Question

(a) The suppressor in Figure 26-9 enables low parts-per-billion conductivity detection for anions such as${\mathbf{Cl}}^{\mathbf{-}}\mathbf{and}\mathbf{}{\mathbf{Br}}^{\mathbf{-}}\mathbf{,}$.but very poor detection limits for anions such as${\mathbf{CN}}^{\mathbf{-}}$and borate. Explain why.

(b) Mixtures of sodium carbonate and bicarbonate can be used as eluent in suppressed-ion anion chromatography. Detection limits are poorer than with hydroxide eluent due to higher background conductivity. Explain why

Short answer

The explanations to the above questions are:

(a). The detection limits for anions such asand borate are poor.

(b).The detection limits are poorer than with hydroxide eluent.

Step-by-step solution

Definition of Dissociation

• Dissociation is a process in which, usually ionic compounds, breakdown into constituents such as ions.
• Acids, in this case HCl, HBr and HCN, are formed by suppression. Both HCl and HBr are strong acids, which means that they fully dissociate, whereas weak acids, HCN and salt borate in this case, barely dissociate.

Therefore, detection limits for anions such as${\mathrm{CN}}^{-}$ and borate are poor.

Partial Dissociation in the above case

b. Mixtures of bicarbonate and sodium carbonate such as eluent in suppressed-ion anion chromatography generates a suppression product${\mathrm{H}}_2{\mathrm{CO}}_3$which partially dissociates.

Therefore, detection limits are poorer than with hydroxide eluent.