2.8. Physical analysis
2.8.1. Solubility
Solubility analysis was performed by the method adapted from
Anema, Pinder,Hunter, andHemar (2006) withmodifications. A sample
of the colourant powder (0.5 g) was added to 50 ml of distilled water.
The solution was stirred with a magnetic stirrer (VELP Scientifica,
Europe) at room temperature for 30 min to allow for complete dispersion
before tests commenced. A subsample (30 ml) of the sample solutionwas
taken and centrifuged (Rotina 48R, Universal 320R) at 2120 ×g
for 15 min. The supernatant was placed in a pre-weighed moisture
can and weighed. The moisture can was dried overnight in an oven at
105 °C, cooled in a desiccator and then reweighed. The percentage of
soluble colourant powder (%Solubility) was calculated by the following
equation:
%Solubility ¼ WeightðgÞ of dried sample
10 WeightðgÞ of sample
100: