Collaborative Study of the Analysis of Erythromycin by Liquid Chromatography on Wide-Pore Poly(styrene-divinylbenzene)

Principal Component Analysis of Nonlinear Chromatography

Principal component analysis (PCA) has been used for the modeling of nonlinear chromatography under overload conditions. A 10-fold range of crude erythromycin samples were loaded onto columns with different stationary-phase chemistries (2 polystyrene, 1 methacrylate) in direct proportion to the bed volumes. The elution profiles indicated slightly concave isotherms for the polystyrene supports and a convex Langmuirian isotherm for the methacrylic support used. The principal component models accounted for over 98% of the original variance in the data for all three columns and were able to give excellent models of complete chromatograms in the absence of first-principle models or physicochemical data. Correlations between sample mass and the principal component scores were made for each that were consistent for the column types despite the different geometries and stationary phases. Linear relationships with high correlation coefficients were observed when the scores of the same principal component were compared between columns. Such correlations offer considerable potential for modeling of nonlinear chromatography.

Investigation of degradation products in a topical gel containing erythromycin and benzoyl peroxide by liquid chromatography–mass spectrometry

Benzamycin, combining benzoyl peroxide and erythromycin, is a topical gel used in the treatment of acne vulgaris. Because of the reactivity of benzoyl peroxide, preparations containing both erythromycin and benzoyl peroxide might be unstable and degradation products could be formed. To investigate and identify these latter products, a gradient-based liquid chromatographic method using volatile mobile phase constituents was developed. Mass spectrometry data were acquired on solutions containing erythromycin and benzoyl peroxide and on freshly prepared, 2-month-old and 18-month-old samples of Benzamycin. With the reference spectra as interpretative templates, it was concluded that erythromycin undergoes oxidation, followed by benzoylation.

Identification of impurities in erythromycin by liquid chromatography–mass spectrometric detection

A simple, isocratic liquid chromatographic (LC) method using volatile mobile phase constituents for the identification of related substances in erythromycin samples is described. For method development, evaporative light scattering detection (ELSD) was used. An XTerra RP18 column was used at 70 degrees C with a mobile phase consisting of acetonitrile-isopropanol-0.2M ammonium acetate pH 7.0-water (165:105:50:680). Mass spectral data were acquired on an ion trap mass spectrometer equipped with an electrospray interface operated in the positive ion mode. First, a library was created using MS/MS and MS(n) spectra of reference substances available in the laboratory. Using these reference spectra as interpretative templates, eight novel related substances in erythromycin samples were identified: N-demethylerythromycin E, erythromycin E N-oxide, anhydroerythromycin C, N-demethylerythromycin B, anhydro-N-demethylerythromycin A, pseudoerythromycin E enol ether, EF lacking the neutral sugar and EA lacking the neutral sugar.

Preparation of monodisperse porous polymethacrylate microspheres and their application in the capillary electrochromatography of macrolide antibiotics

Monodisperse poly(glycidyl methacrylate-divinylbenzene) microspheres were prepared by a simple one-step dispersion polymerization process. Examination of the polymeric microspheres showed that they had a mean particle diameter of 3 microm and dual pore size distribution with mean pore diameters of 300 and 800 A. The microspheres were functionalized by introducing quaternary ammonium/octadecyl groups to obtain positively charged beads in a wide pH range. The functionalized beads were packed into fused-silica capillary having 50 microm inner diameter and used to separate erythromycin derivatives by capillary electrochromatography (CEC). These samples require gradient elution when separated by high-performance liquid chromatography (HPLC) or micro-HPLC, but with the new columns isocratic elution suffices for their separation by CEC. The column efficiency ranged from 40,000 to 50,000 theoretical plates.

Separation of erythromycin and related substances on base-deactivated reversed-phase silica gel columns

An official liquid chromatographic method for the analysis of erythromycin and related substances, which is based on a polymer reversed-phase, is described in the European Pharmacopoeia and in the United States Pharmacopeia. The pH of the mobile phase used in this system is 9.0. Recent advanced technology has led to the introduction of a new generation of silica-based reversed-phase column packings, which are claimed to be much more stable towards bases. They are useful for the analysis of basic compounds. Studies to verify the separation of erythromycin and related substances on Hypersil BDS C18, Luna C18(2), Inertsil ODS-2 and Supelcosil ABZ+ have been performed and the results are presented. It is shown that these base-deactivated phases give a better sensitivity and selectivity towards erythromycins than the polymer phase, provided that an adapted mobile phase is used. This is the first liquid chromatographic method described for the separation of erythromycin D from erythromycin A.

Investigation of unknown related substances in commercial erythromycin samples with liquid chromatography/mass spectrometry

A selective reversed phase liquid chromatography/mass spectrometry (LC/MS(n)) method is described for the identification of erythromycin impurities and related substances in commercial erythromycin samples. Mass spectral data are acquired on a LCQ ion trap mass spectrometer equipped with an electrospray interface operated in positive ion mode. The LCQ is ideally suited for identification of impurities and related substances because it provides on-line LC/MS(n) capability. Compared with UV detection, this hyphenated LC/MS(n) technique provides as a main advantage efficient identification of novel substances without time-consuming isolation and purification procedures. Using this method four novel related substances were identified in commercial samples.

Analysis of macrolide antibiotics

The following macrolide antibiotics have been covered in this review: erythromycin and its related substances, azithromycin, clarithromycin, dirithromycin, roxithromycin, flurithromycin, josamycin, rokitamycin, kitasamycin, mycinamycin, mirosamycin, oleandomycin, rosaramicin, spiramycin and tylosin. The application of various thin-layer chromatography, paper chromatography, gas chromatography, high-performance liquid chromatography and capillary zone electrophoresis procedures for their analysis are described. These techniques have been applied to the separation and quantitative analysis of the macrolides in fermentation media, purity assessment of raw materials, assay of pharmaceutical dosage forms and the measurement of clinically useful macrolide antibiotics in biological samples such as blood, plasma, serum, urine and tissues. Data relating to the chromatographic behaviour of some macrolide antibiotics as well as the various detection methods used, such as bioautography, UV spectrophotometry, fluorometry, electrochemical detection, chemiluminescence and mass spectrometry techniques are also included.

Study of the stability of erythromycin in a hydrophilic creme basis by liquid chromatography

The stability of the macrolide antibiotic erythromycin, incorporated at a 2% m/m concentration in a hydrophilic creme basis containing 2% m/m of chlorocresol, was monitored over a period of 2 months using liquid chromatography as the analytical method. Extracts of the creme were analysed using wide-pore poly(styrene-divinylbenzene) PLRP-S 1000 A as the stationary phase and a mixture of 2-methyl-2-propanol-acetonitrile-potassium phosphate buffer (pH 11.0; 0.02 M)-water (165:30:50:755, v/v/v/v) as the mobile phase. The method showed good selectivity towards chlorocresol, erythromycin A, its related substances and degradation products. As the pH of the creme containing erythromycin was 8.6, alkaline degradation products were expected to be formed. The presence of pseudoerythromycin A enol ether was observed after storage of the creme for 1 week at a temperature of 25 degrees C. After 1 month the content of erythromycin was still more than 95%.

How to better define the characteristics of dispersion of results in liquid chromatographic analyses through an interlaboratory study. Example of collaborative studies on ketoprofen and spiramycin

The aim of this study was to use statistical tools, especially the analysis of variance (ANOVA), to improve knowledge of the characteristics of the dispersion of results in high-performance liquid chromatography (HPLC) methods for quantitative analysis. It is in this regard that two interlaboratory studies have been carried out in collaboration with Rhône-Poulenc Rorer. The first concerned the analysis of a single drug product (ketoprofen) and was typically a "simple analysis". The second one involved a complex mixture of drug products and related substances (spiramycin), requiring far more constraining analysis conditions. Preliminary studies of the analyses were carried out to develop an optimized protocol. Statistical exploitation of the data for ketoprofen showed that there was no significant influence of the factors "laboratory" and "preparation", under the conditions of the study. On the other hand, in the case of spiramycin, a significant influence of the factors "laboratory" and "preparation" was observed under the conditions of the collaborative study, indicating that the latter factor must be taken into account to establish certified assays. Results of these two studies will help to determine the factors that have a significant influence, depending on the product and the chromatographic method used. By completing the statistical data base, interlaboratory studies will also contribute in the near future to the elaboration of more rigorous protocols for analytical transfers.

Sensitive determination of erythromycin in human plasma by LC-MS/MS

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the analysis of erythromycin in human plasma (EDTA as anticoagulant) was developed and validated. The concentration ranges were 0.5-50 and 50-5000 ng ml-1. The procedure involved alkalization of 0.5 ml of plasma, one step liquid-liquid extraction, dryness of the extract and reconstitution in 80:20 water:acetonitrile. An Inertsil ODS-2 5 microns, 3.0 x 50 mm column (Metachem) with a C8 guard column and isocratic mobile phase were used for liquid chromatography. The mobile phase consisted of 1:1 acetonitrile:water with 2 mM NH4OAc and 0.1% HOAc. A flow rate of 0.7 ml min-1 was used. The analysis time on LC-MS/MS for one sample was approximately 2 min. A Turbo-Ionspray source was interfaced between the HPLC and triple quadrupole mass spectrometer (Sciex API III Plus). MS/MS analysis used Multi-Reaction Monitoring (MRM) mode. The lowest limit of quantitation (LOQ) was 0.5 ng ml-1 with all Quality Control (QC) sample recoveries varying between 88 and 105%. Nine intraday and interday calibration curves were generated yielding correlation coefficients ranging from 0.995 to 1.000. Average recovery for erythromycin at 1 ng ml-1 was 105% (+/- 4.5%). Average recovery for the internal standard was 83-103%. Short-term and long-term stability in the freezer (-20 degrees C), bench stability, and stability after 3 freeze/thaw cycles at -20 and -80 degrees C were conducted. The samples were found to be stable under all conditions. The method developed and validated proved useful for clinical pharmacokinetic study sample analysis with high throughput due to its high sensitivity and very short analysis time.

Analysis of macrolide antibiotics by capillary electrophoresis

Capillary electrophoresis was utilized in the study of the macrolide antibiotics (i.e. pharmaceutical glycoconjugates) clarithromycin, erythromycin, oleandomycin, troleandomycin, and spiramycin. In order to assist in analyte solubilization, two buffer systems using acetonitrile were developed. The first system involved 30 mM sodium cholate and 20% acetonitrile in 80 mM sodium phosphate, pH 6. This buffer permitted the baseline resolution of all five glycoconjugated antibiotics. In addition, erythromycin was separated from its derivatives estolate and ethylsuccinate. In the absence of surfactants, a higher acetonitrile quantity, 65%, was used in the second buffer system, with 35 mM sodium phosphate, pH 6. Selectivity between oleandomycin and clarithromycin was reversed in this system compared to the cholate buffer, indicating solute interaction with the cholate micelles in the previous system. Calibration linearity and detection sensitivity were improved in the high acetonitrile buffer, due to decreased background absorbance. It was demonstrated that both buffer systems can be utilized for the visualization of minor components that may be present in bulk pharmaceuticals.