Mass Spectrometric Sensitivity

When comparing TIMS and ICP-MS, it seems that ICP-MS is the best choice for stable isotope-based metabolic studies. It commonly surpasses in terms of mass spectrometric sensitivity and also permits the measurement of isotope ratios at comparable and sometimes better precision than TIMS, at least for MC-ICP-MS. 

In addition, samples can be presented to the instrument in aqueous solution directly after digestion, which requires fewer preparative steps than in TIMS, for which the element has to be chemically separated from the sample matrix. 

As measurements do not require a heating up procedure of the sample as in TIMS, measurements require about 50% of the time, which increases sample throughput. This is a considerable advantage for studies involving compartmental modeling, taking into account that such studies involve usually 10-20 subjects who generate dozens of samples to be analyzed. 

Isotope fractionation is a major source of bias in any mass spectrometric technique. For mass spectrometric analysis, the element in the sample to be analyzed 

Over the past decade, awareness has grown significantly that isotopic analysis by ICP-MS is full of potential sources of bias that need to be controlled carefully to generate not only precise but also accurate data. Whereas in the early days the speed advantage of ICP-MS over TIMS in isotope ratio measurements has been emphasized has been emphasized because it permits direct analysis of digested samples, this advantage has now mostly vanished. Because of much better control of spectral and non-spectral interferences, it is now common practice in ICP-MS as in TIMS to separate the element chemically from the matrix when high analytical accuracy is of concern. This does not equalize the two 

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K. Tang, Y. Lin, D. W. Matson, T. Kim, R. D. Smith Generation of multiple electrosprays using microfabricated emitter arrays for improved mass spectrometric sensitivity. Anal. Chem. 2001, 73, 1658-1663. 

Tang, K. Lin, Y. Matson, D.W. Kim, T. Smith, R.D. Generation of Multiple Electrosprays Using Microfabricated Emitter Arrays for Improved Mass Spectrometric Sensitivity, Anal. Chem. 73, 1658-1663 (2001). 

In addition, chromatographic integrity and mass spectrometric sensitivity must be maintained ... 

Generation of multiple electrosprays using microfabricated emitter arrays for improved mass spectrometric sensitivity. Anal Chem 73 1658-1663... 

The past decade has seen tremendous developments in the measurement of metal isotope ratios by ICP-MS, namely the introduction of MC-ICP-MS, at precisions similar to or better those that achievable with MC-TIMS at commonly higher mass spectrometric sensitivity [59]. Developments driven mainly by the geological community made it finally possible to study the systematics of isotope fractionation phenomena in higher organisms, including the human body. Of the essential elements, iron, calcium, and zinc have received the most attention in this context and will be discussed in more detail in this chapter. 

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