Zeeman Atomic Absorption Spectrometry

Atomic absorption spectroscopy (AAS) is based on resonance light absorption by atoms of determined elements. AAS is widely used for elemental analysis of various matrices. One of the factors that complicates the application of AAS is the influence of background non-selective absorption and scattering of resonance radiation.

There are several methods to reduce this influence, with one being the use of differential optical schemes that generate reference and analytical signals at different wavelengths.

Mercury (Hg) determination with AAS often involves separation Hg from the matrix using a selective sorbent, such as gold (amalgamation, double amalgamation). However, gold can unpredictably change its properties due to the influence of volatile components and surface changes (aging), which requires constant control in order to avoid analytical errors.

To ensure high selectivity, Lumex Instruments mercury analyzers utilize Zeeman correction for background absorption and scattering (Zeeman AAS, or ZAAS). The Zeeman effect refers to the splitting of a spectral line into several components in the presence of a magnetic field.

In Lumex Instruments RA-915-series mercury analyzers, a mercury lamp is placed in a permanent magnetic field. The 254-nm mercury resonance line is split into Zeeman polarized components (direct Zeeman effect).

One of the components (Ϭ-) within the Hg absorption line envelope is used as analytical radiation; the other component (Ϭ+) lies outside the Hg absorption line and serves as reference radiation. The analytical and reference components are separated in time using a high-frequency (HF) polarization modulator.

How does it work? As long as there are no mercury atoms in the analytical cell, the intensities of both Ϭ-components are equal. When mercury enters the cell, the difference in intensity between the two Ϭ-components increases as a function of the mercury concentration. The logarithm of the ratio of the Ϭ+ and Ϭ- components is used as the analytical signal which is directly proportional to the mercury concentration in the analytical cell. The spectral shift between the Ϭ-components is significantly smaller than the widths of molecular absorption bands and scattering spectra. Background absorption leads to the same attenuation of the intensities of the Ϭ-components and, correspondingly, their ratio does not change. Thus, any background absorption by interfering compounds can be neglected, providing the highest selectivity of the analysis. The combination of built-in and external analytical cells enables low Limit of Detection (LoD) and a wide dynamic measurement range.

The Lumex Instruments mercury analyzers and monitors (models RA-915M, RA-915AM и RA-915AMNG) have a built-in multipath cell with an optical length of 10 m for the real-time determination of the background concentration of mercury in air (below 1 ng/m3) and in water using Cold Vapour technique (0.5 ppt).

The versatile ZAAS technology empowers to create portable, laboratory and on-line analyzers and monitors for mercury determination in air, gases, solids, biota, and liquids.

The main advantages of ZAAS mercury analyzers and monitors are: high selectivity, low limit of detection, wide dynamic range of measurement, versatility for various field and laboratory applications, low maintenance and running cost.

ZAAS HF background correction using the inverse Zeeman effect is also applied to the Lumex Instruments MGA-1000 multi-element laboratory analyzer.