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Thick Target Particle-Induced X-Ray Emission
Published in Zeev B. Alfassi, Max Peisach, Elemental Analysis by Particle Accelerators, 2020
Internal standards can take the form of either the addition of a known amount of a selected element not present in the sample or by selecting one element in the sample as a reference element. While the former procedure can yield absolute concentrations, only relative values can be deduced from the latter procedure unless further intercalibrations with other standards are subsequently carried out.
Chemical Analysis Basics
Published in Thomas J. Bruno, Paris D.N. Svoronos, CRC Handbook of Basic Tables for Chemical Analysis, 2020
Thomas J. Bruno, Paris D.N. Svoronos
An internal standard is a compound added to a sample at a known concentration, the purpose of which is to exhibit a similar signal when measured in an instrument, but be distinguishable from the signal of the desired analyte. It provides the highest level of reliability in quantitation by chromatographic methods and is not affected by large differences in sample size [8]. Unlike the internal normalization method, it is not necessary to elute or measure all the components of the sample, one needs focus only on the component(s) of interest. In atomic spectrometry, this method is not affected by changes in gas flow rates, sample aspirations rates, and flame suppression or enhancement. Another situation in which this method is valuable is when the sample matrix is either unknown or very complex, precluding the preparation of external standards.
Methods for Analysis of Solid Samples
Published in Somenath Mitra, Pradyot Patnaik, Barbara B. Kebbekus, Environmental Chemical Analysis, 2018
Somenath Mitra, Pradyot Patnaik, Barbara B. Kebbekus
The GC is calibrated by injection of standards of each component of interest at a minimum of five concentrations in isooctane. These calibration mixtures may be prepared in the lab, and are also commercially available. Internal standard calibration may be used, in which case the analyst must select one or more internal standard compounds which are similar in their analytical behavior of the analytes of interest. This means that they must elute well on the selected GC column, but not interfere with any of the components present in the samples. The internal standard must also not be contained in the sample, and must have a similar volatility to the analytes. There is no single internal standard which is recommended for this method because of these limitations. The analyst must use good chemical judgment here.
Comparative analysis of various waste cooking oils for esterification and transesterification processes to produce biodiesel
Published in Green Chemistry Letters and Reviews, 2021
Ikram ul Haq, Ayesha Akram, Ali Nawaz, Xin Zohu, Syed Zaghum Abbas, Yong Xu, Mohd Rafatullah
Internal standards measure the process's capacity to extract required analytes from the sample matrix, and are used to monitor and regulate instrument fluctuations. Chloroform is added in a specific amount to samples, the blank and calibration samples in a chemical analysis. It is used to correct for the damage of any analyte during sample preparation, injection or ionization. Higher ester amount indicates the good quality biodiesel formation with lower side products. The largest peak in Figure 10(a) showed the presence of high amount of esters of octadecanoic acid (62.02%) followed by octadecadienoic (10.85%), hexadecadienoic acid (8.91%) along with eicosadienoic acid (6.45%), pentadecanoic acid (4.23%), tetradecanoic acid (4.10%) and heptacosanoic acid (3.92%) in alkali catalyzed process. The chemical composition of lipase catalyzed biodiesel Figure 10(b) gave the presence of high amount of octadecenoic methyl esters (60.09%) in the final product followed by hexadecadienoic acid methyl esters (7.38%), octadecadienoic acid methyl esters (12.31%) (51).
An overview of the current progress, challenges, and prospects of human biomonitoring and exposome studies
Published in Journal of Toxicology and Environmental Health, Part B, 2019
Mariana Zuccherato Bocato, João Paulo Bianchi Ximenez, Christian Hoffmann, Fernando Barbosa
In recent years, targeted metabolome analyses have become more rapid and straightforward with the ability to measure several target compounds with the use of several commercial kits (Siskos et al. 2017). For these analyses, methods were developed for the selected metabolite(s), which undergoes an analytical validation, after standardized protocols that examine selectivity, precision, linearity, limits of detection (LOD) and limits of quantification (LOQ), and robustness before application. Internal standards and compounds with labeled isotopes are used to improve accuracy and handle matrix effects. A Certified Reference Standard (SRM) for human plasma was recently produced by NIST (National Institute of Standards and Technology) which displays the capacity to identify approximately 100 metabolites and environmental contaminants with certified values (Simón-Manso et al. 2013). The use of this material enables an advancement in the validation of results in routine metabolomic analysis (Phinney et al. 2013).
Ecological and human health risks associated with metals in water from Anka Artisanal Gold Mining Area, Nigeria
Published in Human and Ecological Risk Assessment: An International Journal, 2021
Adeniyi JohnPaul Adewumi, Temitope Ayodeji Laniyan
An internal standard was analyzed after every 10 samples; a calibration standard was analyzed to check the response and efficiency of the analytical instrument alongside the blank which was used to constantly check for contamination. Calibration curves were adjusted by the use of quality control standards at every step of sample reading. All glassware were soaked in 10% HNO3 overnight and thoroughly washed with distilled water and dried in an oven overnight at 50–60 °C. After oven-drying, the glassware were dried in a desiccator for about 20 min before use. The analytical precision, determined by quality assurance/quality control procedures, using duplicates, reagent blanks, and internal standards, was better than ±10%.