Bohman and colleagues described a reversed-phase HPLC method for the quantitativ

Question

Bohman and colleagues described a reversed-phase HPLC method for the quantitative analysis of vitamin A in food using the method of standard additions. In a typical example, a 10.067-g sample of cereal is placed in a 250-mL Erlenmeyer flask along with 1 g of sodium ascorbate, 40 mL of ethanol, and 10 mL of 50% w/v KOH. After refluxing for 30 min, 60 mL of ethanol is added and the solution cooled to room temperature. Vitamin A is extracted using three 100-mL portions of hexane. The combined portions of hexane are evaporated and the residue containing vitamin A transferred to a 5-mL volumetric flask and diluted to volume with methanol. A standard addition is prepared in a similar manner using a 10.093-g sample of the cereal and spiking with 0.0200 mg of vitamin A. Injecting the sample and standard addition into the HPLC gives peak areas of, respectively, 6.77x103 and 1.32x104 . Report the vitamin A content of the sample in milligrams/100 g cereal

Explanation / Answer

10.067-g sample 6.77x103

10.093-g sample + 0.0200 mg vitamin A 1.32x104

In this we can assume that 10.067-g sample and 10.093-g sample will have same amount of Vitamin A

so the remaining area in 1.32x104 is due to actual spiked vitamin A

1.32x104 - 6.77x103 = 6.43 x 103

so 0.0200 mg of vitamin A gives  6.43 x 103 area in HPLC

so 6.77 x 103 is due to 0.021 mg of Vitamin A.

So 10.067 g of the sample contains 0.021 mg of Vitamin A

so 100 g of the cereal contains 0.2091 mg of Vitamin A

0.2091 mg Vitamin A/100g of cereal

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