Estimation of phytoconstituents MCQs With Answer is an essential review resource for B.Pharm students focusing on quantitative estimation and analytical techniques for plant secondary metabolites. This introduction covers core keywords: phytoconstituents, quantitative estimation, spectrophotometry, chromatography, HPLC, TLC, gravimetry, titrimetry, assay methods, validation parameters (linearity, accuracy, precision, LOD, LOQ), extraction techniques, and common groups like alkaloids, flavonoids, tannins, saponins and phenolics. Questions emphasize practical assay steps, sample preparation, standardization, reagent reactions (AlCl3, Dragendorff’s), and interpretation of results. The MCQs train students to apply theory to analytical method selection, troubleshooting, and regulatory compliance. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which statement best describes the Beer–Lambert law used in spectrophotometric estimation?
- Absorbance is inversely proportional to concentration
- Absorbance is directly proportional to concentration and path length
- Absorbance depends only on solvent polarity
- Absorbance is independent of molar absorptivity
Correct Answer: Absorbance is directly proportional to concentration and path length
Q2. Which reagent is commonly used to form a colored complex with flavonoids for spectrophotometric assays?
- Dragendorff’s reagent
- Aluminium chloride (AlCl3)
- Folin–Ciocalteu reagent
- Vanillin–sulfuric acid
Correct Answer: Aluminium chloride (AlCl3)
Q3. For quantitative estimation of non-volatile polar phytoconstituents, which chromatographic technique is most appropriate?
- Gas chromatography (GC)
- Reversed-phase HPLC (C18)
- Paper chromatography
- Gel electrophoresis
Correct Answer: Reversed-phase HPLC (C18)
Q4. Limit of detection (LOD) is defined as:
- The highest concentration that can be measured accurately
- The lowest concentration that can be detected but not necessarily quantified
- The concentration giving maximum absorbance
- The concentration at which the reagent decomposes
Correct Answer: The lowest concentration that can be detected but not necessarily quantified
Q5. Which analytical approach is most useful to correct matrix effects in complex plant extracts?
- Standard addition method
- External standard calibration only
- Using pure solvent as blank
- Dilution without standards
Correct Answer: Standard addition method
Q6. The primary purpose of using an internal standard in chromatographic assays is to:
- Increase detector sensitivity
- Compensate for variability in sample preparation and injection
- Eliminate the need for calibration curves
- React chemically with analytes to form detectable complexes
Correct Answer: Compensate for variability in sample preparation and injection
Q7. A typical mobile phase for reversed-phase HPLC analysis of phytoconstituents contains:
- Pure hexane only
- Strong acid without organic solvent
- Aqueous buffer mixed with organic solvent like acetonitrile
- CCl4 as the main component
Correct Answer: Aqueous buffer mixed with organic solvent like acetonitrile
Q8. In thin-layer chromatography (TLC), the Rf value is defined as:
- Distance traveled by solvent front divided by distance traveled by solute
- Distance traveled by solute divided by distance traveled by solvent front
- Ratio of solute concentration to solvent concentration
- Height of the chromatographic peak
Correct Answer: Distance traveled by solute divided by distance traveled by solvent front
Q9. Which solvent is commonly used for extracting phenolic compounds from plant material for spectrophotometric assays?
- Methanol
- n-Hexane
- Carbon tetrachloride
- Liquid nitrogen
Correct Answer: Methanol
Q10. Which detector is most suitable for quantifying UV-absorbing phytoconstituents in HPLC?
- Refractive index detector
- Flame ionization detector
- UV–Visible or photodiode array (PDA) detector
- Thermal conductivity detector
Correct Answer: UV–Visible or photodiode array (PDA) detector
Q11. Total phenolic content in plant extracts is commonly estimated using which reagent?
- Aluminium chloride
- Folin–Ciocalteu reagent
- Ninhydrin reagent
- Dragendorff’s reagent
Correct Answer: Folin–Ciocalteu reagent
Q12. Which colorimetric reagent is often used for spectrophotometric estimation of saponins or triterpenoids?
- Folin–Ciocalteu reagent
- Vanillin–sulfuric acid
- Biuret reagent
- Iodine solution
Correct Answer: Vanillin–sulfuric acid
Q13. Which validation parameter assesses the closeness of measured values to the true value?
- Precision
- Linearity
- Accuracy
- Specificity
Correct Answer: Accuracy
Q14. Precision of an analytical method is commonly expressed as:
- Mean absolute error
- Percent relative standard deviation (%RSD)
- Limit of detection
- Slope of calibration curve
Correct Answer: Percent relative standard deviation (%RSD)
Q15. Which of the following is NOT a typical class of phytoconstituents?
- Alkaloids
- Flavonoids
- Tannins
- Pure elemental silica
Correct Answer: Pure elemental silica
Q16. The main advantage of using a rotary evaporator in extract preparation is to:
- Lyophilize the extract
- Remove solvent under reduced pressure at low temperature
- Increase boiling point of solvent
- Perform filtration of particulate matter
Correct Answer: Remove solvent under reduced pressure at low temperature
Q17. In normal-phase TLC, the stationary phase is typically:
- Octadecylsilane (C18)
- Silica gel
- Polystyrene
- Cellulose acetate membrane
Correct Answer: Silica gel
Q18. Which separation technique is based primarily on volatility and is therefore suitable for volatile phytoconstituents?
- High-performance liquid chromatography (HPLC)
- Gas chromatography (GC)
- Thin-layer chromatography (TLC)
- Capillary electrophoresis
Correct Answer: Gas chromatography (GC)
Q19. For GC analysis of non-volatile plant constituents, what is commonly required?
- Use of larger injection volumes only
- Derivatization to form volatile derivatives
- A switch to ionic detectors
- Solid-phase TLC prior to injection
Correct Answer: Derivatization to form volatile derivatives
Q20. Which HPLC detector feature helps assess peak purity and detect co-eluting impurities?
- Single-wavelength UV detection
- Photodiode array (PDA) spectral analysis
- Refractive index only
- Fixed-wavelength fluorescence
Correct Answer: Photodiode array (PDA) spectral analysis
Q21. Limit of quantification (LOQ) is best defined as:
- The lowest amount that can be detected but not quantified
- The lowest amount that can be quantitatively determined with acceptable precision and accuracy
- The highest concentration measurable
- Concentration at which calibration curve fails
Correct Answer: The lowest amount that can be quantitatively determined with acceptable precision and accuracy
Q22. Which test is used to evaluate method robustness?
- Change in analyst only
- Deliberate minor variations in parameters like pH and flow rate
- Measuring blank solution repeatedly
- Using a different brand of glassware only
Correct Answer: Deliberate minor variations in parameters like pH and flow rate
Q23. Recovery studies in phytoconstituent estimation primarily assess:
- Precision of the measuring instrument
- Accuracy of extraction and assay procedures
- Detector linearity
- Stability of standard solutions only
Correct Answer: Accuracy of extraction and assay procedures
Q24. Which reagent commonly gives an orange or orange–red precipitate with many alkaloids?
- Folin–Ciocalteu reagent
- Dragendorff’s reagent
- Aluminium chloride
- Biuret reagent
Correct Answer: Dragendorff’s reagent
Q25. Which stationary phase is most widely used for reversed-phase HPLC columns in phytochemical analysis?
- Silica gel (normal phase)
- C18 (octadecylsilane)
- CN (cyano)
- Cellulose powder
Correct Answer: C18 (octadecylsilane)
Q26. The aluminum chloride colorimetric assay for flavonoids is typically measured at which wavelength?
- 254 nm
- 415 nm
- 600 nm
- 900 nm
Correct Answer: 415 nm
Q27. Solid-phase extraction (SPE) is commonly employed in phytoconstituent analysis to:
- Increase sample viscosity
- Clean up and concentrate analytes prior to analysis
- Change analyte chemistry irreversibly
- Replace chromatography completely
Correct Answer: Clean up and concentrate analytes prior to analysis
Q28. Which requirement must be demonstrated when preparing a calibration curve for quantitative assays?
- Detector response shows non-linearity across the range
- Linearity of detector response across the working concentration range
- Only one calibration point is necessary
- Calibration is unnecessary if standards are pure
Correct Answer: Linearity of detector response across the working concentration range
Q29. A stability-indicating method for a phytoconstituent should:
- Ignore degradation products
- Separate analyte from its degradation products
- Only quantify the main peak without resolution
- Rely solely on UV spectra without separation
Correct Answer: Separate analyte from its degradation products
Q30. In normal-phase TLC, polar compounds typically show which range of Rf values?
- High Rf values close to 1.0
- Low Rf values (e.g., <0.3)
- Rf values always equal to 0.5
- Rf values greater than solvent front
Correct Answer: Low Rf values (e.g., <0.3)
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