C. You are asked to measure the levels of the antioxidants BHT, benzoic acid and

Question

C. You are asked to measure the levels of the antioxidants BHT, benzoic acid and ascorbic acid in a prepared meal. In order to do this the meal is first homogenized, then a 50.2g sample is freeze dried resulting in a dry weight of 10.7g. A 2.4g portion of the freeze- dried meal homogenate is dissolved in 20.0mL of water in a separating funnel. This solution is shaken with 20.0mL of octanol and left to separate into 2 layers. For each antioxidant, give an explanation for which layer (upper or lower) it primarily resides in The concentration of benzoic acid in the upper layer is found to be 0.15mg/mL. What is the total amount of benzoic acid in the initial 50.2g sample of the meal? a. b. The octanol-water partition coefficient logPow for the antioxidants BHT, benzoic acid and ascorbic acid 5.1, 1.87 and -1.85 respectively and the density of octanol is 0.82g/mL.

Explanation / Answer

C. antixoidants separation with water-octanol solvent system

a. antioxidant BHT would be found in octanol (upper layer). Benzoic acid would be found in octanol (upper layer) and ascorbic acid would be found in water layer (lower layer). This is based upon the solubility of compounds in the solvents.

b. The concentration of benzoic acid was found after separation to be 0.15 mg/ml

So the total concentration of benzoic acid in 20 ml octanol would be = 20 x 0.15 = 3 mg

partition coefficient of benzoic acid in octanol/water = 1.87

let x amount of benzoic acid was present in original solution

then,

1.87 = {3/20)/[(x-3)/20]

0.0935x - 0.2805 = 0.15

x = 0.4305/0.0935 = 4.60 mg

So the original concentration of benzoic acid in 50.2 g sample = 4.60 mg

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