The color intensity of each of the 60 model MRPs prepared from the
different combinations of the five sugars and 12 amino acids was determined with an HP 8435 spectrophotometer (Germany) as the absorbance
at 420 nm against distilled water. The rate of change of color intensity
caused by the addition of a metal ion or NaCl was also measured against
the same MRP without the metal ion or NaCl as a control. The rate of
change of color intensity (%) was expressed as [(absorbance of MRP with
a metal ion or salt 100 =absorbance of control) 100]