International standard , stable isotope

White, J. W. (1992). Internal standard stable carbon isotope ratio method for determination of C-4 plant sugars in honey Collaborative trial study, and evaluation of improved protein preparation procedure. J. Assoc. Ojfic. Anal. Chem. 75,543-548. 

Table 7.6 Internationally accepted stable isotope standards for hydrogen, carbon, oxygen, nitrogen, and sulfur.

Characterization of various types of damage to DNA by oxygen-derived species can be achieved by the technique of gas chromatography-mass spectrometry (GC-MS), which may be applied to DNA itself or to DNA-protein complexes such as chromatin (Dizdaroglu, 1991). For GC-MS, the DNA or chromatin is hydrolysed (usually by heating with formic acid) and the products are converted to volatile derivatives, which are separated by gas chromatography and conclusively identified by the structural evidence provided by a mass spectrometer. Stable isotope-labelled bases may be used as internal standards... 

Tebuconazole (provided by Bayer), Q -[2-(4-chlorophenyl)ethyl]-o -(l,l-dimethyl-ethyl)-li/-l,2,4-triazole-l-ethanol. Molar mass 307.8, (M- -H)+ ion observed at approximately m/z 308.1 [liquid chromatography/mass spectrometry (LC/MS)] Tebuconazole-fnflzoZe-i,2,4-- fV3 (provided in acetonitrile solution by Bayer), [ NsJtebuconazole stable-isotope internal standard, o -[2-(4-chlorophenyl)ethyl]-Q -(l,l-dimethylethyl)-li/- A3-l,2,4-triazole-l-ethanol. Molar mass 310.8, (M -I- H)+ ion observed at approximately m/z 311.1 (LC/MS)... 

Cyfluthrin-met/ty/-fi(6 (provided in acetonitrile solution by Bayer Corp.) Cyfluthrin stable-isotope internal standard (IS), Cyclopropanecarboxylic acid, 3-(2,2-dichloroethenyl)-2,2-dimethyl-, cyano(4-fluoro-3-Phenoxyphenyl)methyl ester-met/tyWe, molecular formula C22H12D6CI2FNO3, molar mass 440.3, ion observed at 213.0 (GC/MS)... 

Flegal and Stukas [406] described the special sampling and processing techniques necessary for the prevention of lead contamination of seawater samples, prior to stable lead isotopic ratio measurements by thermal ionisation mass spectrometry. Techniques are also required to compensate for the absence of an internal standard and the presence of refractory organic compounds. The precision of the analyses is 0.1 -0.4% and a detection limit of 0.02 ng/kg allows the tracing of lead inputs and biogeochemical cycles. 

H6]-Leukotriene A4 methyl ester, 17, has been synthesized14 by Wittig olefination of epoxy dienal 18 with the key reagent 3,4,6,6,7,7-[2H6]-(Z)-(3-nonen-1-yl)triphenylphosphonium iodide, 19 (equation 9). 17 is employed as stable isotope internal standard for the MS trace analysis of eicosanoids15-17. 

In radiocarbon dating, the quantity to be measured is the ratio of the abundances of the rare isotope (14C) to that of the stable isotopes (12C, 13C). These abundance ratios are not measured on an absolute basis, but are compared to that of an internationally-accepted standard. (It is likely that a similar standard will be adopted for 10Be dating.) These measurement requirements have several consequences ... 

Waste water Add stable isotopically labeled analogs of the compounds to 1 L of waste-water sample extract sample at pH 12-13, then at pH <2, with methylene chloride using continuous extraction techniques dry extract over sodium sulfate concentrate add internal standard inject GC/MS 10 pg/L NR EPA 1990b (Method 1625)... 

Gonfiantini, R., W. Stichler, and K. Rozanski. 1995. Standards and intercomparison materials distributed by the International Atomic Energy Agency for stable isotope measurements. In Reference and Intercomparison Materials for Stable Isotopes of Light Elements. International Atomic Energy Agency, Vienna, IAEA-TECDOC-825, pp. 13-29. 

It is critical when performing quantitative GC/MS procedures that appropriate internal standards are employed to account for variations in extraction efficiency, derivatization, injection volume, and matrix effects. For isotope dilution (ID) GC/MS analyses, it is crucial to select an appropriate internal standard. Ideally, the internal standard should have the same physical and chemical properties as the analyte of interest, but will be separated by mass. The best internal standards are nonradioactive stable isotopic analogs of the compounds of interest, differing by at least 3, and preferably by 4 or 5, atomic mass units. The only property that distinguishes the analyte from the internal standard in ID is a very small difference in mass, which is readily discerned by the mass spectrometer. Isotopic dilution procedures are among the most accurate and precise quantitative methods available to analytical chemists. It cannot be emphasized too strongly that internal standards of the same basic structure compensate for matrix effects in MS. Therefore, in the ID method, there is an absolute reference (i.e., the response factors of the analyte and the internal standard are considered to be identical Pickup and McPherson, 1976). 

Jemal, M., Schuster, A., and Whigan, D. B. (2003). Liquid chromatography/tandem mass spectrometry methods for quantitation of mevalonic acid in human plasma and urine method validation, demonstration of using a surrogate analyte, and demonstration of unacceptable matrix effect in spite of use of a stable isotope analog internal standard. Rapid Commun. Mass Spectrom. 17, 1723-1734. 

Liang, H.R. Foltz, R.L. Meng, M. Bennett, P. Ionization enhancement in atmospheric pressure chemical ionization and suppression in electrospray ionization between target drugs and stable-isotope-labeled internal standards in quantitative liquid chromatography/tandem mass spectrometry. Rapid Commun. Mass Spectrom. 2003, 17, 2815—2821. 

The accuracy with which absolute isotope abundances can be measured is substantially poorer than the precision with which relative differences in isotope abundances between two samples can be determined. Nevertheless, the determination of absolute isotope ratios is very important, because these numbers form the basis for the calculation of the relative differences, the 5-values. Table 1.6 sununarizes absolute isotope ratios of primary standards used by the international stable isotope community. 

System (4) has been reported for the simultaneous determination of cortisol and cortisone in human plasma by stable-isotope dilution-MS [178]. For the determination, capillary GC-MS with H5 -cortisol and H5 -cortisone (as internal standards) was used. The method used a SPB-1 fused-silica capillary column (7 m x 0.25 mm) and helium as the carrier gas (at 29.4 Pa), with 70 eV EIMS being used for selective-ion monitoring. The concentrations were determined from the peak height ratios of the [M-31] fragment ions of the methoxime-TMS derivatives of cortisol, cortisone, and their internal standards. The sensitivity of the method was 200 pg per injection for both cortisol and cortisone. 

As discussed in [1], precise quantitative results will be obtained when a stable isotope dilution assay (SIDA) is performed. In this procedure, stable isoto-pomers of the analytes are used as internal standards. Consequently, the major effort in the development of SIDA is the synthesis of the labelled standards since most of them are not commercially available. 

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