Selective detection, alkaloids

Mateus, L., Cherkaoui, S., Christen, R, and Veuthey, J. L. (1999). Capillary electrophoresis-diode array detection-electrospray mass spectrometry for the analysis of selected tropane alkaloids in plant extracts. Electrophoresis 20, 3402—3409. 

CD active compounds can be selectively detected when present in a complex matrix comprised of other, specifically achiral, compounds such as might normally be encountered in the extracts of either natural products or biological fluids. Pyrethrines, tryptophans, rotenoids, and amaryllidacae alkaloids have been used to evaluate the system [27]. Monitoring at selected wavelengths has enabled detection levels in the low microgram range to be realized. By using stopped-flow techniques, full CD spectra can be obtained. 

Belladonna alkaloids including hyoscyamine have been analyzed by capillary GC and GC-mass selective detection (MSD) (151). 

Selective detection of Amaryllidaceae alkaloids in the low ug range with a circular di-... 

The major alkaloids in the vapor phase of environmental tobacco smoke are discussed and detailed procedures for their determination are outlined. Time-integrated sampling involves concentrating the alkaloids from the air matrix by trapping on either XAD-4 sorbent resin or on bisulfate-treated glass fiber filters with extraction and analysis by gas chromatography and N-selective detection. These methods are widely used in studying the impact of ETS on indoor air quality in real-life situations. 

For detection, UV absorption is most widely used. Some alkaloids can also be detected by means of their fluorescence. Some type of alkaloids have poor UV-absorptive properties, e.g., tropane alkaloids, pyrro-lizidine alkaloids, and steroidal alkaloids, necessitating detection at a lower wavelength (200-220 nm). Electrochemical detection has been applied for alkaloids, enabling selective detection in the presence of interfering compounds. 

MS coupled with LC is the most selective detection for alkaloids. As all-volatile eluents are needed for LC-MS, the acidic eluents often contain formic acid, acetic acid, or trifluoroacetic acid. 

To be effective chemical deterrents alkaloids must be detected by potential insect herbivores so that a selective choice can be made. To evaluate the possibility that insect herbivores could detect alkaloids Ishikawa used two sensilla styloconica on the maxilla of the larva of the silkworm, Bombyx mori. Various chemicals and extracts from plants fed on by the silkworm were tested to see if they had any effect in stimulating these maxillary hairs. Two alkaloids, nicotine and strychnine nitrate, had the strongest stimulatory effect at the lowest concentration and these results were interpreted as showing that these substances are easily detected by a feeding insect and can act as feeding deterrents (114). 

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]. 

The fact that the EP wants to replace old TEC methods with more selective, efficient, and sensitive separation methods provides the chance for the introduction of more CE methods. The continuous development of analytical methods is reflected in the national and international pharmacopoeias. This might be demonstrated for atropine sulfate. Whereas the Deutsches Arzneibuch, 7th Edition (DAB 7) only limits the tropic acid by extraction and titration with NaOH and phenolphthalein indication, the 4th edition of the EP looked for foreign alkaloids and decomposition products by means of TEC with a potassium iodobismuthate for detection. By intensity comparison of the obtained spots, it was possible to limit these impurities to 0.5%. The EP 5 utilizes an ion-pair HPLC method that is able to limit most of the impurities to less than 0.2%. To make the method more robust, an HPLC method using a polar embedded was applied, which might be the next step for the EP. However, recently the same authors have reported on a MEEKC method being as robust and precise as the latter HPLC method (see Eigure 6) but far more sensitive and, therefore, a future perspective for the EP. 

ILs have been used in the CE-electrochemiluminescence (ECL) method to determine bioactive constituents in Chinese traditional medicine [58]. CE/Tris(2,2-bipyridyl) ruthenium(II) (Ru(bpy)3 +) ECL, CE-ECL, with an IL detection system was established to determine bioactive constituents in Chinese traditional medicine opium poppy, which contains large amounts of coexistent substances. Running buffer containing 25 mM borax-8 mM [C2CiIm][BF4] (pH 9.18) was used, which resulted in significant changes in separation selectivity and obvious enhancement in ECL intensities for those alkaloids with similar structures. Quantitative analysis of four alkaloids was... 

For any speciation process based on pheromonal communication to be effective, variation in CHC production should tightly co-evolve with factors regulating CHC processing. This has been observed for the desatl gene in D. melanogaster (Marcillac et al., 2005b). Such coevolution requires that pre-existing sensory structures can detect and respond to new CHC molecules. This basic assumption of the theory of sexual selection is supported by the observation that taste neurons normally used to detect bitter molecules also serve to detect an aversive sex pheromone (Lacaille et al., 2007). It is thus possible that taste neurons that were initially used by the fly to detect noxious food molecules (bitterness is often associated with alkaloids and toxic molecules) have been more recently used to detect inhibitory sex pheromones. 

The on-line coupling of CE with electrospray ionization mass spectrometry (CE-ESI-MS) allows high separation efficiency together with high sensitivity and selectivity as well as molecular structural information. A CE-UV-ESI-MS method was developed for the analysis of hoscyamine, scopolamine, and other tropane derivatives [131]. The differentiation of hyoscyamine from littorine, commonly encountered in plant material, was demonstrated using in-source collision-induced dissociation. The developed method was applied to the analysis of these alkaloids in Belladonna leaf extract and in Datura Candida x D. awreahairy root extract. Recently, CE coupled with electrochemiluminescence detection has been used for the determination of atropine and scopolamine in Flos daturae [132]. 

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