Isotope-dilution mass spectrometry IDMS

Conventional calibration MDRD equation [used only with those creatinine methods that have not been recalibrated to be traceable to isotope dilution mass spectrometry (IDMS)]... 

Isotope dilution mass spectrometry (IDMS) can be applied with most of the ionisation methods used in mass spectrometry to determine isotope ratios with greater or lesser accuracy. For calibration by means of isotope dilution, an exactly known amount of a spike solution, enriched in an isotope of the element(s) to be determined, is added to an exactly known amount of sample. After isotopic equilibration, the isotope ratio for the mixture is determined mass spectrometrically. The attraction of IDMS is its potential simplicity it relies only on the measurement of ratios. The... 

Isotope Dilution Mass Spectrometry (IDMS) A quantitative mass spectrometry technique in which an isotopically enriched compound is used as an internal standard. See Chapter 14 for a more detailed explanation. 

K. G. Heumann. Isotope Dilution Mass Spectrometry (IDMS) of the Elements. Mass Spectrom. Rev., 11(1992) 41-67. 

Isotope dilution mass spectrometry (IDMS) is another method to overcome the problem of sample recovery [370-372]. The 13C-labeled isotope of the analyte is added to the sample at the commencement of the analysis and the ratio of the labeled and unlabeled compound is measured by MS. This technique eliminates the need for recovery measurements and automatically accounts for any losses in the determination [373]. The two major limitations of this method are the cost and availability of the labeled compounds and the need to use the MS as a detector. 

The fundamentals and several applications of isotope dilution mass spectrometry requiring accurate isotope ratio measurements are reviewed by Heumann.50,51 Today isotope dilution mass spectrometry (IDMS) is recognized as a primary measurement method, by means of which accurate results with sufficiently small uncertainties can be achieved and therefore it has been used in certifying the composition of reference materials. A requirement of isotope dilution analysis in mass spectrometry is to achieve equilibration of spike and sample so that very careful sample preparation steps, especially in solid mass spectrometry, are necessary when a homogeneous sample spike mixture is to be prepared. 

Keywords Traceability Clinical chemistry Reference measurement procedure Isotope dilution mass spectrometry (IDMS) External quality assessment... 

In view of these issues, we have over several years undertaken a substantial research programme to develop definitive methods appropriate for in-house certification of matrix RMs, particularly for analytes at trace levels. These definitive measurement methods, most of which use isotope dilution mass spectrometry (IDMS), been the subject of extensive validation, including CCQM key comparisons and pilot studies involving other national measurement institutes. Hence, we are now able to augment interlaboratory data with data obtained at LGC using these very accurate measurements. We have also... 

Table 2 A comparison of isotope dilution mass spectrometry (IDMS) values and interlaboratory consensus values, n is the number of laboratories...

There are two main types of internal standards. The first ones are stable isotope labeled (SIL) internal standards. They are compounds in which several atoms in the analytes are replaced by their respective stable isotopes, such as deuterium (2H, D or d), 13C, 15N, or 170. Labeling with the first three isotopes are most common, particularly labeling with deuterium (due to less difficulty in synthesis and therefore less expensive). For examples, raloxifene-d4-6-glucuronide was used as the internal standard for the determination of raloxifene-6-glucuronide [5] and 1, 2, 3, 4-13C4 estrone (PCJEl) was used as the internal standard for estrone (El) [6], The usage of stable isotope labeled internal standards in quantitative LC-MS or GC-MS analysis is often termed as isotope dilution mass spectrometry (IDMS) [7],... 

Targeted analysis refers to metabolome analysis that targets one, or a few metabolites, and typically uses an internal standard for quantitation. The most common method is isotope dilution mass spectrometry (IDMS) [34], which relies on the use of stable isotope internal standards to enable the absolute quantitation of metabolites. This method has proven highly effective and has been successfully used in numerous studies. 

For analysis of solutions, ICP-mass spectrometry (ICP-MS) is very promising (Houk et al., 1980 Houk, 1986 Bacon et al., 1990). Recent advances in separation and preconcentration techniques are discussed by Horvath et al. (1991). Bacon et al. (1990) report that although ICP-MS is a multi-element technique, recent papers tend to concentrate on a small number of target elements. With isotope dilution mass spectrometry (IDMS), detection limits are further reduced (Heumann, 1988) IDMS is also suitable for accurate speciation in very low concentration levels of elements (Heumann, 1990). For the direct analysis of solid samples, glow discharge mass spectrometry (GD-MS) (Harrison etal., 1986) is of interest. Tolg (1988) has suggested that a substantial improvement in the absolute detection power of GD-MS, as applied to micro analysis, can be expected, at least in comparison with the ICP as ion source. 

Today, the development of quantitative procedures has become at least as important in biomedical mass spectrometry as identification work. Since excellent reviews on the current status of quantitative MS are available (Burlingame et al., 1982 De Leenheer and Cruyl, 1980 Garland and Powell, 1981 Halpem, 1981 Millard, 1978a Schulten and Lehmann, 1978 Sweeley et al., 1977), this contribution will focus on one of the new developments in this field the use of isotope-dilution mass spectrometry (IDMS) in the development of reference methodology. 

Isotope dilution mass spectrometry (IDMS) can be considered as a special case of the internal standard method the internal standard that is used is an isotopomer of the compound to be measured, for example a deuterated derivative. Note that an internal standard is necessary for every compound to be measured. This internal standard is as close as possible to perfection since the only property that distinguishes it from the compound to be measured is a slight mass difference, except for some phenomena that involve the labelled atoms, such as the isotopic effect. In that case, we have an absolute reference, that is the response coefficients of the compound and of the standard are identical. This method is often used to establish standard concentrations. The basic theory of this method rests on the analogy between the relative abundance of isotopes and their probability of occurrence [23]. 

Murozumi et al. (9) determined the concentration of Pb in Greenland and Antarctic snow and ice by Isotope Dilution Mass Spectrometry (IDMS) (27). They added pure Pb tracer to their samples before chemically processing them. Both the mass of tracer and the water sample were measured. After thoroughly mixing the tracer with the sample Pb was isolated in a chemically pure form and the isotopic ratios were measured in a mass spectrometer. Simple comparison of the ° Pb abundance with the abundance of other isotopes in the mass spectrum allowed the amount of Pb in the sample to be determined. The technique is not limited to Pb, but is applicable to any element with two or more stable or... 

Dimethyl-Tl (Me2Tl ) was determined in 500 ml sea water samples by combining Isotope Dilution Mass Spectrometry (IDMS) with a species-specific extraction method (18). A ° Tl-enriched spike solution was applied for the isotope dilution step and the production of positive thermal ions was used for mass spectrometric measurements. After species-unspecific T1 enrichment at an anion exchanger, inorganic T1 was oxidized to Tl(III) by a Br2 solution and then separated by extraction with methyl xo-butyl ketone, whereas Me2Tl remained in the aqueous phase. The detection limit for Mc2Tl is 440 pg 1 (as Tl). 

SA White, AS Kidd, KS Webb. The determination of lysergide (LSD) in urine by high-performance liquid chromatography-isotope dilution mass spectrometry (IDMS). J Forensic Sd 44 375—379, 1999. 

Definitive method method with a high scientific status applied in a laboratory of high proven quality [10]. In brief it means that only negligible systematic errors may remain compared to the precision and trueness required for the final result. Isotope Dilution Mass Spectrometry (IDMS), in its thermo-ionisation mode, for the determination... 

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