Department of Chemistry, Iowa State University, Ames, Iowa 50011, United States.
Anal Chem. 2023 Apr 4;95(13):5618-5626. doi: 10.1021/acs.analchem.2c05243. Epub 2023 Mar 21.
In time-of-flight mass spectrometry (TOFMS), ion detection is often achieved via electron multiplication followed by fast analog-to-digital conversion (ADC). This detection approach is chosen over time-to-digital conversion because it extends the dynamic range of TOFMS measurements, especially for transient analyses. However, fast ADC detection also introduces measurement noise fundamental to the electron multiplication process. In previous research, we demonstrated that TOFMS signals acquired with fast ADC follow a compound Poisson distribution in which the Poisson-distributed arrival of ions at the detector is compounded with the response profile of the electron multiplier. Here, we consider the influence of mass-to-charge (/)-dependent detector responses and their impact on particle-finding accuracy in single-particle inductively coupled plasma TOFMS (spICP-TOFMS). In spICP-TOFMS, highly time-resolved ion signals are recorded and particle signals are distinguished from background signals based on thresholding the data at /-specific critical values. Through Monte Carlo modeling with measured /-dependent detector responses, we generate compound Poisson model distributions and critical values that accurately account for the dispersion of measured signals. We test the accuracy of critical values through the analysis of dissolved element solutions and comparison of measured versus predicted event rates above critical value thresholds. The use of /-dependent compound Poisson critical values reduces false-positive particle identifications by one to two orders of magnitude compared to thresholding criteria based on normal or Poisson statistics. The improved accuracy and robustness of compound Poisson critical values enables automated multi-element particle finding in spICP-TOFMS.
在飞行时间质谱（TOFMS）中，离子检测通常通过电子倍增 followed by 快速模拟-数字转换（ADC）来实现。与时间数字转换相比，选择这种检测方法是因为它扩展了 TOFMS 测量的动态范围，特别是对于瞬态分析。然而，快速 ADC 检测也会引入测量噪声，这是电子倍增过程的固有特性。在之前的研究中，我们证明了使用快速 ADC 采集的 TOFMS 信号遵循复合泊松分布，其中离子以泊松分布到达探测器的到达与电子倍增器的响应分布复合。在这里，我们考虑了质量电荷比（/）依赖性检测器响应的影响及其对单颗粒电感耦合等离子体飞行时间质谱（spICP-TOFMS）中颗粒检测精度的影响。在 spICP-TOFMS 中，高度时间分辨的离子信号被记录，并且基于将数据阈值化为/-特定的临界值，从背景信号中区分出颗粒信号。通过使用测量的/-依赖性检测器响应进行的蒙特卡罗建模，我们生成复合泊松模型分布和临界值，这些分布和临界值准确地说明了测量信号的分散情况。我们通过分析溶解元素溶液并比较超过临界值阈值的测量和预测事件率来测试临界值的准确性。与基于正态或泊松统计的阈值标准相比，使用/-依赖性复合泊松临界值将假阳性颗粒识别的错误率降低了一到两个数量级。复合泊松临界值的准确性和稳健性的提高使 spICP-TOFMS 中的自动多元素颗粒检测成为可能。
