Bernard A. Olsen

Hydrophilic interaction chromatography using amino and silica columns for the determination of polar pharmaceuticals and impurities.

Hydrophilic interaction chromatography (HILIC) is described as a useful alternative to reversed-phase chromatography for applications involving polar compounds. In the HILIC mode, an aqueous-organic mobile phase is used with a polar stationary phase to provide normal-phase retention behavior. Silica and amino columns with aqueous-acetonitrile mobile phases offer potential for use in the HILIC mode. An examination of the retention and separation of several pyrimidines, purines, and amides on silica and amino columns from three manufacturers revealed that mobile phases should contain a buffer or acid for pH control to achieve similar and reproducible results among columns from different sources. Amino columns may also be used in an anion-exchange mode, which provides an advantage for some applications. In some cases, silica can provide different selectivity and better separation than an amino column. Example applications include: low-molecular-mass organic acids and amides as impurities in non-polar drug substances, 5-fluorouracil in 5-fluorocytosine, guanine in acyclovir, and different selectivity for polar basic compounds compared to an ion-pairing system.

Determination of fluoxetine hydrochloride enantiomeric excess using high-performance liquid chromatography with chiral stationary phases

Chromatographic methods using chiral stationary phases have been developed for the separation of fluoxetine hydrochloride enantiomers. Ovomucoid and tris(3,5-dimethylphenyl carbamate) cellulose stationary phases were used in the reversed- and normal-phase modes, respectively. Acceptable isomer separation was achieved at pH 3.5 with the ovomucoid phase. Isopropyl alcohol and methyl-tert- butyl ether mobile phase modifiers each provide complete resolution using the derivatized cellulose column. Better separation robustness was obtained with a column temperature of 1 degree C the isopropyl alcohol modifier. The methyl-tert-butyl ether system was robust at room temperature. Differences in relative enantiomer amounts of as little as 2% could be determined. The chromatographic conditions provided a much more discriminating test compared to an optical rotation method proposed for pharmacopeial use which had difficulty distinguishing individual enantiomers. The chiral chromatographic conditions were also applied to capsule formulations to demonstrate the presence of racemic fluoxetine hydrochloride.

Chemometric categorization of octadecylsilyl bonded-phase silica columns using test mixtures and confirmation of results with pharmaceutical compound separations

Abstract The chromatographic properties of seventeen commercial octadecylsilyl phases were characterized in order to determine column similarities and differences that would aid in column selection for method development, choice of an alternate column and method ruggedness testing. Chromatographic test mixtures from the literature were used to probe the hydrophobicity, free silanol interactions, trace metal activity, and shape selectivity of these columns. Principal components and cluster analysis methods were used to categorize the columns into groups that tended to display similar chromatographic properties. The validity of the groups was tested with mixtures of pharmaceutical compounds under a variety of mobile phase conditions. In general, columns that were categorized together from the test mixture analysis showed similar behavior for the analysis of the pharmaceutical compound mixtures.

The determination of oxalic acid, oxamic acid, and oxamide in a drug substance by ion-exclusion chromatography

Oxalic acid, oxamic acid and oxamide are potential impurities in some active pharmaceutical ingredients (API). The retention and separation of oxalic and oxamic acids are particularly challenging using conventional reversed-phase HPLC due to their high polarity. An ion-exclusion chromatography (IEC) method has been shown to provide good separation and sensitivity for the three oxalate-related impurities in a hydrophobic API matrix. The method uses a Dionex IonPac ICE-ASI column with 95/5 (v/v) 0.1% sulfuric acid/acetonitrile as the mobile phase and UV detection at 205 nm. Development and validation of this method are described.

A simple and efficient approach to reversed-phase HPLC method screening

The development and utility of an efficient HPLC method screening strategy using only four columns for the separation of pharmaceutical compounds and related impurities is presented. The strategy established a two-column approach to enable rapid early method development, along with a four-column approach for commercial method development of the analytical methods utilized to verify the quality of drug substance or drug product. Mobile phases consisted of acetonitrile or methanol with aqueous trifluoroacetic acid for low pH screening, and ammonium hydroxide for high pH screening. Examples are provided to demonstrate the practicality and orthogonality of the method screening process. A unique system suitability check, using commercially available compounds, was incorporated as a tool for troubleshooting and for ensuring adequate system performance prior to screening. Initial testing of the strategy revealed that the columns chosen were successful in leading to assay and impurity methods for 40 pharmaceutical compounds.

Multidimensional evaluation of impurity profiles for generic cephalexin and cefaclor antibiotics

A multidimensional approach is described for characterizing impurities in samples of generic cefaclor and cephalexin antibiotics. High-performance liquid chromatography (HPLC) with gradient elution followed by photodiode array or mass spectrometric detection provides valuable information concerning the nature of impurities observed. Results are presented which demonstrate the utility of these techniques for identifying impurities and distinguishing among process-related impurities, degradation products and formulation excipients. Preparative HPLC isolation and spectroscopic identification of some impurities is also described.

HPLC Method Development for Duloxetine Hydrochloride Using a Combination of Computer-Based Solvent Strength Optimization and Solvent Selectivity Mixture Design

Abstract Computer simulation software for solvent strength optimization and statistical mixture design based on the solvent | selectivity triangle were useful tools employed for the development of a reversed-phase HPLC method to separate duloxetine, a new anti-depressant compound, and structurally-related impurities. Solvent strength optimization was used to show that adequate separation for all impurities could not be obtained with a single organic modifier and to aid in choosing appropriate boundary conditions for a mixture design study. The mixture design was used to obtain resolution maps for organic modifier mixtures consisting of acetonitrile, methanol, and tetrahydrofuran. Overlapping resolution maps for the peak pairs of interest revealed the solvent composition that would provide the maximum resolution. Finally, solvent strength was optimized at the best solvent composition and information about method robustness obtained.

Determination of EDTA in vancomycin by liquid chromatography with absorbance ratioing for peak identification

An LC method is described for the determination of EDTA in vancomycin formulations. EDTA is complexed with iron and the Fe(EDTA)- complex is separated from vancomycin components on a reversed-phase column using an ion pair mobile phase. Quantitation is achieved using UV detection, with absorbance ratioing employed to discriminate between the analyte and vancomycin-related compounds. The complexity of the sample matrix and the trace levels of EDTA that are of interest dictate unique development considerations. This method offers good specificity and precision over the range 20-300 ppm EDTA in vancomycin formulations, while maintaining a degree of simplicity. Wavelength selection is optimized to demonstrate the potential application of absorbance ratioing to trace determinations. This method has been effectively applied to vancomycin formulations containing a wide range of chemical impurities and is not affected by vancomycin degradation products.

Recent Trends in Product Development and Regulatory Issues on Impurities in Active Pharmaceutical Ingredient (API) and Drug Products. Part 2: Safety Considerations of Impurities in Pharmaceutical Products and Surveying the Impurity Landscape

The American Association for Pharmaceutical Scientists (AAPS) Workshop on Predicting and Monitoring Impurities in API and Drug Products: Product Development and Regulatory Issues was held on 13–14 October 2012 at the McCormick Place in Chicago, IL, USA. The goal of the workshop was to discuss control strategies of chemical and physical changes of active pharmaceutical ingredients (API) and drug products in the drug development process. These changes can affect both the safety and efficacy of drugs; therefore, the ability to rapidly predict and assess the potential for drug product performance changes for impurity formation and the associated safety concerns are important parts of speeding the development of innovative drug therapies without compromising quality. The workshop comprised four different sessions. Each session focused on separate fundamental issues to build a comprehensive understanding of the physical and chemical processes that affect drug impurities and drug degradation products, the control of impurities, and the impact of these factors on safety and regulatory areas. Taken together, this comprehensive understanding is used to achieve a more robust development approach that enables predictability with a concomitant assurance of safety and efficacy. Innovative methodologies for development of effective stability control strategies were also presented. This article summarizes sessions 3 and 4 of the American Association for Pharmaceutical Scientists (AAPS) Workshop on Predicting and Monitoring Impurities in API and Drug Products: Product Development and Regulatory Issues and addresses issues of safety considerations of impurities in pharmaceutical products and surveying the impurity landscape. Sessions 1 and 2 of the American Association for Pharmaceutical Scientists (AAPS) Workshop on Predicting and Monitoring Impurities in API and Drug Products: Product Development and Regulatory Issues are summarized in Recent Trends in Product Development and Regulatory Issues on Impurities in active Pharmaceutical Ingredient (API) and Drug Products Part 1: Predicting Degradation Related Impurities and Impurity Considerations for Pharmaceutical Dosage Forms published separately.

Strategies for investigation and control of process- and degradation-related impurities

Publisher Summary This chapter discusses the strategies for investigation and control of process- and degradation-related impurities. The chapter describes strategies for the investigation of process-related and degradation-related impurities in drug substances and drug products. Particular emphasis is given to a chemistry-guided approach and the iterative nature of investigations as knowledge is gained. The delineation of impurity type and source used is presented in the chapter. Considerations for investigating and controlling crystal forms, residual solvents, and microbiological impurities have been addressed in International Conference on Harmonization (ICH) guidelines. One strategy for impurity investigation might be termed as the “technique-oriented approach.” The main feature of this approach is to use as many techniques as possible to search for impurities. This would include various types of chromatographic techniques with multiple detection schemes. Duloxetine hydrochloride is a secondary amine that is a potent inhibitor of both serotonin and norepinephrine reuptake. Because the drug is unstable in acid, oral dosing requires encapsulation within an enteric coating that consists of hydroxypropylmethylcellulose (HPMC) and HPMC acetate succinate (HPMCAS).