Spectroscopie d'émission atomique: instrumentation

An atomic emission spectrometer consists of a sample nebulizer, plasma source, wavelength-isolating device, transducers, and microprocessor controller. The nebulizer converts the sample solution into fine droplets carried by argon gas to the plasma. The plasma atomizes samples into gas-phase atoms and ions, which emit radiation that is separated by a monochromator, polychromator, or spectrograph and converted into electrical signals for analysis.

A nebulizer draws sample solution using a peristaltic pump and converts it into fine droplets through nebulization. Larger droplets are directed to a drain, while fine droplets are carried by argon gas to the plasma for atomization. This process ensures efficient introduction of the sample into the plasma as an aerosol, enabling consistent and complete atomization of the sample material.

Monochromators separate individual wavelengths sequentially through a single exit slit, measuring one emission line at a time. Polychromators use multiple exit slits to isolate and measure several wavelengths concurrently. Spectrographs enable simultaneous monitoring of a range of wavelengths, making them ideal for rapid multi-element analysis compared to sequential measurement approaches.

The plasma atomizes sample material into gas-phase atoms and ions through high-temperature excitation. Upon collision within the plasma, these atoms and ions become excited and emit characteristic radiation. Common plasma sources include inductively coupled plasma and direct current plasma, both providing the thermal energy necessary to generate atomic emission for elemental analysis.

Transducers, such as photomultiplier tubes or array detectors, convert isolated radiation into electrical signals. Single photomultiplier transducers measure one wavelength at a time, while multiple transducers or array detectors can simultaneously capture signals from several wavelengths. These electrical signals are then processed and analyzed by the microprocessor controller for quantitative and qualitative results.

Continuous atomizers, like plasmas and flames, introduce samples in a constant stream for steady-state analysis. Discrete atomizers inject individual samples using syringes or autosamplers, with the electrothermal atomizer being the most common type. Each approach offers different advantages depending on sample volume, analysis speed, and the number of elements requiring simultaneous determination.

Sequential spectrometers scan different emission lines in sequence, measuring one element at a time using a monochromator. Simultaneous spectrometers use polychromators or spectrographs to measure multiple wavelengths and elements at once. Simultaneous instruments enable faster analysis and are particularly useful for rapid multi-element determinations in complex samples.