(a)Xanthine absorbs at 260 nm with an extinction coefficient of 3.85 x 103 M-1 c
ID: 488047 • Letter: #
Question
(a)Xanthine absorbs at 260 nm with an extinction coefficient of 3.85 x 103 M-1 cm-1 . An absorbance of 0.72 was recorded in a 1 cm cuvette containing 3 mL of solution. Stock solution (100 L ) had been added to 2.9 mL diluents to prepare sample for the measurement. Calculate the xanthine concentration in the stock solution
(b) The 280 nm absorbance of a solution of a pure protein was 0.86. The protein content, determined by BCA method, was 510 g per mL. If the molecular weight of the protein is 40,000, what is the molar (M) extinction coefficient? The mM extinction coefficient?
Explanation / Answer
a)
From Beer Lambert Law
A=Ecl
A = Absorbance = 0.72
E = 3.85 x 10^3 M-1cm-1 = Molar absorptivity
l = 1 cm = Path length
c = Concentration
Hence , c = A/El = 0.72 / 3.85 x 10^3 x 1 =1.87 x 10^-4 M
Hence,
S1 = 3 x1.87 x 10^-4 / 10^-4 =5.61 M
Hence stock solution concentration is 5.61 M
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