4. Spectroscopy Method Choice

FAAS

Flame atomic absorption spectroscopy; good for one/few elements at moderate concentration, cheaper and faster than GFAAS.

GFAAS

Graphite furnace AAS; more sensitive than FAAS, small sample volumes, slower, one element at a time.

ICP-AES / ICP-OES

Inductively coupled plasma atomic emission; multi-element, sensitive, good for complex samples, expensive.

XRF / XFS

X-ray fluorescence; direct solid analysis, non-destructive, useful for screening elements.

When choose ICP-AES?

Several metals/elements in solution and detection limits are sufficient; advantage: simultaneous multi-element analysis.

When choose GFAAS?

Trace metal concentration is very low and high sensitivity is needed for one/few elements.

When choose FAAS?

One/few elements at higher concentration where sensitivity is sufficient and cheaper fast method is desired.

When choose XRF?

Solid sample or surface screening where minimal preparation and non-destructive analysis are important.

Disadvantage of ICP-AES

Expensive instrument, complex operation, often requires digestion/sample solution.

Disadvantage of GFAAS

Slow, one element at a time, lamp/conditions element-specific.

Disadvantage of FAAS

Less sensitive than GFAAS/ICP; one element at a time; matrix/flame interferences.

Disadvantage of XRF

Detection limits and quantification can be worse for some elements; matrix/surface effects important.

Metals in blood at µg/L

Use GFAAS or ICP-AES depending detection limits; mention sample digestion/matrix, sensitivity and calibration.

Hg spectroscopy method

Use cold vapor AAS if taught/allowed, otherwise high-sensitivity atomic method with Hg-specific handling; motivate by low concentration and volatility.

Metals in leachate/water

ICP-AES if several metals simultaneously and concentrations above detection limits; GFAAS for trace elements needing lower LOD.

Metals in organs/tissue

Digest sample then ICP-AES/GFAAS depending elements and LOD; discuss matrix and sample preparation.

Metals in solid soil/toys/direct sample

XRF if direct non-destructive solid analysis is desired; otherwise digest then ICP/AAS.

Depth profile in skin

Use surface/depth-capable method; if MS allowed LA-ICP-MS, if not consider XRF-type surface spectroscopy depending course context.

Metals in hair

Digest hair then ICP-AES/AAS/GFAAS; XRF can be mentioned for direct screening if suitable.

Phosphate by spectrophotometry

Phosphate does not absorb strongly by itself; form colored molybdate complex then measure UV/VIS.

D-vitamin by spectrophotometry

Need extraction/solvent/sample prep; choose wavelength where D-vitamin absorbs; use calibration, avoid interferences, consider matrix and sensitivity.

Fish selenium iodine D-vitamin spectrophotometry factors

Extraction/sample preparation, chromophore/derivatization or suitable wavelength, calibration/standard, matrix interferences, LOD and blank.

PCB by spectrophotometry main problem

Several similar compounds have overlapping spectra and weak selectivity; difficult to distinguish individually.

Solve PCB spectrophotometry problem

Separate first with chromatography or use a more selective method/detector.

Aromatic/polyconjugated molecule by UV-VIS

Likely absorbs UV/VIS if chromophore present; can be analyzed spectrophotometrically with calibration if matrix is controlled.

No natural luminescence but want luminescence analysis

Derivatize or react analyte with fluorophore/fluorescent tag, or use indirect fluorescence method.

Two variants of luminescence used for analysis

Fluorescence and phosphorescence.

Factors for reliable spectrophotometry

Correct wavelength, complete reaction/derivatization, suitable pH/reaction time/reagent amount, blank, calibration, matrix/interference control, proper cuvette.

Atomic vs molecular absorption instrumentation difference

Atomic needs atomization and often element lamp; molecular UV-VIS measures molecules in solution with cuvette and broad lamp.

Atomic spectroscopy sample state

Often requires free atoms in flame, furnace or plasma.

Molecular UV-VIS sample state

Usually solution containing molecules; no atomization needed.

Emission vs luminescence instrument difference

Emission needs excitation by heat/plasma/flame and no lamp; luminescence uses excitation light source and detector at angle.

Absorption vs luminescence instrument difference

Absorption detects transmitted light along beam; luminescence detects emitted light, often at 90° and with two analyzers.