Smith Skyler W, Hanks Nicole, Creed Patricia A, Kovalcik Kasey, Wilson Robert A, Kubachka Kevin, Brisbin Judith A, Figueroa Julio Landero, Creed John T
U.S. Environmental Protection Agency (USEPA) Research Trainee, National Exposure Research Laboratory (NERL), University of Cincinnati, Cincinnati, OH 45268, USA.
Student Service Contractor, USEPA, NERL, Cincinnati, OH 45268, USA.
J Anal At Spectrom. 2019 Oct 1;34(10):2094-2104. doi: 10.1039/C9JA00086K.
Rare earth elements (REE) can produce M ions in ICP-MS and Nd, Sm, and Gd can produce false positives on As and Se. Alternative instrumental tuning conditions, that utilize lower He flows within the collision cell, reduce these false positives by a factor of 2 (to 0.8 ppb As and 19 ppb Se in solutions containing 50 ppb Nd and Gd) with comparable OCl reduction (<100 ppt false V in 0.4% HCl) and Se sensitivity (DL < 1 ppb). Further reduction of these false positives is achieved by estimating the M correction factors and utilizing them in the interference-correction software. Approaches to estimating the M correction factor were evaluated with an emphasis on techniques that tolerate daily variability in end-user backgrounds and their ability to reduce the initial and ongoing purity requirements associated with the rare earth standards used to estimate the M correction factor. The direct elemental and polyatomic overlaps associated with unit-mass approaches tend to overcorrect as non-rare-earth signals as small as 30 cps at the unit mass can induce bias relative to the <300 cps signals associated with the M from a 50 ppb REE standard solution. Alternatively, shifting the M estimate to a half mass (, / 71.5: Nd) eliminates the direct overlap source of bias and allows the unit mass signal to approach 150000 cps before it bleeds over on the 1/2 mass because of abundance sensitivity limitations. The performance of the half-mass approach was evaluated in reagent water and regional tap waters fortified with Nd, Sm, and Gd at 2 ppb and 50 ppb. In addition, a half-mass in-sample approach was also evaluated. This approach was found to be beneficial relative to the external or fixed-factor half-mass approach as it could compensate for instrument drift and matrix-induced shifts in the M factors. Finally, all results were evaluated relative to the As and Se concentrations determined using an ICP-QQQ in mass shift mode and a high-resolution ICP-MS.
稀土元素（REE）在电感耦合等离子体质谱（ICP-MS）中会产生M离子，钕（Nd）、钐（Sm）和钆（Gd）会在砷（As）和硒（Se）上产生假阳性结果。利用碰撞池内较低氦气流的替代仪器调谐条件，可将这些假阳性结果减少一半（在含有50 ppb钕和钆的溶液中，砷降至0.8 ppb，硒降至19 ppb），同时实现类似的氧化氯减少（在0.4%盐酸中，假钒<100 ppt）和硒灵敏度（检测限<1 ppb）。通过估算M校正因子并将其应用于干扰校正软件，可进一步减少这些假阳性结果。对估算M校正因子的方法进行了评估，重点是能够容忍最终用户背景日常变化的技术，以及它们降低与用于估算M校正因子的稀土标准相关的初始和持续纯度要求的能力。与单位质量方法相关的直接元素和多原子重叠往往会过度校正，因为单位质量处低至30 cps的非稀土信号相对于50 ppb稀土标准溶液中M产生的<300 cps信号会引起偏差。或者，将M估算值移至半质量处（例如，/ 71.5：钕）可消除偏差的直接重叠来源，并使单位质量信号在因丰度灵敏度限制而在半质量处溢出之前接近150000 cps。在添加了2 ppb和50 ppb钕、钐和钆的试剂水和区域自来水中评估了半质量方法的性能。此外，还评估了半质量进样方法。相对于外部或固定因子半质量方法，该方法被发现是有益的，因为它可以补偿仪器漂移和基质引起的M因子变化。最后，所有结果均相对于使用质量转移模式的电感耦合三重四极杆质谱（ICP-QQQ）和高分辨率电感耦合等离子体质谱（ICP-MS）测定的砷和硒浓度进行评估。
