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The Development of the Radiotracer Concept
Published in Garimella V. S. Rayudu, Lelio G. Colombetti, Radiotracers for Medical Applications, 2019
Every radiochemical tag could, of course, be a tracer; but not every tracer had to be a chemical tag. Under some experimental conditions the behavior of the chemical made no difference. Hevesy and Rona’s 1914 paper had laid down strict limitations but also allowed considerable latitude. For example, only thorough and uniform mixing of active and stable nuclides is required in isotope-dilution studies; no tag is necessary. However, if we assume that no physical or chemical sequestration occurs in isotope-dilution, we expose ourselves to significant experimental hazard. This assumption would lead to the first major error in tracer methodology: the 1945 to 1955 red cell volume studies.17
Analysis of Clinical Specimens Using Inductively Coupled Plasma Mass Spectrometry
Published in Steven H. Y. Wong, Iraving Sunshine, Handbook of Analytical Therapeutic Drug Monitoring and Toxicology, 2017
K. Owen Ash, Gabor Komaromy-Hiller
Isotope analysis—the ability to measure specific isotopes avoids much of the interference, allows use of the powerful isotope dilution methods,15,16 and opens the way for in vitro investigations using nonradioactive isotopes. Isotope ratio comparisons can quite readily be determined and may prove helpful for identification of the sources of trace element exposures.10
Dictionary
Published in Mario P. Iturralde, Dictionary and Handbook of Nuclear Medicine and Clinical Imaging, 1990
Isotope dilution analysis. A method of analysis whereby the amount of a particular element in a specimen is found by observing how the isotopic composition of that element is changed by the addition of a known amount of one of the isotopes of the element. The method can be used both mass spectroscopically with stable isotopes or radiometrically with radioactive isotopes.
Evaluation of urine dipsticks for quality control of residual erythrocytes and leukocytes in leukocyte-depleted donor plasma
Published in Scandinavian Journal of Clinical and Laboratory Investigation, 2020
In order to eliminate a possible interference of plasma protein and glucose when performing dipstick leukocyte detection, plasma was replaced by phosphate buffered saline (PBS) without Ca2+ and Mg2+ (Gibco/Thermo Fisher Scientific, Gothenburg, Sweden). The samples from the plasma dilution series were centrifuged and washed in PBS, and the pellets were then resuspended in PBS. All samples were run in triplicates on the dipstick analyzers, ADAM-rWBC and Sysmex XN-10. By using these values as reference when calculating the agreement between methods after centrifugation and replacement with PBS, any changes in cell concentration introduced by centrifugation were taken into account. Albumin was used as an indicator of plasma protein. After the removal of cells by centrifugation, albumin concentration was determined in both plasma- and PBS diluted samples. The samples were analyzed in triplicate on Cobas 8000 c701 with the Tina-quant Albumin gen.2 method (Roche) traceable to the Institute for Reference Materials and measurements (ERM-DA470k/IFCC). Albumin was analyzed on plasma samples using the P-Albumin routine (measuring range 3–101 g/L), and PBS diluted samples were analyzed with the U-Albumin program (measuring range 0.003–0.4 g/L). Glucose was analyzed on Cobas 8000 c701 using the GLUC3 reagent (Roche). The calibrator was traceable to an isotope dilution mass spectrometry method.
Regulatory context and validation of assays for clinical mass spectrometry proteomics (cMSP) methods
Published in Critical Reviews in Clinical Laboratory Sciences, 2018
Christophe Hirtz, Pauline Bros, Cato Brede, Pierre Lescuyer, Aleksandra M. Maceski, Jerome Vialaret, Vincent Delatour, Sylvain Lehmann
The strategy most commonly used for the absolute quantification of peptides or proteins in biological fluids is the isotope dilution (ID) method. To minimize the variability and the potential loss of material in the various steps of the assay (e.g. the extraction of the peptides and proteins of interest, the injected volume, the ionization efficiency, fragmentation in the collision cell, and matrix effects) an internal standard is introduced into the sample, preferably at the beginning of the sample preparation procedure. Ideally, the internal standard results from synthesis of endogenous protein after substituting one or more atoms with a stable isotope (12C by 13C, 1H by 2H, 14N by 15N, 16O by 18O), giving it a known mass increment, hence the name “labeled” or “heavy” standard. The labeled standard should have the same or at least very similar behavior to that of the endogenous compound. In this case, the compound of interest subjected to LC–MS/MS is not quantified by measuring the intensity of the MS signals directly, but on the basis of the ratio between the MS signal of the endogenous peptide and that of the labeled standard. The specificity of the transitions must be checked by examining various parameters. First, the endogenous peptide and the labeled peptide must strictly co-elute. The ratios between the transitions should subsequently remain unchanged between the labeled and non-labeled compounds. These points should be checked in the matrix of interest.
Simultaneous analysis of mycotoxins in corn flour using LC/MS-MS combined with a modified QuEChERS procedure
Published in Toxin Reviews, 2018
Maryam Amirahmadi, Shahram Shoeibi, Hossein Rastegar, Mehdi Elmi, Amin Mousavi Khaneghah
The matrix effect as a common obstacle in the LC-MS/MS analysis could show some adverse effects on the accuracy and precision of established analytical method. The use of the stable isotope dilution internal standard is recognized as the most efficient way to compensate for matrix effect calibration (Fabregat-Cabello et al.2016) in routine analysis, owing to some limitations such as poor availability and high cost of stable isotope dilution substance; in addition to low stability (possibly due to exchange with hydrogen) of deuterium-labeled standards (Chavez-Eng et al.2002), this method cannot be approached (Hewavitharana 2011). So in routine performance, the two other methods namely matrix-matched calibration and standard addition methods can be applied (Fabregat-Cabello et al.2016).