High-precision determination of carbonate Mg/Ca and Sr/Ca ratios by inductively coupled plasma sector field mass spectrometry
Date Issued
2006
Date
2006
Author(s)
Lu, Chia-Jung
DOI
en-US
Abstract
A permil-level analytical technique for determination of carbonate Mg/Ca and Sr/Ca ratios using inductively coupled plasma sector-field mass spectrometry (ICP-SF-MS, Thermo Electron ELEMENT2) has been established. Cold plasma technique with a RF power of 800-W were employed to diminish spectral interference. A wet introduction system with Scott-type double-pass spray chamber and an ESI micro-nebulizer with a sample uptake rate of 50 µl/min were used, which can offer low blank and high stability. Intensities of ion beams, 24Mg, 43Ca and 86Sr, were detected in pulse-counting mode. Mg/Ca and Sr/Ca ratios were determined directly from intensity ratios using external, matrix-matched standard to correct for mass discrimination and low-frequency ratio drift. Al/Ca, Mn/Ca, Fe/Ca, Cd/Ca, Ba/Ca and Th/Ca were also determined. Three different matrix effects are observed. (1) Acid effect on the elemental intensities and ratios decreases with increasing HNO3 from 1-6%. 5% HNO3 was suggested be used for routine measurement. (2) For the effect of Ca level, Mg/Ca ratio varies by 2.5% with [Ca] from 0.5-2.5 ppm and changes insignificantly for [Ca] higher than 3 ppm. (3) Different Sr/Ca slightly affects Mg/Ca determination with a slope of 0.18% per mmol/mol. It is caused by the formation of 86Sr double charged ions, which biases the measurement of 43Ca+ and affects the accuracy of Mg/Ca analysis. This effect causes only 0.1% or less for Mg/Ca ratio in both foraminiferal and coral samples. Replicate measurements made on standards and samples show that our method can give an internal precision of 0.1-0.2% (2RSD). Reproducibility of 0.45% for Mg/Ca and 0.35% for Sr/Ca can be attained. The corresponding errors are 0.05 ℃ for foraminiferal Mg thermometer and 0.5 ℃ for coral Sr thermometer. Advantages of this new technique include a small sample size of only 2 µg and high throughput of 10 samples per hour.
Subjects
鎂鈣比值
鍶鈣比值
有孔蟲
珊瑚
磁場式感應耦合電漿質譜儀
Mg/Ca
Sr/Ca
ICP-MS
Foraminifera
Coral
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-95-R93224106-1.pdf
Size
23.53 KB
Format
Adobe PDF
Checksum
(MD5):d835948fcbd70ae10e378c1b9f265464