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 ${\mathbf{}}^{\mathbf{87}}{\mathbf{Rb}}^{\mathbf{+}}$and ${\mathbf{}}^{\mathbf{87}}{\mathbf{Sr}}^{\mathbf{+}}$ . A dynamic reaction cell with ${\mathbf{CH}}_{\mathbf{3}}\mathbf{F}$ converts ${\mathbf{Sr}}^{\mathbf{+}}$to localid="1663656054620" ${\mathbf{SrF}}^{\mathbf{+}}$but does not convert${\mathbf{Rb}}^{\mathbf{+}}$to ${\mathbf{RbF}}^{\mathbf{+}}$. 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 ${\mathrm{NH}}_{3,}{\mathrm{N}}_2\mathrm{O}$or CO to remove interfering molecular ions like ${\mathrm{ArO}}^{+}$.

(b) When ${}^{87}{\mathrm{Sr}}^{+}$reacts with ${\mathrm{CH}}_3\mathrm{F}$to generate ${}^{87}{\mathrm{Sr}}^{19}\mathrm{Fe}$, which has a mass of 106 , the mass spectrum does not overlap with ${}^{87}\mathrm{Rb}$.

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 ${\mathrm{NH}}_3,{\mathrm{N}}_2\mathrm{O}$or $\mathrm{CO}$to remove interfering molecular ions like ${\mathrm{ArO}}^{+}$or convert analyte into a molecular ion that can be detected without interference.

(b)

When ${}^{87}\mathrm{Sr}$ reacts with ${\mathrm{CH}}_3\mathrm{F}$to generate ${}^{87}{\mathrm{Sr}}^{19}\mathrm{Fe}$, which has a mass of 106 , the mass spectrum does not overlap with ${}^{87}\mathrm{Rb}$.