Using Reaction Mechanisms in a Collision Cell

After nearly 10 years of solving real-world application problems, the practical capabilities of both hexapole and octapole collision cells using KED are fairly well understood. It is clear that the majority of applications are being driven by the demand for routine multielement analysis of well-characterized matrices, where a rapid sample turnaround is required. This technique has also been promoted by the vendors as a fast, semiquantitative tool for unknown samples. The fact that it requires very little method development, just one collision gas and one set of tuning conditions, makes it very attractive for these kinds of applications.  

However, it is well-recognized that this approach will not work well for many of the more complex interfering species, especially if the analyte is at ultratrace levels. For example, the collision mode using helium is not the best choice for quantifying 

Practical Guide to ICP-MS A Tutorial for Beginners, Second Edition 

Another example of the benefits of using more reactive gases, such as an ammonia and helium mixture over pure helium or hydrogen gas, is in the determination of vanadium in a high-concentration chloride matrix. The collision mode using helium works reasonably well on the reduction of the C1 0+ interference at 51 amu. However, when 1% NHj in helium is used, the interference is dramatically reduced by the process of charge/electron transfer. This allows the most abundant isotope, to be used for the quantitation of vanadium in matrices such as seawater or hydrochloric acid. Vanadium detection capability in a chloride matrix is improved by a factor of 50-100 times using the reaction chemistry of NH3 in helium compared to pure helium in the collision mode. T z 

FIGURE 10.9 Comparison of calibration plots and detection limits using the collision mode with helium (left) and reaction mode with hydrogen (right) (courtesy of Thermo Scientihe). 

Likewise, helium has very little effect on reducing the Ar interference in the determination of °Ca+. So, when using a collision cell with helium, the quantification of calcium must be carried out using the Ca+ isotope, which is about 50 times less sensitive than °Ca . For this reason, in order to achieve the lowest detection limits for calcium, a low-reactivity gas such as pure hydrogen is the better option. By initiating an ion-molecule reaction, it allows the most sensitive calcium isotope 

Another example of the benefits of using more reactive gases, such as an ammonia and helium mixture over pure helium or hydrogen gas, is in the determination of vanadium in a high-concentration chloride matrix. The collision mode using helium works reasonably well on the reduction of the interference at 51 amu. 

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