Isotope dilution analysis determination

Isotopic dilution analysis is widely used to determine the amounts of trace elements in a wide range of samples. The technique involves the addition to any sample of a known quantity (a spike) of an isotope of the element to be analyzed. By measuring isotope ratios in the sample before and after addition of the spike, the amount of the trace element can be determined with high accuracy. The method is described more fully in Figure 48.13. 

Separation and detection methods Ion chromatography is routinely used for the isolation of bromate. Diverse detection methods are mentioned in the literature, including isotope dilution analysis (Creed and Brockhoff 1999), conductivity measurement (Jackson et al. 1998), fluorimetric determination (Gahr et al. 1998), ICP-MS (Seubert and Nowak 1998) and spectrophotometry (Achilii and Romele 1999),... 

The main advantages of plasma-source mass spectrometry (PS-MS) over other analytical techniques, such as PS-AES and ETAAS, are the possibilities of quantitative isotope determination and isotope dilution analysis the rapid spectral scanning capability of the mass spectrometer and semiquantitative determinations to within a factor of two or three. Several labelling methods are used for the quantification of analytes present in complex mixtures. In these methods, the sample is spiked... 

Fractional separation of tin compounds used as stabilisers in PVC was based on substoichiometric isotope dilution analysis [446]. The tin compounds were isolated by extraction and complexed with salicylideneamino-2-thiophenol, followed by controlled addition of y-irradiated tributyl tin oxide and measurement of the y-activity. PVC containing a nominal 0.63% (Bu Sn analysed 0.614 0.016% in nine determinations. 

Elderfield and Greaves [629] have described a method for the mass spectromet-ric isotope dilution analysis of rare earth elements in seawater. In this method, the rare earth elements are concentrated from seawater by coprecipitation with ferric hydroxide and separated from other elements and into groups for analysis by anion exchange [630-635] using mixed solvents. Results for synthetic mixtures and standards show that the method is accurate and precise to 1% and blanks are low (e.g., 1() 12 moles La and 10 14 moles Eu). The method has been applied to the determination of nine rare earth elements in a variety of oceanographic samples. Results for North Atlantic Ocean water below the mixed layer are (in 10 12 mol/kg) 13.0 La, 16.8 Ce, 12.8 Nd, 2.67 Sm, 0.644 Eu, 3.41 Gd, 4.78 Dy, 407 Er, and 3.55 Yb, with enrichment of rare earth elements in deep ocean water by a factor of 2 for the light rare earth elements, and a factor of 1.3 for the heavy rare earth elements. 

Stable-isotope dilution analysis is an analytical technique in which a known quantity of a stable-labelled isotope is added to a sample prior to extraction, in order to quantitate a particular compound. The ratio of the naturally abundant and the stable-labelled isotope is a measure of the naturally abundant compound and can be determined only by gas chromatography-mass spectrometry since the naturally abundant and the stable-labelled isotope cannot be completely separated gas chromatographically. 

A major attraction is the ability to perform isotope ratio measurements, e.g. in many geological applications to determine the age of rocks, and isotope dilution analysis. The latter in particular is gaining-popularity as a highly accurate, precise and hence traceable, method of analysis, so it is worthwhile describing these techniques in more detail. 

The best precision is obtained for isotope ratios near unity (unless the element to be determined is near the detection limit, when the ratio of spike isotope to natural isotope should be between 3 and 10) so that noise contributes only to the uncertainty of natural isotope measurement. Errors also become large when the isotope ratio in the spiked sample approaches the ratio of the isotopes in the spike (overspiking), or the ratio of the isotopes in the sample (underspiking), the two situations being illustrated in Fig. 5.11. The accuracy and precision of the isotope dilution analysis ultimately depend on the accuracy and precision of the isotope ratio measurement, so all the precautions that apply to isotope ratio analysis also apply in this case. 

ICP - MS Determination of metal content and isotope dilution analysis 147)... 

Consequently, the contamination danger can be minimized. Furthermore, isotope dilution analysis with LA-ICP-MS can be used as a microlocal analytical technique for multi-element determination in thin layers or nanowires of high purity platinum and palladium nanoclusters on DNA. LA-ICP-MS allows microlocal analysis for studying the elemental distribution in layered systems and bulk material. 

Accurate determination of the biological important element, selenium, in blood serum by isotope dilution analysis using ICP-QMS with octopole collision cell (Agilent 7500ce, Tokio, Japan) is described by Schaumloffel and coworkers.55 A recovery of selenium from human serum reference material was only 78 % when hydrogen was applied as collision gas but 96.7 % using xenon as a non-reactive collision gas to eliminate isobaric interferences. A detection limit of 3.3p,gl-1 was achieved.55... 

P. Rodriguez-Gonzalez, M. Monperrus, J. I. Garcia Alonso, D. Amouroux and O. F. X. Donard, Comparison of different numerical approaches for multiple spiking species-specific isotope dilution analysis exemplified by the determination of butyltin species in sediments, J. Anal. At. Spectrom., 22, 2007, 1373-1382. 

Spark source (SSMS) and thermal emission (TEMS) mass spectrometry are used to determine ppb to ppm quantities of elements in energy sources such as coal, fuel oil, and gasoline. Toxic metals—cadmium, mercury, lead, and zinc— may be determined by SSMS with an estimated precision of 5%, and metals which ionize thermally may be determined by TEMS with an estimated precision of 1% using the isotope dilution technique. An environmental study of the trace element balance from a coal-fired steam plant was done by SSMS using isotope dilution to determine the toxic metals and a general scan technique for 15 other elements using chemically determined iron as an internal standard. In addition, isotope dilution procedures for the analysis of lead in gasoline and uranium in coal and fly ash by TEMS are presented. 

Closely related to tracer analysis is the method of isotopic dilution analysis. Here, instead of checking the effectiveness of a method from known amounts of an element in the sample, and of its radioactive isotope, one knows only the amount of radioactive isotope added, and by precipitating or otherwise separating the total amount of that element present, and then measuring its radioactivity, one determines its amount, and hence the amount present in the original sample. 

One of the key steps in any isotope dilution analysis concerns the isolation and purification of the diluted activity, plus the measurement of its specific activity. Two techniques are usually preferred for the separation precipitation and solvent extraction. As a purification step, precipitation has the advantage that the precipitate can easily be weighed at the time of separation, thereby allowing a quick determination of the specific activity. The main problem with the use of precipitation techniques involves the occurrence of co-precipitation phenomena, in which unwanted materials are precipitated along with the desired substance, thus altering the sample specific activity. Precipitation techniques are used for the isolation of inorganic components. 

Solvent extraction is a frequently employed technique in isotope dilution analysis. It gives very clean separations, resulting in high-purity samples. It has the disadvantage of requiring further chemical processing to determine the mass of material isolated and the specific activity. 

In summary, we can say that isotope dilution analysis is a highly sensitive, selective analytical method capable of high precision. It offers the opportunity to determine the amount of material present in a system without the need for a quantitative separation of the material from the system. The applications of isotope dilution analysis cited in the literature are myriad. Perhaps the best summary of these applications is the book by Tolgyessy, Braun, and Krys (1972). 

Isotope dilution analysis permits one to determine the purity of a radiochemical. Compound X, molecular weight of 150 (specific activity 1.0 mCi/mmol), was checked for purity by carefully weighing 1.5 mg of the radiochemical and mixing with 1000 mg of unlabeled compound X and recrystallizing until a... 

Certain techniques such as neutron activation analysis and stable isotope dilution analysis offer very powerful and sensitive methods for the determination of trace metals, but involve considerable effort and access to extensive facilities and so are not suited for routine laboratory determinations. However, they have been used to determine trace metal levels accurately in homogeneous biological materials, which are now used as reference materials for other techniques. 

In most of the examples, the isotopic methods are used essentially for analytical purposes. In this connection, their great value lies in extreme sensitivity and specificity. Many of the problems are concerned with the accurate determination of low concentrations of particular groups in polymer molecules. Another type of problem involves the determination of small weights of substances of low molecular weight formed simultaneously with polymer, or formed from polymer by chemical reactions for this purpose, the technique of isotope dilution analysis is of great value. The substances are usually present as minor components in rather complex mixtures so that determination by conventional methods would be extremely difficult. The method of isotope dilution analysis involves the addition to the mixture of a substantial quantity of the substance to... 

The use of labelled initiators to obtain accurate information concerning the relative reactivities of radical scavengers towards reference radicals, has been reviewed (4). Product analysis, by isotope dilution analysis, has been used in the examinations of the decompositions of certain initiators in the absence of monomers. It is possible to work with very dilute solutions and small extents of decomposition so that the conditions are similar to those prevailing when the substances are used as initiators of polymerizations. The decompositions of dibenzoyl (12) and di-anisoyl peroxides (13), for example, have been followed by determinations of the carbon dioxide evolved. 

Garcia Alonso, J. I., Determination of fission products and actinides by inductively coupled plasma mass spectrometry using isotope dilution analysis A study of random and systematic errors, Anal. Chim. Acta, 312, 57-78, 1995. 

The determination of caesium in soil by multi-element analysis is discussed in Sect. 2.55 (isotope dilution analysis). 

A variety of elements have been measured in fish tissue to determine the cause of fish kills and to assess water quality. Slurry samples were introduced into the ICP by using electrothermal vaporization in one report [254] with isotope dilution based determination of Cu, Zn, Cd, and Pb. Sample preparation was simplified by using slurries rather than complete dissolution. Electrothermal vaporization can be used to reduce spectral overlaps due to molecular ions that contain oxygen. The sample can be dried in the furnace before vaporization of the analytes. The time-dependent vaporization can also be used to reduce some matrix effects. Isotope dilution improves precision and accuracy of the analysis. The uptake and organ-dependent accumulation of cadmium in carp have also been investigated by ICP-MS analysis [255]. 

R. M. Roberts, Browder, and Kobe [10] carried out a number of experiments using isotope dilution analysis to determine the proportion of m- nitrotoluene formed in the course of nitration of toluene. 

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