Extraction Considerations

The need for separation and/or preconcentration in trace metal analyses are fundamentally related to available instrumentation and instrumental

Figure 1 Inorganic preparation flow diagram.

Table 1 Comparison of a select list of analytical techniques"


Flame AAS




General detection limits

General sensitivity

Instrument maturity


Instrument availability

Instrument-specific inorganic extraction

0.1-0.01 mg L~1 1-5000 mgL~1 0.1-0.001 mg L~1 1-100mg L~1

Excellent, select Moderate, Excellent, elements refractories poor refractories limited

Well established Well established Well established




Few, well understood


Numerous, well developed

Many, controllable Readily

Well developed

Moderate, refractories excellent

Established and growing

Spectral Readily Developed

Moderate Excellent

Established Few

Specialized laboratory

New and growing

Moderate, mass overlap

Specialized laboratory

Well developed Undeveloped aAbbrevations: ASV, anodic stripping voltametry; Flame AAS, flame atomic absorption spectrometry; ET-AAS electrothermal atomic absorption spectrometry; ICP-AES, inductively coupled plasma atomic emission spectrometry; NAA, neutron activation analysis; ICP-MS: inductively coupled plasma mass spectrometry.

capabilities. Basically, separation and/or preconcen-tration are needed when one of the following situations occurs: concentration of analyte is below the sensitivity of the instrumental method; interferences exist in the sample (relative to the instrument to be used); or physical or chemical states of the sample are not appropriate for the instrument. Sensitivities for elements varies with the instrumental method and are relative to matrix type; however, a general listing of sensitivities of commonly used analytical equipment is given in Table 1.

The impetus for doing an extraction will therefore depend on the availability of instruments and the capability of the instrument relative to the matrix type (i.e. interferences). Inorganic extraction schemes are typically instrument specific. Although instrument development has significantly reduced detection limits, availability of some of the more state-of-the-art equipment is still limited to specialized or well-equipped laboratories. The need for separation and preconcentration therefore still exist. Speciation studies will also continue to support development and research into inorganic separations from complex matrices.

Because atomic absorption spectrometry (AAS) is readily available, but the detection limits are high in relation to today's needs, there are numerous solvent extraction methods available for metals in AAS analysis. Several excellent sources are listed in Further Reading; these have lengthy tables of inorganic extraction schemes.

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