Phase identification and quantification

One application of powder diffraction is phase identification. Since zeolites of the same structure type give similar powder patterns, the powder pattern can be used as a fingerprint to identify the zeolite type. Furthermore, when multiple phases are present, the powder pattern is a superposition of the patterns for each of the separate phases and the relative overall intensities of the peaks is related to the amount of each phase. Thus patterns from mixtures of phases can be analyzed to determine the identity and relative amount of each phase. 

This approach is commonly employed for bound zeolites. In this manner the relative amount of crystalline zeolite present can be determined. As usually implemented, the method provides a number that is the ratio of intensities for peaks in the diffraction pattern of the sample of interest to the intensity of the same peaks in the pattern of a reference zeolite. Since the intensity ratio is often expressed as a percentage, it is commonly referred to as percent zeolite crystallinity. The better terminology is relative amount of crystalline zeolite compared to a specific reference. 

Typically several diffraction peaks are used for comparison. ASTM method D3906 for faujasite materials uses a comparison of eight different peaks. Although the method was developed for FCC catalysts, it is also applicable to other FAU-type 

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X-ray scattering techniques are the most commonly applied complementary discipline to microscopy for structural studies. The type of information that is obtained by x-ray scattering experiments includes phase identification and quantification, crystallinity, crystallite size, lattice constants, molecular orientation and structure, molecular packing and order, and amorphous structure [26-30]. Diffraction techniques that will be described include powder diffraction, wide angle x-ray scattering (WAXS), and fiber diffraction. Small angle x-ray scattering (SAXS) will be described in Section 7.4.4. 

Finally, the XRD pattern-fitting procedures in QPA often indicate the presence, in the difference curve, of minor or trace phases previously hidden by extensive peak overlap with major phases. An iterative procedure, going back and forth between phase identification and quantification, is therefore very common and instrumental in obtaining a complete analysis. 

Knowledge of the identity of phenolic compounds in food facilitates the analysis and discussion of potential antioxidant effects. Thus studies of phenolic compounds as antioxidants in food should usually by accompanied by the identification and quantification of the phenols. Reversed-phase HPLC combined with UV-VIS or electrochemical detection is the most common method for quantification of individual flavonoids and phenolic acids in foods (Merken and Beecher, 2000 Mattila and Kumpulainen, 2002), whereas HPLC combined with mass spectrometry has been used for identification of phenolic compounds (Justesen et al, 1998). Normal-phase HPLC combined with mass spectrometry has been used to identify monomeric and dimeric proanthocyanidins (Lazarus et al, 1999). Flavonoids are usually quantified as aglycones by HPLC, and samples containing flavonoid glycosides are therefore hydrolysed before analysis (Nuutila et al, 2002). 

Fractions are concentrated under vacuum below 35°C. Alternatively, they can be purified and concentrated by solid phase extraction (SPE) before identification and quantification, which is a valuable procedure for samples containing low amounts of pigments. After concentration, fractions can be stored in small flasks, protected from light, sealed under inert atmosphere, and kept below -20°C until analysis. 

The identification and quantification of potentially cytotoxic carbonyl compounds (e.g. aldehydes such as pentanal, hexanal, traw-2-octenal and 4-hydroxy-/mAW-2-nonenal, and ketones such as propan- and hexan-2-ones) also serves as a useful marker of the oxidative deterioration of PUFAs in isolated biological samples and chemical model systems. One method developed utilizes HPLC coupled with spectrophotometric detection and involves precolumn derivatization of peroxidized PUFA-derived aldehydes and alternative carbonyl compounds with 2,4-DNPH followed by separation of the resulting chromophoric 2,4-dinitrophenylhydrazones on a reversed-phase column and spectrophotometric detection at a wavelength of378 nm. This method has a relatively high level of sensitivity, and has been successfully applied to the analysis of such products in rat hepatocytes and rat liver microsomal suspensions stimulated with carbon tetrachloride or ADP-iron complexes (Poli etui., 1985). 

Vandecasteele, K., Gaus, I., Debreuck, W., and Walraevens, K., Identification and Quantification of 77 Pesticides in Groundwater Using Solid Phase Coupled to Liquid-Liquid Microextraction and Reversed-Phase Liquid Chromatography, Anal. Chem. 72, 3093, 2000. 

The inventory tasks is to collect environmentally important information about relevant processes involved in the product system. Inventory collects information about unit processes at first and subsequently, an inventory of inputs and outputs of the system and its surroundings is carried out. The goal is the identification and quantification of all elementary flows associated with product system. Inventory analysis is the nature of the technical implementation of LCA studies. It is an essential part of a study, has high demands for data availability, practical experience in modelling product systems and, in the case of using database tools, it is necessary to master them perfectly and to understand their function [46]. The inventory phase principle is data collection that is used to quantify values of the elementary flows. This phase represents a major practical part of the LCA study, time consuming and with demands for data availability and author s experience with modelling product system studies [47],... 

Identification and quantification of natural dyes need high performance analytical techniques, appropriate for the analysis of materials of complicated matrices containing a small amount of coloured substances. This requirement perfectly fits coupling of modern separation modules (usually high performance liquid chromatography in reversed phase mode, RPLC, but also capillary electrophoresis, CE) with selective detection units (mainly mass spectrometer). 

Recent studies, including the use of Microtox and ToxAlert test kits [55,56], were carried out for the determination of the toxicity of some non-ionic surfactants and other compounds (aromatic hydrocarbons, endocrine disruptors) before implementation on raw and treated wastewater, followed by the identification and quantification of polar organic cytotoxic substances for samples with more than 20% inhibition. Furthermore, the study of their contribution to the total toxicity was obtained using sequential solid-phase extraction (SSPE) before liquid chromatography-mass spectrometry (LC-MS) detection. This combined procedure allows one to focus only on samples containing toxic substances. 

Endo, Y., Tagiri-Endo, M., Seo, H. S., and Fujimoto, K. (2001). Identification and quantification of molecular species of diacylglyceryl ether by reversed-phase high-performance liquid chromatography with refractive index detection and mass spectrometry. J. Chro-matogr. A 911, 39-45. 

For the determination of cresol in water, CLP guidelines state that the aqueous sample be brought to pH 11 by the addition of sodium hydroxide (NaOH). The basic mixture is then extracted with methylene chloride either in a separatory funnel or a continuous liquid-liquid extractor. The aqueous phase is then acidified to pH 2 and reextracted with methylene chloride. This second extract is concentrated by evaporation and subjected to GC/mass spectrometry (MS) analysis for identification and quantification. 

Nicoletti I, De Rossi A, Giovinazzo G, Corradini D. Identification and quantification of stUbenes in fruits of transgenic tomato plants (Lycopersicon esculentum Mill.) by reversed phase HPLC with photodiode array and mass spectrometry detection. Journal of Agricultural and Food Chemistry 55, 3304-3311, 2007. 

BAs are extracted with a Ci8 reversed-phase column, identified and quantified by simultaneous monitoring of their parent and daughter ions, using the MRM mode. Identification and quantification of conjugated BAs in bile is achieved in 5 min. The detection limit is 1 ng, and the response is linear for concentrations up to 100 ng. 

Chromatography, the process by which the components of a mixture can be separated, has become one of the prime analytical methods for the identification and quantification of compounds from a liquid or homogeneous gas phase. The principle is based on the concentration equilibrium of the compounds of interest between two phases one of which is called stationary because it is immobilised in a column, the other of which is called mobile because it is the transport mechanism through the system. The differential migration of compounds through the column leads to their separation. 

Since considerable amounts of potential interfering materials can be extracted along with the polyphenolics, an isolation/purification step is often required to eliminate components that may interfere with analysis. The fractionation techniques presented in Basic Protocol 2 and Alternate Protocol 2, using solid-phase extraction to minimize the effects of sample preparation/cleanup on the integrity of the extract, will make possible the identification and quantification of individual polyphenolics by HPLC (unit ii j), MS, and NMR. 

GC combined with mass spectroscopic (MS) detection provides very accurate identification and quantification of FFAs. Pinho et al. (2003) monitored changes in the FFA content during the ripening of ewe cheese. Sampling was done by headspace solid-phase microextraction (SPME). An excellent correlation was observed between the initial concentration of the sample and the amount absorbed on the SPME fiber. SPME sampling was done at 65 °C with a fiber coated with 85-p.m polyacrylate film. After equilibration at 65 °C for 40 min, the fiber was exposed to the sample headspace for 20 min and inserted into the GC port. Despite its accuracy, the GC-MS method is not widely used, presumably because of its cost and complexity. 

Another LC-APCI-MS method has been developed and validated by Zhang et al. for the identification and quantification of zaleplon in human plasma using estazolam as an IS. After the addition of estazolam and 2.0 M sodium hydroxide solution, plasma samples were extracted with ethyl acetate and then the organic layer was evaporated to dryness. The reconstituted solution of the residue was injected onto a prepacked Shim-pack VP-ODS C18 (250 mm x 2.0 mm i.d.) column and chromatographed with a mobile phase comprised methanol-water (70 30) at a flowrate of 0.2 ml/min. 

The other form of on-line solid-phase extraction procedures involves column-switching techniques. Column switching employs valves that can be switched manually or automatically between a number of columns at predetermined times.67-69 For sample cleanup the analyte of interest is retained on the primary or precolumn while the interfering matrix components are eluted to waste. The analytes are then diverted to a second or analytical column where they are separated for identification and quantification. 

The most useful method for solvent residue analysis is GC. It can be performed by direct injection technique, or by headspace, solid phase microextraction (SPME), or single-drop microextraction (SOME) techniques [96]. GC has high selectivity, good specificity, is easy to perform, and involves simple sample preparation. Modem capillary GC allows separation of many compounds, together with their identification and quantification [96]. GC uses different detector systems, which are presented in Table 8.7. 

The application of multidimensional gas chromatography (MDGC) to essential oil analysis is a great development in the determination of such complex samples. This is an appropriate approach when there are zones on the chromatogram where the peaks are not well resolved, which is a common situation in natural samples. The fractions corresponding to the zones with unresolved peaks are transferred to a second column containing a different stationary phase, where they are separated and completely resolved. Therefore MDGC permits the separation of poorly resolved peaks and increases resolution, with the final result of an improvement in both identification and quantification of components of essential oils. 

Identification and quantification of low molecular weight and volatile phenols is usually performed by Gas Chromatography and Mass Spectrometry (GC-MS). For analysis and structural characterization of more polar compounds such as polyphenols, liquid-phase and Liquid Chromatography Mass Spectrometry (LC-MS) and Multiple Mass Spectrometry (MS/MS and MSn) techniques are used (Niessen and Tinke, 1995 de Hoffmann, 1996 Abian, 1999 Flamini et al., 2007). 

Despite recent efforts toward settling operational conditions for metal and metalloid fractionation assays—in terms of concentration, pH, and temperature for each of the leaching reagents, sample weight/extractant volume ratio, extraction time, shaking protocol, analytical instrumentation, and phase separation method —conventional sequential extraction schemes lack automation and are inherently rather time consuming and laborious. This is the consequence of a number of steps needed for the separation, identification, and quantification of TEs in each fraction. For example, the SM T recommended protocol lasts more than 50 hours, whereas the operating time of Tessier s scheme approaches 20 hours. 

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