Which component is NOT required when measuring magnesium using atomic absorption spectrophotometry?

When measuring magnesium using atomic absorption spectrophotometry, the critical components include a hollow cathode lamp specifically designed for magnesium, a chopper to mitigate optical interference, and a monochromator that isolates the specific wavelength corresponding to magnesium's absorption, which is typically around 285 nm.

The purpose of each essential component is fundamental to the technique: the hollow cathode lamp provides the specific light source required for magnesium, while the chopper helps to reduce noise and improve signal quality by interrupting the light beam, thereby enhancing measurement accuracy. The monochromator is crucial for selecting the appropriate wavelength for analysis, ensuring that only light at the specific frequency associated with magnesium absorption is evaluated.

In contrast, a 285-nm reference beam is not a necessary component for the measurement of magnesium in atomic absorption spectrophotometry. The technique does not require a simultaneous reference beam at the same wavelength for background correction; instead, any background absorption is typically accounted for using a blank sample and calibration curve without the need for a separate reference beam at that specific wavelength. Therefore, this component is not essential, highlighting why it is the correct choice in this context.