Natural Product Analysis

We can list the following areas as prime targets essential oil and natural product analysis, chiral analysis (e.g. of fragrances), trace multi-residue analysis, pesticide monitoring, and further petroleum products applications, in fact any separation where simply greater resolution and sensitivity is demanded-which means probably almost... 

The hyphenation of CE and NMR combines a powerful separation technique with an information-rich detection method. Although compared with LC-NMR, CE-NMR is still in its infancy it has the potential to impact a variety of applications in pharmaceutical, food chemistry, forensics, environmental, and natural products analysis because of the high information content and low sample requirements of this method [82-84]. In addition to standard capillary electrophoresis separations, two CE variants have become increasingly important in CE-NMR, capillary electrochromatography and capillary isotachophoresis, both of which will be described later in this section. 

Exarchou V, Krucker M, van Beek TA, et al, LC-NMR coupHng technology Recent advancements and applications in natural products analysis, Magn Resort... 

Naphthaleneacetic acid, 296 Narrow bore columns, 33, 34 Natural products, analysis by RPC, 293 Neohesperidin dihydrochalcone, 295 Netilmicin, 282 Niacin, 260, 263, 296 Niacinamide, 263... 

Natural-product analysis 75 mM SDS, 1000 mM n-butanol, 90 mM n-octanol, phosphate-borate buffer, pH 7 29, 37... 

Schmidt H-L, Gleixner G (1998) Isotopic patterns in natural compounds origin and importance in authenticity analysis. In SchreierP, Herderich M, Humpf H-U, Schwab W (eds) Natural Product Analysis. Vieweg, Braunschweig, p 271... 

The specific constraints and requirements of continuous-flow NMR will be explained in the first chapter, whereas specific applications, such as biomedical and natural product analysis, LC-NMR-MS and LC-NMR in an industrial environment, together with polymer analysis, will be discussed separately. Thus, the reader will obtain a broad overview of the application power of LC-NMR and the benefits of its use. He/She will also be introduced to the pitfalls of this technique. Special attention will be given to the exciting newer coupled techniques such as SFC-NMR and capillary HPLC-NMR. However, new emerging future developments will also be discussed thoroughly. 

In natural products analysis, most frequently the stop-flow mode is chosen to acquire H spectra of the compounds of interest, or if further structural information is required to perform two-dimensional H NMR spectra, such as COSY, TOCSY, NOESY or ROESY. In many cases an on-flow NMR chromatogram (usually at flow rates between 0.3 and 1ml min-1) is recorded beforehand, either to screen for the presence of particular groups of compounds or to gain a general overview on the sample composition. (Heteronuclear LC-NMR experiments, such as HSQC and HMBC of a natural product, have been reported in the literature once [9] however, this was of a highly enriched fraction.) More recently, time-sliced stop-flow [14,16] and on-flow approaches at low flow rates [34,35] have been applied to natural product extracts in order to combine the advantages of both on-flow (a ready overview on the entire sample) and stop-flow (sufficient acquisition time for minor compounds) modes. 

The first application of LC-NMR-MS to natural products analysis was presented in 1999 [37]. The additional mass spectroscopic information allowed the identification of a further ecdysteroid in an extract of Silene otides which could not be identified by LC-NMR alone [24], Further applications of this double hyphenation dealt with the identification of napthodianthrones [38] and flavone glycosides [38,39] in natural products extracts. Taking the hyphenated technique one step further, the suitability of an integrated LC-UV-IR-NMR-MS system for natural products analysis has been assessed [40] - again using ecdysteroids as an example. Such systems still suffer from different requirements of the individual detectors (mainly in terms of sensitivity). However, the results obtained are promising. 

In the following sections, some examples of the advantageous use of LC-NMR and LC-NMR-MS in natural products analysis are presented in order to demonstrate the possibilities and limitations of these hyphenated techniques. 

S. Zhou and M. Hamburger, Application of liquid chromatography-atmospheric pressure ionization mass spectrometry in natural product analysis. Evaluation and optimization of electrospray and heated nebulizer interfaces, J. Chromatogr., A, 755, 189-204 (1996). 

R. Clery, Natural Product Analysis in the Fragrance Industry. In The Chemistry of Fragrances From Perfumer to Consumer, 2nd ed. C. Sell, Ed. The Royal Society of Chemistry Cambridge, 2006 pp 214-228. 

Wolfender, J. 2009. HPLC in natural product analysis the detection issue. Plant Anal. 75 719-734. 

The key to natural products analysis using this approach is dependable molecular weight determination. This information is used with existing natural product databases that contain information on the... 

The application of gas chromatography (GC) to steroid analysis seems to have many difficulties due to then-insufficient volatility and thermolability. The development of high-resolution gas chromatography (HRGC) and various derivatization procedures enables the efficient separation of complex steroid mixtures for application in clinical, forensic toxicology, and natural products analysis. The development of low-cost MS detectors, in recent years, has also promoted the application of GC-MS systems for the analysis of the complex mixtures. 

As an example, in natural product analysis, SFC offers perspectives in the analysis of several classes of compounds that present difficulties in either conventional LC or GC. In this area, it is very common that the analytes do not have chromophore groups, thus making difficult the detection through UV-vis, the most popular HPLC detector. At the same time. 

Over the last two decades, HPLC has to a large extent superseded the classical modes of open column, thin-layer or paper chromatography previously used for natural product separation and has become an integral part of natural product analysis and preparative isolation. This can be attributed to various factors, including (1) availability of numerous chromatographic modes, robust high-resolution chromatographic materials and... 

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