Analytical chemistry Trinidad & Tobago Lab resources
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Analysis Interferences in atomic absorption Spectroscopy

Absorption lines, Spectral and chemical interferences associated with atomic absorption analysis
and methods used to eliminate them
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Types and causes of AA interferences
Hg cold vapor and As hydride generation
1000 ppm AA standards
AA Instrument

Interference Effects in Atomic Absorption


ELEMENT line
nm
INTERFERENCES
Aluminium
13Al26.98
309.27 Enhanced effect caused by ionization. Add an ionization buffer such as 0.1%w/v potassium chloride to both sample and calibration standards
Antimony
15Sb121.75
206.83
217.58
231.15
High concentrations of Pb an Cu absorb at 217.58 line. Use line 206.83 or 231.15 if these elements are present. Acids cause depression of the response. Calibration solutions should be matched to the acid concentrations in the sample solutions. Can be determined by a hydride generation or Furnace method.
Arsenic
33As74.92
193.70 Flame interferences and scatter effects at arsenic wavelengths. Change to nitrous oxide/acetylene flame. Spike samples and add 1% nickel nitrate solution to digeststes prior to analysis. Can be determined by a hydride generation method.
Barium
56Ba137.34
553.55
455.40
Caused by presence of Ca or Ba ionization. Phosphate, silicon and aluminium cause depression in air/acetylene flame. Use nitrous oxide/acetylene flame and an ionisation buffer 0.1% w/v potassium as chloride. No ionization buffer is needed for determination at line 455.40 since this is the barium ion line.
Beryllium
4Be9.012
234.86 Acids enhances the response. Al, Si, Mg, depresses the response. Add 0.1% hydrofluoric acid to sample and calibration standards. Can use Furnace method.
Bismuth
83Bi208.98
223.06 No serious interference effects with air/acetylene flame.
Boron
5B10.81
249.77 No serious interference effects using nitrous oxide/acetylene, fuel fich flame.
Cadmium
48Cd112.40
228.80 Adsorption and light scattering. Large excess of silicate depress response. Calibration solutions should be matched with conc.of sample solutions. Can use Furnace method with ammonim phosphate as a matrix modifier.
Caesium
55Cs132.91
852.11 Ionisation effects. Add 0.5% potassium as chloride to both sample and calibration solutions.
Calcium
20Ca40.08
422.67 Response is depressed by Al, Be,P, Si, Ti, and Zr in air acetylene flame. The addition of releasing agent 0.2% w/v lanthanum to both samples and calibration stds. reduces this effect. The N2O/acetylene flame eliminates many of these problems but an ionisation buffer 0.1% of potassium as chloride must be added to all solutions. Protein in biological samples depress response and 0.5% EDTA should be added to reduce this effect.
Chromium
24Cr52
357.87 Reduced sensitivity with air/acetylene flame. Ca, P, and chloride interference. Phosphate depresses response. Add a 0.25% w/v calcium nitrate to all solns. The N2O flame reduces interference effects with a x2 sensitivity
Cobalt
29Co26.98
240.73 Large amounts of transition elements affect the response. Calibration stds. should be matched to the concentrations of any of these elements present as major components in the sample soln. Use standard addition. Can use Furnace method.
Copper
29Cu63.55
324.75 Transition elements and mineral acids depress the response. Adsorption and scatter. Calibration stds.should be matched to the concentrations of any of these elements present as major components in the sample.
Gold
79Au196.97
242.80 Cyanide depresses the response and should be destroyed by fuming with a mix.of sulphuric and perchloric acids.Nitric and HCl give a slight depression, and sulphuric gives a severe depression. Calibration solns. should be matched to the concentrations of these acids in the sample solns. Use ionisation buffer 0.1% w/v of potassium as chloride.
Iron
26Fe55.85
248.33 Perchloric acid. Nitric acid, Ni and Si depress the response. Add 0.2% w/v calcium chloride to all solns. Citric acid depress response and this effect can be reduced by adding 0.5% v/v phosphoric acid to both sample and standards. Most of these interference effects can be solved by using the hotter N2O/acetylene flame.
Lithium
03Li6.941
670.78 Ionisation effects. Use ionisation buffer 0.1% w/v potassium as chloride to both samples and calibration stds. Strontium gives enhancement due to absorption by SrOH species. Standards should be matched to concentration of strontium in sample. Can be analysed by Flame photometry.
Lanthanum
57La138.91
550.13 Ionisation effects. Use ionisation buffer 0.1% w/v potassium as chloride to both samples and calibration stds. Use the N2O/acetyleny fuel rich flame.
Lead
82Pb207.20
217.00 The 283.31 line is preferred for routine analysis because of better S/N ratio and lower background interference effects.
Magnesium
12Mg24.31
285.21
279.55
Al and Si depress the response in the air/acetylene flame. Add 0.1% La or Sr as chloride to both sample and calibration stds. These effects are reduced in the hotter N2O/acetylene flame with addition of ionisation buffer 0.1% w/v potassium as chloride to all solns. Determination at the 279.55 line however, is the magnesium ion line and requires no KCl buffer with the hotter flame.
Manganese
25Mn54.94
279.48 Si depresses the response. Add 0.2% w/v calcium chloride to both samples and calibration stds. Mo and W depress response when acetylene pressure drops below 100 lb. (7Kg cm-2 or 100 lb in -2) Change to a full acetylene cylinder.
Mercury
80Hg200.59
253.65 Large amounts of Cobalt enhance response. Reducing agents (SnCl2) should be added in xs to all solutions. The cold vapour flameless method is recommended.
Molybdenum
42Mo95.94
313.26 Ca, Fe, Mn, Sulphate, and Sr depress response in air/acetylene flame. Add 0.5% w/v aluminium chloride or 2% w/v NH4Cl to both samples and calibration stds. or use the N2O/acetylene flame which gives a x2 increase in sensitivity. The presence of calcium and iron in the hotter flame may cause depressed response which can be reduced by adding 0.5% w/v aluminium or 1% w/v sodium sulphate to both sample and standards. Change acetylene cylinder when pressure falls below 100 lb (7Kg cm-2 or 100 lb in -2)
Nickel
28Ni58.71
341.48
232.00
Nickel line interference. Use line at 341.48 for routine work. A large excess of iron causes enhancement and calibration stds. should be matched to the concentration of this element in the sample solutions.
Potassium
19K39.10
766.49 Ionisation effects. Add 0.1% w/v sodium or caesium to both sample and calibration solns. High conc. of mineral acids depress response. Calibration stds. should contain the same conc. of acids. Usually analysed by Flame photometry.
Silicon
14Si28.09
251.61 Ionisation effects depress response. Use the N2O/acetylene fuel rich flame. Add ionisation buffer 0.1% w/v of an alkali metal as chloride.
Silver
47Ag107.87
328.07 Al, Zn, Th, KmnO4, iodate and tungstate depress the response. Do not use hydrochloric acid unless silver is in solution as a chloride complex. Calibration stds. should match the conc. of any of these present as major components in the sample.
Sodium
11Na22.99
589.00
589.59
Ionisation effects. Add ionisation buffer 0.1% w/v potassium or caesium chloride to sample and calibration stds. Can be determined by Flame photometry.
Strontium
38Sr87.62
460.73 Phosphate, Al, Si, depress response. Add 0.5% w/v lanthanum or calcium chloride to all solutions or use the N2O/acetylene flame
Tin
50Sn118.69
224.61 The N2O / acetylene flame should be used for routine determinations in anything but aqueous solutions.
Uranium
92U238.01
358.49
356.66
CN in the flame gives a high noise level at 358.49nm. For this reason, the 356.66nm line is used for most determinatios. Use ionisation buffer 0.1% alkali metal as chloride.
Vanadium
23V50.94
318.54 Al and Ti enhances the response. Add 0.5% aluminium to all solutions. Ionisation effects can be eliminated by addition of 0.1% alkali metal as chloride to all solns.
Zinc
30Zn65.37
213.86 Response is depressed with large excess of silicon. The calibration solns. should be matched to the conc. of the element in the sample solns. Strontium removes Cu and phosphate contamination.
Zirconium
40Zr91.22
360.12 The response is enhanced in the presence of ammonium ions, chloride, fluoride and iron. Response is depressed by nickel (NiBr ), nitrate and sulphate. The addition of 0.2% m/v of ammonium fluoride to both sample and standard helps reduce interference effects.



Reference: Pye Unicam "Atomic Absorption Data Book" 1979.