GPAT practice: Pharmaceutical analysis
20 original GPAT-style questions on titrimetry, UV-Vis and IR spectroscopy, HPLC basics and analytical method validation with answers and explanations. Tap an option to check your answer, or open "Show answer".
1. Which substance is commonly used as a primary standard to standardise hydrochloric acid?
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Answer: C — A primary standard is pure, stable and non-hygroscopic with a known composition; anhydrous sodium carbonate suits acid standardisation. NaOH absorbs water and CO2, so it is a secondary standard.
2. Titration of a weak acid with a strong base is best performed with which indicator?
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Answer: C — The equivalence point lies in the basic range, matching phenolphthalein (about pH 8.3–10).
3. In non-aqueous titration of weakly basic drugs, the usual titrant and solvent are
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Answer: A — Glacial acetic acid is a protogenic solvent that enhances the basicity of weak bases, and perchloric acid is the strongest acid in it. Crystal violet is a common indicator.
4. In the EDTA titration of calcium and magnesium (water hardness), the buffer and indicator used are typically
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Answer: B — EBT works at about pH 10, where the metal–EBT complex is wine red and free EBT is blue; the colour change marks the end point.
5. EDTA forms complexes with most metal ions in the ratio
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Answer: A — EDTA is hexadentate and binds metal ions in a 1 : 1 ratio irrespective of charge, which simplifies calculations.
6. Potassium permanganate titrations are generally carried out in the presence of
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Answer: B — Dilute sulphuric acid supplies the needed H+ without being oxidised. Chloride in HCl is oxidised by permanganate and gives an error. KMnO4 is self-indicating.
7. In iodometric titration of liberated iodine with sodium thiosulphate, starch indicator is added
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Answer: B — Adding starch early forms a stable iodine–starch complex that is slow to release iodine; adding it near the end point gives a sharp blue-to-colourless change.
8. A solution transmits 10 % of the incident light at a wavelength. Its absorbance is
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Answer: B — A = 2 − log10(%T) = 2 − 1 = 1.
9. Which factor causes a real deviation from the Beer–Lambert law?
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Answer: B — At high concentrations interactions between molecules change the absorptivity, so absorbance is no longer linear with concentration. Polychromatic light (instrumental) and association or dissociation of the analyte (chemical) cause apparent, not real, deviations.
10. A shift of the absorption maximum to a longer wavelength is called
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Answer: C — Bathochromic (red) shift is toward longer wavelength; hypsochromic is toward shorter wavelength. Hyper- and hypochromic describe intensity changes.
11. Which of the following is an auxochrome?
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Answer: A — An auxochrome has non-bonding electrons and itself does not absorb in the near UV, but modifies the absorption of a chromophore. The other groups are chromophores.
12. The carbonyl (C=O) stretching vibration typically appears in the IR spectrum near
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Answer: C — C=O stretching gives a strong band around 1650–1800 cm⁻¹; 3300 cm⁻¹ is O–H/N–H and 2200 cm⁻¹ the C≡C/C≡N region.
13. Potassium bromide is used for preparing pellets for IR spectroscopy because it
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Answer: A — KBr does not absorb in the mid-IR range, so only the sample bands appear. It is hygroscopic, so moisture can add a spurious O–H band.
14. In reversed-phase HPLC, which statement is correct?
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Answer: B — The non-polar stationary phase retains hydrophobic analytes, so more polar compounds elute first.
15. In an HPLC run the retention time of an analyte is 6.0 min and the column dead time is 2.0 min. The retention factor (k′) is
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Answer: B — k′ = (tR − t0)/t0 = (6 − 2)/2 = 2.0.
16. Which system suitability parameter describes peak symmetry?
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Answer: B — The tailing (or asymmetry) factor measures symmetry. Plates indicate column efficiency, resolution separation of two peaks, and capacity factor retention.
17. In method validation, 'accuracy' means
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Answer: B — Accuracy is closeness to the true value. Option A is precision, C specificity and D robustness.
18. Intermediate precision differs from repeatability in that it
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Answer: B — Repeatability uses the same conditions over a short interval; intermediate precision adds within-laboratory variations; reproducibility is between laboratories.
19. Linearity of an analytical procedure is demonstrated by
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Answer: A — Linearity is checked with a series of concentrations, usually evaluated by regression (slope, intercept, correlation coefficient and residuals). Q2(R2) covers this under "Range", as the linear response of the calibration model.
20. The quantitation limit of an analytical procedure is the
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Answer: B — The detection limit is the lowest amount that can be detected, whereas the quantitation limit requires acceptable precision and accuracy.