Isotope ratio measurements biological samples

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... 

The principle of the isotope dilution analysis (IDA) is described in Section 6.4. Due to its advantages as a definitive and accurate analytical method for the determination of element concentration via isotope ratio measurements, IDA is being increasingly applied in mass spectrometry, especially in ICP-MS and LA-ICP-MS as one of the most frequently used techniques. For example, the isotope dilution technique is employed in species analysis in biological systems, " e.g., for the determination of mercury species in tuna material,or in aquatic systems. Further applications of the isotope dilution technique are the determination of selenomethionine in human blood serum by capillary HPLC-ICP (ORC) MS ° or sulfur speciation in gas oil, diesel or heating fuel by LA-ICP-MS. Evans and co-workers have reported on the high accuracy analysis of sulfur in diesel fuel by IDA. ICP-SFMS has been employed for Si species analysis in biological or clinical samples and... 

Less expensive and less precise Instrumentation can be used for meaningful Isotope ratio measurements within biological sampling uncertainties However ... 

Described herein Is a convenient, accurate, sensitive and rapid method for measuring stable Isotopes of selenium In biological materials A rapid sample preparation technique Is used which does not require perchloric acid, with Its associated dangers Based on Isotope dilution techniques and Isotope ratio measurements, the method employs one enriched stable Isotope as the Internal standard and another as the metabolic tag This permits the quantitative measurement of the enriched tracer, unenrlched (natural) selenium present with It, and total selenium In the samples Some examples of the type of Information that can be obtained with these techniques will be described ... 

The technique based on laser-induced breakdown coupled to mass detection, which should thus be designated LIB-MS, is better known as laser plasma ionization mass spectrometry (LI-MS). The earliest uses of the laser-mass spectrometry couple were reported in the late 1960s. Early work included the vaporization of graphite and coal for classifying coals, elemental analyses in metals, isotope ratio measurements and pyrolysis [192]. Later work extended these methods to biological samples, the development of the laser microprobe mass spectrometer, the formation of molecular ions from non-voIatile organic salts and the many multi-photon techniques designed for (mainly) molecular analysis [192]. 

For the determination of isotope ratios, the precision of TOF-ICP-MS has been studied in a preliminary comparison with other mass spectrometer systems [643]. Typical isotope ratio precisions of 0.05% were obtained, thus overtaking sector field mass spectrometry with sequential detection, for which values of 0.1-0.3% for Cu/ Cu in Antarctic snow samples have been reported [644]. Similar results were obtained by Becker et al. [645] for Mg and Ca in biological samples (0.4-0.5%). In principle, the features of TOF-ICP-MS may be superior to those of sequential sector field or quadrupole mass spectrometry however, true parallel detection of the signals, as is possible with multi-collector systems or array detector mass spectrometry, may be the definitive solution, as shown by Hirata et al. [646]. Here, the use of detectors which allow true parallel measurement of the signals within the relevant mass range, just as the CCDs do for optical atomic spectrometry, may be the ultimate solution and bring about the final breakthrough for ICP-MS isotope ratio measurements as is required in isotope dilution mass spectrometry. 

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. 

Mass spectrometers have been used at some level in all of these types of investigations because of their unsurpassed sensitivity and specificity, their multicomponent analytical capability and, in some cases, their ability to provide precise and accurate isotope ratios. Traditional methods of analysis typically involve the collection of water and sediment samples, or biological specimens, during field expeditions and cmises on research vessels (R/Vs), and subsequent delivery of samples to a shore-based laboratory for mass spectrometric analyses. The recent development of field-portable mass spectrometers, however, has greatly facilitated prompt shipboard analyses. Further adaptation of portable mass spectrometer technology has also led to construction of submersible instruments that can be deployed at depth for in situ measurements. 

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