Question

Explain why atomic emission spectroscopy can be used for multi-elemental analysis, but atomic absorption is used mostly for quantification of single element.

Answer 1

Let me put you the principle and basis for both, and from there, try to get the answer. Although I think you have the answer in here.

Atomic Emission Spectroscopy

Atomic emission occurs when a valence electron in a higher energy atomic orbital returns to a lower energy atomic orbital. Atomic emission requires a means for converting a solid, liquid, or solution analyte into a free gaseous atom. The same source of thermal energy usually serves as the excitation source. The most common methods are flames and plasmas, both of which are useful for liquid or solution samples. Solid samples may be analyzed by dissolving in a solvent and using a flame or plasma atomizer.

Atomic emission spectroscopy is ideally suited for multielemental analysis because all analytes in a sample are excited simultaneously. If the instrument includes a scanning monochromator, we can program it to move rapidly to an analyte’s desired wavelength, pause to record its emission intensity, and then move to the next analyte’s wavelength. This sequential analysis allows for a sampling rate of 3–4 analytes per minute.

Another approach to a multielemental analysis is to use a multichannel instrument that allows us to simultaneously monitor many analytes. A simple design for a multichannel spectrometer couples a monochromator with multiple detectors that can be positioned in a semicircular array around the monochromator at positions corresponding to the wavelengths for the analytes.

Atomic absorption

Atomic absorption spectroscopy is one of the most frequently used tools in analytical chemistry. This is because for the determination of most metals and metalloids the technique offers sufficient sensitivity for many applications and is relatively interference free. There are two basic atom cells (a means of converting the sample, usually a liquid, into free atoms) used in atomic absorption spectroscopy: (1) the flame and (2) the electrothermal heating of a sample cell. It is generally acknowledged that if sufficient analyte is present in the sample, then it should be determined using a flame technique because this has added advantages of being rapid (assuming only a few elements need be determined) and, in comparison with alternative techniques, very simple to use. Electrothermal atomic absorption spectroscopy (ETAAS) or electrothermal vaporization atomic absorption spectroscopy (ETVAAS) requires more operator skill and is less rapid, but yields substantially superior limits of detection when compared with flame atomic absorption spectroscopy (FAAS).

Hope this helps