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 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 for HPLC by automatic tablet extraction

Summary An automatic device combining high-performance liquid chromatography and continuous flow analysis (HPLC/CFA) has been developed for the individual analysis of pharmaceutical tablets. With this fully automated system up to 60 tablets can be analysed in sequence. Between each sequence of tablets up to 3 reference solutions can also be automatically analysed. The reproducibility is better than 2% for all compounds, by repetitive injections of a mixture of drugs.     

Sample preparation for the analysis of flavors and off-flavors in foods

Off-flavors in foods may originate from environmental pollutants, the growth of microorganisms, oxidation of lipids, or endogenous enzymatic decomposition in the foods. The chromatographic analysis of flavors and off-flavors in foods usually requires that the samples first be processed to remove as many interfering compounds as possible. For analysis of foods by gas chromatography (GC), sample preparation may include mincing, homogenation, centrifugation, distillation, simple solvent extraction, supercritical fluid extraction, pressurized-fluid extraction, microwave-assisted extraction, Soxhlet extraction, or methylation. For high-performance liquid chromatography of amines in fish, cheese, sausage and olive oil or aldehydes in fruit juice, sample preparation may include solvent extraction and derivatization. Headspace GC analysis of orange juice, fish, dehydrated potatoes, and milk requires almost no sample preparation. Purge-and-trap GC analysis of dairy products, seafoods, and garlic may require heating, microwave-mediated distillation, purging the sample with inert gases and trapping the analytes with Tenax or C18, thermal desorption, cryofocusing, or elution with ethyl acetate. Solid-phase microextraction GC analysis of spices, milk and fish can involve microwave-mediated distillation, and usually requires adsorption on poly(dimethyl)siloxane or electrodeposition on fibers followed by thermal desorption. For short-path thermal desorption GC analysis of spices, herbs, coffee, peanuts, candy, mushrooms, beverages, olive oil, honey, and milk, samples are placed in a glass-lined stainless steel thermal desorption tube, which is purged with helium and then heated gradually to desorb the volatiles for analysis. Few of the methods that are available for analysis of food flavors and off-flavors can be described simultaneously as cheap, easy and good.     

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 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.     

Sample preparation for planar chromatography

High-performance thin-layer chromatography has favorable properties for high-throughput separations with a high matrix tolerance. Sample preparation, however, is sometimes required to control specific matrix interferences and to enhance the detectability of target compounds. Trends in contemporary applications have shifted from absorbance and fluorescence detection to methods employing bioassays and mass spectrometry. Traditional methods (shake-flask, heat at reflux, Soxhlet, and hydrodistillation) are being challenged by automated instrumental approaches (ultrasound-assisted and microwave-assisted solvent extraction, pressurized liquid extraction, and supercritical fluid extraction) and the quick, easy cheap, efficient, rugged, and safe extraction method for faster and streamlined sample processing. Liquid-liquid extraction remains the most widely used approach for sample clean-up with increasing competition from solid-phase extraction. On-layer sample, clean-up by planar solid-phase extraction is increasingly used for complex samples and in combination with heart-cut multimodal systems. The automated spray-on sample applicator, the elution head interface, biological detection of target and non-target compounds, and straightforward mass spectrometric detection are highlighted as the main factors directing current interest toward faster and simpler sample workflows, analysis of more complex samples, and the determination of minor contaminants requiring high concentration factors.     

Sample preparation by in-gel digestion for mass spectrometry-based proteomics

The proteomic characterization of proteins and protein complexes from cells and cell organelles is the next challenge for investigation of the cell. After isolation of the cell compartment, three steps have to be performed in the laboratory to yield information about the proteins present. The protein mixtures must be separated into single species, broken down into peptides, and, finally, identified by mass spectrometry. Most scientists engaged in proteomics separate proteins by electrophoresis. For characterization and identification of proteomes, mass spectrometry of peptides is the method of choice. To combine electrophoresis and mass spectrometry, sample preparation by “in-gel digestion” has been developed. Many procedures are available for in-gel digestion, which inspired us to review in-gel digestion approaches. Figure Classical in-gel digestion process for a protein band stained with CBB. Protein bands are cut from the polyacrylamide gel (1). CBB molecules (blue circles) bound to the protein are released by iterative incubation in a buffered organic solvent system (2). To increase digestion efficiency and sequence coverage proteins are reduced (3) and alkylated (4). Proteins are subsequently digested with proteolytic enzymes (scissors symbols), typically trypsin (5). Trypsin cleaves at the amino acid residues arginine (R) and lysine (K). The resulting peptides (A, B, and C) are extracted from the polyacrylamide matrix (6). The peptide solution can be further purified for analysis by mass spectrometry (Section “Concentration and desalting of peptides”)     

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 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 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.     

大气颗粒物中有机物色谱分析的样品制备技术

大气颗粒物中有机物成分分析对深入研究大气颗粒物对人类健康、环境、气候、生态的影响,解析气溶胶来源,制定颗粒物控制相关法规,以及风险管理方法具有重要意义。由于颗粒物中的有机组分种类繁多,分析复杂,目前仅10%~20%的有机物得到了定性和定量分析。因此,大气细颗粒中有机物的分析已成为环境分析领域的优先发展方向。色谱是大气颗粒物中有机物分析的主要方法,而样品制备则是影响分析速度和精度的关键步骤。本文对颗粒物中有机组分色谱分析前的样品制备方法进行了综述,介绍了索氏提取、超声辅助提取、微波辅助提取、加压溶剂提取等溶剂提取方法以及热解吸提取方法,并重点介绍了这些方法在大气颗粒物样品处理中的应用,总结了各种方法的优缺点。