Spectroscopie d'absorption atomique: méthodes d'atomisation

Flame atomization uses a nebulizer to aerosolize the sample and a spray chamber assembly to mix it with fuel and oxidant. Only about 5% of aerosol droplets are fine enough to reach the flame, where they desolvate in the primary combustion zone. Bare particles then atomize in the inner flame, and gaseous atoms flow through the interzonal region for analysis before exiting.

Flame atomization has low efficiency because most aerosol droplets don't reach the flame and combustion gases dilute the sample significantly. Only a small fraction of analyte is successfully atomized and detected, making flame atomization unsuitable for samples with low analyte concentrations or limited volumes.

Electrothermal atomization, also called graphite furnace atomization, uses a graphite tube to capture and concentrate analytes from small, discrete samples. The sample is dried and charred before being atomized at high temperatures. This method works well for samples with limited volumes and low analyte concentrations, unlike flame atomization.

Elements like arsenic, selenium, antimony, bismuth, germanium, tin, tellurium, and lead can be atomized under milder conditions by chemically converting them into volatile hydride products first. Mercury determination uses a unique cold-vapor method due to its natural volatility, avoiding the need for high-temperature atomization.

Flame atomization efficiency can be enhanced by continuously aspirating the sample, optimizing fuel-to-oxidant ratios, adjusting nebulizer flow rates, and setting the burner height appropriately. These adjustments help maximize the fraction of sample that reaches the flame and undergoes successful atomization.

The spray chamber assembly mixes the aerosolized sample with a fuel-oxidant mixture in approximately stoichiometric ratio, though fuel-rich mixtures may be advantageous for easily oxidized atoms. This assembly helps create a fine aerosol mist that enters the burner for subsequent desolvation and atomization.

Graphite furnace atomization concentrates analytes within a graphite tube before atomization, making it ideal for small, discrete samples where analyte concentration matters. The sample undergoes drying and charring stages before high-temperature atomization, allowing efficient detection of trace elements that flame atomization would miss.