Current Chromatographic Methods

Current chromatographic methods for these alkaloids are based on TLC or electrophoresis on silica gel plates and RP-HPLC (362-368). The most significative HPLC methods presented in the literature are summarized in Table 9. An example is shown in Fig. 12. 

This review outlines current chromatographic methods utilized in the analysis of carbohydrates in biological systems and pharmaceutical products. 

As HPLC is the most widely used pharmaceutical analysis technique among current chromatographic methods, a short comparison of HPLC and CE should be very informative to the reader. Some comparisons will also be made to GC. This section will illustrate the advantages, disadvantages, and complementary natures of HPLC and CE. 

In current industrial practice gas chromatographic analysis (glc) is used for quahty control. The impurities, mainly a small amount of water (by Kad-Fischer) and some organic trace constituents (by glc), are deterrnined quantitatively, and the balance to 100% is taken as the acetone content. Compliance to specified ranges of individual impurities can also be assured by this analysis. The gas chromatographic method is accurately correlated to any other tests specified for the assay of acetone in the product. Contract specification tests are performed on product to be shipped. Typical wet methods for the deterrnination of acetone are acidimetry (49), titration of the Hberated hydrochloric acid after treating the acetone with hydroxylamine hydrochloride and iodimetry (50), titrating the excess of iodine after treating the acetone with iodine and base (iodoform reaction). 

Current interest is, however, mainly in the coupling of HPLC and TLC, to which considerable attention has been devoted for the solution of difficult separation problems. Since Boshoff et al. (39) first described the direct coupling of HPLC and TLC, several papers (40-43) have been published describing the on-line coupling of liquid chromatographic methods and PC, usually with different interfaces, depending on the first technique applied. If PC is used as the second method, all the MD methods discussed above can be applied to increase the separating power. 

The PSP toxins represent a real challenge to the analytical chemist interested in developing a method for their detection. There are a great variety of closely related toxin structures (Figure 1) and the need exists to determine the level of each individually. They are totally non-volatile and lack any useful UV absorption. These characteristics coupled with the very low levels found in most samples (sub-ppm) eliminates most traditional chromatographic techniques such as GC and HPLC with UVA S detection. However, by the conversion of the toxins to fluorescent derivatives (J), the problem of detection of the toxins is solved. It has been found that the fluorescent technique is highly sensitive and specific for PSP toxins and many of the current analytical methods for the toxins utilize fluorescent detection. With the toxin detection problem solved, the development of a useful HPLC method was possible and somewhat straightforward. 

In this chapter, the main analytical techniques and the methods currently employed in industrial and research laboratories for the analysis of important classes of additives are reviewed. The use of both gas chromatographic and liquid chromatographic methods coupled with mass spectrometry features prominently. Such methodology enables the sensitive and specific detection of many types of organic additives in polymeric materials to parts per billion (jig/kg) levels. Much of the development of these methods has been undertaken as part of research into the migration or extraction of species from food-contact and medical materials [5-7], This chapter also includes some discussion on the analysis of residual monomers and solvents. 

Several of the chapters in the current volume are comprehensive in nature, but others are more specialized. Volume 32 also contains a methodology review article on the validation of chromatographic methods of analysis. New to the series are annual reviews, and volume 32 contains a summary of the publications appearing during 2004 that dealt with polymorphism and solvatomorphism. It is anticipated that future volumes in the Profiles series will contain similar methodology reviews, as well as other types of review articles that summarize the current state in a particular field of pharmaceutics. As always, I welcome communications from anyone in the pharmaceutical community who might want to provide an opinion or a contribution. 

As with other chromatographic methods, there are a number of electrophoretic methods, including paper and gel electrophoreses and CE. Electrophoresis uses an electric current to move ionic species, either simple ions, amino acids, or complex proteins, through a medium (i.e., a gel) or a capillary (i.e., CE). During this process, typically, the ionic species move at different rates and are thus separated. 

Wegmann and Hofstee [43] have developed a capillary gas chromatographic method for the determination of organochlorine insecticides in river sediments. Bottom soils from rivers, collected in slow current areas may contain high concentrations of organochlorine insecticides and polychlorobiphenyls. When the current moves more rapidly or benthic animals become more active, these compounds are stirred into the water along with suspended particles and become accessible to organisms that live in the bottom layer. 

Gas chromatographic methods are currently the preferred laboratory methods for measurement of total petroleum hydrocarbon measurement because they detect a broad range of hydrocarbons and provide both sensitivity and selectivity. In addition, identification and quantification of individual constituents of the total petroleum hydrocarbon mix is possible. 

Nowadays, the pharmacopoeias make use of chromatographic methods and try to replace less sensitive TLC methods with HPLC tests. However, CE methods are rarely used even though they can at times he more useful than HPLC for determining the impurity evaluation of a drug (Chapter 11). CE is currently used, especially in the case of peptides and proteins, in the EP and the USP. These methods and perspectives for new applications are given in the same Chapter. 

Electromigration and chromatographic methods developed as separate techniques over many decades. Today both methods have converged into a single approach capillary electrochromatography. The approach is still under development, but has already demonstrated to be very promising. From the current findings and the overall CE expertise that was... 

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