Question

(a) Explain the purpose of the dynamic reaction cell in Figure 21-30. (b) In geologic strontium isotopic analysis, there is isobaric interference between${}^{\mathbf{87}}\mathit{R}{\mathit{b}}^{\mathbf{+}}$and${}^{\mathbf{87}}\mathit{S}{\mathit{r}}^{\mathbf{+}}$ . A dynamic reaction cell with $\mathit{C}{\mathit{H}}_{\mathbf{3}}\mathit{F}$converts to but does not convert$\mathit{R}{\mathit{b}}^{\mathbf{+}}$ to$\mathit{R}\mathit{b}{\mathit{F}}^{\mathbf{+}}$ . How does this reaction eliminate interference?

Short answer

(a) A dynamic reaction cell reduces isobaric interference by performing a thermodynamically favourable reaction with a gas such as $N{H}_3,N_{2}O$or $CO$to remove interfering molecular ions like $Ar{O}^{+}$.

(b) When ${}^{87}S{r}^{+}$ reacts with $C{H}_{3}F$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 $N{H}_3,N_{2}O$or $CO$to remove interfering molecular ions like $Ar{O}^{+}$or convert analyte into a molecular ion that can be detected without interference.

(b)

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