China 
Africa 
Explore chapters and articles related to this topic
Sample Preparation Techniques
Published in Somenath Mitra, Pradyot Patnaik, Barbara B. Kebbekus, Environmental Chemical Analysis, 2018
Somenath Mitra, Pradyot Patnaik, Barbara B. Kebbekus
Sample preparation is the step between sampling and analysis. This is the point at which the pollutants are transferred from the environmental matrix to a form suitable for analysis. Extraction is often the first step in sample preparation. The analytes must be separated from the sample because most environmental samples cannot be directly introduced into an instrument. Extraction is done for both organic and inorganic pollutants. Some of the methods of extraction and the types of sample for which they are appropriate are shown in Figure 6.1. For example, traces of pesticides can be extracted from a large volume of water using a relatively small quantity of an organic solvent such as methylene chloride. If the pollutants are strongly bound to the matrix, the extraction may be difficult. Many metals are strongly bound to soil and require aggressive solvents to recover them quantitatively. Organics may also be strongly attached and the solvents in this case cannot be too aggressive or the organic compounds will be destroyed. Similarly, the more soluble an organic analyte is in water, the more difficult it is to extract it into an organic solvent.
Instrumentation and Analysis
Published in Karen D. Sam, Thomas P. Wampler, Analytical Pyrolysis Handbook, 2021
It is not enough to have a pyrolyzer for which the endpoint temperature and heating rate are well characterized to guarantee reproducible results. Sampling, sample handling, introduction, and transfer from the pyrolyzer into the analytical device must be performed with attention to all the inaccuracies that may be introduced. The effects of instrument design and interfacing have been discussed. The most common sources of error in sample manipulation will now be briefly described. The most important areas of concern are sample preparation, including size and shape, homogeneity, and contamination.
Thin-Layer Chromatography in Food Analysis
Published in Bernard Fried, Joseph Sherma, Practical Thin-Layer Chromatography, 2017
It is of interest to point out that proper sample preparation must not only produce a representative portion for analysis, but must also prevent changes in the sample that may result in biased analytical results.36 The mechanical equipment usually generates heat during the processing, which can possibly change the sample composition, such as for fatty foods where the heat may be sufficient to partially melt the fat.36 In such cases, hand chopping and mixing may be the best procedure.36
Effects of miscellaneous plasticity on behavior of lime-treated kaolinites
Published in International Journal of Geotechnical Engineering, 2021
Mahmood Reza Abdi, Amir Chehregosha, Roohollah Farzalizadeh
Sample preparation is one of the most critical steps of an experimental research. In the current study, to prepare samples, predetermined quantities of kaolinites and lime were weighted and thoroughly dry mixed. Then, appropriate OMC determined from compaction tests was gradually sprayed with continuous mixing until complete homogenization. The mixtures were subsequently poured into a metal mould 38 mm in diameter and 80 mm in height in three equal amounts and each layer separately compacted. Specimens were then carefully extruded from the mould using a plunger and a hydraulic jack and weighted. Samples were wrapped in several layers of cellophane to prevent moisture loss during curing and placed in a sealed plastic container and put in an oven set a temperature of 35 ± 2°C. At the end of appropriate curing periods, specimens were taken out and their weight controlled before testing. A maximum difference in weights of samples before and after curing of 1% was recorded which was considered acceptable. For each particular mixture, three samples were prepared and only two were tested. If the test result varied by more than 5%, the third sample was also tested.
Emerging contaminants in the atmosphere: Analysis, occurrence and future challenges
Published in Critical Reviews in Environmental Science and Technology, 2019
Pedro José Barroso, Juan Luis Santos, Julia Martín, Irene Aparicio, Esteban Alonso
Generally, the samples to be analyzed in a laboratory are not in the proper form to perform the analysis directly. The target analytes present in the air samples must be passed to a solvent capable of retaining them, i.e. to say, the analytes must pass from one matrix (air) to another matrix (solvent). Sample preparation usually involves extraction, clean-up and pre-concentration prior to final determination by instrumental techniques. The most common techniques applied for the extraction of EC (Figure 3) are Soxhlet (Bossi et al., 2016; Castro-Jiménez et al., 2016; Xie et al., 2015) (about 69% of the methods described in the literature for the determination of EC in the atmosphere), ultrasonic solvent extraction (USE) (about 23%) (Ferrey et al., 2018; Liu et al., 2015; Lyons & Benvenuti, 2016), pressurized liquid extraction (PLE) (7%) (Clark, Yoon, Sheesley, & Usenko, 2015; Salapasidou et al., 2011; Viana et al., 2011) and, to a lesser extent, microwave assisted extraction (MAE) (Wurl, Potter, Durville, & Obbard, 2006) (1%).
Improving the accuracy of mineral aggregate surface energy estimation based on goniometry
Published in Road Materials and Pavement Design, 2023
Daybis Tencio, Alejandra Baldi, José P. Aguiar-Moya, Ana-Luisa Elizondo-Salas
It is necessary to highlight that the physical characteristics of the sample's surface are crucial for a correct drop placement and subsequent measurements. Consequently, sample preparation is fundamental for ensuring reliable data. In this sense, aggregates appear as a difficult material for SFE determination, since they are porous, highly heterogeneous, and their surface might not be smooth enough for an adequate drop placement.