Atomic Spectroscopy (AAS, ICP-OES, ICP-MS)
Atomic Spectroscopy (AAS, ICP-OES, ICP-MS)
This domain tests conversion of a sample into atoms or ions and measurement by absorption, emission or mass: flame and graphite furnace AAS, ICP-OES and ICP-MS, including interferences and quantification strategies.
Core rules
- AAS measures ground-state atom absorption. Flame AAS typically reaches mg/L; graphite furnace reaches µg/L. Lamp current, slit width and atomization temperature control sensitivity.
- ICP-OES measures atomic or ionic emission. Axial view is more sensitive but more matrix-prone; radial view is more robust.
- ICP-MS measures m/z and is the most sensitive, but suffers isobaric, polyatomic and matrix-induced mass bias. Collision/reaction cells and internal standards mitigate these.
- External standards should match the acid matrix. Standard addition is used when matrix suppression is significant. Internal standards correct drift and matrix effects.
- Control total dissolved solids; high salt causes cone blockage and signal suppression. Report detection limits on both solution and sample basis, including dilution.
Worked example
5.00 mL sample is diluted to 50.00 mL and gives signal 0.220. A 1.00 mL aliquot of 10.0 mg/L standard added to another 5.00 mL sample, diluted to 50.00 mL, gives 0.360. Added concentration in the measured solution = 10.0 × 1.00/50.00 = 0.200 mg/L. Ratio 0.360/0.220 = 1.636 = (c + 0.200)/c, so c = 0.314 mg/L. Original = 0.314 × (50.00/5.00) = 3.14 mg/L. Standard addition assumes linear response and identical matrix.
Traps
- Using external calibration in a strongly suppressive matrix.
- Ignoring Ar-based polyatomic ions such as ArCl+ and ArO+ in ICP-MS.
- Reporting µg/L without the dilution factor.
- Memory effects from mercury or boron.
- Assuming every emission line is free of overlap.