14.14 : Atomic Emission Spectroscopy: Lab

AES is a powerful analytical technique, especially effective when used with plasma sources, producing abundant spectra in characteristic emission lines. The Inductively Coupled Plasma (ICP), in particular, yields superior quantitative analytical data due to its high stability, low noise, low background, and minimal interferences under optimal experimental conditions. However, newer air-operated microwave sources are emerging as promising alternatives that could be more cost-effective than conventional ICP sources. AES is primarily used to analyze liquid samples. However, plasma emission also allows for the direct analysis of solid samples, which can be achieved through various procedures like electrothermal vaporization, laser and spark ablation, and glow-discharge vaporization.

In theory, all metallic elements can be determined by plasma emission spectrometry. This method's effectiveness for alkali metals is limited due to the challenging operating conditions and the placement of their prominent spectral lines in the near-infrared region. This can lead to detection problems in many plasma spectrometers primarily designed for ultraviolet radiation. As a result, plasma emission spectroscopy is generally limited to determining approximately 60 elements. Most elements have several prominent lines suitable for identification and quantification. Typically, a suitable line for each element can usually be found, with selection based on overlap with lines from other elements present in the sample.

Plasma sources often yield linear calibration curves, but departures from linearity can occur due to factors like self-absorption, erroneous background corrections, ionization, and nonlinear responses of the detection systems. When possible, quantitative analyses are best conducted using external standards. However, many parameters can significantly affect emission intensity, including the excitation source's temperature and the atomization efficiency. In cases where variations in source parameters are difficult to control, internal standards can be used.