1.1 与国际纯化学和应用化学联合会（IUPAC）计量指南联合委员会（JCGM）和检测概念协调一致 ( 1. , 2. ) 2. ，该测试方法使用一系列剂量水平下分析物的重复测量，给出包含临界值的仪器响应、截断正态分布模型和置信限，以建立估计实际和统计稳健检测限的标准。 注1: 其他标准可用于评估复杂基质中各种分析物检测技术的一般性能（例如，实践 E2520 ). 1.2 在这里，化合物的检测限（LOD90）定义为沉积在采样拭子上的该化合物的最低质量，其中有90 % 特定轨迹检测器中的单个测量的真实检测概率至少为90的置信度 % 真正的未检测概率至少为90 % 测量过程空白样品时。 1.3 这种特殊的测试方法是基于测试的痕量探测器、分析物和部署条件的可靠性、实用性和全面性而选择的。本试验方法中涉及的计算在别处发布 ( 3. ) ，并通过国家标准与技术研究所（NIST）网站上提供的交互式网络计算器执行:https://www-s.nist.gov/loda. 1.4 预期用户- 跟踪探测器开发商和制造商、供应商、测试实验室以及负责公共安全和有效遏制恐怖主义的机构。 1.5 虽然该测试方法可适用于产生数值输出的任何检测技术，但该方法特别适用于受异质误差源影响的测量系统，这些误差源导致非线性和异方差剂量/反应关系，以及在低分析物水平下截断或删失的反应分布。 在基于离子迁移光谱法、气相色谱法和质谱法的痕量探测器中使用爆炸物和药物化合物对程序进行了测试 ( 4. ) . 化合物作为液体溶液沉积在拭子上，并在使用前干燥。引入测试样本的背景干扰代表了部署期间预期的各种条件，但这些条件并不全面，无法代表所有可能的场景。用户应意识到未经测试的场景可能导致无法估计可靠的LOD90值。 1.6 单位- 以国际单位制表示的数值应视为标准。本标准不包括其他计量单位。 1.7 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的用户有责任在使用前制定适当的安全、健康和环境实践，并确定监管限制的适用性。 第节给出了一些具体的危害说明 8. 关于危险。 1.8 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认标准化原则制定的。 ====意义和用途====== 5.1 第一反应人员、安全审查人员、军方和执法部门使用商业跟踪探测器快速检测和识别爆炸威胁和感兴趣的毒品。这些痕量探测器通常通过检测从表面取样的残留物和颗粒中的化学试剂来运行，并且对某些延伸至1ng以下的化合物具有检测限。当跟踪检测器对任何目标分析物的响应超过该分析物的编程阈值水平时，跟踪检测器设置为报警。 假设标准操作和部署条件，此类水平的工厂设置通常会平衡灵敏度和选择性。 5.2 物质的LOD通常被认为是通过特定测量过程在给定类型的介质中可以可靠检测到的该物质的最小量 ( 2. ) . 该量的分析信号应足够高，高于环境背景变化，以提供信号真实性的统计置信度。确定标称LOD值的方法众所周知，但在具体应用中存在缺陷。痕量检测器的供应商通常只报告单个化合物的检测限，而不定义术语的含义或测定方法的参考。 注2: 可以为分析程序确定几种不同的“检测限”。这些包括最小可检测值、仪器检测限、方法检测限、识别限、定量限和最小一致可检测量。 即使使用相同的术语，根据所用定义、假设响应模型和影响测量的噪声类型的细微差别，LOD也可能存在差异。 5.3 部署时，跟踪检测器的单个性能（例如，真实LOD）受到以下因素的影响:( 1. )制造差异、历史和维护；( 2. )操作配置（例如，热解吸温度、分析仪温度和拭子类型）；和( 3. )环境条件（例如，环境湿度、温度和化学背景）。因此，工厂规范可能无法很好地估计轨迹检测器的实际LOD值。这些基本性能指标对于评估仪器在特定环境中检测特定化合物痕量水平的能力至关重要，因此需要一种可靠且可访问的方法来估计实际的LOD值，尤其是在现场。 5.4 跟踪检测器中LOD值估计和最佳报警阈值设置的技术挑战和陷阱: 5.4.1 范围- 美国司法部列出了230多种爆炸性材料和270多种极有可能被滥用的受管制药物。 4. 有许多技术用于痕量检测，仪器制造商设计其系统并平衡操作条件，以在尽可能多的分析物中提供检测能力。然而，通常使用非常有限的分析物子集来测试和验证检测器性能。因此，默认操作条件和报警阈值可能无法最佳设置，以可靠地检测特定场景中被视为重要的某些化合物。 5.4.2 环境- 环境条件和化学背景因部署位置而异，这将影响响应灵敏度和LOD值。 5. 4.3 风险容忍度和平衡- 应根据安全优先级（例如，警报级别、可能的威胁化合物、吞吐量要求、人为因素和风险容忍度）平衡并设置α风险（工艺空白的假阳性概率）和β风险（检测极限下分析物的假未检测概率）的值。跟踪检测器中的默认风险平衡可能不足以满足部署情况。 5.4.4 信号可变性（异方差）- 仪器响应的方差可能与引入痕量检测器的分析物质量水平不一致。在基于离子迁移率光谱法（IMS）的技术中，大气压电离（具有有限数量的可用反应物离子）和离子迁移率分离的物理化学机制可能在整个响应区域中是不均匀的。LOD估计的典型方法通常假设方差为常数。 5.4.5 专有信号处理- 典型的LOD确定假设高斯分布，并将背景变化作为一个重要参数。不幸的是，跟踪探测器中的报警决策很少基于原始测量信号；相反，使用专有算法处理原始测量值。这种处理可能试图通过截断或抑制背景信号来最小化alpha风险，因此背景信号可能不存在，或者这些处理后的信号中的真实分布可能是非高斯的，从而混淆了精确LOD的计算。 5.4.6 多变量考虑- 为了提高选择性并降低α风险，跟踪探测器中的报警决策可能基于多峰值响应，而不是单峰幅度测量。下一步将致力于识别和量化热脱附和漂移时域中独特的离子碎裂模式- 发电探测器。 5.4.7 技术的多样性- 市场上和开发中的各种痕量探测器和技术对准确估计LOD的通用响应模型提出了挑战。 5.4.8 安全性- 由于安全和分类问题，可能不会公开公布微量探测器中炸药的LOD值。

1.1 In harmony with the Joint Committee for Guides in Metrology (JCGM) and detection concepts of the International Union of Pure and Applied Chemistry (IUPAC) ( 1 , 2 ) 2 , this test method uses a series of replicated measurements of an analyte at dosage levels giving instrumental responses that bracket the critical value, a truncated normal distribution model, and confidence bounds to establish a standard for estimating practical and statistically robust limits of detection. Note 1: Other standards are available that evaluate the general performance of detection technologies for various analytes in complex matrices (for example, Practice E2520 ). 1.2 Here, the limit of detection (LOD90) for a compound is defined to be the lowest mass of that compound deposited on a sampling swab for which there is 90 % confidence that a single measurement in a particular trace detector will have a true detection probability of at least 90 % and a true nondetection probability of at least 90 % when measuring a process blank sample. 1.3 This particular test method was chosen on the basis of reliability, practicability, and comprehensiveness across tested trace detectors, analytes, and deployment conditions. The calculations involved in this test method are published elsewhere ( 3 ) , and are performed through an interactive web-based calculator available on the National Institute of Standards and Technology (NIST) site: https://www-s.nist.gov/loda. 1.4 Intended Users— Trace detector developers and manufacturers, vendors, testing laboratories, and agencies responsible for public safety and enabling effective deterrents to terrorism. 1.5 While this test method may be applied to any detection technology that produces numerical output, the method is especially applicable to measurement systems influenced by heterogeneous error sources that lead to non-linear and heteroskedastic dose/response relationships and truncated or censored response distributions at low analyte levels. The procedures have been tested using explosive and drug compounds in trace detectors based on ion mobility spectrometry, gas chromatography, and mass spectrometry ( 4 ) . Compounds are deposited as liquid solutions on swabs and dried before use. Background interferences introduced to the test samples were representative of a variety of conditions expected during deployment, but these conditions were not intended as comprehensive in representing all possible scenarios. The user should be aware of the possibility that untested scenarios may lead to failure in the estimation of a reliable LOD90 value. 1.6 Units— The values stated in SI units are to be regarded as the standard. No other units of measurement are included in this standard. 1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Some specific hazards statements are given in Section 8 on Hazards. 1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 5.1 Commercial trace detectors are used by first responders, security screeners, the military, and law enforcement to detect and identify explosive threats and drugs of interest quickly. These trace detectors typically operate by detecting chemical agents in residues and particles sampled from surfaces and can have detection limits for some compounds extending below 1 ng. A trace detector is set to alarm when its response to any target analyte exceeds a programmed threshold level for that analyte. Factory settings of such levels typically balance sensitivity and selectivity assuming standard operating and deployment conditions. 5.2 The LOD for a substance is commonly accepted as the smallest amount of that substance that can be reliably detected in a given type of medium by a specific measurement process ( 2 ) . The analytical signal from this amount shall be high enough above ambient background variation to give statistical confidence that the signal is real. Methods for determining nominal LOD values are well known but pitfalls exist in specific applications. Vendors of trace detectors often report detection limits for only a single compound without defining the meaning of terms or reference to the method of determination. Note 2: There are several different “detection limits” that can be determined for analytical procedures. These include the minimum detectable value, the instrument detection limit, the method detection limit, the limit of recognition, the limit of quantitation, and the minimum consistently detectable amount. Even when the same terminology is used, there can be differences in the LOD according to nuances in the definition used, the assumed response model, and the type of noise contributing to the measurement. 5.3 When deployed, the individual performance of a trace detector (for example, realistic LODs) is influenced by: ( 1 ) manufacturing differences, history, and maintenance; ( 2 ) operating configurations (for example, thermal desorption temperature, analyzer temperature, and type of swab); and ( 3 ) environmental conditions (for example, ambient humidity and temperature and chemical background). As a result, realistic LOD values for a trace detector may be poorly estimated by the factory specifications. These fundamental measures of performance are critically important for assessing the ability of an instrument to detect trace levels of particular compounds in a particular setting, so a reliable and accessible method is needed to estimate realistic LOD values, especially in the field. 5.4 Technical Challenges and Pitfalls to the Estimation of LOD Values in Trace Detectors and the Setting of Optimal Alarm Thresholds: 5.4.1 Scope— The U.S. Department of Justice lists over 230 explosive materials and over 270 controlled drugs having a high potential for abuse. 4 There are many technologies used for trace detection, and instrument manufacturers design their systems and balance operating conditions to provide detection capabilities across as many analytes as possible. However, a very limited subset of analytes is normally used to test and verify detector performance. Therefore, default operating conditions and alarm thresholds may not be optimally set to detect reliably certain compounds deemed important in particular scenarios. 5.4.2 Environment— Ambient conditions and chemical background vary with the deployment location, which would influence response sensitivities and LOD values. 5.4.3 Risk Tolerance and Balance— Values of alpha risk (false positive probability of process blanks) and beta risk (false nondetection probability of analytes at the detection limit) should be balanced and set according to security priorities (for example, alert level, probable threat compounds, throughput requirements, human factors, and risk tolerance). The default risk balance in a trace detector may not be adequate for the deployment situation. 5.4.4 Signal Variability (Heteroskedasticity)— The variance in instrument response may not be consistent across analyte mass levels introduced into the trace detector. In ion mobility spectrometry (IMS)-based technologies, the physicochemical mechanisms underlying atmospheric pressure ionization (with a finite number of available reactant ions) and ion mobility separation may be non-uniform across the response regions. Typical methods of LOD estimation usually assume constant variance. 5.4.5 Proprietary Signal Processing— Typical LOD determinations assume Gaussian distributions and use background variation as an important parameter. Unfortunately, alarm decisions in trace detectors are rarely based on raw measurement signals; rather, proprietary algorithms are used to process the raw measurements. This processing may attempt to minimize alpha risk by truncating or dampening background signals, so background signals may be absent or the true distribution in these processed signals may be non-Gaussian, confounding the calculation of an accurate LOD. 5.4.6 Multivariate Considerations— To improve selectivity and decrease alpha risk, alarm decisions in trace detectors may be based on multiple-peak responses rather than a single-peak amplitude measurement. Efforts to recognize and quantify unique ion fragmentation patterns across both the thermal desorption and drift-time domains are being developed for next-generation detectors. 5.4.7 Diversity of Technologies— The wide variety of trace detectors and technologies on the market and those under development challenge general response models for accurate estimation of LOD. 5.4.8 Security— LOD values for explosives in trace detectors may not be openly published because of security and classification issues.