Question

(a) Explain the purpose of the dynamic reaction cell in Figure 21-30. (b) In geologic strontium isotopic analysis, there is isobaric interferencebetween ${}^{87}{\mathrm{Rb}}^{+}$and ${}^{87}{\mathrm{Sr}}^{+}$A dynamic reaction cell with ${\mathrm{CH}}_3\mathrm{F}$converts ${\mathrm{Sr}}^{+}$to ${\mathrm{SrF}}^{+}$but does not convert ${\mathrm{Rb}}^{+}$to ${\mathrm{RbF}}^{+}$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 $\mathrm{CO}$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 , 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 ${}^{87}S{r}^{-}$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${}^{87}\mathrm{Rb}$