Isotopes sample preparation

A major advantage of this hydride approach lies in the separation of the remaining elements of the analyte solution from the element to be determined. Because the volatile hydrides are swept out of the analyte solution, the latter can be simply diverted to waste and not sent through the plasma flame Itself. Consequently potential interference from. sample-preparation constituents and by-products is reduced to very low levels. For example, a major interference for arsenic analysis arises from ions ArCE having m/z 75,77, which have the same integral m/z value as that of As+ ions themselves. Thus, any chlorides in the analyte solution (for example, from sea water) could produce serious interference in the accurate analysis of arsenic. The option of diverting the used analyte solution away from the plasma flame facilitates accurate, sensitive analysis of isotope concentrations. Inlet systems for generation of volatile hydrides can operate continuously or batchwise. 

Before sample preparation, surrogate compounds must be added to the matrix. These are used to evaluate the efficiency of recovery of sample for any analytical method. Surrogate standards are often brominated, fluorinated, or isotopically labeled compounds that are not expected to be present in environmental media. If the surrogates are detected by GC/MS within the specified range, it is... 

Apart from the need for a specialized instrument, sample preparation before analysis is extremely important for reliable results. The sample preparation must not itself alter the ratios of isotopes in the samples under investigation. 

Determination of gold concentrations to ca 1 ppm in solution via atomic absorption spectrophotometry (62) has become an increasingly popular technique because it is available in most modem analytical laboratories and because it obviates extensive sample preparation. A more sensitive method for gold analysis is neutron activation, which permits accurate determination to levels < 1 ppb (63). The sensitivity arises from the high neutron-capture cross section (9.9 x 10 = 99 barns) of the only natural isotope, Au. The resulting isotope, Au, decays by P and y emission with a half-life of 2.7 d. 

This equation predicts a value of 26.8%ofor the zebra at Turkana assuming an average value of 6%o for Lake Turkana water. This predicted value is l%o less than the actual value of 27.8%o. Given the variation in methods of sample preparation and analysis, variation between bone and tooth enamel (Stuart-Williams and Schwarcz 1997), and uncertainty in surface water oxygen isotopic composition, these values are extraordinarily close. Alternatively, if the equation is solved for using the actual value of the Turkana zebra. 

State-of-the-art TOF-SIMS instruments feature surface sensitivities well below one ppm of a mono layer, mass resolutions well above 10,000, mass accuracies in the ppm range, and lateral and depth resolutions below 100 nm and 1 nm, respectively. They can be applied to a wide variety of materials, all kinds of sample geometries, and to both conductors and insulators without requiring any sample preparation or pretreatment. TOF-SIMS combines high lateral and depth resolution with the extreme sensitivity and variety of information supplied by mass spectrometry (all elements, isotopes, molecules). This combination makes TOF-SIMS a unique technique for surface and thin film analysis, supplying information which is inaccessible by any other surface analytical technique, for example EDX, AES, or XPS. 

In this chapter, we present the principles of conventional Mossbauer spectrometers with radioactive isotopes as the light source Mossbauer experiments with synchrotron radiation are discussed in Chap. 9 including technical principles. Since complete spectrometers, suitable for virtually all the common isotopes, have been commercially available for many years, we refrain from presenting technical details like electronic circuits. We are concerned here with the functional components of a spectrometer, their interaction and synchronization, the different operation modes and proper tuning of the instrument. We discuss the properties of radioactive y-sources to understand the requirements of an efficient y-counting system, and finally we deal with sample preparation and the optimization of Mossbauer absorbers. For further reading on spectrometers and their technical details, we refer to the review articles [1-3]. 

In most alpha and mass spectrometric methods for which sample preparation is extensive and chemical recoveries can vary considerably from sample to sample, precise elemental concentrations are determined by isotope dilution methods (e.g., Faure 1977). This method is based on the determination of the isotopic composition of an element in a mixture of a known quantity of a tracer with an unknown quantity of the normal element. The tracer is a solution containing a known concentration of a particular element or elements for which isotopic composition has been changed by enrichment of one or more of its isotopes. 

Of the radioassays that are commonly used to quantify americium, a-spectroscopy is used when isotopic analyses of americium must be conducted (e.g., 241Am and 243Am). 243Am is often added as a tracer to estimate the efficiency of the sample preparation method when quantifying 241Am in biological matrices. 

Gehre, M., Hoefling, R., Kowski, P. and Strauch, G. (1996) Sample preparation device for quantitative hydrogen isotope analysis using chromium metal. Analytical Chemistry 68, 4414 4417. 

The chemistry of rare earth elements makes them particularly useful in studies of marine geochemistry [637]. But the determination of rare earths in seawater at ultratrace levels has always been a difficult task. Of the various methods applied, instrumental neutron activation analysis and isotope dilution mass spectrometry were the main techniques used for the determination of rare earths in seawater. However, sample preparation is tedious and large amounts of water are required in neutron activation analysis. In addition, the method can only offer relatively low sample throughputs and some rare earths cannot be determined. The main drawbacks of isotopic dilution mass spectrometry are that it is time-consuming and expensive, and monoisotopic elements cannot be determined as well. 

A good sample preparation would be one that produces from the original sample a form of carbon that 1) yields a large beam current strength 2) with a minimum of handling and processing 3) with small or no isotopic fractionation 4) from a very small (mg) size sample 5) in minimum time. 

Non-quantitative sample preparation, e.g., conversion to C02 provides two opportunities for bias. First, if the sample is a pure substance, such as methane or cellulose, isotopic fractionation can take place. Correction, using the stable isotope ratio 13C/12C, is possible provided the initial 13C concentration is... 

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