Below is data collected for the analysis of Ca in a supplement tablet using atom

Question

Below is data collected for the analysis of Ca in a supplement tablet using atomic absorption spectrometry. Absorbances were measured for standards, the sample and two sample solutions to which standard Ca was added to increase the Ca concentration by 10 and 20 ppm. Why is standard addition necessary to get an accurate measurement of the Ca? (A) Both curses are linear indicating that there is a matrix effect. (B) The standard addition plot shows that adding standard to the sample causes an increase in the absorbance. (C) The intercept of the standard addition plot is significantly larger than the intercept of the calibration curve. (D) The standard addition slope is less than the calibration curse slope indicating that there is interference in the sample. What type of interference does a standard addition method help prevent? (A) chemical interference that reduces the absorption of light by Ca atoms (B) signal interference caused by lamp drift (C) spectral interference that requires Zeeman background correction (D) spectral interference that adds to the absorption of light by flame components

Explanation / Answer

27. (A) Both curves are linear indicating that there is matrix effect. So, an unknown concentration can be found out from the matrix of concentration-absorbance matrix.

The method of standard addition is a type of quantitative analysis used in analytical chemistry. This method is used in cases where the sample matrix contributes to the analytical signal, known as the matrix effect.

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