Isotope Ratio Measurements in Environmental Samples

As the most important inorganic mass spectrometric technique, ICP-MS is also employed for the precise and accurate isotope ratio measurements of a multitude of elements (such as Li, B, S, Fe, Sr, Pb, U, Pu) in environmental samples (see Chapter 8).9,88-90 Isotope ratio measurements of environmental samples require special careful sample preparation techniques including trace/matrix separation and enrichment procedures if the analytes are at the trace and ultratrace level. As an example, the schematic diagrams of the separation and enrichment procedures for the precise isotope analysis of Pu, U and Sr in water samples from the Sea of Galilee using double-focusing 

Samples/ matrix Equipment/sample preparation Analyte Detection limits References 

Alpine snow and ice ICP-SFMS (Element) ice melted, acidified Pb Pt 2.7pgg-1 3Pgg, 0.008 pgg 1 Schwikowski et al.62 Brabante58 

Groundwater ICP-SFMS (Element), analyte separation 226 Ra 0.02 pg I-1 Zoriy et al. 02 

Sediments ETV-ICP-MS (slurry sampling) (permanganate as modifier) H Hg 0.07ixgg (Tl) 0.1 8fxgg 1 (Hg) Da Silva et al.46 

Soils (Chernobyl) ICP-SFMS (Element) and APEX nebulizer ion exchange chromatography 236 u 3 X 10 gg- Boulyga and Heumann O  

---

Gwiazda, R., Woolard, D., and Smith, D. (1998). Improved lead isotope ratio measurements in environmental and biological samples with a double focussii magnetic sector inductively coupled plasma mass spectrometer (ICP-MS).J. Anal. Ar. Spearom. 13(11), 1233. 

For direct isotope ratio measurements on solid samples, laser ablation ICP-MS (LA-ICP-MS) is applied to an increasing extent in geology, geochronology, biology and environmental research.6... 

Accurate, precise isotope ratio measurements are important in a wide variety of applications, including dating, examination of environmental samples, and studies on drug metabolism. The degree of accuracy and precision required necessitates the use of special isotope mass spectrometers, which mostly use thermal ionization or inductively coupled plasma ionization, often together with multiple ion collectors. 

In principle to all elements at low (ppb) concentrations. Valuable for first look analysis, at solid samples. Isotopic ratio measurements can distinguish between sources of elements in tracer studies and environmental samples. Use in geological dating based upon isotopic ratios. 

An isotope dilution mass spectrometric method involves the addition of a known quantity of Tc followed by chemical separation, purification, and measurement of the Tc/ Tc isotopic ratio . An improved technique has been developed for the analysis of Tc in environmental samples. After spiking with Tc the isolated technetium is concentrated onto anion exchange beads. Determination of as little as 1 pg has been achieved through the enhanced ionization efficiency afforded by the resin bead source ... 

This chapter provides an overview of mass spectrometer function and operation. It describes specific instrument types with demonstrated or potential application for measuring radionuclides and surveys the application of these instruments to radionuclide detection. Finally, it discusses the circumstances under which use of mass spectrometers is advantageous, the type of mass spectrometer used for each purpose, and the conditions of sample preparation, introduction and analysis. Its perspective is from a national laboratory active in environmental and non-proliferation monitoring. It emphasizes isotope ratio measurements, but mass spectrometric measurements also provide isotope mass information. Several recent books describe elemental and isotope ratio mass spectrometry in far greater detail than is presented here (Barshick et al., 2000 De Laeter, 2001 Montaser, 1998 Nelms, 2005 Platzner, 1997 Tuniz et al., 1998). High-resolution mass spectrometry forms the basis of the mass scale used for elemental and isotopic masses (Coplen, 2001), but this application of MS falls outside the scope of this chapter. 

For some radionuclides, only the direct measurement is needed, based on calibration with a radionuclide standard and reference to the measured sample mass. For other radionuclides, the isotope ratio to its stable element is needed. An example of a more complex situation is measurement of the 14C/12C isotope ratio of an environmental or archeological sample in comparison to the modern atmospheric CO2 value. This value must be adjusted for anthropogenic 14C produced by atmospheric testing of nuclear weapons and by other nuclear operations, and also for changes in atmospheric CO2 with cosmic-ray flux fluctuations over time. For an element such as Pu, which has no stable isotope, the total quantity is measured by isotope dilution mass spectrometry in which the sample is traced (or spiked) with 242Pu or 244Pu (see Section 17.3.3). 

Boulyga, S. F., Becker, J. S., Matusevitch, J. L., and Dietze, H. J. 2000. Isotope ratio measurements of spent reactor uranium in environmental samples by using inductively coupled plasma mass spectrometry. Int J Mass Spectrom 203(1-3), 143-154. 

Magara, M., Sakakibara, T., Kurosawa, S., Takahashi, M., Sakurai, S., Hanzawa, Y., Esaka, R, Watanabe, K., and Usuda, S. E. 2002. Isotope ratio measurement of uranium in safeguards environmental samples by inductively-coupled plasma mass spectrometry (ICP-MS). J Nucl Sci Technol 39(4), 308-311. 

---