You are measuring lycopene in samples of tomato sauce. You extract a 2.1 mL samp
ID: 933971 • Letter: Y
Question
You are measuring lycopene in samples of tomato sauce. You extract a 2.1 mL sample of tomato sauce 3X with 5 mL hexane. You pool the extracts and bring to a final volume of 25 mL with hexane. You then evaporate the extract under N2 and resolubilize to a final volume of 3 mL hexane. You then measure the sample at 502 nm on an
You are measuring lycopene in samples of tomato sauce. You extract a 2.1 mL sample of tomato sauce 3X with 5 mL hexane. You pool the extracts and bring to a final volume of 25 mL with hexane. You then evaporate the extract under N2 and resolubilize to a final volume of 3 mL hexane. You then measure the sample at 502 nm on an ??old school?? spectrophotometer that only measures intensity of the incident light (I0, 158 units) and the light transmitted through the sample (I, 54 units), and has a path length of 0.94 cm. The molar absorptivity of lycopene at 502 nm is 1.72 ? 105 L?mol?1 cm?1 . The serving size of tomato sauce is 1 US ??legal?? cup. Lycopene MW=536.89 g/mol, formula=C40H56 6. What is the concentration (µg/mL) of the original sample? (Hint: the concentration (µg/mL) of the diluted sample = 154.6 mg/mL)Explanation / Answer
1. Determination of absorptivity of the diluted sample
? = 1.72 x 105 L/mol cm
b = 0.94 cm
c = 154.6 mg/mL
A = ?bc
A = ( 1.72 x 105 L/mol cm ) x ( 0.94 cm ) x ( 154.6 mg/mL ) x ( 1000 mL/1 L ) x ( 1 mol/536.89 g ) x( 1 g/1000 mg )
A = 46556.52
2. Determination of the concentration of the original sample
A = ?bc (dilution factor)
( 46556.52 ) = ( 1.72 x 105 L/mol cm ) x ( 0.94 cm ) x ( 1 mol/536.89 g ) x (3/25) x [c]
[c] = 1288.33 g/L x ( 1 L/1000 mL) x ( 1000000 ?g/ 1 g)
[c] = 1288333.33 ?g/mL
Concentration of the original sample = 1288333.33 ?g/mL
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