Identify the fundamental components of an atomic absorption spectrometer and explain the purpose of each component

It is critical for the chemical technician working with atomic absorption spectrometry to understand the importance of each component of the AA instrument, since each plays a role in the quality of analytical results. Adjustable parameters that the technician should understand include:

• the light source (hollow cathode lamp -HCL or electrodeless discharge lamp - EDL) - the current is the adjustable parameter for HCLs and the power for EDLs. In either case, to high a current or power will destroy the lamp at worse or reduce sensitivity and cause response nonlinearity at best. Too low a current or power will cause lamp instability and poor detection limits.
• the atomic vapor cell (flame, furnace, or gas generator) - most adjustments to an AA are made to this component. These include alignment; type, stoichiometry, and gas and solution flow rates using flames; alignment, temperature program, purge gases, matrix modifiers, and sample size for furnaces; and alignment, temperature, and gas and solution flow rates for gas generation devices. This is the component where most problems occur in the AA spectrometer.
• the monochromator - the adjustable parameter is the slit width, often designated as the spectral bandpass, which is typically varied from 0.2 to 1.0 nm depending on the spectral characteristics (intensity and spectral complexity) of the light source.
• the radiation detector - typically a photomultiplier tube (PMT) but sometimes a solid-state detector. In the case of the PMT, the voltage to the PMT is often adjusted by the user, sometimes described as gain control, to bring the electrical signal into the proper range for measurement.

Proper understanding of the fundamental components of the AA will allow the technician to properly plan and troubleshoot an analytical procedure.

Explain Beer's law and the factors that cause nonlinearity of instrument response in AAS

Understanding the limits of Beer's law and sources of nonlinearity in an AA spectrometer will facilitate troubleshooting and prevent technicians from making serious errors. Experiments designed to illustrate the interplay of parameters such as analyte concentration, absorption cell path length, source current or power, and spectrometer bandwidth are crucial to bring about this understanding. For example (a true story): a technician was asked to confirm that the relative concentrations of two solutions of a metal at around 10,000 ug/mL were identical within a defined error. The technician diluted the solutions to bring the concentrations into the linear range as defined by the instrument manual, but because the instrument was not properly optimized, the instrument response was not linear and no difference between the solutions was detected. In fact, there was a difference in the solution concentrations that was later detected, resulting in a product recall and considerable expense to the technician's company. The technician should have verified linear response by diluting each solution by 50% and determining that the instrument response was also decreased by a similar factor.