Amarasiriwardena C J, Lupoli N, Potula V, Korrick S, Hu H
Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
Analyst. 1998 Mar;123(3):441-5. doi: 10.1039/a704686c.
Measurement of arsenic (As) in biological samples such as urine has important clinical applications and is being undertaken more frequently in epidemiologic studies because of concern about the carcinogenicity of low to moderate levels of As exposure. The objective of this study was to evaluate and improve the accuracy of As determination in urine by inductively coupled plasma mass spectrometry (ICP-MS). Determination of As in biological samples by ICP-MS is difficult for two reasons: the formation of the molecular ion 40Ar35Cl, which overlaps with monoisotopic As at a mass-to-charge ratio (m/z) of 75 (causing spectral interference), and signal enhancement due to organic matrix (nonspectral interference). Available procedures were examined, including the application of different correction procedures using 40Ar37Cl and 16O35Cl molecular-ion formation; the addition of N2 into plasma or nebulizer gas flows; and the addition of organic molecules to the sample and to calibration standards to eliminate or correct for interference due to molecular-ion formation. The accuracy and precision of determination of As [m/z 75, ionization potential (IP) 9.81 eV] with use of an internal standard was also investigated. Three elements were studied as candidate internal standards: germanium (Ge: m/z 74, IP 7.90 eV), indium (In: m/z 115, IP 5.79 eV), and tellurium (Te: m/z 128, IP 9.01 eV). It was found that these three elements performed more or less equally well with Ar-N2 plasma; it was also found that accuracy was significantly improved when Te was used as the internal standard instead of Ge or In for ethanol-added samples. Our results indicate that accurate and precise measurement of As in urine by ICP-MS can be obtained by either of two methods (< 5% error, approximately 2% RSD, limit of detection 0.1 ng ml-1): (1) the addition of 1% N2 to plasma gas flow or 3% N2 to nebulizer gas flow, along with use of any of the internal standards tested, or (2) the addition of ethanol to the sample and to calibration standards, with use of Te as the internal standard. The most accurate results (< 1% error) for National Institute of Standard and Technology Standard Reference Material (NIST SRM) 2670 (toxic elements in urine) were obtained with Ar-N2 plasma with either Te or In as the internal standard.
测量生物样品（如尿液）中的砷（As）具有重要的临床应用价值，并且由于人们担心低至中等水平的砷暴露具有致癌性，因此在流行病学研究中对其进行测量的频率也越来越高。本研究的目的是评估并提高电感耦合等离子体质谱法（ICP-MS）测定尿液中砷的准确性。采用ICP-MS测定生物样品中的砷存在两个难点：一是形成分子离子40Ar35Cl，其在质荷比（m/z）为75时与单同位素砷重叠（导致光谱干扰）；二是有机基质导致信号增强（非光谱干扰）。研究了现有的方法，包括应用不同的校正程序利用40Ar37Cl和16O35Cl分子离子的形成；向等离子体或雾化器气流中添加N2；以及向样品和校准标准品中添加有机分子以消除或校正分子离子形成引起的干扰。还研究了使用内标物测定砷 [m/z 75，电离电位（IP）9.81 eV] 的准确性和精密度。研究了三种元素作为候选内标物：锗（Ge：m/z 74，IP 7.90 eV）、铟（In：m/z 115，IP 5.79 eV）和碲（Te：m/z 128，IP 9.01 eV）。结果发现，这三种元素在Ar-N2等离子体中的表现大致相同；还发现，对于添加乙醇的样品，使用碲作为内标物而不是锗或铟时，准确性有显著提高。我们的结果表明，通过两种方法中的任何一种都可以实现通过ICP-MS准确、精确地测量尿液中的砷（误差<5%，相对标准偏差约2%，检测限0.1 ng/ml）：（1）向等离子体气流中添加1%的N2或向雾化器气流中添加3%的N2，并使用所测试的任何一种内标物；或（2）向样品和校准标准品中添加乙醇，并使用碲作为内标物。对于美国国家标准与技术研究院标准参考物质（NIST SRM）2670（尿液中的有毒元素），使用以碲或铟作为内标物的Ar-N2等离子体可获得最准确的结果（误差<1%）。
