Assume that you are asked to prepare a set of five, 1ml standards to measure β-carotene. You have been given a stock solution of 10mg/ml and you must design the concentrations of your standards to provide an appropriate range that reflects the β-carotene concentrations found in hexane extractions from various fruits. When you measure the absorbance of your five standards, your lowest concentration in the set returns an absorbance of 0.1. What would the concentration of β-carotene be in the lowest concentration standard? Round answers to 3 sf.Note: the molar absorptivity for β-carotene at 444nm in hexane is 127,500 M-1cm-1. The Mwt of β-carotene is 536.89 g/mol.Selected Answer: [None Given]Answers: A. 400ng/mlB. 421ng/mlC. 338ng/mlD. 444ng/mlE. 150ng/ml
Question
Assume that you are asked to prepare a set of five, 1ml standards to measure β-carotene. You have been given a stock solution of 10mg/ml and you must design the concentrations of your standards to provide an appropriate range that reflects the β-carotene concentrations found in hexane extractions from various fruits. When you measure the absorbance of your five standards, your lowest concentration in the set returns an absorbance of 0.1. What would the concentration of β-carotene be in the lowest concentration standard? Round answers to 3 sf.Note: the molar absorptivity for β-carotene at 444nm in hexane is 127,500 M-1cm-1. The Mwt of β-carotene is 536.89 g/mol.Selected Answer: [None Given]Answers: A. 400ng/mlB. 421ng/mlC. 338ng/mlD. 444ng/mlE. 150ng/ml
Solution
To solve this problem, we need to use the Beer-Lambert Law, which states that the absorbance of a solution is directly proportional to its concentration. The formula for this law is A = εlc, where A is the absorbance, ε is the molar absorptivity, l is the path length (which is 1 cm by default), and c is the concentration.
Given: A = 0.1 (absorbance) ε = 127,500 M^-1cm^-1 (molar absorptivity) l = 1 cm (path length)
We need to find c (concentration).
Rearranging the formula to solve for c gives us c = A / (εl).
Substituting the given values into the formula gives us c = 0.1 / (127,500 * 1) = 7.84 x 10^-7 M.
However, the answer needs to be in ng/ml. To convert from M to ng/ml, we need to use the molecular weight (Mwt) of β-carotene, which is 536.89 g/mol.
First, convert the concentration from M to g/l: 7.84 x 10^-7 M * 536.89 g/mol = 4.21 x 10^-4 g/l.
Then, convert from g/l to ng/ml: 4.21 x 10^-4 g/l * 1,000,000 ng/g * 1/1000 l/ml = 421 ng/ml.
So, the concentration of β-carotene in the lowest concentration standard is 421 ng/ml. Therefore, the correct answer is B. 421ng/ml.
Similar Questions
elow are the absorbances of a set of β-carotene standards.Concentration (ng/ml) Absorbance0 0.000400 0.096800 0.1901000 0.2602000 0.5004000 0.990When you analysed a hexane extract of tomatoes via spectrophotometry, it recorded an absorbance of 0.700. Using the data points to calculate gradient, what would be the closest estimate for the concentration of β-carotene in the tomato sample? (Note: the pathlength was 1cm.)Selected Answer: [None Given]Answers: A. 150ng/mlB. 1500ng/mlC. 725ng/mlD. 300ng/mlE. 3000ng/m
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