Magnesium isotope ratio measurements

One problem is the availability of reliable reference materials for isotope ratio measurements. Certified isotope standard reference materials are available from NIST (National Institute of Standard Reference Materials, http //www.nist.gov/srd/, formerly NBS - National Bureau of Standards) and IRMM (Institute for Reference Materials and Measurements, http //www.irmm.jrc.de). There are isotope standard reference materials for light elements (H, Li, , C, N, O), Mg (magnesium metal isotopic standard NIST SRM 980), and for moderately heavy elements such as (potassium chloride isotopic standard NIST SRM 985), Cr (chromium metal isotopic standard NIST... 

Numerous applications of quadrupole ICP-MS (without a collision cell) for isotope ratio measurements can be found in quite different fields. For example, magnesium isotope ratios on... 

Thermal ionization has been used to determine isotopic abundance of virtually all the elements We have recently extnded our own capability in this direction by adapting the silica gel/phosphoric acid filament coating technique (5) to our system Five 1 of a fine silica gel suspension is placed on a filament Five l of the analyte ion solution is coated, dried then coated with 2 pi of a 0 7N phosphoric acid solution and heated until dry again The analysis is performed in a similar manner as before, except that the signal is more transient and somewhat less intense than the calcium analysis With this approach, however, we have made natural abundance isotope ratio measurements on zinc, copper, and magnesium Table II shows our measurements compared to the accepted values, shown in parenthesis, for these elements The isotope used as reference... 

Dombovari, )., Becker, J.S., and Dielze, H.J. (2000) Isotope ratio measurements of magnesiiun and determination of magnesium concentration by reverse isotope dilution technique on small amounts of Mg-spiked nutrient solutions with inductively coupled plasma mass spectrometry. Int. J. Mass Spectrom., 202, 231-240. 

Aluminum-magnesium isotope measurements of aluminum-rich chondrules in ordinary and carbonaceous chondrites were summarized by Huss et al. (2001). About 10-15% of all aluminum-rich chondrules smdied show Mg. The inferred ( Al/ Al)o ratio of these chondrules is (0.5-2) X 10 , which is consistent with the values found in ferromagnesian chondrules from type 3.0-3.1 unequilibrated ordinary chondrites (Kita et al, 2000 McKeegan et al, 2000b Mostefaoui et al, 2000 2002). 

Apparent magnesium absorption can be determined even with basic quadru-pole-based ICP-MS instruments, which can deliver precisions of 0.2-0.5% RSD for measuring the Mg/ Mg and Mg/ " Mg isotope ratios [208, 209], which is similar to what can be achieved using sector field ICP-MS [210] or collision cell ICP-MS [211]. Such precisions require isotope doses of the order of 20-50 mg to reach enrichments in the percent range in the collected fecal material. This compares with a dietary magnesium intake of about 300 mg per day. 

Becker, J.S., Fiillner, K., Seeling, U.D., Fornalczyk, G., and Kuhn, A.J. (2008) Measuring magnesium, calcium and potassium isotope ratios using ICP-QMS with an octopole collision cell in tracer studies of nutrient uptake and translocation in plants. Anal. Bioanal. Chem., 390, 571-578. 

The first few decades of space exploration went by without any MS better than m/Am 4 because understanding the solar wind flow, its density, its pressure, or its temperature did not require mass resolution. Not until 1984 did a space MS fly with a resolution of about 10 [10], and it was 1994 before that increased to 100 [11], Suddenly for the first time, the solar wind isotopes of carbon, oxygen, magnesium, silicon, and iron were known, and the models could be tested. Even then, space MS had difficulty measuring rare isotopes, so that it wasn t until 2005 that solar wind samples were returned to Earth inside ultra-pure silicon wafers (the ill-fated Genesis mission [12]) to determine the important triple ratios of ieO 170 lsO. 

At present, uses of Mg are restricted to objectives that can be attained by oral Isotope administration onlyt One of these Is the measurement of "true magnesium absorption in which Mg is given orally, and Mg by Injection. "True absorption Is then computed either by estimation of the ratio %g Mg in urine or, more precisely, by measuring net absorption Csubtractlon of fecal exr ... 

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