Chapter 20, Problem 20.20P

(a)

Interpretation Introduction

Interpretation:

Reason for apparent increase in concentration of ${\text{Li}}^{+}$ in samples 1 to 3 has to be suggested.

Concept Introduction:

Any change that might have been triggered by signal fluctuation although analyte concentration is maintained the same is termed as interference. Several different interferences are observed, namely spectral, chemical, ionization, or Isobaric interference.

Spectral interference is found when the signal due to furnace or flame tends to overlap with the analyte signal.  Usually, elements known for the formation of highly stable oxides give such spectral interference.

Chemical interference is observed due to sulfates or phosphates that might hinder the extent of atomization for the analyte. With higher flames, such interference can be reduced.

Alkali metals pose ionization interference that involves reduced concentration of analyte atoms due to ionization.

Isobaric interference occurs as when ions that possess the same nominal mass are found within mass spectrometer and instruments is not able to distinguish between them. For instance, ionized ${}^{138}{\text{Ba}}^{2+}$ has mass by charge ratio of 138/2 or 69/1 similar to $\text{m/z}$ for ${}^{69}{\text{Ga}}^{+}$. So the former interferes with the latter. Similarly, ${}^{40}{\text{Ar}}^{16}{\text{O}}^{+}$ interferes with ${}^{56}\text{Fe}$.

(b)

Interpretation Introduction

Interpretation:

Reason behind constant result for samples 4 to 6 has to be given.

Concept Introduction:

Refer to part (a).

(c)

Interpretation Introduction

Interpretation:

Value for real concentration of ${\text{Li}}^{+}$ in sample has to be recommended.

Concept Introduction:

Refer to part (a).