Atomic absorption spectrometry modulation

Bishop [75] determined barium in seawater by direct injection Zeeman-modulated graphite furnace atomic absorption spectrometry. The V203/Si modifier added to undiluted seawater samples promotes injection, sample drying, graphite tube life, and the elimination of most seawater components in a slow char at 1150-1200 °C. Atomisation is at 2600 °C. Detection is at 553.6 nm and calibration is by peak area. Sensitivity is 0.8 absorbance s/ng (Mo = 5.6 pg 0.0044 absorbance s) at an internal argon flow of 60 ml/min. The detection limit is 2.5 pg barium in a 25 ml sample or 0.5 pg using a 135 ml sample. Precision is 1.2% and accuracy is 23% for natural seawater (5.6-28 xg/l). The method works well in organic-rich seawater matrices and sediment porewaters. 

In atomic absorption spectrometry (AA) the sample is vaporized and the element of interest atomized at high temperatures. The element concentration is determined based on the attenuation or absorption by the analyte atoms, of a characteristic wavelength emitted from a light source. The light source is typically a hollow cathode lamp containing the element to be measured. Separate lamps are needed for each element. The detector is usually a photomultiplier tube. A monochromator is used to separate the element line and the light source is modulated to reduce the amount of unwanted radiation reaching the detector. 

Groll H., Schnurer-Patschan C., Kuritsyn Yu. and Niemax K. (1994) Wavelength modulation diode laser atomic absorption spectrometry in analytical flames, Spectrochim Acta, Part B 49 1463-1472. 

Our initial objective in the development of ACexpert, was to develop a system that could offer expert assistance during the analysis of metals. We also intended that the modules developed here for atomic absorption spectrometry would become more generally usable for analysis by other instruments. 

A remarkable adaptation of technology borrowed from another analytical method was demonstrated for an electrospray ionization (ESI) IMS instrument ion injection to a drift tube was achieved through modulation with a mechanical chopper as found in atomic absorption spectrometry. The chopper was a disk with a small hole that would align with the source and drift tube and would operate as an ion injector. The disk had a second window that was used with optical sensors to synchronize ion injection and drift time, and ion injections were made at pulse rates of 5 to 200 Hz with pulse widths of 200 to 500 ps. 

Figure 3 Principle of construction of atomic absorption spectrometers. (A) Single-beam spectrometer with electrically modulated lamp radiation (B) double-beam spectrometer with reflection and splitting of the primary radiation by a rotating, partially mirrored quartz disk (chopper). 1 - radiation source, 2 -sample cell (atomizer), 3 - monochromator, 4 - detector, 5 -electronics and readout (by permission of Wiley-VCH from Welz B and Sperling M (1999) Atomic Absorption Spectrometry, 3rd, completely revised edition. Weinheim Wiley-VCH).

Li, Pb, wavelength modulation diode laser atomic absorption spectrometry (WMDLAAS)... 

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