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Standard methods for the examination of water and waste water.

The major difference is that in flame photometry the amount of light emitted is measured, whereas in atomic absorp- tion spectrometry a light beam is directed through the flame, into a monochromator, and onto a detector that measures the amount of light absorbed by the atomized element in the apha 2005 standard method.

For some metals, atomic absorption exhibits superior sensitivity Approved by Standard Methods Committee, 1 Because each metal has its own character- apha 2005 standard method absorption wavelength, apha 2005 standard method source lamp composed of that element is used; this makes the method relatively free from spec- tral or radiation interferences.

The amount of energy at the characteristic wavelength absorbed in the flame is proportional to the concentration of the element in the sample over a limited concentration range. Most atomic absorption instruments also are equipped for operation in an emission mode.

Selection of Method See Section Many metals can be determined by direct aspiration of sample into an air-acetylene flame.


The most troublesome apha 2005 standard method of interference is termed "chemical" and re- sults from the lack of absorption by atoms bound in molecular apha 2005 standard method in the flame.

This can occur when the flame is not hot enough to dissociate the molecules or when the dissociated atom is oxidized immediately to a compound that will not dis- sociate further at the flame temperature. Such interferences may be reduced or eliminated by adding specific elements or com- pounds to the sample solution.

For example, the interference of phosphate in the magnesium determination can be overcome by adding lanthanum.

Similarly, introduction of calcium eliminates silica interference in the determination of manganese.


However, silicon and metals such as aluminum, barium, beryllium, and apha 2005 standard method require the higher- temperature, nitrous oxide-acety- lene flame to dissociate their molecules. The nitrous oxide-acet- ylene flame also can be useful in minimizing certain types of chemical interferences encountered in the air-acetylene flame.

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For example, the interference caused by high concentrations of phosphate in the determination of calcium in the air-acetylene flame does apha 2005 standard method occur in the nitrous oxide-acetylene flame. This procedure also concentrates the sample so that the detection limits are extended.

Brines and seawater can be analyzed by direct aspiration but sample dilution is recommended.

Standard methods for the examination of water and wastewater. 14th edition.

Aspiration of solutions con- taining high concentrations of dissolved solids often results in solids buildup on the burner head.

This requires frequent shut- down of the flame and cleaning of apha 2005 standard method burner head. Make more frequent recovery checks when analyzing brines and sea waters to insure accurate results in these concentrated and complex matrices.

Barium and other metals ionize in the flame, thereby reducing the ground state potentially absorbing population.

The addition of an excess of a cation sodium, potassium, or lithium having a similar apha 2005 standard method lower ionization potential will overcome this prob- lem.

The wavelength of maximum absorption for arsenic is The sensitivity apha 2005 standard method arsenic and selenium can be improved by conversion to their gaseous hy- drides and analyzing them in either a nitrogen-hydrogen or an argon-hydrogen flame with a quartz tube see Section 31 Molecular absorption and light scattering caused by solid particles in the flame can cause er- roneously high absorption values resulting in positive errors.

When such phenomena occur, use background correction to ob- tain accurate values.