The leaves were washed with distilled water to remove impurities and at last rinsed in deionized water. The leaves were cut in smaller pieces, filled
in a heavy-duty blender, and covered with deionized water to 5 cm above the plant material. The device must work until obtaining a greenish juice of
the leaves. The liquefied material was sifted through a 0.20 mm sieve. A sample of 20 crystals extracted from croton leaves was measured and the
values varied from 0.004 to 0.018 mm. The 0.20 mm sieve was adequate to separate the fibrous leaf material from the plant juice and the CaOx crystals.
The plant material retained in the sieve was ground again in the blender. The procedure must be repeated until the plant juice becomes totally clear.
The volume of extracted plant juice was placed in 1000 mL test tubes for sedimentation of the calcium oxalate crystals and plant material. The
sedimentation process must be repeated until the supernatant is light-colored and free of chlorophyll, pigments as well as other organic water-soluble
compounds. The solid material containing the calcium oxalate crystals and other not water-soluble impurities were at the bottom of the test tube. The
supernatant was removed by draining off.
In the end of the extraction, the formed sediment can be transferred to smaller test tubes (100 mL) to concentrate the extracted material. After
concentrating the suspension, the solid product was dried at 60 ºC.
Hydrogen peroxide (30 %) was added to the dry material and the suspension formed was left to rest for 24 h to remove the organic impurities. Hydrogen
peroxide was added until it covering the solid material by 2 cm. After 24 h reacting with the organic substances the CaOx crystals were free of
impurities. The optical microscope was used to observe the purity of the calcium oxalate crystals. The procedure with hydrogen peroxide can be
repeated in case of any remaining impurities. The resulting solid material was washed with deionized water to remove impurities and dried at 60 ºC.
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