Jia Chunrong, Batterman Stuart, Chernyak Sergei
Environmental Health Sciences, University of Michigan, Ann Arbor, MI 48109-2029, USA.
J Environ Monit. 2006 Oct;8(10):1029-42. doi: 10.1039/b607042f.
Adsorbent sampling with analysis by thermal desorption, gas chromatography and mass spectrometry (TD/GC/MS) offers many advantages for volatile organic compounds (VOCs) and thus is increasingly used in many applications. For environmental samples and other complex mixtures, the MS detector typically is operated in the scan mode to aid identification of co-eluting compounds. However, scan mode does not achieve the optimal sensitivity, thus compounds occurring at low concentrations may not be detected. This paper develops and evaluates the application of a more sensitive TD/GC/MS method using selective ion monitoring (SIM) that is applicable to VOC mixtures found in ambient and indoor air. Based on toxicity and prevalence, 94 VOCs (including terpenes, aromatic, halogenated and aliphatic compounds) were selected as target compounds. Two analytical methods were developed: a conventional full scan method for ions from 29 to 270 m/z; and a SIM method using 16 time windows and different ions selected for the compounds in each window. Both methods used the same Tenax GR adsorbent sampling tubes, TD and GC parameters, and target and qualifier ions. Laboratory tests determined calibrations, method detection limits (MDLs), precisions, recoveries and storage stability. Field tests compared scan and SIM mode analyses for duplicate samples of indoor air in 51 houses and outdoor air at 41 sites. Statistical analyses included the development of error/precision models. The laboratory tests showed that most compounds demonstrated excellent precision (<10% for concentrations exceeding approximately 0.5 microg m(-3)), good linearity, near identical calibrations for scan and SIM modes, a wide dynamic range (up to 1500 microg m(-3)), and negligible storage losses after 1 month (7 compounds showed moderate losses). SIM mode MDLs ranged from 0.004 to 0.27 microg m(-3), representing a modest (1.1 to 22-fold) improvement compared to scan mode. However, in field tests the SIM method detected significantly more compounds (e.g., styrene and chloroform). Error models fit most compounds and allow quantification of errors at selected percentiles. Overall, while the new SIM method is somewhat time-consuming to develop, it offers greater sensitivity and maintains the high selectivity of traditional scan methods.
采用热脱附、气相色谱和质谱联用（TD/GC/MS）的吸附剂采样法在分析挥发性有机化合物（VOCs）方面具有诸多优势，因此在许多应用中越来越多地被采用。对于环境样品和其他复杂混合物，质谱检测器通常以扫描模式运行，以辅助鉴定共洗脱化合物。然而，扫描模式无法实现最佳灵敏度，因此低浓度的化合物可能无法被检测到。本文开发并评估了一种更灵敏的TD/GC/MS方法的应用，该方法采用选择性离子监测（SIM），适用于环境空气和室内空气中的VOC混合物。基于毒性和普遍性，选择了94种VOCs（包括萜烯、芳香族、卤代和脂肪族化合物）作为目标化合物。开发了两种分析方法：一种是针对29至270 m/z离子的传统全扫描方法；另一种是SIM方法，使用16个时间窗口，并为每个窗口中的化合物选择不同的离子。两种方法都使用相同的Tenax GR吸附剂采样管、TD和GC参数以及目标离子和定性离子。实验室测试确定了校准、方法检出限（MDLs）、精密度、回收率和储存稳定性。现场测试比较了51所房屋室内空气和41个地点室外空气重复样品在扫描和SIM模式下的分析结果。统计分析包括误差/精密度模型的建立。实验室测试表明，大多数化合物表现出优异的精密度（浓度超过约0.5 μg m⁻³时<10%）、良好的线性、扫描和SIM模式下几乎相同的校准、宽动态范围（高达1500 μg m⁻³）以及1个月后可忽略不计的储存损失（7种化合物表现出中等损失）。SIM模式的MDLs范围为0.004至0.27 μg m⁻³，与扫描模式相比有适度（1.1至22倍）的提高。然而，在现场测试中，SIM方法检测到的化合物明显更多（例如苯乙烯和氯仿）。误差模型适用于大多数化合物，并允许在选定百分位数下对误差进行量化。总体而言，虽然新的SIM方法开发起来有点耗时，但它具有更高的灵敏度，并保持了传统扫描方法的高选择性。
