Sample preparation for the analysis of heavy metals in foods

The analysis of foodstuffs for heavy metals continues to be an area of intense activity for analytical chemists. Methods of sample preparation are changing to allow a growing number of samples to be handled and to facilitate 'speciation' studies.     

Sample preparation techniques for the determination of trace residues and contaminants in foods

The determination of trace residues and contaminants in complex matrices, such as food, often requires extensive sample extraction and preparation prior to instrumental analysis. Sample preparation is often the bottleneck in analysis and there is a need to minimise the number of steps to reduce both time and sources of error. There is also a move towards more environmentally friendly techniques, which use less solvent and smaller sample sizes. Smaller sample size becomes important when dealing with real life problems, such as consumer complaints and alleged chemical contamination. Optimal sample preparation can reduce analysis time, sources of error, enhance sensitivity and enable unequivocal identification, confirmation and quantification. This review considers all aspects of sample preparation, covering general extraction techniques, such as Soxhlet and pressurised liquid extraction, microextraction techniques such as liquid phase microextraction (LPME) and more selective techniques, such as solid phase extraction (SPE), solid phase microextraction (SPME) and stir bar sorptive extraction (SBSE). The applicability of each technique in food analysis, particularly for the determination of trace organic contaminants in foods is discussed.     

Sample preparation in analysis of pharmaceuticals

Sample preparation is a very important and essential step in environmental analysis. This article presents an overview of extraction methods for environmental samples, focusing especially on pharmaceuticals as there is great concern about them as pollutants.     

Sample preparation for chromatographic analysis of food.

Sampling, homogenisation and sample preparation prior to chromatographic injection of food analytes are designed to enhance accuracy and precision. The reduction of inherent errors introduced by these steps requires the analyst's attention as a matter of course. Methods and examples of minimising errors in each step are reviewed.     

Sample preparation of archaeological materials for PIXE analysis

A method to prepare thin samples of archeological materials such as potteries and bones for PIXE analysis is presented. In this method fine powder of the matter under analysis is suspended and deposited on polycarbonate filters. The process takes place in a chamber where clean air and the powder are mixed and forced to pass through the filter. Thin samples with typical mass density of about 50 g cm^–2 are obtained. The uniformity of the mass deposit has been optically tested with a He–Ne laser showing fluctuations of the order of one percent. Samples of clay standards from NIST were prepared with this method and analyzed by PIXE. The agreement between our results and NIST values is very good, with linear correlation factors close to unity. The method was applied to study the elemental composition of clay from different fragments of a Chilean pre-Hispanic pottery piece. These results are very consistent showing that the analysis of samples from a small fragment can represent the whole piece.Work supported in part by FONDECYT Grant 1052-92.     

Sample preparation for the chemical analysis of debris in suspect arson cases

Abroad review of current methods for the recovery of liquid residual accelerants in fire debris is given. A summary of current practices of sample preparation methods in U.S. laboratories is presented. Sampling of heated headspace is useful as a screening method. It is also applicable for samples that contain a high concentration of accelerant. Distillation-based methods are effective only when large amounts of accelerants are present but they permit the physical isolation of relatively pure liquids, including some water-soluble materials such as alcohols. Solvent extraction is particularly advantageous for accelerants of low volatility such as diesel fuel or highly evaporated petroleum-based products, but it is very susceptible to interferences from the matrix. Dynamic enrichment by adsorption/elution is the most popular and widely used recovery method for liquid accelerants. It offers high enrichment factors but shows weaknesses with respect to polar and low-volatility liquids. No single method is universally effective for all types of accelerants that are commonly encountered in practice. It appears that currently applied recovery methods are particularly weak for water-soluble organics such as alcohols. Sample preparation methods have to be viewed in conjunction with the method to be used to characterize and identify suspect accelerants. Gas chromatography is used almost exclusively for separation and measurement. Selective detection of components that are diagnostic of accelerants allows important trade-offs between sensitivity, chromatographic efficiency and the level of interferences that can be tolerated. Pattern recognition with comparison of chromatographic profiles is greatly simplified if interferences from the matrix can be suppressed. Application of capillary columns capable of high resolution facilitates the recognition of diagnostically important components. Petroleum-based fluids and products are ubiquitous in the human environment and it is therefore particularly important to pay attention to petroleum-based fluids that are derived from such sources. Many common inconspicuous household materials contain petroleum-based solvents and are thus a part of the natural background. The term sensitivity as it relates to the effectiveness of a recovery method must be critically viewed in this light.     

Solid-phase microextraction in the analysis of food taints and off-flavors

Selected food taints and off flavors, for which solid phase microextraction (SPME) has been used as a method for volatiles isolation, are the subject of review. Compounds responsible for musty and earthy odor off-flavors and taints in foods are discussed. This group contains haloanisoles, geosmin, and methylisoborneol. Chlorophenols are discussed as precursors of chloroanisoles and compounds impairing the flavor of food. Also described are volatile phenolic compounds responsible for medicinal off flavors, mainly ethyl phenols and vinyl phenols. Sulfur compounds that contribute to off-flavor are also discussed. Finally, a group of volatile compounds being the products of lipid oxidation are summarized. A short review of the formation, occurrence, and information on odor properties of all of these groups of compounds is given. Examples of SPME use for the analysis of compounds belonging to all described groups are shown. Elaboration of method parameters, fiber selection, experimental conditions, and quantitation of compounds are subjects of interest. Also, applications of SPME as a method for introduction of volatiles in mechanical olfaction technologies are shortly outlined.     

A review of sample preparation methods for the pesticide residue analysis in foods

The pesticide residues in foods have received increasing attention as one of the most important food safety issues. Therefore, more strict regulations on the maximum residue limits (MRLs) for pesticides in foods have been established in many countries and health organizations, based on the sensitive and reliable analysis methods of pesticide residues. However, the analysis of pesticide residues is a continuing challenge mainly because of the small quantities of analytes as well as the large amounts of interfering substances which can be co-extracted with them, often leading to experimental errors and damage to the analytical instruments. Thus, extensive sample preparation is often required for the pesticide residue analysis for the effective extraction of the analytes and removal of the interferences. This paper focuses on reviewing the recent development in the sample preparation methods for the pesticide residue analysis in foods since 2006. The methods include: liquid-liquid extraction (LLE), supercritical-fluid extraction (SFE), pressurized-liquid extraction (PLE), microwave-assisted extraction (MAE), ultrasound-assisted extraction (UAE), gel permeation chromatography (GPC), solid-phase extraction (SPE), molecularly imprinted polymers (MIPs), matrix solid-phase dispersion (MSPD), solid-phase micro-extraction (SPME), QuEChERS, cloud point extraction (CPE) and liquid phase micro-extraction (LPME), etc. Particularly their advantages, disadvantages and future perspectives will be discussed.     

Sample preparation for the analysis of volatile organic compounds in air and water matrices

This review summarizes literature data from the past 5 years on new developments and/or applications of sample preparation methods for analysis of volatile organic compounds (VOC), mainly in air and water matrices. Novel trends in the optimization and application of well-established airborne VOC enrichment techniques are discussed, like the implementation of advanced cooling systems in cryogenic trapping and miniaturization in adsorptive enrichment techniques. Next, focus is put on current tendencies in integrated sampling-extraction-sample introduction methods such as solid phase microextraction (SPME) and novel in-needle trapping devices. Particular attention is paid to emerging membrane extraction techniques such as membrane inlet mass spectrometry (MIMS) and membrane extraction with a sorbent interface (MESI). For VOC enrichment out of water, recent evolutions in direct aqueous injection (DAI) and liquid-liquid extraction (LLE) are highlighted, with main focus on miniaturized solvent extraction methods such as single drop microextraction (SDME) and liquid phase microextraction (LPME). Next, solvent-free sorptive enrichment receives major attention, with particular interest for innovative techniques such as stir bar sorptive extraction (SBSE) and solid phase dynamic extraction (SPDE). Finally, recent trends in membrane extraction are reviewed. Applications in both immersion and headspace mode are discussed.     

Sample preparation for CE-DAD analysis of the water soluble vitamins in food products

The capillary electrophoretic separation of six water-soluble vitamins (thiamine, nicotinic acid, nicotinamide, d-pantothenic acid, pyridoxine and ascorbic acid) was studied. Four CE backgrounds electrolytes were optimized and the most suitable ones were applied for investigation of analytes in real samples (yeast, beer, syrups). Several extraction procedures were performed in order to extract vitamins from proteins and phosphate groups. The research showed that it is possible to minimize interference from the solution with a complex composition and overcome the problem of peak overlapping by exchanging separation BGEs. Moreover, the second order data generated by CE-DAD instrument and Chemstation software (Agilents Technologies) were used to check of the peak purity.     

Sample preparation and fractionation techniques for intact proteins for mass spectrometric analysis

The analysis of proteins in biological samples is highly desirable, given their connection to myriad biological functions and disease states, as well as the growing interest in the development of protein‐based pharmaceuticals. The introduction and maturation of “soft” ionization methods, such as electrospray ionization and matrix‐assisted laser desorption/ionization, have made mass spectrometry an indispensable tool for the analysis of proteins. Despite the availability of powerful instrumentation, sample preparation and fractionation remain among the most challenging aspects of protein analysis. This review summarizes these challenges and provides an overview of the state‐of‐the‐art in sample preparation and fractionation of proteins for mass spectrometric analysis, with an emphasis on those used for top‐down proteomic approaches. Biological fluids, particularly important for clinical and pharmaceutical applications and their characteristics are also discussed. While immunoaffinity‐based methods are addressed, more attention is given to non‐immunoaffinity‐based methods, such as precipitation, coacervation, size exclusion, dialysis, solid‐phase extraction, and electrophoresis. These techniques are presented in the context of a significant number of studies where they have been developed and utilized.     

Sample preparation for gas chromatographic analysis of organic solvents in aerosol cans

Summary A method for the sampling of chemical products from aerosol cans is described. An aerosol can is frozen in liquid nitrogen, followed by puncturing the can and allowing the propellant to distill off. The conditions for the smaple preparation have been optimized. Solvent content in the products were analysed by headspace gas chromatography-mass spectrometry.     

Sample preparation procedure for PIXE elemental analysis on soft tissues

Neutral aqueous solutions of Nickel II-diethylenetriaminepentaacetate (DTPA) were irradiated using -rays both in the presence and in the absence of oxygen. A radiolytic mechanism has been proposed and discussed. It has been suggested that the radiolytic degradation of the ligand is due to the formation of OH^* during radiolysis.     

Sample preparation in routine analysis for quartz in dust by x-ray diffractometry

To achieve better reproducibility in the x-ray diffractometric determinations of quartz, the particle size of samples and of the internal standard substance, and the pore size of filters, should be set in the ranges <10 μm and 0.5–0.8 μm, respectively with loadings less than 10 mg cm^?2.     

Solid-phase microextraction for the enantiomeric analysis of flavors in beverages

Solid-phase microextraction combined with gas chromatographic/mass spectrometric analysis and separation on a chiral cyclodextrin stationary phase was a rapid, reliable technique for profiling chiral aroma compounds in flavored alcoholic beverages. Several enantiomeric terpenes, esters, alcohols, norisoprenoids, and lactones were identified in berry-, peach-, strawberry-, and citrus-flavored wine and malt beverages (wine coolers). Using this technique, we were able to confirm the addition of synthetic flavoring to several beverages, consistent with label designations.