Isotope dilution assays

Isotope dilution analysis (IDA) involves mixing an aliquant of the sample with an aliquant of an artificially enriched isotope of the element to be analyzed. The content of the latter in the original sample is derived from the results of the isotopic analysis of the mixture compared to the isotopic compositions of the sample and of the enriched isotope. The term spiking is often used to refer to the mixing step. The aliquant of enriched isotope added to the sample is also commonly called a spike. IDA is used in particular for the determination of uranium, plutonium, or thorium in solutions of irradiated nuclear fuels. It has also been used for an independent measurement of the total volume or mass of solution in accountability tanks of chemical processing plants. 

Although the technique is more expensive than radiometry, mass spectrometry is, however, the preferred method for IDA of samples of nuclear materials taken for accountability verifications. Traditionally, separated or highly enriched isotopes, absent from the samples or only present as minor isotopes, such as Pu, Pu or Th were used as spike material in isotope dilution mass spectrometry. IDMS is the standard operator method for the accountability of nuclear materials in input solutions of irradiated nuclear fuels. The method involves taking a representative sample from the input accountability tank and diluting it accurately 100-1,000-fold in a heavily shielded cell. A portion of the diluted solution is transferred to 

IAEA (Kuno et al. 1989), the spike is a mixture of uranyle and plutonium nitrate carefully dried in a 10 ml penicillin vial. For the assay of spent fuel solutions and MOX products with U/Pu ratios around 100 1, each vial contains about 50 mg of uranium-enriched just below 20% in and 2 mg of plutonium with a Pu abundance of 95% or more. Calculations (Laszlo et al. 1991) and experience show that these amounts are appropriate to reach relative uncertainties around 0.1% in a single measurement of samples carrying about 100 mg of depleted uranium and 1 mg of high burn plutonium with a Pu abundance of 50%. 

The mass of uranium or plutonium, m, in the sample aliquant, in g, is derived from O Eq. (63.9) below  

The diagrams in O Fig- 63.25 assume that the Pu/ Pu atom ratios in the unspiked and spiked samples can be measured with a relative uncertainty of 0.05%. The uranium enrichment should not exceed 20% so that the spike does not come in the category of high enriched uranium (HEU), subject to stricter safeguards controls, and wUl not be allowed in facilities, which are not licensed for the processing of HEU materials. 

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Isotope Dilution Assay. An isotope dilution assay for biotin, based on the high affinity of avidin for the ureido group of biotin, compares the binding of radioactive biotin and nonradio active biotin with avidin. This method is sensitive to a level of 1—10 ng biotin (82—84), and the radiotracers typically used are p C]biotin (83), [3H]biotin (84,85) or an I-labeled biotin derivative (86). A variation of this approach uses I-labeled avidin (87) for the assay. 

Semmelroch, P., Laskawy, G., Blank, I., Grosch, W., Determination of potent odorants in roasted coffee by stable isotope dilution assays, Flavour Fragrance J. 10(1), 1, 1995. 

Deutsch, J.C., Determination of p-hydroxyphenylpyruvate, p-hydroxyphenyllactate and tyrosine in normal human plasma by gas chromatography-mass spectrometry isotope-dilution assay, J. Chromatogr. B, 690, 1, 1997. 

Majcenovic, A. B., Schneider, R., Lepoutre, J.-P., Lempereur, V., and Baumes, R. (2002). Synthesis and stable isotope dilution assay of ethanethiol and diethyl disulfide in wine using solid phase microextraction. Effect of aging on their levels in wine. /. Agric. Food Ghem. 50, 6653-6658. 

Freisleben, A., Sehieberle, P, Ryehlik, M. (2003 May). Specific and sensitive quantification of folate vitamers in foods by stable isotope dilution assays using high-performance liquid chromatography-tandem mass speetrometry. Anal. Bioanal. Chem., 376 2), 149-156. 

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. 

Schor DS, Struys EA, Hogema BM, Gibson KM, Jakobs C (2001) Development of a stable-isotope dilution assay for gamma-aminobutyric acid (GABA) transaminase in isolated leukocytes and evidence that GABA and beta-alanine transaminases are identical. Clin Chem 47 525-531... 

QUANTIFICATION OF AROMA COMPOUNDS BY ISOTOPE DILUTION ASSAY (IDA)... 

Quantification of aroma compounds by isotope dilution assays... 

Aubry, V., Etievant, P.X., Ginies, C., and Henry, R. 1997. Quantitative determination of potent flavor compounds in Burgundy pinot noir wines using a stable isotope dilution assay. J. Agric. FoodChem. 45 2120-2123. 

Blank, I., Schieberle, P., and Grosch, W. 1993. Quantification of the flavour compounds 3-hy-droxy-4,5-dimethyl-2(5H)-furanone and 5-ethyl-3-hydroxy-4-methyl-2(5H)-furanone by stable isotope dilution assay. In Progress in Flavour and Precursor Studies (P. Schreier and P. Winterhalter, eds.). Allured Publishing, Wheaton, 111. 

Blank, I., Fay, L.B., Lakner, F.J., and Schlosser, M. 1997. Determination of 4-hydroxy-2,5-di-methyl-3(2/f)-furanone and 2(or 5)-ethyl-4-hy-droxy-5(or 2)-methyl-3(2/f)-furanone in pentose sugar-based Maillard model systems by isotope dilution assays. J. Agric. Food Chem. 45 2642-2648. 

Blank, I., Milo, C., Lin, J., and Fay, L.B. 1999. Quantification of aroma-impact components by isotope dilution assay Recent developments. In... 

H., and Schreier, P. 1996. Quantitative analysis of 2-aminoacetophenone in off-flavored wines by stable isotope dilution assay. JAOAC (J. Assoc. Off. Anal. Chem.) Int. 79 583-586. 

Fay, L.B., Metairon, S., and Blank, I. 2000. Stable isotope dilution assay mass spectometry in flavour research Internal standard and calibration issues. In Frontiers of Flavour Science (P. Schieberle and K.-H. Engel, Eds.) Deutsche For-schungsanstalt ftlr Lebensmittelchemie, Garching, Germany. 

Guth, H. and Grosch, W. 1990. Deterioration of soya-bean oil Quantification of primary flavour compounds using a stable isotope dilution assay. Lebensm.-Wiss. Technol. 23 513-522. 

I. 1999b. Synthesis of deuterated volatile lipid degradation products to be used as internal standards in isotope dilution assays. 2. Vinyl ketones. 

Lin, J.M., Fay, L.B., Welti, D.H., and Blank, 1.1999. Synthesis of trans-4,5-epoxy-(E)-2-decenal and its deuterated analog used for the development of a sensitive and selective quantification method based on isotope dilution assay with negative chemical ionization. Lipids 34 1117-1126. 

Milo, C. and Blank, I. 1998. Quantification of impact odorants in food by isotope dilution assay Strength and limitations. In Flavor Analysis Developments in Isolation and Characterization (C.J. Mussinan and M.J. Morello, eds.) pp. 250-259. American Chemical Society, Washington, D.C. 

Pfnuer, P., Matsui, T., Grosch, W., Guth, H., Hofmann, T., and Schieberle, P. 1999. Development of a stable isotope dilution assay for the quantification of 5-methyl-(E)-2-hepten-4-one Application to hazelnut oils and hazelnuts. J. Agric. Food Chem. 47 2044-2047. 

Schieberle, P. 1995b. Quantification of important roast-smelling odorants in popcorn by stable isotope dilution assays and model studies on flavor formation during popping. J. Agric. Food Chem. 43 2442-2448. 

The measurement of odor intensity using OAVs is described by Grosch (1993, 1994). It requires the determination of the concentration of each odorant in the sample, and for those present in trace quantities, a stable isotope dilution assay must be used (Guth, 1997). This may make the determination of OAVs very tedious if many values are required. OS Vs are normalized peak areas from an odor chromatogram and represent a more realistic representation of the importance of the odors in a sample as perceived by the nose. Their determination is described by Acree (1997). 

Concentration of odorants in sample being analyzed, determined by use of internal standards, GC-MS in selected ion monitoring (SIM) mode or a stable isotope dilution assay for trace quantities (see unitgu). 

Important food odorants, for which a quantification by a stable isotope dilution assay has been developed ... 

In the meantime, stable isotope dilution assays have been developed for nearly 60 important food odorants (Table 8). The OAV concept has been applied to characterize the... 

The caramel-like smelling HDF has been established as a main contributor to the flavors of several processed foods (Table 17). In addition, it should be noted that in all these foods, on the basis of a high FD-factor, HDF was also by far the most important caramel-like smelling odorant. In the following, the strategy in the HDF precursor analysis will be shown using wheat bread crust, popcorn [88] and malt as the examples. Quantitative measurements were performed by using a stable isotope dilution assay (cf. Section 3.2.). 

Some typical isotope dilution assay data on HMX are shown in Table 2... 

W. Dieterle and J. W. Faigle, Multiple inverse isotope dilution assay for the stereospecific determination of R( +) and S( -) oxprenolol in biological fluids, J. Chromatogr., 259 311-318 (1983). 

The use of an isotope dilution assay is the best method to quantify labile and low level odorants. He applied this technique to the determination of 2-acetyl-l-pyrroline and 2-methyl-3-ethylpyrazine, the two compounds which showed the highest FD-factors among the compounds with roasty odor notes in extracts from wheat or rye bread crust, respectively ( 7, 38). The results are summarized in Table III. The high level of the acetylpyrroline in the crusts of the wheat breads was striking compared to the level in the rye breads. These quantitative data confirm that 2-acetyl-l-pyrroline is a character impact odor compound of the wheat bread crust. 

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