Quantify elements with standards, blanks and calibration graphs.
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Method and worked examples
AAS measures absorption of element-specific radiation by atomised sample atoms. Known standards define a calibration graph within its validated range. A blank accounts for reagent and instrument background. AAS measures the selected element, not the original complete compound containing it. Read an unknown by interpolation or rearrange the supplied calibration equation.
For A=mc+b, concentration c=m(A−b). Subtract the intercept before dividing by the slope. Multiply a diluted sample’s result by final volume / original aliquot volume. Dilute signals above the calibration range rather than extrapolating without validation. Contamination can bias results upward; a known check standard helps identify calibration errors.
Example 1
For A=0.050c+0.010 with c in mg L−1, find c when A=0.210.
c=0.0500.210−0.010=4.00 mg L−1. The blank/intercept is subtracted before dividing by the slope.
Example 2
10.0mL original sample is diluted to 50.0mL. AAS finds 0.80 mg L−1 in the dilution. Find original concentration.
Dilution factor =10.050.0=5.00. Original concentration =5.00×0.80=4.0 mg L−1.
Watch out:Atomisation destroys much of the original chemical structure; AAS measures the selected element, not its original molecular species.
Atomic absorption calibration and dilution practice | Year 12 Chemistry | Ascent Arcade