利用四極桿式感應耦合冷電漿質譜術精確測量碳酸鹽類之鎂鈣及鍶鈣比值

我們利用四極桿式感應耦合電漿質譜儀發展了一個高精確度量測碳酸鹽類中鎂鈣及鍶鈣比值的分析技術，這些元素比值已經廣泛應用在地球科學的研究上。我們使用650瓦無線電波功率的冷電漿技術減低頻譜干擾，並搭配乾式霧化器導入系統，增強訊號、改進偵測極限和降低樣品需求量。鎂、鈣和鍶同位素(24Mg, 43 Ca, 86Sr)的訊號強度皆使用脈衝計數模式測得。鎂鈣及鍶鈣比值是由離子訊號強度比值(24Mg/43Ca及86Sr/43Ca)計算而得，而樣本間的基質成分相似之標準溶液測量則用來校正儀器的質量分化和低頻飄移。鎂鈣比值測定受鈣濃度影響，此基質效應為0.018 Mg/Ca (mmol/mol) / [Ca] (ppm)，克服方法是將標本溶液的鈣濃度範圍調整在6-8 ppm或利用經驗關係式加以校正。不同的鍶鈣比值亦會影響到鎂鈣比值的量測，其主要原因來自86Sr++二價離子的形成干擾到43Ca+離子強度測定，其效應為0.017 Mg/Ca (mmol/mol)/ Sr/Ca (mmol/mol)，所幸對於第四紀珊瑚及有孔蟲標本鎂鈣比值測量僅造成小於千分之一的偏差。本方法的測量準確度可達到0.1-0.2%，標準溶液和標本的重複測量顯示鎂鈣及鍶鈣比值長期重現性可各達到0.5%和0.4% (2σ)。利用此技術所測得的結果與熱游離質譜儀法及重量測定所得到的結果並無統計上的差異。碳酸鹽標本大小只需3.5微克，故本技術甚至可以進行有孔蟲單一房室的研究探討。

關鍵字

感應耦合電漿質譜術；鍶鈣比；鎂鈣比

並列摘要

We have developed a high-precision analytical technique using quadrupole inductively coupled plasma mass spectrometry (Q-ICPMS, Agilent 7500s) for simultaneously measuring Mg/Ca and Sr/Ca ratios in carbonates, which are broadly used as environmental and climatic proxies in the Earth Sciences. Cool plasma technique with 650-W RF power was employed to diminish spectral interference. A desolvation introduction system with a micro-nebulizer was used to enhance sensitivity, improve detection limit and reduce sample size. Intensities of isotopes, including 24Mg, 43Ca and 86Sr, were all detected in pulse-counting mode. Mg/Ca and Sr/Ca ratios were calculated directly from intensity ratios, 24Mg/43Ca and 86Sr/43Ca, using external matrix-matched standards to correct for instrumental mass discrimination and low-frequency ratio drift. For Mg/Ca analysis, matrix effect of Ca level is 0.018 Mg/Ca (mmol/mol) / [Ca] (ppm). This problem can be overcome by holding [Ca] from 6-8 ppm in sample solution or correcting measured ratio with an empirical formula. Different Sr/Ca also slightly affects Mg/Ca determination with a slope of 0.017 Mg/Ca (mmol/mol) / Sr/Ca (mmol/mol). It is mainly caused by the formation of doubly-charge ion of 86Sr, which biases intensity measurement of 43Ca+ ion beam. This effect brings about only a trivial offset less than 1

並列關鍵字

ICP-MS ； Mg/Ca ； Sr/Ca

參考文獻

Anand, P., and Elderfield, H. (2003) Calibration of Mg/Ca thermometry in planktonic foraminifera from a sediment trap time series. Paleoceanography 18, doi:10.1029/2002PA000846.

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利用四極桿式感應耦合冷電漿質譜術精確測量碳酸鹽類之鎂鈣及鍶鈣比值

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