Analytical methods oxygen isotopes

Two alternate methods have recently been developed and both are used in the present study. A laser probe analytical method provided the majority of the oxygen isotope data (see Kohn et al. 1996 for details on testing and developing the method). Laser probes were originally developed for the stable isotope analysis of silicates, oxides, and sulfides in ciystalline rocks (Crowe... 

An important criticism of the use of combustion trains is that combustion is not site specific, that is all atoms in the analyte end up in the gas transferred to the IRMS. For studies of carbon isotope effects this is invariably C02. The question is especially important for carbon isotope analysis because analyte molecules of interest usually contain several different kinds of carbon atoms and therefore combustion methods average or dilute the IE s of interest. Should site specific isotope ratios be required another method of sample preparation (usually much more tedious) is necessary. Combustion methods, however, are frequently used to study nitrogen and sulfur IE s because many organic molecules are singly substituted with these atoms. Obviously, oxygen isotope effects cannot be determined using combustion trains because external oxygen is employed. Rather some type of pyrolytic sample preparation is required. 

The opponents of fundamental studies with idealized electrocatalysts and reactions cannot deny the unique insight into surface molecular and electronic or energetic interactions that new surface and mechanistic techniques generate. A combination of surface spectrometries, isotopic reactions, and conventional electrode kinetics could help unravel some of the surface mysteries. The application of such methods in electrocatalysis is limited at present to hydrogen and oxygen reactants on simple catalytic surfaces. Extension to a variety of model and complex reactions should be attempted soon. The prospective explorer, however, should strive and attend with care the standardization of analytical methods for meaningful interpretations and comparisons. 

The aim of this review is to provide a critical evaluation of recently published analytical methods available for (i) the quantification of fuel oxygenates in environmental aqueous samples and (ii) the characterization of the environmental fate of MTBE in groundwater with the use of compound-specific isotope analysis (CSIA). For a detailed evaluation of methods available for air, water and soil analysis of dialkyl ethers and alcohols and their specific advantages and drawbacks, the reader is also referred to previous reviews. [3-6]. 

Fortier SM (1994) An on-line experimental/analytical method for measuring the kinetics of oxygen isotope exchange between CO2 and saline/hypershline salt solutions at low (25-50°C) temperatures. Chem Geol (Isotope Geosci Section) 116 155-162... 

Sauer, P. E. L. D. S. L. O. Sternberg, 1994. Improved method for the determination of oxygen isotopic composition of cellulose. Analyt. Chem. 66 2409-2411. 

Highlights. Uranium oxide particles that are the most common form of nuclear fuel can be characterized by spectroscopic methods (NIR and Raman) with or without a combination of SEM and the isotopic composition of oxygen is also an indicator of the geographic source. The production process used in the manufacture of the particles is reflected in the analysis and can thus help to identify the origin of the particles. It should be noted that the analytical method used may have an effect on the particle consistence and morphology and should thus be used with care. 

Spencer (1959) has developed an analytical method for the determination of oxygen-18 in sulfate by the infrared absorption of nujol mulls of barium sulfate with an accuracy of 2 to 4%. He has used this method for the isotopic analysis of inorganic sulfate formed by the enzymic hydrolysis of arylsulphates in -enriched water. 

Mass Spectral Techniques. Samples for isotope ratio analysis are typically converted to sulfates or sulfides, then to S02(g) for analysis on a mass spectrometer (MS). The precision of the S02 measurement is commonly reported as 0.1 to 0.2 0/00 (16.241. yet systematic errors of 1 0/00 or larger may result from 1) memory effects due to adsorption of S02 on the walls of the MS, and 2) secondary isotope effects due to the existence of two stable isotopes of oxygen, 160 and lsO (251. Both of these errors can be eliminated by using SF6 rather than S02 as the analyte in the MS (25.261. However, existing sulfur fluorination procedures are relatively dangerous and tedious, making the SF6 method less desirable as a routine environmental technique (261. 

The following three analytical techniques have been developed for multielement determination after oxygen flask combustion inductively coupled plasma (ICP)-atomic emission spectrometry (AES), IC, and RNAA. ICP-AES is mainly used for trace metal analysis and RNAA for multiple isotope determination in inorganic materials. From the summary of new procedures developed since 1995 using the oxygen flask method for elemental analysis listed in Table 1, it is clear that IC is the major analytical technique behind the recent development of multielement determination for oxygen flask combustion, in particular for organic samples. 

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