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      Ca同位素分析
      發布時間: 2021-03-18 17:12:35來源:上譜分析瀏覽次數: 841

      測試項目:Ca同位素比值分析

      測試對象:巖石、土壤、沉積物、海水、地下水

      測試周期:45-90個工作日,可提供樣品測試加急服務。

      送樣要求:

      樣品類型 送樣要求 測試元素
      全巖、礦物 CaO>0.5%,25g
      ≥200
      (捻在手中無明顯顆粒感),紙袋包裝,請勿用塑料袋,勿裝訂
      δ44/42CaSRM915a(2SD<0.06‰)
      天然水體 Ca>100ppm,無懸浮物和沉淀, 50100ml

      完成標準:前處理在超凈室100級超凈臺內進行,保證監測空白及樣品無污染,標樣和重復樣在允許誤差范圍內。
      標樣數據:


      方法描述:
      14.1Ca同位素比值分析
      全巖Ca同位素前處理和測試由武漢上譜分析科技有限責任公司完成。
      前處理流程:
      前處理在配備100級操作臺的千級超凈室完成。樣品消解:(1)將200目樣品置于105 ℃烘箱中烘干12小時;(2)準確稱取粉末樣品50 mg置于Teflon溶樣彈中;(3)先后依次緩慢加入1 ml高純HNO3和1 ml高純HF;(4)將Teflon溶樣彈放入鋼套,擰緊后置于190℃烘箱中加熱24小時以上; 5)待溶樣彈冷卻,開蓋后置于140℃電熱板上蒸干,然后加入1 ml HNO3 并再次蒸干;(6)用10 ml 1 M HNO3溶解樣品,待上柱分離?;瘜W分離:移取一份含有40 µg Ca的溶液至PFA材質交換柱上,柱中填充250 µl DGA樹脂。用4 M HNO3淋洗去除基體元素,而接近100%的Ca在高純水淋洗下被洗脫并收集。收集的Ca溶液蒸干后用2 % HNO3再溶解,制備為10 ppm Ca溶液等待上機測試。前處理的全流程空白一般小于20 ng,與巨大的Ca溶樣量相比可以忽略不計。
      儀器測試流程:
      Ca同位素分析在上譜公司采用美國Thermo Fisher Scientific 公司的MC-ICP-MS(Neptune Plus)完成。Ca同位素的測試在濕法條件下進行,使用石英雙氣旋霧室和50 μL min−1流速的自提升微量霧化器進樣系統。通過高靈敏度的Jet+X錐組合和大抽力的干泵系統的配合,大大提升了儀器的靈敏度。通常10 ppm的Ca溶液能夠獲取5 V以上的44Ca信號。每次進樣之前,進樣系統都要用5 % HNO3清洗2-3分鐘,使得44Ca信號低于1  mV,避免樣品間的交叉污染。為了消除來自氬化物和氮化物的多原子離子干擾,測試在中分辨模式下進行。儀器的同位素質量分餾采用樣品-標樣插值法(SSB法)進行校正。所有的Ca同位素數據都采用相對于標準物質的千分比值形式報道。我們采用一個Alfa Ca純溶液作為日常插值法測試的參考標樣。但是為了能夠更好的與發表數據進行比較,所有的Ca同位素結果都轉換為相對于NIST SRM 915a報道。每份樣品溶液報道多次測試的平均值和標準偏差(n≥3)。日常測試中,儀器的精確度和準確度通過反復測試內部標準溶液Alf Ca來評估。此外,在樣品的前處理階段就引入一個Ca同位素的碳酸鹽標準樣品(NIST SRM 915b),一個玄武巖標樣BHVO-2和海水標樣當做未知樣品用來監控全流程。
      對NIST SRM 915a的長期測試結果為0.001 ± 0.058 ‰ (2SD, n = 155),表明儀器的測試精度優于0.06 ‰ (2SD)。 通過反復地測試,獲取的NIST SRM 915b,BHVO-2和海水的Ca同位素組成分別為0.35 ± 0.04 ‰ (2SD, n = 9),0.38 ± 0.04 ‰ (2SD, n = 14) 和0.88 ± 0.03‰ (2SD, n = 5). 這些結果與前人文獻報道值在誤差范圍內一致(Heuser and Eisenhauer 2008; Amini et al., 2009; Feng et al., 2018; Li et al., 2018; Kang et al., 2017),證明了我們對地質樣品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: δ44/42Caref = [44Ca/42Casample/44Ca/42Caref -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 δ44/42CaSRM915a 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 δ44/42CaSRM915a 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 (δ44/40Ca) 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 (δ44/40Ca) 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.

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