Two dissolved species are present in a sample

CHEMISTRY · Single correct · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures

Problem

Two dissolved species are present in a sample. Their molar absorptivities (

\epsilon

, in

\text{L}\,\text{mol}^{-1}\,\text{cm}^{-1}

) are listed below. Species X (analyte):

\epsilon_{510}=1.2\times10^{4}

\epsilon_{600}=3.0\times10^{3}

Species Y (interferent):

\epsilon_{510}=1.4\times10^{4}

\epsilon_{600}=1.0\times10^{3}

To determine the concentration of X with minimal error from the presence of Y, which wavelength should be selected? (a)

450\,\text{nm}

, because both species have negligible absorbance and therefore negligible interference. (b)

600\,\text{nm}

, because the ratio of absorbance due to X relative to Y is greatest there. (c)

510\,\text{nm}

, because it gives the largest absolute absorbance for X. (d)

550\,\text{nm}

, because it is midway between the two listed wavelengths and should balance the two signals.