Extraction photometry, metals

Pyridylazo ligands have been widely used in the extraction photometry of various metal ions. For example, l-(2-pyridylazo)-2-naphthol (Hpan) is one of the most well-known reagents, but it shows slow extraction rate for some metal ions such as Ni(II) and Pd(II). 2-(5-Bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) is a relatively new reagent, which is more sensitive than Hpan for Cu(II), Ni(II), Co(II), and Zn(II), giving the metal complexes of molar absorptivities in the order of 105M-1 cm-1. 

Atomic absorption spectrometry is one of the most widely used techniques for the determination of metals at trace levels in solution. Its popularity as compared with that of flame emission is due to its relative freedom from interferences by inter-element effects and its relative insensitivity to variations in flame temperature. Only for the routine determination of alkali and alkaline earth metals, is flame photometry usually preferred. Over sixty elements can be determined in almost any matrix by atomic absorption. Examples include heavy metals in body fluids, polluted waters, foodstuffs, soft drinks and beer, the analysis of metallurgical and geochemical samples and the determination of many metals in soils, crude oils, petroleum products and plastics. Detection limits generally lie in the range 100-0.1 ppb (Table 8.4) but these can be improved by chemical pre-concentration procedures involving solvent extraction or ion exchange. 

An official method has been published for the determination of nickel in 1M ammonium nitrate extracts of potassium from soil [178]. The level of potassium in the extract is determined by flame photometry. Inductively coupled plasma atomic emission spectrometry (Sect. 2.55) and stable isotope dilution (Sect. 2.55) have been applied to the determination of potassium in multi-metal analyses. 

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