Pesticide Residue Analysis: Organophosphorus and organochlorine methods in foods MCQs With Answer

Pesticide Residue Analysis: Organophosphorus and organochlorine methods in foods MCQs With Answer

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Pesticide Residue Analysis: Organophosphorus and organochlorine methods in foods provides focused MCQs to help M.Pharm students deepen understanding of analytical strategies used to detect pesticide residues in food matrices. This set emphasizes practical aspects: sample preparation (QuEChERS, Soxhlet, GPC), cleanup sorbents (PSA, C18, GCB, florisil), extraction solvents, chromatographic choices (GC, LC), detectors (ECD, NPD, FPD, MS), derivatization, and validation parameters (LOD/LOQ, recovery, matrix effects). Questions also cover regulatory context (MRLs, Codex) and the physicochemical properties of organophosphorus and organochlorine pesticides that influence method selection. These MCQs are designed for exam preparation and to reinforce method selection and troubleshooting in real laboratory workflows.

Q1. Which sample preparation method is most widely used today for multi-residue analysis of organophosphorus and organochlorine pesticides in fruits and vegetables due to speed and minimal solvent use?

  • Classical Soxhlet extraction with hexane
  • QuEChERS extraction using acetonitrile and salts
  • Supercritical fluid extraction with CO2
  • Liquid–liquid extraction with dichloromethane

Correct Answer: QuEChERS extraction using acetonitrile and salts

Q2. Which dispersive solid-phase extraction sorbent is primarily used in QuEChERS cleanup to remove fatty acids and some organic acids from food extracts?

  • Graphitized carbon black (GCB)
  • Primary secondary amine (PSA)
  • Florisil
  • Silica gel

Correct Answer: Primary secondary amine (PSA)

Q3. For gas chromatographic detection of chlorinated pesticides, which detector is most sensitive to electron-capturing organochlorines?

  • Flame ionization detector (FID)
  • Electron capture detector (ECD)
  • Nitrogen–phosphorus detector (NPD)
  • Photodiode array detector (PDA)

Correct Answer: Electron capture detector (ECD)

Q4. Which GC detector is specially designed to give enhanced sensitivity for nitrogen- and phosphorus-containing pesticides?

  • Electron capture detector (ECD)
  • Flame photometric detector (FPD)
  • Nitrogen–phosphorus detector (NPD)
  • Mass spectrometer (MS) with EI

Correct Answer: Nitrogen–phosphorus detector (NPD)

Q5. When using GC–MS for trace quantitation of pesticides, which acquisition mode increases sensitivity and selectivity by monitoring a few target ions?

  • Full-scan MS
  • Selected ion monitoring (SIM)
  • Time-of-flight (TOF) scanning
  • Total ion chromatogram integration

Correct Answer: Selected ion monitoring (SIM)

Q6. For thermally labile organophosphorus pesticides that degrade in GC, which analytical technique is preferable for direct analysis without derivatization?

  • GC–ECD with cold on-column injection
  • LC–MS/MS with electrospray ionization
  • Pyrolysis GC–MS
  • TLC followed by densitometry

Correct Answer: LC–MS/MS with electrospray ionization

Q7. Which derivatization reagent is commonly used to silylate polar pesticide functional groups (e.g., –OH, –COOH) to improve volatility for GC analysis?

  • N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA)
  • Dansyl chloride
  • Tetrabutylammonium fluoride (TBAF)
  • 2,4-dinitrophenylhydrazine (DNPH)

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

Q8. Which cleanup technique is especially effective at removing high-molecular-weight lipids from fatty food matrices prior to pesticide analysis?

  • Solid-phase extraction with PSA only
  • Gel permeation chromatography (GPC)
  • Graphitized carbon black (GCB) dispersive cleanup
  • Liquid–liquid partitioning into methanol

Correct Answer: Gel permeation chromatography (GPC)

Q9. What is the main purpose of using matrix-matched calibration curves in pesticide residue analysis?

  • To reduce instrument maintenance time
  • To correct for matrix-induced signal suppression or enhancement
  • To eliminate the need for internal standards
  • To increase solvent evaporation rate during sample prep

Correct Answer: To correct for matrix-induced signal suppression or enhancement

Q10. Which internal standard type provides the most reliable compensation for losses and matrix effects in quantitative pesticide analysis by MS?

  • Structural analog without isotopes
  • Isotopically labeled (e.g., 13C or 15N) pesticide analogs
  • External calibration standard in solvent
  • Non-volatile polymer standard

Correct Answer: Isotopically labeled (e.g., 13C or 15N) pesticide analogs

Q11. Which international body publishes maximum residue limits (MRLs) used as global reference for food safety?

  • World Health Organization (WHO)
  • Codex Alimentarius Commission
  • International Organization for Standardization (ISO)
  • Food and Agriculture Organization (FAO) only

Correct Answer: Codex Alimentarius Commission

Q12. Which analytical parameter defines the lowest concentration of a pesticide that can be reliably distinguished from background noise?

  • Limit of quantitation (LOQ)
  • Limit of detection (LOD)
  • Maximum residue limit (MRL)
  • Recovery percentage

Correct Answer: Limit of detection (LOD)

Q13. The primary mechanism of acute toxicity for many organophosphorus pesticides is:

  • Inhibition of cytochrome P450 enzymes
  • Antagonism of GABA receptors
  • Inhibition of acetylcholinesterase (AChE)
  • Activation of mitochondrial uncoupling

Correct Answer: Inhibition of acetylcholinesterase (AChE)

Q14. For exhaustive extraction of nonpolar organochlorine pesticides from high-fat samples, which solvent or solvent mix is traditionally preferred in Soxhlet extraction?

  • Methanol:water (80:20)
  • Hexane:acetone (1:1)
  • Acetonitrile alone
  • Isopropanol

Correct Answer: Hexane:acetone (1:1)

Q15. To minimize degradation of pesticide residues between sampling and analysis, which storage practice is recommended?

  • Store extracts at room temperature in daylight
  • Keep samples frozen (e.g., −20 °C) in the dark
  • Acidify samples to pH 2 and store warm
  • Dry samples and store at 40 °C

Correct Answer: Keep samples frozen (e.g., −20 °C) in the dark

Q16. Which dispersive sorbent is best used to remove pigments and planar interferences from extracts prior to pesticide analysis?

  • C18 silica
  • Primary secondary amine (PSA)
  • Graphitized carbon black (GCB)
  • Alumina-neutral

Correct Answer: Graphitized carbon black (GCB)

Q17. In method validation for pesticide residue analysis, which metric is most commonly used to express method accuracy?

  • Limit of detection (LOD)
  • Percent recovery from spiked samples
  • Signal-to-noise ratio (S/N)
  • Retention time reproducibility

Correct Answer: Percent recovery from spiked samples

Q18. Which physicochemical characteristic of organochlorine pesticides primarily explains their environmental persistence and tendency to bioaccumulate?

  • High water solubility and rapid hydrolysis
  • High vapor pressure and low Koc
  • High lipophilicity (high log Kow) and chemical stability
  • High reactivity with sunlight leading to quick breakdown

Correct Answer: High lipophilicity (high log Kow) and chemical stability

Q19. In GC–MS pesticide analysis, which ionization technique is most commonly used for creating reproducible fragmentation patterns for library matching of organochlorines and organophosphates?

  • Electrospray ionization (ESI)
  • Atmospheric pressure chemical ionization (APCI)
  • Electron ionization (EI)
  • MALDI

Correct Answer: Electron ionization (EI)

Q20. In the original QuEChERS partitioning step, which salt combination is typically used to induce phase separation between aqueous sample and acetonitrile extract?

  • Sodium acetate and ammonium sulfate
  • Magnesium sulfate (MgSO4) and sodium chloride (NaCl)
  • Potassium carbonate and sodium bicarbonate
  • Calcium chloride and magnesium chloride

Correct Answer: Magnesium sulfate (MgSO4) and sodium chloride (NaCl)

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