Question

You are asked to develop a method for the quantitative analysis of the red dye cochineal red A, a synthetic dye used in the food industry (structure given below). This dye is commonly used in small amounts in food and cosmetics. Of the techniques we have discussed so far in class, choose a method that would be suitable for this analysis. List the specific instrument components (source, sample container, wavelength selector, and detector) that would be appropriate for this analysis. Explain briefly why the technique you chose would be appropriate. OH Na Na ' 05 "SO: Nat SO, Nat

Please help with this question. Thank you!

Answer 1

A method useful for quantitative analysis of the dye would be UV-Vis absorbance spectroscopy

The description of the instrument is given below:

Source: The source in UV-Vis spectroscopy is a light beam of wavelength 180 nm to 1100 nm

Sample container: The sample container is a quartz cuvette of path length either 0.2 cm or 1 cm (different cuvettes can have different path lengths). the volume of the cuvette can also vary from 0.6 ml to 3 ml.

Light Source UV Diffraction Grating Mirror 1 Slit 1 Light Source Vis Slit 2 Filter Mirror 4 Reference Cuvette Detector 2 Reference HI, Beam " Lens 1 Half Mirror Mirror 2 Sample Cuvette Detector 1 Sample Beam ample lenti MI Mirror 3 V Lens 2

Wavelength selector: The wavelength of the instrument ranges from 180 nm to 1100 nm. Hence the compounds absorbing in this range can show an absorption peak at their specific wavelength. For eg, let the incident light be denoted as I0, then the intensity of the incident light after passing through the cuvette would be I. Therefore, I/I0 indicates the concentration of the sample that is present in the cuvette.

Detector: UV-Vis spectrometers generally use a deuterium lamp as a source for detection of the emitted light. The wavelength of the Deuterium lamp ranges from 180 nm to 390 nm, which is used as reference.

Reason for the choice of the technique:

As mentioned in the section above for wavelength selector, The absorbance is directly proportional to I/I0

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and according to Beer Lambert law, A=Ecl, and by determining teh absorbance of the sample, we can easily determine the concentration of the sample. Hence, it is one of the convenient techniques for determining the concentration of dyes, which are used extensively in many laboratories.