Spectroscopic Measurements

This text discusses the importance of preparing blanks, standards, and samples correctly when performing spectroscopic measurements. It also provides examples of how errors in the preparation of these solutions can lead to inaccurate results.

Questions

1. What is the purpose of a blank in a spectroscopic measurement?
2. What is the effect of including ammonium citrate and thioglycolic acid in the blank?
3. Why is it important to use a sample that contains approximately 0.1 g of Fe3+?
4. What is the effect of underestimating the true volume of a volumetric flask?
5. How can we avoid the need to extrapolate the calibration curve to a higher concentration of iron?

Answers

1. A blank is used to measure the absorbance of the reagents used in the measurement, so that the absorbance of the analyte can be determined.
2. Including ammonium citrate and thioglycolic acid in the blank ensures that the contribution of any trace impurities of iron is accounted for.
3. Using a sample that contains approximately 0.1 g of Fe3+ ensures that the concentration of Fe3+ in the sample falls within the range of concentrations of the external standards.
4. Underestimating the true volume of a volumetric flask results in an overestimation of the concentration of the standard solution. This, in turn, leads to an underestimation of the concentration of the analyte in the sample.
5. To avoid the need to extrapolate the calibration curve to a higher concentration of iron, we can dilute the sample in a volumetric flask that has a larger volume.