Chapter 21: Q9P (page 556)

(a) Explain the purpose of the dynamic reaction cell in Figure 21-30. (b) In geologic strontium isotopic analysis, there is isobaric interference between ${}^{87}{Rb}^{+}$ and ${}^{87}{Sr}^{+}$ . A dynamic reaction cell with ${CH}_{3} F$ converts ${}^{87}{Sr}^{+}$ to ${SrF}^{+}$ but does not convert ${}^{87}{Rb}^{+}$ to ${}^{87}{RbF}^{+}$ . How does this reaction eliminate interference?

Short Answer

Expert verified

(a) A dynamic reaction cell reduces isobaric interference by performing a thermodynamically favourable reaction with a gas such as ${NH}_{3}, N_{2} O,$ or CO to remove interfering molecular ions like ${ArO}^{+}$ .

(b) When ${}^{87}{Sr}^{+}$ reacts with ${CH}_{3} F$ to generate ${}^{87}{Sr}^{19}$ Fe, which has a mass of 106, the mass spectrum does not overlap with ${}^{87}{Rb}$ .

Step by step solution

Define isotopic interference.

Isotopic interference occurs when two isotopes in a sample solution have the same mass but are from different elements.

Explain the elimination of the interference in the given reaction.

(a)

A dynamic reaction cell reduces isobaric interference by performing a thermodynamically favourable reaction with a gas such as ${NH}_{3}, N_{2} O,$ or CO to remove interfering molecular ions like ${ArO}^{+}$ or convert analyte into a molecular ion that can be detected without interference.

(b)

When ${}^{87}{Sr}^{+}$ reacts with ${CH}_{3} F$ to generate ${}^{87}{Sr}^{19} Fe$ , which has a mass of 106 , the mass spectrum does not overlap with ${}^{87}{Rb}$ .