Natural products analysis sample preparation

Preparation of samples for use in RRAs varies. If the substance of interest is in biological fluids (e.g., urine, spinal fluid, plasma) it may be possible to add fluid directly to the RRA. In many instances, however, components (salts, proteins) interfere with assay integrity. In this case, it is necessary to devise a preparation scheme suitable for use with the RRA and which does not alter the quantities of the substance of interest, or to incorporate an appropriate internal standard in the method (e.g., radioactive tracer amounts of the compound of interest preferably labeled with an isotope different from that incorporated in the ligand). In the case of natural product analysis, standard aqueous or organic extraction procedures are followed and the sample is freeze-dried or dried to provide the final preparation. Aqueous fractions can be redissolved in assay buffers whereas dimethylsulfoxide (DMSO) is a useful solvent for organic extracts since many RRAs tolerate < 1 % DMSO in the final assay. 

Application of rotating coiled columns has become attractive for preparative-scale separations of various substances from different samples (natural products, food and environmental samples) due to advantages over traditional liquid-liquid extraction methods and other chromatographic techniques. The studies mainly made during the last fifteen years have shown that using rotating coiled columns is also promising for analytical chemistry, particularly for the extraction, separation and pre-concentration of substances to be determined (analytes) before their on-line or off-line analysis by different determination techniques. 

Natural products, from plants and foods to rocks and minerals, are complicated systems, but their analysis by Raman spectroscopy is a growing area. Most examples come from quality control laboratories, motivated to replace current time-consuming sample preparation and analysis steps with a less labor-intensive, faster technique but most authors anticipated the eventual application to process control. Often a method will be practiced in a trading house or customs facility to distinguish between items perceived to be of different qualities, and thus prices. 

Authenticity evaluation has recently received increased attention in a number of industries. The complex mixtures involved often require very high resolution analyses and, in the case of determining the authenticity of natural products, very accurate determination of enantiomeric purity. Juchelka et al. have described a method for the authenticity determination of natural products which uses a combination of enantioselective multidimensional gas chromatography with isotope ratio mass spectrometry (28). In isotope ratio mass spectrometry, combustion analysis is combined with mass spectrometry, and the 13C/12C ratio of the analyte is measured versus a C02 reference standard. A special interface, employing the necessary oxidation and reduction reaction chambers and a water separator, was used employed. For standards of 5-nonanone, menthol and (R)-y-decalactone, they were able to determine the correct 12C/13C ratios, with relatively little sample preparation. The technical details of multidimensional GC-isotope ratio MS have been described fully by Nitz et al. (29). A MDGC-IRMS separation of a natural ds-3-hexen-l-ol fraction is... 

Even though sample preparation is usually the most time-consuming step in natural product research, this particular case study demonstrated that phytochemical investigations can positively benefit from fast GC methods to reduce the overall analysis time. 

Chromatography techniques with different detectors followed by skillful sample preparation are usually applied to quantify these antioxidants in natural sources. These techniques offer sensitive and specific analysis methods for most of the antioxidants. This is the first book that particularly covers and summarizes the details of sample preparation procedures and methods developed to identify and quantify various types of natural antioxidants in plants and food products. In the book, the principle of quantification methods for natural antioxidant-rich phytochemicals is introduced and current methods used in the determination of antioxidants in different sources are reviewed and summarized by experts in the field. As a handbook of analysis of natural antioxidant-rich phytochemicals, the book provides useful information for many researchers in this area to learn ideal analysis methods for the antioxidants they are examining. The book may also serve as a lecture resource for courses in food analysis, functional foods, and nutrition. 

Analysis strategies that use on-line ESI-LC/MS approaches provide an integrated format for natural product dereplication by combining traditional fraction collection, sample preparation, and multi-component analysis into a single step. In this way, crude extracts are screened without extensive purification and chemical analysis. Furthermore, less material is required due to the sensitivity of the technique and chromatographic resolution is retained. 

In 1982, Ciurczak and Torlini published on the analysis of solid and liquid dosage forms [74], They contrasted NIR calibrations for natural products versus those for pharmaceuticals. Samples prepared in the laboratory are spectrally different from production samples. Using laboratory samples for calibration may lead to unsatisfactory results production samples for calibration are preferred for calibration. 

The development of a method for preparative HP-RPC purification for the purpose of isolation of one or more component(s) from a natural product sample (or alternatively the purification of a synthesized product from natural occurring precursors) is usually performed in four steps (1) development, optimization, and validation of an analytical method, (2) scaling up of this method to a preparative chromatographic system, (3) application of the preparative method to the fractionation of the product, and (4) analysis of the individual fractions. 

A specific application of environmental SPE is sample preparation of extra-large volumes (from 10 to 100 L). This work was pioneered in the early 1970s by Junk and co-workers (1974) for the analysis of trace organic compounds in water using styrene-divinylbenzene copolymers (XAD-2 resin from Rohm and Haas) and by Thurman and Malcolm (1981) and Leenheer and Stuber (1981) for the analysis of natural organic substances in water (humic substances). One can obtain the XAD resins from Supelco (Appendix Products Guide) and still follow the protocol of this early work for the isolation of contaminants and humic substances from large volumes of water (10-1000 L of water). 

The sample preparation and FIPLC analysis are more elaborate for formulations with multiple APIs (e.g., over-the-counter (OTC) products) or with natural products. Examples of HPLC analysis of two OTC multi-vitamin products are shown in Figure 6.5, with a summary of method performance for both water-soluble and fat-soluble vitamins17 listed in Table 6.5. Other examples of HPLC analysis of extracts of natural products (white and red ginseng)18 are... 

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