测试项目：Ca同位素比值分析

测试对象：岩石、土壤、沉积物、海水、地下水

测试周期：45-90个工作日，可提供样品测试加急服务。

送样要求：

完成标准：前处理在超净室100级超净台内进行，保证监测空白及样品无污染，标样和重复样在允许误差范围内。
标样数据：

方法描述：
14.1Ca同位素比值分析
全岩Ca同位素前处理和测试由武汉上谱分析科技有限责任公司完成。
前处理流程：
前处理在配备100级操作台的千级超净室完成。样品消解：（1）将200目样品置于105 ℃烘箱中烘干12小时；（2）准确称取粉末样品50 mg置于Teflon溶样弹中；（3）先后依次缓慢加入1 ml高纯HNO₃和1 ml高纯HF；（4）将Teflon溶样弹放入钢套，拧紧后置于190℃烘箱中加热24小时以上； 5）待溶样弹冷却，开盖后置于140℃电热板上蒸干，然后加入1 ml HNO₃ 并再次蒸干；（6）用10 ml 1 M HNO₃溶解样品，待上柱分离。化学分离：移取一份含有40 µg Ca的溶液至PFA材质交换柱上，柱中填充250 µl DGA树脂。用4 M HNO₃淋洗去除基体元素，而接近99%的Ca在高纯水淋洗下被洗脱并收集。收集的Ca溶液蒸干后用2 % HNO₃再溶解，制备为10 ppm Ca溶液等待上机测试。前处理的全流程空白一般小于20 ng，与巨大的Ca溶样量相比可以忽略不计。
仪器测试流程：
Ca同位素分析在上谱公司采用美国Thermo Fisher Scientific 公司的MC-ICP-MS（Neptune Plus）完成。Ca同位素的测试在湿法条件下进行，使用石英双气旋雾室和50 μL min⁻¹流速的自提升微量雾化器进样系统。通过高灵敏度的Jet+X锥组合和大抽力的干泵系统的配合，大大提升了仪器的灵敏度。通常10 ppm的Ca溶液能够获取5 V以上的⁴⁴Ca信号。每次进样之前，进样系统都要用5 % HNO₃清洗2-3分钟，使得⁴⁴Ca信号低于1  mV，避免样品间的交叉污染。为了消除来自氩化物和氮化物的多原子离子干扰，测试在中分辨模式下进行。仪器的同位素质量分馏采用样品-标样插值法（SSB法）进行校正。所有的Ca同位素数据都采用相对于标准物质的千分比值形式报道。我们采用一个Alfa Ca纯溶液作为日常插值法测试的参考标样。但是为了能够更好的与发表数据进行比较，所有的Ca同位素结果都转换为相对于NIST SRM 915a报道。每份样品溶液报道多次测试的平均值和标准偏差（n≥3）。日常测试中，仪器的精确度和准确度通过反复测试内部标准溶液Alf Ca来评估。此外，在样品的前处理阶段就引入一个Ca同位素的碳酸盐标准样品(NIST SRM 915b)，一个玄武岩标样BHVO-2和海水标样当做未知样品用来监控全流程。
对NIST SRM 915a的长期测试结果为0.001 ± 0.058 ‰ (2SD, n = 155)，表明仪器的测试精度优于0.06 ‰ (2SD)。 通过反复地测试，获取的NIST SRM 915b，BHVO-2和海水的Ca同位素组成分别为0.35 ± 0.04 ‰ (2SD, n = 9)，0.38 ± 0.04 ‰ (2SD, n = 14) 和0.88 ± 0.03‰ (2SD, n = 5). 这些结果与前人文献报道值在误差范围内一致(Heuser and Eisenhauer 2008; Amini et al., 2009; Feng et al., 2018; Li et al., 2018; Kang et al., 2017)，证明了我们对地质样品Ca同位素分析方法的可靠性。
14.2 Scheme for Ca isotope ratio analyses using MC-ICP-MS
All chemical preparations were performed on class 100 work benches within a class 1000 over-pressured clean laboratory. Sample digestion: (1) Sample powder (200 mesh) were placed in an oven at 105 ℃ for drying of 12 hours; (2) 10 - 50 mg sample powder was accurately weighed and placed in an Teflon bomb; (3) 1 ml HNO₃ ａnd 1 ml HF were added into the Teflon bomb; (4) Teflon bomb was putted in a stainless steel pressure jacket and heated to 190 ℃ in an oven for at least 24 hours; (5) After cooling, the Teflon bomb was opened and placed on a hotplate at 140 ℃ and evaporated to incipient dryness, and then 1 ml HNO₃ was added and evaporated to dryness again; (6) The sample was dissolved in 10 mL of 4 M HHNO₃. Column chemistry: An aliquot sample solution containing 40 μg Ca was loaded onto the pre-cleaned PFA column which filled with 250 µl DGA resin. All the sample matrices were removed by 4 mol L^-1 HNO₃ while quantitative recovery (>99 %) of Ca was achieved by the elution of MQ-H₂O. The collected Ca fractions were evaporated to dryness and re-dissolved in 2 % HNO₃ to obtain 10 ppm Ca solution prior to MC-ICP-MS analysis. The total procedural blank was no more than 20 ng which is negligible compared to the digestions.
Calcium isotopes analyse were performed on a Neptune Plus MC-ICP-MS (Thermo Fisher Scientific, Dreieich, Germany) at the Wuhan Sample Solution Analytical Technology Co., Ltd, Hubei, China. A “wet” plasma, using a quartz dual cyclonic-spray chamber and an Savillex 50 μL min⁻¹ PFA MicroFlow Teflon nebulizer (Elemental ScientificInc., U.S.A.), was utilized to measure Ca isotopes. The large dry interface pump (120 m³ hr^-1 pumping speed) and newly designed X skimmer cone and Jet sample cone were used to increase the instrumental sensitivity. Typically, the signal intensities of ⁴⁴Ca⁺ in 10 ppm sample solution were > 5 V. Cross-contamination between samples was eliminated by washing the sample-introduction system with 5% HNO₃ for 2-3 min between each measurement until the ⁴⁴Ca signal is less than 1 mV. Medium resolution mode was used to resolve polyatomic interference, such as ⁴⁰Ar¹H²⁺ａnd ¹⁴N³⁺. The instrumental drift was corrected by the standard-sample bracketing technique. All the Ca isotopic compositions were reported relative to a reference standard by using δ-notation: δ^44/42Ca_ref = [⁴⁴Ca/⁴²Ca_sample/⁴⁴Ca/⁴²Ca_ref -1] × 1000. An in-house Alfa Ca standard solution (Lot:9192737) was used as bracketing reference standard in our laboratory. However, in order to achieve better comparability of published Ca isotope data, all Ca isotope results were reported relative to commonly used reference standard NIST SRM 915a by adding a conversion factor 0.58 (the δ^44/42Ca_SRM915a value of Alfa Ca). Each sample solution has been measured multiple times (≥3), and the two times standard deviation is reported as the analytical uncertainty. The instrumental precision and accuracy during routine Ca isotope measurements was monitored by intermediate measurements of Alf Ca. A calcium carbonate standard NIST SRM915b, a basalt rock standard BHVO-2 and seawater samples were processed as unknowns to assess accuracy and reproducibility.
The long-term (>3 months) average δ^44/42Ca_SRM915a of NIST 915a is 0.001 ± 0.058 ‰ (2 SD, n = 155) indicated that the reproducibility of our instrument is better than 0.06‰ (2 SD). The repeated analyzed NIST SRM 915b, BHVO-2 and seawater are 0.35 ± 0.04 ‰ (2 SD, n = 9), 0.38 ± 0.04 ‰ (2 SD, n = 14) and 0.88 ± 0.03‰ (2 SD, n = 5). These results are consistent with previous studies within analytical uncertainty, conforming the accuracy of our analytical method for Ca isotopes in geological samples (Heuser and Eisenhauer 2008; Amini et al., 2009; Feng et al., 2018; Li et al., 2018; Kang et al., 2017). 
References
Heuser A. and Eisenhauer A. (2008). The Calcium Isotope Composition (δ^44/40Ca) of NIST SRM 915b and NIST SRM 1486 Geostandards and Geoanalytical Research, 32, 311-315.
Amini M., Eisenhauer A., Böhm F., Holmden C., Kreissig K., Hauff F. and Jochum K.P. (2009). Calcium Isotopes (δ^44/40Ca) in MPI-DING Reference Glasses, USGS Rock Powders and Various Rocks: Evidence for Ca Isotope Fractionation in Terrestrial Silicates Geostandards and Geoanalytical Research, 33, 231-247.
Feng L., Zhou L., Yang L., Zhang W., Wang Q., Tong S. and Hu Z. (2018). A rapid and simple single-stage method for Ca separation from geological and biological samples for isotopic analysis by MC-ICP-MS Journal of Analytical Atomic Spectrometry, 33, 413-421.
Li M., Lei Y., Feng L., Wang Z., Belshaw N.S., Hu Z., Liu Y., Zhou L., Chen H. and Chai X. (2018). High-precision Ca isotopic measurement using a large geometry high resolution MC-ICP-MS with a dummy bucket Journal of Analytical Atomic Spectrometry, 33, 1707-1719.