HELP ASAP PLEASE

Question

You want to determine the amount of Phycocyanin in a 500 mg herbal tablet. Before analysis by UV-Vis spectroscopy, five Phycocyanin tablets (each 500 mg) were crushed in a pestle and mortar. 1.2 g of the crushed tablets were then dissolved in 100 ml of ethanol. 50 ml of the solution was filtered to remove undissolved particles. 2 ml of the filtered solution was then diluted by a factor of 10 (i.e., dilution factor is 10). The diluted sample was analysed using UV-Vis spectroscopy and had an absorbance of 0.324. Show each calculation step clearly. What was the amount in mg of Phycocyanin in a 500 mg tablet? What is the percent (%w/w) of Phycocyanin in a tablet?

Answer 1

Since you don't give the extinction coefficient for Phycocyanin nor the wavelength, we cannot calculate the concentration of Phycocyanin in the sample, hence we cannot find the mass (mg) of Phycocyanin in the tablet.  If you have the extinction, then use Beer Lambert to find concentration.  A = ecl and solve for c.  Once you have c you can correct for dilutions and extractions.  Multiply by 10 to get c in 2 ml sample.  Convert to mg using molar mass of Phycocyanin. Multiply by 25 to get mg in the 50 ml aliquot. Multiply by 2 to get mg in the 100 ml ethanol.  That will give you mg Phycocyanin/1.2 g of tablet.  Divide that value by 1.2 and multiply by 0.5 to get the final answer.

 

If you have the extinction coefficient, go ahead and re-post the question with that included, and I or someone will show you how to do this Also include the molar mass (molecular weight of Phycocyanin if you have it).