Pharmaceuticals impurity applications

As liquid chromatography plays a dominant role in chemical separations, advancements in the field of LC-NMR and the availability of commercial LC-NMR instrumentation in several formats has contributed to the widespread acceptance of hyphenated NMR techniques. The different methods for sampling and data acquisition, as well as selected applications will be discussed in this section. LC-NMR has found a wide range of applications including structure elucidation of natural products, studies of drug metabolism, transformation of environmental contaminants, structure determination of pharmaceutical impurities, and analysis of biofiuids such as urine and blood plasma. Readers interested in an in-depth treatment of this topic are referred to the recent book on this subject [25]. 

This chapter provides an overview of modern HPLC method development and discusses approaches for initial method development (column, detector, and mobile phase selection), method optimization to improve resolution, and emerging method development trends. The focus is on reversed-phase methods for quantitative analysis of small organic molecules since RPLC accounts for 60-80% of these applications. Several case studies on pharmaceutical impurity testing are presented to illustrate the method development process. For a detailed treatment of this subject and examples of other sample types, the reader is referred to the classic book on general HPLC method development by L. Snyder et al.1 and book chapters2,3 on pharmaceutical method development by H. Rasmussen et al. Other resources include computer-based training4 and training courses.5... 

Basak, Amp K., Raw, Andre S., A1 Hakim, Ali H., Furness, Scott, Samaan, Nashad L, Gill, Devinder S., Patel, Hasmukh B., Powers, Roslyn F., and Yu, Lawrence, Pharmaceutical impurities regulatory perspective for abbreviated new drug applications. Advanced Drug Delivery Reviews, 59, 64-72, 2007. Guidance issued by the EMEA (European Medicines Agency, Evaluation of Medicines for Human Use, London, June 23, 2004. See also Reference 6. 

Major applications of modern TLC comprise various sample types biomedical, pharmaceutical, forensic, clinical, biological, environmental and industrial (product uniformity, impurity determination, surfactants, synthetic dyes) the technique is also frequently used in food science (some 10% of published papers) [446], Although polymer/additive analysis takes up a small share, it is apparent from deformulation schemes presented in Chapter 2 that (HP)TLC plays an appreciable role in industrial problem solving even though this is not reflected in a flood of scientific papers. TLC is not only useful for polymer additive extracts but in particular for direct separations based on dissolutions. 

Modern spectroscopy plays an important role in pharmaceutical analysis. Historically, spectroscopic techniques such as infrared (IR), nuclear magnetic resonance (NMR), and mass spectrometry (MS) were used primarily for characterization of drug substances and structure elucidation of synthetic impurities and degradation products. Because of the limitation in specificity (spectral and chemical interference) and sensitivity, spectroscopy alone has assumed a much less important role than chromatographic techniques in quantitative analytical applications. However, spectroscopy offers the significant advantages of simple sample preparation and expeditious operation. 

Two important applications of DSC are in the pharmaceutical industry and in the polymer industry. In the pharmaceutical industry, the purity of formulations and raw materials can be measured. Various levels of purity give different melting points and melting ranges. Very pure materials melt sharply (within 1 to 2°) and melt at expected temperatures. Impure materials have broader melting ranges and melt at lower temperatures than pure materials. Such phenomena can easily be detected with DSC. 

In short, all prescribed tests for impurities in the Pharmacopoeia usually fix certain limits of tolerance. For lead, arsenic and iron general quantitative or limit tests are precisely laid down which, with necessary variations and modification are rigidly applicable to pharmaceutical substances. 

Acid radical impurities constitute a serious but unavoidable source of impurities in a large number of pharmaceutical chemicals. However, the two most commonly found acid radical impurities are chloride (Cl ) and sulphate (S042 ) that evidently arise from the inevitable use of raw tap-water in various manufacturing operations. As these two acid radical impurities are found in abundance due to contamination, the Pharmacopoeia categorically stipulates limit tests for them which after due minor modifications are applicable to a number of pharmaceutical substances. 

With capillary electrophoresis (CE), another modern primarily analytically oriented separation methodology has recently found its way into routine and research laboratories of the pharmaceutical industries. As the most beneficial characteristics over HPLC separations the extremely high efficiency leading to enhanced peak capacities and often better detectability of minor impurities, complementary selectivity profiles to HPLC due to a different separation mechanism as well as the capability to perform separations faster than by HPLC are frequently encountered as the most prominent advantages. On the negative side, there have to be mentioned detection sensitivity limitations due to the short path length of on-capillary UV detection, less robust methods, and occasionally problems with run-to-run repeatability. Nevertheless, CE assays have now been adopted by industrial labs as well and this holds in particular for enantiomer separations of chiral pharmaceuticals. While native cyclodextrins and their derivatives, respectively, are commonly employed as chiral additives to the BGEs to create mobility differences for the distinct enantiomers in the electric field, it could be demonstrated that cinchona alkaloids [128-130] and in particular their derivatives are applicable selectors for CE enantiomer separation of chiral acids [19,66,119,131-136]. 

Finally, we will discuss the determination of the limit of quantitation or LOQ. Establishing an LOQ is required for many pharmaceutical applications such as impurity testing and cleaning validation. Limit of quantitation is the lowest concentration (%, ppm) that can be determined with acceptable precision (RSD of —5%). It is generally accepted that a signal/noise ratio at the LOQ should be at least There are... 

The concurrent identification and quantification of organic impurities is a principal use of liquid chromatography in the pharmaceutical industry. However, the application of liquid chromatography to this task highlights a weakness of this technique when compared to gas chromatography specifically, the lack of a universal detector. Great strides have been made to create detectors and hyphenated techniques to address these problems. However, multiple detectors and analytical procedures may be necessary to accurately and specifically identify and quantify the impurities in complex systems. 

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