Rare earth elements (REE) can produce M²⁺ ions in ICP-MS and ¹⁵⁰Nd²⁺, ¹⁵⁰Sm²⁺, and ¹⁵⁶Gd²⁺ can produce false positives on ⁷⁵As and ⁷⁸Se. 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 ¹⁶O³⁵Cl⁺ reduction (<100 ppt false ⁵¹V in 0.4% HCl) and Se sensitivity (DL < 1 ppb). Further reduction of these false positives is achieved by estimating the M²⁺ correction factors and utilizing them in the interference-correction software. Approaches to estimating the M²⁺ 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 M²⁺ 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 M²⁺ from a 50 ppb REE standard solution. Alternatively, shifting the M²⁺ estimate to a half mass (i.e., m/z 71.5: ¹⁴³Nd²⁺) eliminates the direct overlap source of bias and allows the unit mass signal to approach 150 000 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 M²⁺ 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.

中文翻译：

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与实施中号相关的分析考虑²⁺美国EPA方法200.8内校正因子，以解决砷和硒误报† ‡

稀土元素（REE）可以在ICP-MS中产生M ²⁺离子，而¹⁵⁰ Nd 2 ⁺，¹⁵⁰ Sm ²⁺和¹⁵⁶ Gd ²⁺可以在⁷⁵ As和⁷⁸ Se上产生假阳性。利用碰撞池中较低He流量的替代仪器调节条件，可将这些误报减少2倍（在含有50 ppb Nd和Gd的溶液中降至0.8 ppb As和19 ppb Se），且还原度可比¹⁶ O ³⁵ Cl ⁺（<100 ppt错误⁵¹V在0.4％HCl中）和Se敏感性（DL <1 ppb）。通过估计M ²⁺校正因子并在干扰校正软件中使用它们，可以进一步减少这些误报。对M ²⁺校正因子的估算方法进行了评估，重点是耐受最终用户背景中每日变化的技术及其降低与用于估算M ²⁺校正的稀土标准品相关的初始和正在进行的纯度要求的能力因素。与单位质量方法相关的直接元素和多原子交叠往往会过度校正，因为单位质量的30 cps的非稀土信号相对于与M ²⁺相关的<300 cps信号会产生偏差。来自50 ppb REE标准溶液。可替代地，M个移位²⁺估计到一半的质量（即，米/ ž 71.5：¹⁴³的Nd ²⁺）消除了偏置的直接重叠源，并且由于丰度灵敏度限制，允许单位质量信号在其流失超过1/2质量之前接近150 000 cps。在试剂水和以2 ppb和50 ppb的Nd，Sm和Gd强化的区域自来水中，评估了半质量方法的性能。此外，还评估了半质量样品方法。发现该方法相对于外部或固定因子半质量方法是有益的，因为它可以补偿仪器漂移和矩阵引起的M ²⁺因子漂移。最后，对所有结果进行了相对于使用质量转移模式下的ICP-MS / MS和高分辨率ICP-MS测定的As和Se浓度的评估。