abstract Two model systems consisting of (1) phenylurea herbicides and (2) nitro aromatics were chosen to demonstrate the potential of on-line trace enrichment. The liquid chromatography—mass spectrometry system consists of a 2-MM-I.D. precolumn and analytical column combined with a direct liquid-inlet interface with a helium jet principle. The mass spectrometer has been operated in the positive and negative chemical-ionisation modes. For the investigated compounds, on-line trace enrichment can give enrichment factors of two to three orders of magnitude. For dinitroaromatics detection limits of 0.01 parts per billion were obtained, which corresponds to absolute detection limits of 1 pg. Band broadening was of the order of 1 sec (σ t ).

Pharmacokinetic Study in Women of Three Different Doses of a New Formulation of Oral Testosterone Undecanoate, Andriol Testocaps

Study Objective. To assess the pharmacokinetic parameters of testosterone undecanoate after administration of a new oral formulation, Andriol Testocaps.

Halogenated mobile phase additives for improved detection performance in liquid chromatography-negative chemical ionization mass spectrometry

Abstract The addition of 0.1–1% of chloroacetonitrile to an acetonitrile—water eluent can significantly improve the detection performance in column liquid chromatography—negative chemical ionization mass spectrometry (LC—NCI MS) using a direct liquid introduction interface. The addition of the chlorine-containing modifier does not change the retention times of the chlorophenols used as test compounds. However, the sensitivity for the lower chlorinated phenols is enhanced up to 30-fold. In addition, fragmentation is suppressed and the mass spectra are often characterized by only one main cluster over the whole 170–330°C temperature range studied. With most test compounds, so-called chloride attachment also occurs to some extent, especially at relatively low ion source temperatures. However, for phenol and mono- and dichlorophenol fairly intense [M + Cl]− clusters are even observed at source temperatures of 300°C. For a further evaluation two phenoxyacetic acids, lindane, l -leucine and l -ascorbic acid were studied, and the utilization of other chlorine-, bromine- and fluorine-containing additives was explored.

EXPERT SYSTEM FOR THE SELECTION OF INITIAL HIGH-PERFORMANCE LIQUID CHROMATOGRAPHIC CONDITIONS FOR THE ANALYSIS OF PHARMACEUTICALS

Abstract The high-performance liquid chromatographic (HPLC) behavior of basic pharmaceutical substances is strongly influenced by the type of column packing, the pH of the mobile phase and the concentration and type of buffer ions. This results in many choices to be made by the chromatographer. In order to assist the chromatographer, an expert system has been developed for the selection of initial HPLC conditions. For this purpose, HPLC data for about 600 basic compounds were used. These compounds belong to the class of CNS-active or cardiovascular drugs. On the basis of this knowledge, which was completed with literature data, rules were defined and a knowledge base was built. The knowledge was implemented in KES (Knowledge Engineering System), a mid-sized expert system shell which runs on an IBM-PC. The system asks for information with respect to the substance(s) to be analysed. This information is given in the form of a table of structural elements. The output of the system specifies the chromatographic characteristics which should be used, i.e., type of stationary phase, mobile phase composition, buffer pH, flow-rate and method of detection.

Applicability of new chiral stationary phases in the separation of racemic pharmaceutical compounds by high-performance liquid chromatography

Abstract The potential of contemporary chiral liquid chromatographic columns for the enantioseparation of racemates of pharmaceutical compounds was studied. Sixteen Organon compounds were selected, mostly cardiovascular or CNS-active drugs. Seven chiral stationary phases were used, viz. , five different cellulose derivatives, an α 1 -acid glycoprotein and a polymethacrylate phase, all coated on silica particles. A good enantioseparation, with a resolution higher than 1.0, was achieved for fifteen of the sixteen racemates. The best results were obtained on a Chiralcel OJ column, on which seven enantiomers were separated. With respect to the chromatographic performance, stability and/or selectivity, the cellulose derivatives (Chiralcel columns) were preferred over the protein and polymethacrylate columns.

Improved design and applications of an on-line thermionic detector for narrow-bore liquid chromatography

Abstract The improvement and application of a previously reported on-line thermionic detection system for reversed-phase liquid chromatography (LC-TID) are described. Modifications have been made to simplify the introduction of the LC effluent to the evaporation interface. The vaporized effluent is directed into the base of a gas chromatographic-thermionic detection (GC-TID) system via a heated fused-silica capillary and is swept into the detector using a minimal flow of nitrogen gas. Minimum detectable amounts of 0.2–0.5 pg/s of phosphorus were achieved for a variety of phosphorus-containing compounds, including several polar pesticides. Repeatability, at a level of 5 ng of injected compound, gives relative standard deviations ranging from 2 to 5%. Applications are reported for the determination of polar phosphorus pesticides in complex plant matrices. Results obtained with the unmodified detector are compared with those obtained using the present modified system.

RES, an expert system for the set-up and interpretation of a ruggedness test in HPLC method validation: Part 3: The evaluation

Abstract Van Leeuwen, J.A., Buydens, L.M.C., Vandeginste, B.G.M., Kateman, G., Cleland, A., Mulholland, M., Jansen, C., Maris, F.A., Hoogkamer, P.H. and Van den Berg, J.H.M., 1991. RES, an expert system for the set-up and interpretation of a ruggedness test in HPLC method validation. Part 3: The evaluation. Chemometrics and Intelligent Laboratory Systems , 11: 161–174. In order to establish the confidence of target users in an expert system, it is important that it has been submitted to a thorough testing procedure. In the case of RES, an expert system on ruggedness testing in HPLC, the testing procedure is divided into two parts: a validation and an evaluation part. In the validation part, the performance of the expert system is measured against the experts performance using simulated test cases. In the evaluation part, the suitability of RES is assessed by evaluators in a real laboratory environment. RES has been evaluated in two laboratories. In one laboratory the emphasis of the evaluation was on the knowledge in RES. In the second evaluation the usability of RES with respect to users who were inexperienced in formalized testing was emphasized. The results and comments of the evaluators are discussed. RES has been found to be useful in practice.