From Chitin to Chitosan - Chitosan Based Hydrogels: Functions and Applications - page 26

TAble 1.3
Coexistence of Different Transition Metal Ions

Accumulation Rate (%)

Ions 1 h 4 h 8 h 16 h 20 h 24 h

Cu 2+ 31.8 70 79 93.5 98.6 98.8

Cu 2+ Cr(VI) 8 58 71 86.7 95.4 96.2

Cr(VI) 18 40 60 74 85 90.3

14 34 43 65.2 65.4 72.1

Cr(VI) Cu 2+

100 mL of 0.4 mol/L (NH 4 ) 2 SO 4 , which contains nanogram grade zinc ions marked by
isotope, by chitosan powder column and testing isotope, the result shows that all the zinc
ions marked by isotope remain at the upper part of the column and only ammonium sul-
fate is left the eluate, which means that all the zinc ions are chelated by chitosan. The chi-
tosan can also separate trace copper ions from ammonium sulfate solution.
In solution containing two or more transition metal ions, chitosan chelates ions with
more suitable radii first. For example, since nickel ions are more suitable for chitosan than
ferrous ions, they can be separated from the solution by chitosan chromatography, which
retains nickel ions in the column and almost all the ferrous ions are left in the eluate.
Table 1.3 shows interactions between Cu ions and a few Cr(VI) ions in solution and the
opposite. Such interactions exist between Cu ions and chromate, and other transition metal
ions (for instance, ferrous ions) strongly affect Cu ions (Table 1.4).
Different oxide valences determine different chelation capacities (Table 1.5). For example,
ferrous ions are easy to remove from the chitin column whereas ferric ions are not.
The combination of chitosan and transition metal ions will be influenced by anions.
Chlorine ions inhibit the amount of combined metal ions whereas sulfates increase it. Due
to soluble chitosan acetate, the solution contains acetates that change the surface property
of chitosan. Sulfonic acid can chelate metal ions itself, and so it also inhibits the combina-
tion of chitosan and metal ions.
A number of papers on the chelation mechanism of chitosan and copper have been
published. Experiments prove that four residues chelate one copper molecule [81], as shown
in Figure 1.20.
Chitosan combines with an Fe molecule and three molecules of water based on two
glucose residues [82].
Guan et al. [83] believe that the coordination number of a coordination polymer formed
by metal and organic macromolecule cannot be simply determined by elementary analy-
sis; instead, the coordination number of the central ion should be determined by the vibra-
tion effect of the photoelectron spectrograph or measured by the conductimetric method.

TAble 1.4
Influence of Ferrous Ion on Cupric Ions

Accumulation Rate (%)

Ions 1 h 4 h 8 h 16 h 20 h

Cu 2+ 31.8 70 79 93.5 98.6

Fe 2+ 30 32 34 36 37

Fe 2+ , Cu 2+ 14 15 16 18 18