Mass spectrometry: calculations.
Mass spectrometry: calculations.
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质谱分析：计算。
DOI：
10.1002/j.1552-4604.1986.tb03547.x
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发表时间：
1986
影响因子：
2.9
通讯作者：
Schoeller,DA
中科院分区：
文献类型：
--
作者：
Schoeller,DA
质谱仪是一种灵敏而特异的设备，可用于定量多种物质。不幸的是，灵敏度不是恒定的，并且信号在化合物之间变化。由于该变化，需要校准以将质谱信号转换为对应于特定分析物浓度的单位。在许多最早的应用中，校准仅仅涉及确定给定量的分析物的响应因子。然后可以从观察到的质谱信号计算未知物中分析物的浓度。这种校准的明显困难在于响应因子随仪器操作条件的变化而变化，并且分析的精度相当低。通过使用同源内标物可以显著提高精密度，但分析物和同源内标物之间提取效率的微小差异、化合物稳定性的差异以及电离效率的差异仍然限制了分析的精密度。2使用同位素标记的分析物作为内标物可以大大消除这些问题，并最大限度地提高质谱分析的精度。2即使使用同位素内标，分析人员仍面临校准问题，以便将质谱响应转换为与分析物浓度对应的单位。然而，在该示例中，质谱仪响应是在对应于分析物和内标物的质量处的离子电流的比率。在通过同位素比质谱法分析单原子物质或小分子（如CO2）时，校准仅需要使用已知同位素组成的单一标准品来校正质谱同位素区分。此后，可根据质量平衡原理进行计算。3'4大型有机化合物的分析不适用于上述原则的校准。对于多原子物种，在给定质量下的离子流几乎从来不是单一同位素物种的结果。多种同位素种类和不同元素组成的碎片产生
T he mass spectrometer is a sensitive and specific device that can be used to quantify a wide range of substances. Unfortunately, the sensitivity is not constant, and the signal varies between compounds. Because of the variation, a calibration is needed to transform the mass spectrometric signal to units corresponding to the concentration of the specific analyte. In many of the earliest applications, the calibration simply involved determination of a response factor for a given quantity of analyte. The concentration of an analyte in an unknown could then be calculated from the observed mass spectrometric signal. The obvious difficulty with this calibration is that the response factor changes as a function of instrument operating conditions, and the precision of the analysis is rather low. A considerable improvement in precision can be obtained by using a homologous internal standard, 1 but minute differences in extraction efficiency between the analyte and homologous internal standard, differences in the stability of the compounds, and differences in ionization efficiencies still limit the precision of the analysis. 2 Use of an isotopically labeled form of the analyte as the internal standard largely eliminates these problems and maximizes the precision of the mass spectrometric analysis. 2Even when an isotopic internal standard is used, the analyst is still faced with the problem of calibration in order to convert the mass spectrometric response to units corresponding to analyte concentration. In this example, however, the mass spectrometer response is a ratio of ion currents at the masses corresponding to the analyte and the internal standard. In the analyses of monoatomic species or small molecules such as CO2 by isotope ratio mass spectrometry, calibration requires little more than the use of a single standard of known isotopic composition to correct for mass spectrometric isotope discrimination. Thereafter, calculations can be made by the principle of mass balance. 3’4 Analysis of larger organic compounds does not lend itself to calibration by the above principles. For polyatomic species, the ion current at a given mass is almost never a result of a single isotopic species. Multiple isotopic species and fragments of different elemental composition produce