A Study on Memory Effects in Lithium and Boron Isotope Analysis Using MC-ICP-MS
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摘要:
锂(Li)和硼(B)同位素是地质作用过程中良好的示踪剂,被广泛应用于岩石起源、矿床成因和环境演化等领域。但锂、硼在MC-ICP-MS仪器分析中的“记忆效应”明显,不同实验室已报道的MC-ICP-MS分析中锂、硼背景占信号比变化范围大(0.01%~5%),所采用的背景控制方法和效果也各不相同,因此给锂、硼同位素的准确测定带来困难。为研究MC-ICP-MS锂、硼同位素记忆效应及其抑制方案,提高测试的稳定性,本文参考前人研究成果,设计不同背景清洗方案,并对各种国际标样(IRMM-016、JG-2、ERM-AE121、ERM-AE122、NASS-7)和实验室内部标准(Alfa Li、Alfa B)进行长期测试,检验实验方案的长期重现性。结果表明:仅使用0.3%氯化钠溶液清洗背景可以显著降低锂背景信号,从20mV下降至4mV,并保证7Li背景值在24h内低于5mV,实验室内部标准溶液Alfa Li的δ7Li长期测试外精度为0.13‰(2SD,n=73)。氟化钠、氨水等清洗液并不能显著降低本研究所使用仪器的硼背景,因此选择使用灵活的空白扣除方法来保证数据稳定性。实验室内部标准溶液Alfa B的δ11B长期测试外精度为0.19‰(2SD,n=60)。本文锂、硼同位素国际标样的测试结果与前人数据在误差范围内一致,证明了实验结论的可靠性。
要点(1)MC-ICP-MS测定锂、硼同位素组成时记忆效应明显,导致不同批次测试的分析精度差异大,数据重现性较差。
(2)使用0.3%氯化钠溶液清洗锂背景时,锂同位素分析稳定性最佳;灵活的空白扣除方法适合硼同位素的准确测定。
(3)使用指定的背景清洗方案,国内外标样锂、硼同位素测试精度分别可达0.2‰和0.3‰。
HIGHLIGHTS(1) The memory effects of Li and B in MC-ICP-MS are obvious, which results in a poor data reproducibility among different measurement batches.
(2) When the Li background is rinsed with 0.3% NaCl solution, the stability of Li isotope analysis is the best. The flexible blank deduction method is suitable for accurate determination of B isotopes.
(3) After using the suggested background cleaning method, the detection accuracy of international standards of Li and B isotopes can reach 0.2‰ and 0.3‰, respectively.
Abstract:Lithium (Li) and boron (B) isotopes are excellent tracers in geological processes. In order to study and eliminate the memory effects of lithium and boron element in isotopic measurements using MC-ICP-MS, different background rinsing protocols were designed with reference to previous research. The δ7Li and δ11B values of different types of reference materials were tested to evaluate the long-term reproducibility of the measurements using designated rinsing protocols for at least six months. The results show that using only 0.3% NaCl solution to clean the background for 60s can significantly reduce the lithium background signal and ensure the 7Li background signal is less than 5mV within 24h. The long-term external precision of δ7Li values for Alfa Li, an in-house standard, was 0.13‰ (2SD, n=73). Rinsing solutions, such as NAF and NH3·H2O could not significantly reduce the boron background of the instrument. However, the flexible blank subtracting method was used for precise determination of δ11B values. The long-term external precision of δ11B values for Alfa B was 0.19‰ (2SD, n=60). The average δ7Li and δ11B values of different types of reference materials were tested using these rinsing protocols, and the results were well consistent with reported data, supporting the applicability of the conclusions. The BRIEF REPORT is available for this paper at http://www.ykcs.ac.cn/en/article/doi/10.15898/j.ykcs.202310260167.
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Keywords:
- memory effect /
- lithium /
- boron /
- MC-ICP-MS /
- 0.3% NaCl solution /
- blank deduction
BRIEF REPORTSignificance: MC-ICP-MS is commonly used to determine the composition of lithium and boron isotopes. However, data quality is often limited due to significant memory effects caused by deposition or adhesion of Li and B into the instrument. The rinsing solutions, including NaCl solution for Li and ammonia or NaF solutions for B, were tried, to eliminate memory effects by previous work[12,16,27-28,32]. However, the sensitivity and background of Li and B elements in different instruments are different, such as in Neptune or Nu MC-ICP-MS, the memory reduction method should be retested in a new instrument. In this paper attention to the Li and B memory effects and their reduction method in the isotopic measurements using Nu Sapphire MC-ICP-MS was given. The results show that using only 0.3% NaCl solution to clean the background can significantly reduce the lithium background signal, and ensure that the 7Li background value is less than 5mV within 24h. The flexible blank deduction technique can be used for precise determination of δ11B values.
Methods: 0.1%(V/V) NaCl, 0.3% NaCl, 2.5% NaCl and 5% NaCl solutions were introduced for 1min to rinse the background of Li before a daily batch run. The background of Li after a normal 2% HNO3 rinsing sequence and the internal precision (SE) of 7Li/6Li when testing 200ng/g Li sample solutions were recorded for several hours. For B isotopes measurement, water, 0.1% ammonia and 0.06mg/g NaF solutions were introduced for 1min or 2min to control the B memory effects. The background of B after a normal 2% HNO3 rinsing sequence were recorded when testing an 80ng/g B sample solution. The blank subtraction method with different frequencies was also used to control the memory effects of B. The δ7Li and δ11B values of standard materials and their external precisions (2SD) were calculated to ensure the accuracy and long-term stability of the measurements using a different memory reduction method.
Data and Results: The fluctuation of sensitivity of 7Li and internal precision (SE) of 7Li/6Li caused by Na were limited when 0.3% NaCl solution was introduced for 60s. In the meanwhile, the 7Li background signal decreased from 20mV to 4mV and remained a low level within 24h. Thus, a washing process included the following steps: 0.3% NaCl solution was introduced for 60s at intervals of about 24h, the background intensity determined (zero test) using 2% HNO3 blank was subtracted before a daily batch run and 2% HNO3 (2min) was used to rinse the background between each standard and samples. The δ7Li values of reference materials and their external precisions (2SD) were obtained in six months to ensure the accuracy and long-term stability of the data. The δ7Li values of IRMM-016, USTC-Li, Alfa Li and JG-2 with respect to L-SVEC were 0.12‰±0.07‰ (n=50), −19.3‰±0.12‰ (n=56), 13.7‰±0.13‰ (n=73), 0.13‰ ±0.11‰ (n=12), respectively.
The 11B background signal could not be effectively reduced when the background rinsing solution was replaced with pure water, acidified NaF, ammonia and dilute nitric acid. To ensure the accuracy of the test, the background deduction method is flexibly selected, that is, each blank is deducted once between each standard and samples within the first 3h of the B isotope test sequence. Typical washing and testing process included the following steps: 120s 2% HNO3 wash–60s wash solution uptake–30s 2% HNO3 zero test–120s 2% HNO3 wash–60s sample uptake–150s sample or standard measurement. The zero-testing process could be lessened to once every nine samples testing after 3h of the batch run. After six months of reference materials testing, the δ11B values of ERM-AE121, ERM-AE122, Alfa B and NASS-7 were
19.78‰±0.31‰ (n=64), 39.54‰±0.33‰ (n=36), −4.66‰±0.19‰ (n=60) and 40.03‰±0.33‰ (n=35), respectively. The results were in good agreement with reported data, which indicates that excellent accuracy and precision can be achieved for Li and B isotope measurements using these designated rinsing protocols. -
金(Au)是中国重要的战略性资源,但金矿的金品位普遍较低,需借助半自磨机或搅拌磨降低颗粒粒度并促进金相颗粒解离[1-2]。为获得较高的金精矿品位,提高金元素富集比,通常需利用复杂的多次粗选扫选和精选配合的浮选工艺,而在长流程浮选体系中,以镍、铜、镉、铅等为代表的有害元素选择性富集或随机分散在各工艺产品中[3-4],影响了各金矿浮选产品的质量,但当前针对金矿浮选过程中有害元素定量的研究较少,有必要建立金矿浮选样品中有害元素的检测方法。
金矿中有害元素含量与金品位相当,但相对于金矿主量伴生元素则存在巨大的浓度差异;而高基体背景下准确定量有害元素的关键是如何有效地控制或消除基体差异带来的非质谱干扰[5-6]。虽然目前分析检测手段已逐步应用于选矿领域,但较多的是针对原矿的工艺矿物学分析,即在分析含金组分的赋存形态、嵌布特征基础上为金矿磨浮工艺优化提供支撑[7-9]。一些痕量元素定量的检测方法包括电感耦合等离子体发射光谱或质谱法(ICP-OES/MS)[10-13]、辉光放电质谱法[14-16]、X射线衍射法(XRD)[17-18]等,在分析复杂基体样品时通常会使用基体纯净的标准溶液或物质,难以高质量校正待测元素标准溶液与样品消解液之间的基体差异。上述检测手段配合基体匹配方法的检测领域,多为基体唯一的合金钢中杂质元素定量,譬如张馨元等[19]分别利用无基体匹配和2000μg/mL镍基体的铜、锌、钡元素标准溶液来定量镍基高温合金标准物质中痕量铜锌钡,前者测试结果较认定值存在15%~20%偏差,而后者检测结果均在标准物质中痕量元素认定浓度范围内。沈健等[20]利用基体匹配ICP-MS测定煤中钽铀镱含量时,采用标准煤样消解液为基体,配制待测元素标准溶液,但未关注标准煤样消解液中无机组分的基体影响,欠缺标准煤样所含微量钽铀镱元素对标准曲线线性和方法检测下限的讨论。因此,当前针对复杂基体自然矿产中有害元素的准确定量方法,仍需进一步优化研究。
本文以金矿浮选过程样品为研究对象,采用基体匹配ICP-MS测试方法,在明确各样品基体元素种类后,开展高浓度基体溶液添加痕量有害元素的测定实验,分析基体种类和浓度对有害元素定量结果相对偏差的影响。在此基础上,利用高浓度基体有害元素标准溶液对金矿各浮选样品进行定量实验,与纯试剂有害元素标准溶液定量结果和测试过程内标回收率比对,并通过消解加标、测试加标以及平行实验分析基体匹配ICP-MS方法的准确度和精密度,评估方法的测试质量。
1. 实验部分
1.1 样品信息
研究对象为金矿浮选矿浆产品,采自紫金矿业集团股份有限公司某金矿选厂,采集物料包括浮选入料、各浮选段精矿和尾矿产品。取样前准备足够数量的料筒并做好标记,样品采集工具为取样勺。浮选入料由溜槽给入浮选设备,取样时使用取样勺对整个料流截面均匀取样;浮选精矿泡沫取样则是用取样勺截取全部溢流面;浮选尾矿取样是用取样勺对准矿浆流取样。每个样品采集点的取样时间均为10min。
1.2 样品前处理
采用实验室小型过滤机处理某金矿浮选流程的22个矿浆产品(样品编号为样品1~样品22),获得各样品滤饼及滤液。滤饼置于烘箱中105℃干燥3h后冷却,缩分后用于样品消解与元素组成分析。为确保有害元素全部从固体矿物转移至溶液,减少有害元素定量的制样误差,样品消解以溶液澄清、无固体颗粒残留为目标。消解实验采用耗酸少、速度快的微波消解,经探索确定了如下消解方案。
(1) 样品称取0.1g,置于可溶性聚四氟乙烯消解罐中;
(2) 向消解罐中加入3.75mL盐酸、1.25mL硝酸和2mL氢氟酸;
(3) 将消解罐置于微波消解仪中,升温到150℃,保持20min;再升温至220℃,保持40min,取下冷却后在通风橱内缓慢泄压后打开消解罐;
(4) 将消解罐置于石墨赶酸仪中,180℃开盖赶酸,待样品蒸干后取下冷却,加入1mL浓硝酸复溶后加超纯水定容至100mL。
经测试,微波消解过程空白中镍、铜、镉和铅元素含量分别为0.2741μg/L、0.3435μg/L、0.0019μg/L和0.0263μg/L。消解过程空白溶液中的有害元素含量较低,对样品中的有害元素定量结果影响较小。
1.3 标准物质和主要试剂
镍、铜、镉、铅单元素标准储备液(1×106μg/L,美国Agilent公司);Re内标储备溶液(100μg/mL,美国Agilent公司),使用时稀释至0.5μg/mL。
硫标准溶液(2×104μg/mL,购自钢研纳克有限公司);铁和铝则分别选用分析纯标准物质三氧化铁和三氧化铝,用硝酸溶解,获得质量浓度为10mg/mL的单元素溶液。
UPS级纯硝酸、盐酸和氢氟酸(晶锐电子材料股份有限公司)。
超纯水(ELGA Option Q15 纯水机纯化,电阻率≥18MΩ·cm)。
1.4 实验仪器
浮选样品元素组成分析采用S8 Tiger型X射线荧光光谱仪(德国Bruker有限公司),并通过元素校正曲线定量。
样品中痕量有害元素定量采用Aglient 7900电感耦合等离子体质谱仪(美国Aglient公司),仪器测试参数列于表1。
表 1 电感耦合等离子体质谱仪测试条件Table 1. Measurement parameters of ICP-MS instrument工作参数 设定值 工作参数 设定值 射频功率 1550W 截取锥直径 0.45mm 取样深度 8mm 扫描方式 跳峰方式 等离子气体(Ar)流速 15L/min 每峰点数 1 辅助气体(Ar)流速 0.80L/min 扫描次数 100 载气(Ar)流速 1.05L/min Cd元素积分时间 1s 镍采样锥直径 1mm Ni、Cu、Pb等
元素积分时间0.30s 本文使用的Agilent 7900型电感耦合等离子体质谱仪,配备了碰撞反应池,可有效地降低有害元素含量测试的质谱干扰;此外,定量测试中还针对性地选择了质量数干扰最低的同位素,即60Ni、65Cu、111Cd和208Pb。金矿浮选样品消解液中的主量基体元素在测试过程会产生非质谱干扰,对有害元素离子流形成抑制。为削弱该影响,本文采用高浓度的代表性基体元素标准溶液稀释有害元素储备溶液后,形成复杂基体有害元素标准溶液。与纯试剂有害元素标准溶液相比,复杂基体有害元素标准溶液与金矿浮选样品消解液具有同一数量级的基体背景[21],再配合内标元素铼(Re,浓度0.50μg/mL)后,可有效地抑制非质谱干扰。
基体匹配ICP-MS方法研究中(技术路线如图1所示),首先使用XRF确定主量基体元素,然后利用基体元素标准溶液配制具有浓度梯度的有害元素标准溶液;利用ICP-MS测试具有浓度梯度的有害元素标准溶液后,获得各有害元素标准曲线;在读取有害元素测试背景值后,调整配制复杂基体有害元素标准溶液所需的基体元素标准溶液与有害元素储备液体积,进而获得有害元素浓度准确的复杂基体有害元素标准溶液,提升基体匹配ICP-MS方法测试结果的准确性。
1.5 数据质量控制
方法准确性:在样品消解和测试环节,采用标准加入方式评价金矿浮选样品中痕量有害元素定量方法的准确性。称取0.10g的14号样品两份,其中一份加入有害元素镍、铜、镉和铅各10μg,消解后定容至100mL测试。分别称取0.10g的6号和13号样品,消解定容至100mL后取两份平行样,一份直接测试,一份加入浓度100μg/L等体积的复杂基体有害元素标准溶液后混匀后测试。
方法精密度:分别称取6份5号和12号样品,每份质量0.10g,按照1.2节样品前处理方法消解获得平行消解溶液后测试各样品中有害元素含量,并计算各有害元素定量结果的相对标准偏差(RSD)。
2. 结果与讨论
2.1 浮选样品的主量基体元素组成
22个金矿浮选样品的主量元素及含量分析结果列于表2。受浮选过程的各组分分离和富集作用影响,样品中主量基体元素种类及含量有所差异。依据元素组成,将样品分为铝基体(样品编号:1、7、14和22),铁硫基体(样品编号:2、3、8、10、12和13),铁铝基体(样品编号:4~6、9、11和15~21)共计三类(Si元素在消解中与氟结合形成四氟化硅SiF4挥发[22-23],因而未将Si列为基体元素)。4种铝基体样品中铝含量接近(1号样品主量元素仅为Si,为简化样品种类将其归类为铝基体样品);6种铁硫基体各样品中铁和硫元素含量差异在10%附近(8号样品主量元素仅为Fe,为简化样品种类将其归类为铁硫基体样品);12种铁铝基体样品的Si、Fe、Al元素含量均较为接近。
表 2 金矿浮选样品的主量基体元素种类及含量Table 2. Major matrix elements in flotation samples of gold ore样品编号 基体类型 主要元素及含量 样品编号 基体类型 主要元素及含量 1 铝基体 Si (29.75%) 5 铁铝基体 Si (27.66%); Fe (10.60%); Al (10.27%) 7 Si (29.84%); Al (9.78%) 6 Si (28.66%); Fe (8.27%); Al (10.58%) 14 Si (31.27%); Al (10.43%) 9 Si (27.93%); Fe (9.35%); Al (11.02%) 22 Si (30.47%); Al (9.63%) 11 Si (24.76%); Fe (15.85%); Al (10.99%) 2 铁硫基体 Si (14.92%); Fe (22.87%); S (12.76%) 15 Si (26.64%); Fe (10.74%); Al (10.23%) 3 Si (19.06%); Fe (22.36%); S (13.52%) 16 Si (28.45%); Fe (10.33%); Al (10.95%) 8 Si (13.16%); Fe (23.50%) 17 Si (27.75%); Fe (10.97%); Al (10.60%) 10 Si (14.08%); Fe (20.57%); S (17.27%) 18 Si (25.64%); Fe (10.92%); Al (10.17%) 12 Si (13.59%); Fe (26.39%); S (22.35%) 19 Si (28.27%); Fe (11.21%); Al (10.71%) 13 Fe (30.48%); S (24.16%) 20 Si (26.96%); Fe (9.39%); Al (10.38%) 4 铁铝基体 Si (25.89%); Fe (14.46%); Al (10.37%) 21 Si (27.43%); Fe (10.62%); Al (10.84%) 2.2 高浓度基体对镍铜镉铅元素测试准确性的影响
为探究高浓度基体加入对Ni、Cu、Cd和Pb元素含量测试准确性的影响,分别利用基体元素浓度为500μg/mL和1000μg/mL的一种和两种基体元素溶液稀释500μg/L纯试剂有害元素标准溶液,获得理论浓度为10μg/L的复杂基体有害元素标准溶液。随后,利用纯试剂有害元素标准溶液测试(内标选用185Re)并扣除基体溶液中有害元素含量(譬如1000μg/mL铝基体中,Cu元素浓度为11μg/L),计算测试结果的相对偏差,结果列于表3。整体上,高浓度基体元素溶液对痕量有害元素在ICP-MS测试过程的影响较小。与理论值(10μg/L)相比,不同浓度和基体元素种类溶液中各有害元素定量结果的相对偏差在±10%以内。因此,利用复杂基体有害元素标准溶液进行金矿浮选样品中有害元素的定量测试,是可行的。
表 3 不同浓度/种类基体元素溶液中痕量有害元素定量的相对偏差Table 3. Relative deviation of each hazardous element after adding different concentrations/types of matrix elements基体元素及浓度
(μg/mL)各有害元素测定值与理论值的相对偏差(%) Ni Cu Cd Pb 铝(500) −0.85 7.96 −0.74 3.00 铁(500) −4.62 6.74 −2.31 −0.79 硫(500) −5.22 3.46 −3.85 6.29 铁硫(500) 0.97 9.72 −9.32 2.03 铁硫(1000) −1.97 8.31 −7.07 1.22 铁铝(1000) 5.74 −5.42 −2.70 −2.48 2.3 基体元素对金矿浮选样品中有害元素定量影响
选择金矿浮选8号样品(铁硫基体)、9号样品(铁铝基体)、13号样品(铁硫基体)和17号样品(铝基体)共4种代表性样品,在分别配制1000μg/mL铝元素、铁元素、硫元素、铁硫、铁铝元素基体溶液后,将有害元素标准储备液逐级稀释至10、20、50、100、200和500μg/L(因铝基体溶液中含一定量Cu,配制铝和铁铝基体的有害元素标准溶液时,依据Cu含量再次计算所用有害元素标准储备液、铝溶液、铁溶液和稀硝酸的用量),测试样品中Ni、Cu、Cd、Pb含量。此外,同步开展纯试剂(2%硝酸)有害元素标准溶液对代表性样品中有害元素定量测试。依据公式(1)将液体样品中的有害元素含量(单位μg/L)转换为固体中的有害元素含量[24](单位μg/g)。
$$ c=\frac{\left(c_1-c_0\right) \times V \times d}{m} \times 10^{-3} $$ (1) 式中:c为样品中有害元素含量(μg/g);c1和c0分别为消解稀释液和消解过程空白中有害元素浓度(μg/L);V为消解液体积,此处为100mL;d为稀释倍数,根据样品浓度与方法定量上限确定;m为样品质量,此处为0.10g。
不同基体有害元素标准溶液对部分金矿浮选样品中有害元素的定量结果列于表4。譬如,铁硫基体样品分别用铁基体、硫基体、铁硫基体和纯试剂有害元素标准溶液测试,其他样品测试安排以此类推。表4数据显示在1000μg/mL基体浓度前提下,复杂基体有害元素标准溶液中基体元素种类和数量,对金矿浮选样品中有害元素测试结果并未产生明显影响。复杂基体与纯试剂有害元素标准溶液,对4个代表性金矿样品中有害元素定量结果的相对标准偏差小于7.73%(大部分小于5%)。因此,可利用有害元素标准溶液开展不同基体类型的所有金矿浮选样品中有害元素的定量分析。
表 4 不同基体有害元素标准溶液对部分金矿浮选样品中有害元素定量分析结果Table 4. Quantification results of harmful elements in some gold ore flotation products using standard solutions of harmful elements in various matrixes样品编号 有害元素标准溶液
基体元素Ni测定值
(μg/g)Cu测定值
(μg/g)Cd测定值
(μg/g)Pb测定值
(μg/g)8号样品
(铁硫基体)铁硫 363.38 596.78 24.61 1540.22 铁 344.59 547.18 23.88 1569.77 硫 372.52 564.39 24.15 1611.48 纯试剂 356.31 574.64 23.50 1625.51 RSD(%) 3.28 3.63 1.94 2.46 9号样品
(铁铝基体)铁铝 112.66 186.65 2.32 263.37 铁 113.77 196.41 2.52 292.44 铝 117.31 210.64 2.57 294.22 纯试剂 115.64 194.62 2.32 264.84 RSD(%) 1.79 5.07 5.41 6.06 13号样品
(铁硫基体)铁硫 336.18 311.63 17.54 1135.47 铁 294.45 315.54 19.18 1199.29 硫 301.20 321.80 19.05 1145.17 纯试剂 317.10 366.45 18.89 1322.70 RSD(%) 5.95 7.73 4.07 7.17 17号样品
(铝基体)铝 124.75 303.10 2.23 275.80 2%硝酸 118.06 288.17 2.20 257.33 RSD(%) 3.90 3.57 0.96 4.90 本文首先使用不同基体元素的复杂基体有害元素标准溶液测试对应基体类型样品中有害元素含量,然后利用铁硫基体有害元素标准溶液开展铝基体和铁铝基体样品中有害元素测试。不同基体的有害元素标准溶液对金矿浮选样品中有害元素定量结果列于表5。利用不同基体元素的有害元素标准溶液对各金矿浮选样品中有害元素的定量结果接近,各有害元素的回收率在80%~120%范围内。因此,在1000μg/mL基体浓度前提下,有害元素标准溶液的基体元素差异并未对测试过程产生影响,基体匹配方法中使用铁硫基体有害元素标准溶液,能够获得准确的测试结果。
表 5 不同基体有害元素标准溶液对铝基体和铁铝基体金矿浮选样品中有害元素测试结果Table 5. Quantification results of harmful elements in gold ore flotation samples with Al- and Fe-Al matrix using standard solutions of harmful elements in various matrixes.样品编号 有害元素标准溶液基体元素 Ni
(μg/g)Cu
(μg/g)Cd
(μg/g)Pb
(μg/g)有害元素标准溶液基体元素 Ni
(μg/g)Cu
(μg/g)Cd
(μg/g)Pb
(μg/g)1 铝 58.62 67.33 1.60 102.58 铁硫 57.22 63.85 1.61 90.96 7 44.56 102.80 0.71 96.42 42.56 98.20 0.63 96.06 14 59.10 125.33 1.00 108.18 59.10 116.57 0.82 119.4 22 34.18 63.03 0.32 70.24 36.13 65.14 0.34 66.88 4 铁铝 160.93 282.57 5.40 497.02 160.93 267.77 5.41 513.4 5 94.30 249.38 5.21 436.7 116.83 206.86 5.89 377.65 6 82.92 159.46 2.45 265.68 92.34 140.05 2.24 254.67 9 112.66 186.65 2.32 263.37 120.39 161.81 2.05 225.93 11 197.97 340.82 6.22 697.57 197.97 290.04 6.31 663.41 15 105.21 428.65 2.25 303.61 111.45 365.18 1.86 303.45 16 107.84 338.23 1.87 186.06 96.84 297.13 1.55 183.48 17 124.75 303.10 2.23 275.8 115.88 297.02 2.10 264.64 18 149.36 422.74 2.51 266.65 136.23 441.74 2.15 268.78 19 68.25 384.89 1.85 256.20 56.95 341.4 1.74 263.90 20 86.69 250.90 1.99 152.05 95.12 253.08 1.83 173.13 21 94.00 349.36 2.40 282.20 92.33 358.58 2.30 276.88 为进一步比较复杂基体与纯试剂有害元素标准溶液对金矿浮选样品有害元素测试过程的影响,对比两类有害元素标准溶液测试22个金矿样品内标回收率,如图2所示(图中样品编号1~7为标准溶液,编号8~29代指金矿浮选的1~22号样品)。基体匹配方法测试各样品内标回收率较纯试剂测试稳定,前者的回收率分布在90%~110%之间,后者则在85%~100%之间。基体匹配测试各样品内标回收率与100%差值绝对值的平均差为1.64%,而后者则为2.16%(平均差,即各差值绝对值与其平均数的离差绝对值的算术平均数),基体匹配法内标回收率平均差较无基体匹配测试低24.07%。纯试剂有害元素标准溶液与消解样品之间有较大的基体差异,在一定程度上对元素离子化产生抑制作用。采用基体匹配方法可降低非质谱干扰,削弱测试过程的信号波动。
2.4 基体匹配ICP-MS法的测试质量评估
2.4.1 方法准确度
在样品消解和测试环节,采用标准加入方式评价金矿选冶样品中有害元素定量方法的准确性。消解和测试加标实验参照1.6节所述,各元素加标回收率列于表6。根据表中数据计算,消解加标实验中各有害元素加标回收率在92.08%~105.36%之间,表明微波消解过程中各有害元素基本无损失;而测试加标实验中各有害元素加标回收率在95.68%~106.05%之间,显示不同基体类型样品的消解溶液对加标有害元素回收率影响较小,与2.2节实验结果相呼应。较好的加标回收率指标表明此测试方法准确性高。
表 6 消解和测试加标回收实验结果Table 6. Results of spiked recovery experiment for the dissolution and measurement样品名称 Ni测定值
(μg/g)Cu测定值
(μg/g)Cd测定值
(μg/g)Pb测定值
(μg/g)14号样品 59.10 116.57 0.82 119.40 14号样品+10μg各元素(消解) 161.72 221.93 97.55 211.48 加标回收率(%) 102.62 105.36 96.73 92.08 6号样品 92.34 140.05 2.24 254.67 6号样品+等体积标液(测试) 97.08 122.16 50.22 177.92 加标回收率(%) 101.82 104.27 98.20 101.17 13号样品 336.18 311.63 17.54 1135.47 13号样品+等体积标液(测试) 215.93 208.84 57.71 619.26 加标回收率(%) 95.68 106.05 97.88 103.05 2.4.2 方法精密度
两组样品的6个平行消解实验样品中有害元素的测定结果列于表7。整体上,平行实验中元素含量较低的Cd元素的RSD值相对较高,但高浓度元素的RSD值则较低。各元素的RSD在1.21%~4.69%之间。精密度实验的指标较高,数据波动小,重现性高。
表 7 加标回收实验结果Table 7. Results of spiked recovery experiments样品编号 元素 6次平行实验检测值(μg/g) 平均值
(μg/g)RSD
(%)5号样品 Ni 116.83 119.04 114.52 121.75 118.08 111.61 116.97 3.04 Cu 206.86 208.96 212.57 204.88 210.73 209.09 208.85 1.31 Cd 5.89 5.98 5.66 5.42 6.07 6.15 5.86 4.69 Pb 377.65 360.19 384.57 366.42 379.76 359.97 371.43 2.86 12号样品 Ni 330.05 344.47 327.59 335.04 338.73 349.62 337.58 2.50 Cu 356.31 347.87 342.46 360.93 354.52 361.42 353.92 2.11 Cd 20.18 18.25 18.57 19.62 19.74 20.09 19.41 4.16 Pb 1227.43 1268.87 1239.15 1241.06 1251.53 1231.50 1243.26 1.21 3. 结论
提出采用基体匹配ICP-MS法定量金矿浮选样品中的痕量有害元素。首先采用XRF确认各浮选样品的主量基体元素后,将其分为铝基体、铁铝基体和铁硫基体三类。在500μg/mL和1000μg/mL基体溶液中,基体元素种类和数量对痕量有害元素定量结果差异较小,其相对偏差在±10%以内。表明采用高浓度的基体元素溶液配制有害元素标准溶液,不会对有害元素定量结果产生影响,且复杂基体有害元素标准溶液在定量金矿浮选样品中有害元素时还可起到削弱基体差异的作用。在有害元素标准溶液基体浓度相同(1000μg/mL)的前提下,金矿浮选样品中有害元素定量结果不受基体元素种类和数量影响,且与纯试剂有害元素标准溶液定量结果的相对标准偏差小于7.73%,而内标回收率与100%理想值差值绝对值的平均差较纯试剂有害元素标准溶液测试低24.07%。因此,采用了铁硫基体有害元素标准溶液测试不同基体类型的金矿浮选样品,该方法消解和测试的加标元素回收率在92.08%~105.36%之间,测试环节加标回收率为95.68%~106.05%,精密度(RSD)为1.21%~4.69%,具有准确度高的特点。
本文方法虽仅针对金矿浮选样品中部分有害元素的定量测试,但对于其他复杂金属矿产或合金类等样品中的痕量有害元素测试仍具有借鉴意义和实践参考,在地质矿产样品检测领域具有一定实用性。
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图 5 在不同类型洗液组合下11B背景信号随时间的变化
① PFA雾化器,1%硝酸酸化NaF溶液清洗1min,随后2%硝酸继续清洗;② PFA雾化器,纯水清洗1min后2%硝酸继续清洗;③ PFA雾化器,纯水清洗2min后2%硝酸继续清洗;④ 玻璃雾化器,0.1%氨水清洗1min后2%硝酸继续清洗;⑤ 玻璃雾化器,纯水清洗1min后2%硝酸继续清洗。
Figure 5. The variations in 11B background signal over time under various combinations of lotions
①100µL/min PFA nebulizer was used. The B background was rinsed by 0.6mg/g NaF in 1% HNO3 solution for 1min before a normal cleaning by 2% HNO3 solution; ②100µL/min PFA nebulizer was used. The B background was rinsed by water for 1min before a normal cleaning by 2% HNO3 solution; ③100µL/min PFA nebulizer was used. The B background was rinsed by water for 2min before a normal cleaning by 2% HNO3 solution; ④100µL/min glass nebulizer was used. The B background was rinsed by 0.1% (V/V) ammonia for 1min before a normal cleaning by 2% HNO3 solution; ⑤100µL/min glass nebulizer was used. The B background was rinsed by water for 1min before a normal cleaning by 2% HNO3 solution.
图 6 标准样品IRMM-016(a)、USTC-Li(b)、Alfa Li(c)和JG-2(d)相对于L-SVEC的δ7Li测定值及其参考值
红色方框及其误差限表示参考值和参考值变化范围或其测试外精度(2SD)。样品误差表示单次测试的外精度(2SD)。
Figure 6. The measured δ7LiL-SVEC of the standards and their reference values. The red box and its errors bars represent the reference value and the range of variation of the values or their external precisions (2SD). The sample error bars represent external precisions (2SD) of individual tests.
图 7 标准样品EPM-AE 121(a)、EPM-AE 122(b)、Alfa B(c)和NASS-7(d)相对于NIST951a的δ11B测定值及其参考值
红色方框及其误差限表示参考值平均值和参考值变化范围。样品误差限表示单次测试的外精度(2SD)。
Figure 7. The measured δ11BNIST951a of the standards and the reference values. The red box and its errors bars represent the reference value and the range of variation of the values or their external precisions (2SD). The sample error bars represent external precisions (2SD) of individual tests.
表 1 Nu Sapphire MC-ICP-MS仪器基本配置
Table 1 Basic configuration of the Nu Sapphire MC-ICP-MS instrument
工作参数 实验条件 工作参数 实验条件 射频功率 1300W 炬管 石英炬管 加速电压 6000V,高能模式 雾化器气体(Ar)压力 ~30psi 冷却气(Ar)流速 13L/min 锥 镍锥,湿锥 辅助气(Ar)流速 0.9~1.0L/min 接收器设置 H6-11B;L6-10B
H9-6Li;L6-7Li雾化器及流速 玻璃雾化器,PFA雾化器,100/50μL/min 分辨率 低分辨 表 2 标准物质锂同位素组成测定值与参考值
Table 2 The measured and reported δ7LiL-SVEC values of standards
标准物质 δ7LiL-SVEC参考值
(‰)δ7LiL-SVEC测试值
(‰)2SD
(‰)n IRMM-016 −0.17~0.40a 0.12 0.07 50 USTC-Li −19.30b −19.37 0.12 56 Alfa Li − 13.71 0.13 73 JG-2 0.15~0.32c 0.13 0.11 12 注:“−”表示无参考值。Alfa Li为实验室内部标准溶液,无参考值。a. IRMM-016的δ7LiL-SVEC参考值来源于GeoReM(Geological and Environmental Reference Materials)数据库及对应参考文献,仅统计MC-ICP-MS测试结果。b. USTC-Li 的δ7LiL-SVEC参考值由中国科技大学肖益林教授提供。c. JG-2的δ7LiL-SVEC参考值来源于Bouman等(2004)[30]、Jeffcoate等(2004)[15]、Li 等(2019)[31]、Lin等(2016)[32]和Zhu等(2020)[33]。Note:“−” indicates the absence of a reference value. Alfa Li serves as the internal standard solution in the laboratory,and no reference value is available. a. The δ7LiL-SVEC reference value of IRMM-016 is derived from the Geological and Environmental Reference Materials (GeoReM) database and corresponding references,considering only the MC-ICP-MS test results. b. The δ7LiL-SVEC reference value of USTC-Li is provided by Professor Xiao Yilin from the University of Science and Technology of China. c. The δ7LiL-SVEC reference values of JG-2 are derived from Bouman et al. (2004) [30],Jeffcoate et al. (2004) [15],Li et al. (2019) [31],Lin et al. (2016) [32] and Zhu et al. (2020) [33]. 表 3 标准物质硼同位素组成测定值与参考值
Table 3 The determined values and reference values of the B isotope composition in the reference materials
标准物质 δ11BNIST951参考值
(‰)δ11BNIST951a测试值
(‰)2SD
(‰)n ERM-AE121 19.54~20.33a 19.78 0.31 64 ERM-AE122 39.3~39.74a 39.54 0.33 36 Alfa B − −4.66 0.19 60 海水标样NASS-7 − 40.03 0.33 35 天然海水 39.98±0.35b − − − 天然海水 39.45~40.26b − − − 海水标样NASS-2 39.63~39.90c − − − 海水标样NASS-5 39.40~39.89c − − − 海水标样NASS-6 39.41~39.81c − − − 注:“−”表示无参考值。Alfa B为实验室内部标准溶液,无参考值。a. ERM-AE121和ERM-AE122的δ11BNIST 951参考值来自GeoReM数据库及对应参考文献。数据包括了样品相对于NIST SRM951和NIST SRM951a的参考值。b. 天然海水δ11BNIST 951参考值引自Chen等(2019)[27]及其中参考文献。c. NASS系列海水δ11BNIST 951参考值引自GeoReM数据库及对应参考文献。Note: “−” indicates the absence of a reference value. Alfa B is a laboratory standard solution without a designated reference value. a. The δ11BNIST 951 reference values of ERM-AE121 and ERM-AE122 are from the GeoReM database and corresponding references. The data include reference values of the sample with respect to NIST SRM951 and NIST SRM951a. b. The reference value of δ11BNIST 951 in natural seawater is cited from Chen et al. (2019) [27] and other references. c. The reference value of δ11BNIST 951 for NASS series seawater is sourced from the GeoReM database and corresponding references. -
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