Microwave-assisted sample preparation in analytical chemistry

The speed and efficiency of instrumentation for chemical analysis has improved dramatically over the past twenty years. Until recently, however, methods of sample preparation had not changed to keep pace, so this had become the slowest step in analytical chemistry methodology. The widespread adoption of domestic microwave ovens during the past twenty-five years has eventually led to their usage in chemical laboratories. Microwave technology has now advanced to the point where it is revolutionizing chemical sample preparation and chemical synthesis. Since the first application of a microwave oven for sample preparation in 1975, many microwave-assisted dissolution methods have been developed - these are applicable to virtually any kind of sample type. This review attempts to summarize all the microwave-assisted dissolution and digestion methods reported up to and including 1994. In addition, some very recent developments in continuous-flow automated dissolution systems are discussed, as is the emergence of databases and software packages related to the application of microwave technology to sample dissolution. There are 344 references.     

Evaluation of sample preparation protocols for proteomic analysis of sunflower leaves

Six protocols for extraction of proteins from sunflower (Helianthus annuus L.) leaves were evaluated for their abilities in both removing interferents and attaining the best resolution in two-dimensional gel electrophoresis. “Classical” phenol extraction followed by precipitation with ammonium acetate in methanol displayed the most efficient protocol, which allowed the detection of 244 protein spots with ca. 485 μg of protein in gel electrophoresis. Tandem mass spectrometry was performed to identify proteins in 61 spots, and cross species identification was used for this task. Proteins from twenty two spots were identified, and 12 of these proteins are up to now not included into the ExPASy sunflower protein databank.     

Green analytical chemistry in sample preparation for determination of trace organic pollutants

The principles of green chemistry are applied to not only chemical engineering and synthesis, but also increasingly analytical chemistry. We describe environment-friendly analytical techniques applied to isolate and to enrich trace organic pollutants from solid and aqueous samples. Amounts of organic solvents used in analytical laboratories are reduced by applying solventless extraction, extraction using other types of solvent, assisted solvent extraction and miniaturized analytical systems.     

Advances in on-site analytical sample preparation for analysis of environmental waters: A review

The collection, storage, and transportation of water samples from far-off places to the labs is a pretty challenging task. It can cause contamination, degradation, or losses of the analytes, leading to errors in the analysis. On-site sample preparation provides an opportunity to extract the analytes into suitable extraction media that preserves the analytes and is easy to handle in terms of storage and transportation. However, the required equipment for on-site sample preparation should be simple, portable, and energy-efficient. Solvent- and sorbent-based microextraction approaches and the modern variants of solid-phase extraction have shown great potential for on-site sample preparation because of reduced consumption of solvents and low energy requirement. This review provides an overview of the application of different extraction techniques in on-site sample preparation, their advantages, and their limitations. The recent advances combining on-site extraction and analysis have also been critically discussed.     

Evaluation of human plasma sample preparation protocols for untargeted metabolic profiles analyzed by UHPLC-ESI-TOF-MS

Eight human plasma preparation protocols were evaluated for their suitability for metabolomic studies by ultra-high-performance liquid chromatography coupled with electrospray ionization time-of-flight mass spectrometry: organic solvent protein precipitation (PPT) with either methanol or acetonitrile in 2:1 and 3:1 (v/v) ratios with plasma; solid-phase extraction (SPE) using C₁₈ or HybridSPE cartridges; and a combination of PPT and SPE C₁₈ cartridges and microextraction by packed sorbent. A study design in which the order of injection of the samples was not randomized is presented. The analyses were conducted in a BEH C₁₈ column (1.7 μm, 2.1 mm?×?100 mm) using a linear gradient from 100 % water to 100 % methanol, both with 0.1 % formic acid, in 21 min. The most reproducible protocol considering both the univariate and the multivariate analysis results was PPT with acetonitrile in a 2:1 (v/v) ratio with plasma, offering a mean coefficient of variation of the area of all the detected features of 0.15 and one of the best clusterings in the principal component analysis plots. On the other hand, the highest number of extracted features was achieved using methanol in a 2:1 (v/v) ratio with plasma as the PPT solvent, closely followed by the same protocol with acetonitrile in a 2:1 (v/v) ratio with plasma, which offered only 1.2 % fewer repeatable features. In terms of concentration of remaining protein, protocols based on PPT with acetonitrile provided cleaner extracts than protocols based on PPT with methanol. Finally, pairwise comparison showed that the use of PPT- and SPE-based protocols offers a different coverage of the metabolome. Graphical Abstract

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High-quality sample preparation by low kV FIB thinning for analytical TEM measurements.

Focused ion beam specimen preparation has been used for NiTi samples and SrTiO3/SrRuO3 multilayers with prevention of surface amorphization and Ga implantation by a 2-kV cleaning procedure. Transmission electron microscopy techniques show that the samples are of high quality with a controlled thickness over large scales. Furthermore, preferential thinning effects in multicompounds are avoided, which is important when analytical transmission electron microscopy measurements need to be interpreted in a quantitative manner. The results are compared to similar measurements acquired for samples obtained using conventional preparation techniques such as electropolishing for alloys and ion milling for oxides.     

复杂样品痕量极性小分子化合物的样品前处理及分析方法研究进展

核苷、胺、氨基酸等极性小分子化合物是生物、食品、环境等领域重要的研究对象,但各种复杂基体中痕量极性小分子的分离分析需要高效的前处理介质和技术以及快速灵敏的分析方法。本文综述了硅胶材料、有机聚合物、炭材料和硼酸材料等样品前处理分离介质及反相液相色谱、亲水作用色谱等分析方法在复杂样品痕量极性小分子化合物分析中的应用,并展望了其发展趋势。     

干果类食品的样品前处理与分析检测方法研究进展

坚果、果脯等干果类食品含有丰富的营养成分,深受国内外广大消费者的喜爱.但这些食品在果实生产、加工、储运时会使用农药或产生霉变等,造成干果中农药、重金属、霉菌毒素或添加剂等有害成分残留,甚至超过国家限量要求,带来严重的食品安全问题.因此,加强干果类食品的质量监督具有重要的经济和社会意义.但干果类食品基质复杂,有害物质种类...     

Sampling, sample preparation, and analytical variability associated with testing wheat for deoxynivalenol

The variability associated with testing wheat for deoxynivalenol (DON) was measured using a 0.454 kg sample, Romer mill, 25 g comminuted subsample, and the Romer Fluoroquant analytical method. The total variability was partitioned into sampling, sample preparation, and analytical variability components. Each variance component was a function of the DON concentration and equations were developed to predict each variance component using regression techniques. The effect of sample size, subsample size, and number of aliquots on reducing the variability of the DON test procedure was also determined. For the test procedure, the coefficient of variation (CV) associated with testing wheat at 5 ppm was 13.4%. The CVs associated with sampling, sample preparation, and analysis were 6.3, 10.0, and 6.3%, respectively. For the sample variation, a 0.454 kg sample was used; for the sample preparation variation, a Romer mill and a 25 g subsample were used; for the analytical variation, the Romer Fluoroquant method was used. The CVs associated with testing wheat are relatively small compared to the CV associated with testing other commodities for other mycotoxins, such as aflatoxin in peanuts. Even when the small sample size of 0.454 kg was used, the sampling variation was not the largest source of error as found in other mycotoxin test procedures.     

The effects of engineering design on heterogeneous biocatalysis in microchannels

The results of a numerical study of the fundamental interactions of engineering design and micromixing on conversion in packed microchannels are presented. Previously, channel-based microreactors made of molded silicon plastic were designed, fabricated, and experimentally tested. These reactors have enzymes immobilized on the channel walls by various methods including layer-by-layer nano self-assembly techniques. They also contain molded packing features to add reactive surface area and to redistribute the fluid. An arbitrary but intuitively sensible packing arrangement was initially chosen and used in experimental studies. The current computer simulation study was undertaken to understand how static laminar mixing affects the conversion efficiency. The reactors previously used experimentally have been simulated using CFD-ACE+multiphysics software (ESI CFD Inc., Huntsville, AL). It is found that packing significantly increases conversion when compared with empty channels over the entire flow rate range of the study (0.25相似文献   

Click chemistry and biocatalysis for the preparation of pancratistatin analogs

Tricyclic compounds that are advanced precursors for the synthesis of analogs of the antitumoral alkaloid pancratistatin were prepared by a short sequence that involved enzymatic dihydroxylation, epoxidation, and intramolecular Huisgen cycloaddition.     

Temperature-responsive Pickering high internal phase emulsions for recyclable efficient interfacial biocatalysis

The field of biocatalysis is expanding owing to the increasing demand for efficient low-cost green chemical processes. However, a feasible strategy for achieving product separation, enzyme recovery, and high catalytic efficiency in biocatalysis remains elusive. Herein, we present thermoresponsive Pickering high internal phase emulsions (HIPEs) as controllable scaffolds for efficient biocatalysis; these HIPEs demonstrate a transition between emulsification and demulsification depending on temperature. Ultra-high-surface-area Pickering HIPEs were stabilized by Candida antarctica lipase B immobilized on starch particles modified with butyl glycidyl ether and glycidyl trimethyl ammonium chloride, thus simplifying the separation and reuse processes and significantly improving the catalytic efficiency. In addition, the switching temperature can be precisely tuned by adjusting the degree of substitution of the modified starches to meet the temperature demands of various enzymes. We believe that this system provides a green platform for various interfacial biocatalytic processes of industrial interest.

The thermoresponsive Pickering high internal phase emulsions stabilized by starch particles as controllable scaffolds for efficient biocatalysis, which simplified the separation and reuse processes and significantly improved the catalytic efficiency.     

Laminar flow-based electrochemical microreactor for efficient regeneration of nicotinamide cofactors for biocatalysis

One of the long-standing challenges in biocatalysis is the search for methods to continuously regenerate essential cofactors such as NADH that would enable a wide range of enzymes to be used in the more environmentally friendly synthesis of chiral fine chemicals including pharmaceuticals, cosmetics, and food additives. This communication reports a microreactor-based cofactor regeneration method that exploits the microfluidic phenomenon of laminar flow: a reactant stream and a buffer stream are introduced in a microchannel and continue to flow side by side without turbulent mixing between two electrodes that cover opposing channel walls. Adjustment of the flow rate ratio of the two streams in laminar flow enables focusing of the reactant stream close to the cathode, thereby reversing a normally unfavorable reaction equilibrium essential for cofactor regeneration. The absence of a bulk phase in these microreactors prevents the undesired reverse reaction to take place, which has prevented the use of electrochemical cofactor regeneration in macroscale processes. Here, we demonstrate the regeneration of NADH with conversion efficiencies as high as 31%. We also show the subsequent in situ conversion of an achiral substrate, pyruvate, into a chiral product, l-lactate, within this microreactor.     

New odourless protocols for efficient Pauson-Khand annulations

An inexpensive and commercially available odourless additive, dodecyl methyl sulfide, has been shown to be a highly effective promoter in the Pauson-Khand cyclisation of both intra- and intermolecular substrates, affording good to excellent yields of cyclopentenone products.     

The preparation and analytical evaluation of a new heterogeneous membrane electrode for cadmium(ii)

The preparation of a new cadmium-selective heterogeneous membrane electrode obtained by hot-pressing a mixture of cadmium and silver sulfides with polythene in a moulding press is described. Nernstian response to cadmium ion was achieved only when the mixture of salts was purified by heat treatment at 600° in an atmosphere of hydrogen sulfide for several hours. This behaviour is discussed in terms of the purity of the salts. Interferences and analytical applications in aqueous and nonaqueous solvents are described.     

Trends in ultrasonic-based equipment for analytical sample treatment

The recent developments achieved in ultrasonic equipment urges the need for the revision of its applications in analytical chemistry. In the present work, the last ultrasonic devices are easily presented and their applications for sample treatment are critically discussed. Comments are given on edge areas of research, such as proteomics or polymer science, which are presently taking advantage of ultrasonic sample treatments. Future applications and trends for ultrasonic-based handling approaches are also given and commented.     

Focused-microwave-assisted strategies for sample preparation

In this work a general discussion is presented about extraction and digestion procedures, assisted by focused-microwave radiation. Applications involving inorganic, organic, and organometallic analytes in different types of samples are presented, taking into account recent literature data. The main advantages of using focused-microwave radiation are highlighted, such as safety, versatility, control of microwave energy released to the sample, and programmed addition of solutions. All these features can be applied properly in sample preparation for speciation analysis. New routes of development are discussed considering partial digestion by acid-vapor and gradual addition of a liquid sample to hot concentrated acids. Some preliminary results using these strategies are presented to demonstrate their potentiality.     

Ultrafiltration for proteomic sample preparation

Proteome analysis represents significant challenges to the existing sample preparation techniques. Traditional methods, such as two-dimensional electrophoresis, typically separate high-molecular-weight proteins while discarding low-molecular-weight species. This approach is well justified considering the complexity of any proteome. However, it is desirable to extract the maximum amount of information from each sample to investigate the entire range of biomolecules. We have demonstrated that ultrafiltration not only improves two-dimensional electrophoresis (2-DE) resolution of the protein fraction but also yields the low-molecular-weight fraction amenable for further analysis by high-resolution mass spectrometry. This approach was successfully adapted to the variety of biological samples including cell and tissue lysates and serum. Therefore, ultrafiltration offers an alternative sample preparation technique that enables more thorough analysis of a proteome.