Oxidation states group 13 elements

The advantage of the selective adsorption of a particular element oxidation state has been exploited for on-line element preconcentration and speciation analysis of Cr by FAAS. Cespon Romero et al. [21] described an FIA system employing a minicolumn made of a chelating resin containing poly(aminopho-sphonic) acid groups, able to selectively retain Cr(III) ions. An FIA manifold was employed for efficient preconcentration and subsequent elution of Cr(III) with a small volume of 0.5 M HC1. The original sample was also treated with ascorbic acid to reduce Cr(VI) to Cr(III) and total Cr is determined as Cr(III) after appropriate retention and elution. Eluates are introduced into an N20-acetylene flame connected to the column outlet. The concentration of Cr (VI) is obtained by difference. Employing a sample volume of 6.6 mL, LoD for total Cr is 0.2 pg l-1. A study of FI operational variables, interferences, and precision is reported for the analysis of tap, mineral, and river waters. 

The most common oxidation states of the 32/-transition elements are +2 and + 3. The elements in the middle of each series exhibit more oxidation states than those to the left or right. As one moves down a group, higher oxidation states become more stable and more common (opposite to the trend for representative elements). This is because the d electrons are more effectively shielded from the nucleus as the group is descended and are therefore more easily lost or more readily available for sharing. For example, cobalt commonly exhibits the +2 and +3 oxidation states. Rh and Ir are just below Co. Their common oxidation states are +3 and +4. The +4 state is slightly more stable for Ir than for the lighter Rh. 

Higher oxidation states are more stable than in the 3 d series, and lower ones less common. The group oxidation state is found up to group 8. 4d and 5d elements of early groups are very similar in later groups higher oxidation states occur in the 5d series. 

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