Pigments and Synthetic Dyes: Natural vs permitted dyes, detection of non-permitted dyes MCQs With Answer

Pigments and Synthetic Dyes: Natural vs permitted dyes, detection of non-permitted dyes MCQs With Answer

This quiz collection is designed for M.Pharm students studying MPA 104T Food Analysis, focusing on pigments and synthetic dyes encountered in food matrices. It contrasts natural and permitted colorants with common illicit dyes, details their chemical features, toxicological concerns and regulatory status, and emphasizes analytical strategies for screening and confirmation. Questions cover chromophores, extraction and clean-up methods, chromatographic and spectrometric detection (TLC, HPLC, LC‑MS/MS, GC‑MS, SERS), validation concepts (LOD/LOQ, matrix effects), and practical case scenarios such as spice and seafood adulteration. Use these MCQs to test conceptual understanding and analytical decision-making in real-world food dye monitoring and enforcement.

Q1. What is the primary difference between a pigment and a dye in the context of food colorants?

• Pigments are insoluble particulate colorants; dyes are soluble molecules that impart color by molecular absorption.
• Pigments always originate from animal sources; dyes are always synthetic.
• Pigments change color with pH; dyes never change color with pH.
• Pigments are volatile; dyes are non‑volatile.

Correct Answer: Pigments are insoluble particulate colorants; dyes are soluble molecules that impart color by molecular absorption.

Q2. Which functional group is the defining chromophore in most synthetic azo food dyes?

• Nitro (-NO2) group
• Azo (-N=N-) group
• Carbonyl (>C=O) group
• Sulfonic acid (-SO3H) group

Correct Answer: Azo (-N=N-) group

Q3. Which of the following is an example of a natural, widely permitted food dye?

• Sudan I
• Curcumin from turmeric
• Malachite green
• Rhodamine B

Correct Answer: Curcumin from turmeric

Q4. Which dye is commonly listed as non‑permitted and carcinogenic in many jurisdictions and often found as an adulterant in spices?

• Tartrazine
• Sudan I
• Chlorophyllin
• Beta‑carotene

Correct Answer: Sudan I

Q5. For preliminary screening of lipophilic banned azo dyes in powdered chili, which analytical screening method and solvent system is most appropriate?

• TLC using hexane:ethyl acetate (7:3) with UV visualization
• Paper chromatography with water as mobile phase
• Direct HPLC without extraction
• GC-MS without derivatization

Correct Answer: TLC using hexane:ethyl acetate (7:3) with UV visualization

Q6. Which technique is considered the gold‑standard confirmatory method for identifying and quantifying non‑permitted dyes in complex food matrices?

• UV‑Vis spectrophotometry
• LC‑MS/MS (liquid chromatography tandem mass spectrometry)
• Paper chromatography
• Simple colorimetric spot test

Correct Answer: LC‑MS/MS (liquid chromatography tandem mass spectrometry)

Q7. Which sample clean‑up approach is commonly used to remove matrix interferences prior to LC‑MS analysis of food dyes?

• Solid‑phase extraction (SPE) using C18 or ion‑exchange cartridges
• No clean‑up; direct injection of raw homogenate
• Macroscopic filtration only
• Steam distillation

Correct Answer: Solid‑phase extraction (SPE) using C18 or ion‑exchange cartridges

Q8. Why is derivatization often required before GC‑MS analysis of many food dyes?

• Because dyes are highly volatile and need stabilization
• Because many dyes are polar and non‑volatile, requiring conversion to volatile derivatives
• To make dyes water‑soluble for GC injection
• Derivatization is never required for dyes prior to GC‑MS

Correct Answer: Because many dyes are polar and non‑volatile, requiring conversion to volatile derivatives

Q9. Which analytical feature of tandem mass spectrometry (MS/MS) is most useful for unambiguous identification of a prohibited dye?

• Retention time only
• High signal intensity without fragmentation
• Characteristic fragmentation pattern (product ions) and precursor/product ion transitions
• Color of the eluate

Correct Answer: Characteristic fragmentation pattern (product ions) and precursor/product ion transitions

Q10. Which commonly used synthetic food colorant is an azo dye and frequently regulated (E‑number designation)?

• Tartrazine (E102)
• Chlorophyll (E140)
• Beta‑carotene (E160a)
• Curcumin (E100)

Correct Answer: Tartrazine (E102)

Q11. In India, which regulatory authority publishes the list of permitted and non‑permitted food colors?

• FDA (United States Food and Drug Administration)
• FSSAI (Food Safety and Standards Authority of India)
• EMA (European Medicines Agency)
• WHO (World Health Organization)

Correct Answer: FSSAI (Food Safety and Standards Authority of India)

Q12. Which natural dye is an anthraquinone derivative traditionally obtained from madder and used historically as a red colorant?

• Alizarin (madder)
• Indigo
• Annatto
• Chlorophyll

Correct Answer: Alizarin (madder)

Q13. Surface‑enhanced Raman spectroscopy (SERS) is valuable in dye detection because:

• It destroys the analyte making quantitation impossible
• It enhances Raman signals enabling trace‑level detection and molecular fingerprinting
• It only detects inorganic pigments
• It replaces the need for any sample preparation

Correct Answer: It enhances Raman signals enabling trace‑level detection and molecular fingerprinting

Q14. Which natural colorant has been implicated in allergic hypersensitivity reactions in some consumers?

• Carminic acid (carmine, cochineal)
• Beta‑carotene
• Chlorophyllin
• Calcium carbonate

Correct Answer: Carminic acid (carmine, cochineal)

Q15. A major toxic concern with several banned azo dyes is their metabolic reduction to which class of compounds?

• Aliphatic alcohols
• Aromatic amines such as p‑aminobiphenyl
• Saturated hydrocarbons
• Inorganic salts

Correct Answer: Aromatic amines such as p‑aminobiphenyl

Q16. For reversed‑phase HPLC separation of many polar food dyes, the preferred stationary phase is:

• C18 (octadecyl) reversed‑phase column with gradient aqueous/organic mobile phase
• Non‑polar silica with hexane mobile phase only
• Glass beads with water mobile phase
• Anion exchange resin used isocratically with pure methanol

Correct Answer: C18 (octadecyl) reversed‑phase column with gradient aqueous/organic mobile phase

Q17. In method validation, the limit of detection (LOD) is commonly defined as the concentration giving a signal‑to‑noise ratio approximately equal to:

• 1
• 3
• 10
• 100

Correct Answer: 3

Q18. Which of the following dyes has been illegally used to color fish and is banned in food‑producing animals due to toxicity?

• Malachite green
• Tartrazine
• Annatto
• Curcumin

Correct Answer: Malachite green

Q19. Which derivatization reagent is commonly used to make polar dye molecules amenable for GC‑MS analysis via silylation?

• BSTFA (N,O‑bis(trimethylsilyl)trifluoroacetamide)
• Sulfuric acid
• Sodium chloride
• Hydrochloric acid

Correct Answer: BSTFA (N,O‑bis(trimethylsilyl)trifluoroacetamide)

Q20. For legally defensible quantitative confirmation of a banned dye in a food sample, the best analytical approach is:

• Visual assessment by eye and a photograph
• Validated LC‑MS/MS method with matrix‑matched calibration, internal standards and quality controls
• Single replicate TLC spot without reference standards
• UV‑Vis scan of raw extract without chromatography

Correct Answer: Validated LC‑MS/MS method with matrix‑matched calibration, internal standards and quality controls

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