PROCEDURE First, the curcumin is separated from turmeric by extraction with isopropyl alcohol. In Part B, the spectrum of diluted extract is taken. The absorption maximum is used with Beer’s Law to find the concentration of curcumin in the turmeric sample. Finally, in Part C, the concentrated curcumin solution is used as a pH indicator. Part A: Extraction of Curcumin from Turmeric 1. Place about 1.0 g turmeric in a 250-mL Erlenmeyer flask. The amount need not be 1.0 g exactly, but must be recorded to the nearest 0.1 g and must not be less than 1.0. Add 80 mL rubbing alcohol (~91% isopropyl alcohol), which can be estimated from the markings on the flask. 2. Using a stirring hot plate and stir bar, allow mixture to heat and stir for 30 minutes at a temperature just below boiling (80-83 °C). 3. Cool extract to room temperature (~10 minutes). Using a fluted filter paper, filter by gravity into a 100-mL volumetric flask. Wash any residue with several 5-mL portions of isopropyl alcohol and filter into the volumetric flask, making sure not to go over the 100-mL mark on the neck of the flask. Add isopropyl alcohol to the 100-mL mark. Part B: Spectrum of Curcumin Solution 1. Transfer a 1-mL volume of the extract into a 50-mL volumetric flask and dilute with isopropyl alcohol to the mark. (A calibrated Pasteur pipet is sufficient here.) At this concentration, the absorbance reading at 425 nm (maximum peak) should be within the working range of conventional spectrometers.
1. the extract diluted before taking the spectrum, because the Lambert-Bears law is only valid in diluted solution when the self agreegation of the analyte is negligible.
3.cucurmin change it’s colour at a pH of 7.4 to 8.6
4. because cucurmin is poorly soluble in water