Food analysis, sample preparation

However, the use of IR spectra is limited for the analysis of food because sample preparation is more complicated in comparison with NIR. Dehydration, homogenization, dissolution or dispersion of samples is necessary. In addition, to make an IR transmission spectra of liquid samples, it is necessary to use a cuvette with very narrow path length of 0.001 - 0.1 mm because the absoiptivities are very high, which causes a sample loading... 

In this chapter, we have discussed some of the basic principles underlying SFE as well as general approaches to the instrumentation used for optimal apphcation of supercritical fluids to the area of analytical-scale SFE. The latter part of this chapter dealt with the apphcation of SFE to specific, representative food product sample preparation. It is expected that these and other new applications will support some needed challenges in food analysis. 

See also Air Analysis Sampling. Chromatography Overview Principles. Clinical Analysis Sample Handling. Drug Metabolism Metabolite Isolation and Identification. Extraction Solid-Phase Extraction. Food and Nutritional Analysis Sample Preparation. Forensic Sciences Volatile Substances. Headspace Analysis Purge and Trap. Perfumes. Sample Handling Sample Preservation Automated Sample Preparation. Sampling Theory. 

See also Atomic Absorption Spectrometry Principles and Instrumentation. Atomic Emission Spectrometry Principles and Instrumentation. Elemental Speciation Overview. Food and Nutritional Analysis Sample Preparation. Ion-Selective Electrodes Overview. Quality Assurance Reference Materials. Sample Dissolution for Elemental Analysis Dry Ashing Oxygen Flask Combustion Wet Digestion Microwave Digestion. Spectrophotometry Inorganic Compounds. Titrimetry ... 

See alsa Chromatography Multidimensional Techniques. Environmental Analysis. Extraction Solid-Phase Extraction. Food and Nutritional Analysis Sample Preparation Contaminants Pesticide Residues. Forensic Sciences Drug Screening in Sport Illicit Drugs. Herbicides. Liquid Chromatography Instrumentation Clinical Applications Food Applications. Mass Spectrometry Peptides and Proteins. Pesticides. Pharmaceutical Analysis Sample Preparation. Proteomics. Sample Handling Automated Sample Preparation. Water Analysis Organic Compounds. 

See also Carbohydrates Overview. Extraction Solid-Phase Extraction Supercritical Fluid Extraction. Food and Nutritional Analysis Sample Preparation Antioxidants and Preservatives Mycotoxins Oils and Fats. Lip-Ids Overview. Peptides. Proteins Overview. Toxins Mycotoxins Neurotoxins. Vitamins Overview Fat-Soluble Water-Soluble. 

See also Air Analysis Sampling. Clinical Analysis Sample Handling. Food and Nutritional Analysis Sample Preparation. Pharmaceutical Analysis Sample Preparation. 

Compatibility physieal influenee with tool ehemieal methods of sample preparation and the stage of determination based on any prineiple of an analytieal signal generation, the opportunity of automation of a sample preparation stage, eontrol, modeling of eonditions of analytieal proeess opens prospeets for their use in the analysis of food-stuffs, environment objeets, geologieal samples, ete. 

On-line coupled LC-GC methods have been developed in food analysis for several reasons, i.e. lower detection limits can be reached, the clean-up is more efficient, and large numbers of samples can be analysed with a minimum of manual sample preparation in shorter times. 

Typical examples that fall in this group would be the determination of the active ingredients in analgesic tablets for pharmaceutical use, such as aspirin or codeine or the analysis of a food product such as margarine. Examples of both these analyses will be described to illustrate the sample preparation procedure. 

Analysis of methyl parathion in sediments, soils, foods, and plant and animal tissues poses problems with extraction from the sample matrix, cleanup of samples, and selective detection. Sediments and soils have been analyzed primarily by GC/ECD or GC/FPD. Food, plant, and animal tissues have been analyzed primarily by GC/thermionic detector or GC/FPD, the recommended methods of the Association of Official Analytical Chemists (AOAC). Various extraction and cleanup methods (AOAC 1984 Belisle and Swineford 1988 Capriel et al. 1986 Kadoum 1968) and separation and detection techniques (Alak and Vo-Dinh 1987 Betowski and Jones 1988 Clark et al. 1985 Gillespie and Walters 1986 Koen and Huber 1970 Stan 1989 Stan and Mrowetz 1983 Udaya and Nanda 1981) have been used in an attempt to simplify sample preparation and improve sensitivity, reliability, and selectivity. A detection limit in the low-ppb range and recoveries of 100% were achieved in soil and plant and animal tissue by Kadoum (1968). GC/ECD analysis following extraction, cleanup, and partitioning with a hexane-acetonitrile system was used. 

Major emphasis in studies of N-nitroso compounds in foods has been placed upon volatile nitrosamines, in part because these compounds are relatively easy to isolate from complex matrices by virtue of their volatility. Procedures utilizing atmospheric pressure or vacuum distillation have been used by most investigators, with variations of the method of Fine e al. (2) being among the most popular. This procedure employs vacuum distillation of a mineral oil suspension of the sample with optional addition of water to improve nitrosamine recovery from low moisture content samples (6) The usual approach to prevention of nitrosamine formation during analysis involves adding sulfamic acid or ascorbate to destroy residual nitrite at an early stage of sample preparation. 

Quality control is intended to monitor and evaluate the performances of both food and human processes that contribute to food quality. The basic principle of this function is the control circle that involves (1) the taking of a process sample by the analysis or measuring unit, (2) determining whether process results meet set tolerances or limits, (3) judging the character and level of any discrepancy, and (4) application of corrective action to adjust the system to an acceptable level (Figure 7.1.1). A distinction is made between measuring and analysis, whereby the first involves direct measurements (e.g., pH, temperature) and the second involves taking samples, sample preparation, and actual analysis. ... 

Sample preparation for AFM analysis is relatively simple. Generally, a desired amount of sample is absorbed onto a smooth and clean substrate surface, for example, a freshly cleaved mica surface. For example, to prepare a food macromolecule sample for AFM imaging in air, the diluted macromolecule solution is disrupted by vortexing. Then, a small aliquot (tens of microliters) of vortexed solution is deposited onto a surface of freshly cleaved mica sheet by pipette. The mica surface is air dried before the AFM scan. A clean surrounding is required to avoid the interference of dust in the air. Molecular combing or fluid fixation may be applied to manipulate the molecule to get more information. 

During the last few years, miniaturization has become a dominant trend in the analysis of low-level contaminants in food and environmental samples. This has resulted in a significant reduction in the volume of hazardous and expensive solvents. Typical examples of miniaturization in sample preparation techniques are micro liquid/liquid extractions (in-vial) and solvent-free techniques such as solid-phase microextraction (SPME). Combined with state-of-the-art analytical instrumentation, this trend has resulted in faster analyses, higher sample throughputs and lower solvent consumption, whilst maintaining or even increasing assay sensitivity. 

Herraiz, T., Sample preparation and reversed phase-high performance liquid chromatography analysis of food-derived peptides, Analytica Chimica Acta, 352, 119, 1997. 

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