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Tissue Preparation for Liquid Scintillation and Gamma Counting — the Counting Processes
Published in Lelio G. Colombetti, Principles of Radiopharmacology, 2019
Howard J. Glenn, Lelio G. Colombetti
The internal standards method51 — This method assumes that an added standard of the same isotope will be quenched in a fashion and in amount similar to that of the unknown sample. Standard amounts of tritium or carbon-14 compounds in toluene solution are avaialble from many suppliers; information is provided as to exact disintegrations per minute (dpm) per volume at different temperatures along with the error in the determination. Therefore, a given volume, if pipetted accurately, when added to a scintillation cocktail, will give a specific number of counts per minute (cpm), and thus the counting efficiency can easily be determined. It is assumed that the unknown sample is counted with the same efficiency as the internal standard. The sample is counted (C,), the standard added to the sample, and the sample counted again (C2). Counting efficiency then equals C2-C1/Dis, where Dis is the calibrated activity of the internally added standard in dpm. When properly carried out, this method may be the most accurate of the methods for quench correction. The accuracy of the method depends on the quality of the pipetting and on the level of activity added as the internal standard. It works well in a variety of situations involving both chemical and color quenching. Since two counts are required for each sample, the method is time consuming, and once the standard is added to the sample, questions regarding the initial counting cannot be resolved.
Development and Evaluation
Published in Joseph Chamberlain, The Analysis of Drugs in Biological Fluids, 2018
Although there is sometimes confusion in the literature on the meaning of internal standard, the generally accepted definition is that it is a compound similar in chemical structure to that being analyzed, which is added at a known concentration to the sample prior to analysis; this standard is measured at the end point and its percentage recovery applied to correct the end point value for the drug being analyzed.
Metabolomic Techniques to Discover Food Biomarkers
Published in Dale A. Schoeller, Margriet S. Westerterp-Plantenga, Advances in the Assessment of Dietary Intake, 2017
Pekka Keski-Rahkonen, Joseph A. Rothwell, Augustin Scalbert
In quantitative MS-based bioanalysis, addition of internal standards is usually performed during the sample preparation. Quantification is then based on the response ratio of the analyte to the internal standard, calculated as a function of the concentration of the analyte. This is an efficient way of compensating for multiple sources of variability, and can cover the entire analytical process from sample extraction to detection. However, due to physicochemical differences between the analytes, any single compound cannot be used as a universal internal standard, and a common practice is to incorporate a stable isotope labeled analogue of each analyte whenever possible. In untargeted metabolomics, the use of individual internal standards is not possible, but it may be feasible to employ carefully selected internal standards to assist in normalizing the data for variability in injection volumes or other factors that are not compound specific.
A MALDI-TOF mass spectrometry-based haemoglobin chain quantification method for rapid screen of thalassaemia
Published in Annals of Medicine, 2022
Jian Zhang, Zhizhong Liu, Ribing Chen, Qingwei Ma, Qian Lyu, Shuhui Fu, Yufei He, Zijie Xiao, Zhi Luo, Jianming Luo, Xingyu Wang, Xiangyi Liu, Peng An, Wei Sun
Compared with common MALDI-TOF MS-based methods for disease diagnosis, our thalassaemia screening method has several unique characteristics, which may contribute to its outstanding performance: (1) Theoretically, the application of MALDI-TOF MS in thalassaemia screening is based on the quantification of globin subunits (e.g. α and β), which are the molecular pathogenic basis for thalassaemia. The features we selected for model construction, including α-globin, β-globin, and α/β were correlated with haemoglobin indices (Figure 2A) and reflected the imbalanced level of α-globin and/or β-globin in thalassaemia (Figure S2, Figure 2B and Figure 2C). (2) Technically, an internal standard was used in mass spectrometry for normalisation to improve the quantitative reproducibility and accuracy [31]. In this study, myoglobin, whose molecular weight is close to those of haemoglobin chains was used as an internal standard, so that all the feature peaks can be clearly distinguished by MALDI-TOF MS. 3) Thirdly, comprehensive evaluation of both 1+ and 2+ charged peak intensities with 8 machine learning methods was performed for optimisation of the effect of the model.
Metabolomics in antimicrobial drug discovery
Published in Expert Opinion on Drug Discovery, 2022
Metabolomic approaches can be targeted or untargeted [12]. In targeted metabolomics, defined groups of known, chemically characterized and biochemically annotated metabolites are monitored, temporally or as a response to a system perturbation. With the use of internal standards, the concentration of metabolites can be evaluated, quantitatively or semi-quantitatively. Contemporary techniques such as LC-MRM/PRM-MS-based analytical strategies allow quantitative analyses of several hundred metabolites, with a wide linearity of the measurement range and high reproducibility [13]. In antimicrobial drug discovery research, this approach can be used to identify the mode of action of a potential drug lead or reveal potential side effects on the host. Thus, multiple reaction monitoring (MRM), parallel reaction monitoring (PRM), and selected reaction monitoring (SRM) could be performed to identify antimicrobial drug targets, both in a pathogen and a host, with the aim of maximizing the drug effect on the former and minimizing it on the latter.
An overview of lipidomics utilizing cadaver derived biological samples
Published in Expert Review of Proteomics, 2021
Luheng Lyu, Neel Sonik, Sanjoy Bhattacharya
Addition of internal standards prior to homogenization or during extraction allows for data normalization as well as improved quantification. Additionally, using internal standards for extraction enables early recognition of differences in extraction efficiency of different samples (for example, samples extracted with 95% efficiency versus 65% efficiency due to differences in technique or operator). The concentration of internal standards varies between studies. Ideally, each class of lipid being measured should include a low, high, and medium mass range lipid standard for extraction. However, such a range or varied inclusion of standards of many classes is not practical and thus only 1–2 standards are added. Currently, addition of standards for the most abundant lipid class is the norm; however, this does not accurately capture the low abundance and more difficult to extract lipids [18].