In a single-beam atomic absorption spectrophotometer, what is the instrument actually measuring?

In a single-beam atomic absorption spectrophotometer, what is the instrument actually measuring?

• A. Intensity of light emitted by the analyte on its return to the ground state
• B. Intensity of light that the analyte absorbs from the hollow-cathode lamp
• C. Intensity of light that the analyte absorbs from the flame
• D. Intensity of the beam from the hollow cathode lamp after it has passed through the analyte-containing flame

Answer: (D)

In this technique the signal comes from how much of the lamp’s light makes it through the flame that contains the analyte. The hollow-cathode lamp provides light at the element’s characteristic wavelength, and as that beam passes through the flame, the ground-state atoms there absorb some photons. The photodetector then measures the transmitted light intensity that emerges from the flame. The smaller this transmitted intensity, the greater the absorption, which relates to concentration via Beer–Lambert behavior. So the instrument is effectively measuring the beam after it has passed through the analyte-containing flame, not light emitted by the analyte or light absorbed in some other way.

In this technique the signal comes from how much of the lamp’s light makes it through the flame that contains the analyte. The hollow-cathode lamp provides light at the element’s characteristic wavelength, and as that beam passes through the flame, the ground-state atoms there absorb some photons. The photodetector then measures the transmitted light intensity that emerges from the flame. The smaller this transmitted intensity, the greater the absorption, which relates to concentration via Beer–Lambert behavior. So the instrument is effectively measuring the beam after it has passed through the analyte-containing flame, not light emitted by the analyte or light absorbed in some other way.