Which instrument is used to measure divalent ions and trace elements via photometric methods?

• A. Flame photometry
• B. AAS
• C. UV-Vis spectrophotometry
• D. Ion-selective electrode

Answer: (B)

Measuring how much light is absorbed by atoms in a sample lets us quantify trace metals, including divalent ions. Atomic absorption spectroscopy uses a light source tuned to the element’s wavelength and passes the sample in a flame or graphite furnace; the amount of light absorbed by the free atoms is proportional to their concentration. This makes it ideal for detecting trace levels of metals like Ca2+, Mg2+, Fe2+, Zn2+, and many others. Flame photometry, while good for a few elements such as sodium and potassium, isn’t as versatile for a broad range of divalent metals. UV-Vis photometry requires specific colored species and suitable reagents, which isn’t as direct for many metals. An ion-selective electrode measures ion activity electrochemically, not by light. So the instrument best suited for measuring divalent ions and trace elements via photometric methods is atomic absorption spectroscopy.