Fish-liver oil is a good source of vitamin A, whose concentration is measured spectrometrically

step 1 Okay, so we want to use a wavelength of 329 nanometers because that is where vitamin A absorbs.

Fish-liver oil is a good source of vitamin A, whose...

Fish-liver oil is a good source of vitamin $\mathrm{A},$ whose concentration is measured spectrometrically at a wavelength of $329 \mathrm{nm}$ (a) Suggest a reason for using this wavelength. (b) In what region of the spectrum does this wavelength lie? (c) When $0.1232 \mathrm{~g}$ of fish-liver oil is dissolved in $500 . \mathrm{mL}$ of solvent, the absorbance is 0.724 units. When $1.67 \times 10^{-3} \mathrm{~g}$ of vitamin $\mathrm{A}$ is dissolved in $250 . \mathrm{mL}$ of solvent, the absorbance is 1.018 units. Calculate the vitamin A concentration in the fish-liver oil.

Fish-liver oil is a good source of vitamin $\mathrm{A},$ whose concentration is measured spectrometrically at a wavelength of $329 \mathrm{nm}$
(a) Suggest a reason for using this wavelength.
(b) In what region of the spectrum does this wavelength lie?
(c) When $0.1232 \mathrm{~g}$ of fish-liver oil is dissolved in $500 . \mathrm{mL}$ of solvent, the absorbance is 0.724 units. When $1.67 \times 10^{-3} \mathrm{~g}$ of vitamin $\mathrm{A}$ is dissolved in $250 . \mathrm{mL}$ of solvent, the absorbance is 1.018 units. Calculate the vitamin A concentration in the fish-liver oil.

Key Concepts

Electromagnetic Spectrum Regions

The electromagnetic spectrum is divided into several regions including ultraviolet (UV), visible, and infrared. A wavelength of 329 nm falls within the ultraviolet (UV) region, which is characterized by higher energy light than visible wavelengths and is often used in spectrophotometric measurements for compounds that absorb strongly in the UV range.

Standard Calibration

Standard calibration is a process in which a series of known concentrations of a pure analyte are measured to establish a relationship between absorbance and concentration. This calibration curve is then used to determine the concentration of the analyte in unknown samples by comparing their absorbance values to the standard curve.

Optimal Wavelength Selection

Optimal wavelength selection involves choosing a wavelength where the analyte has its maximum absorbance, often termed the absorption maximum. Measuring at this wavelength minimizes interference from other substances and enhances the sensitivity and accuracy of the analysis, making it ideal for quantifying compounds like vitamin A.

Spectrophotometry

Spectrophotometry is an analytical technique that measures how much a chemical substance absorbs light by measuring the intensity of light as a beam passes through sample solution. It is widely used to determine the concentration of an analyte in solution as the absorbance is directly proportional to the concentration according to Beer's Law.

Beer-Lambert Law

The Beer-Lambert Law states that the absorbance of light by a substance is directly proportional to its concentration and the path length through which the light travels. This relationship allows for the creation of calibration curves from standard solutions to determine the concentration of an unknown sample by measuring its absorbance.

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