Chromatography (GLC TLC) MCQ Quiz | Analytical Toxicology

1. In Thin-Layer Chromatography (TLC), the separation of components is primarily based on which principle?

• Adsorption
• Partition
• Ion-exchange
• Size exclusion

2. What is the mobile phase in Gas-Liquid Chromatography (GLC)?

• A liquid solvent
• An inert gas
• A solid adsorbent
• An aqueous buffer

3. The Retention Factor (Rf value) in TLC is calculated as:

• Distance travelled by solvent / Distance travelled by solute
• Distance travelled by solute / Distance travelled by solvent
• Distance travelled by solute x Distance travelled by solvent
• Total length of the plate / Distance travelled by solute

4. Which GLC detector is particularly sensitive for detecting organophosphate and nitrogen-containing pesticides?

• Flame Ionization Detector (FID)
• Thermal Conductivity Detector (TCD)
• Nitrogen-Phosphorus Detector (NPD)
• Electron Capture Detector (ECD)

5. A common method for visualizing colorless compounds on a TLC plate is:

• Exposure to iodine vapor
• Viewing under UV light (if fluorescent)
• Spraying with a chemical reagent like ninhydrin
• All of the above

6. In a GLC chromatogram, the ‘retention time’ is used for:

• Qualitative identification of a compound
• Quantitative determination of a compound
• Measuring the purity of the carrier gas
• Determining the molecular weight of a compound

7. Why is derivatization sometimes performed on a sample before GLC analysis?

• To increase the compound’s volatility
• To improve its thermal stability
• To enhance detector response
• All of the above

8. The most commonly used stationary phase in TLC for drug screening is:

• Silica gel
• Alumina
• Cellulose
• Polyamide

9. For a substance to be analyzed by GLC, it must be:

• Soluble in water
• Volatile and thermally stable
• A large, non-polar molecule
• Solid at room temperature

10. A Flame Ionization Detector (FID) in GLC primarily responds to:

• Halogenated compounds
• Inorganic gases
• Organic compounds containing C-H bonds
• Water and carbon dioxide

11. In a toxicology lab, TLC is most commonly used for:

• Precise quantification of blood alcohol
• Rapid qualitative screening of urine for drugs of abuse
• Identification of heavy metals like lead and mercury
• Analysis of toxic gases from a fire

12. Which of the following factors affects the Rf value in TLC?

• The composition of the mobile phase
• The activity of the stationary phase
• Temperature and chamber saturation
• All of the above

13. Which type of GLC column generally provides higher resolution and efficiency?

• Packed column
• Capillary (open-tubular) column
• Both are equally efficient
• Adsorption column

14. The Electron Capture Detector (ECD) in GLC is highly sensitive to which class of compounds?

• Alcohols like ethanol
• Simple hydrocarbons
• Halogenated compounds like pesticides and PCBs
• Amines

15. In normal-phase TLC with a silica gel plate (polar), a very polar compound developed with a non-polar solvent will exhibit:

• A high Rf value
• A low Rf value
• An Rf value close to 1.0
• No movement from the origin (Rf = 0)

16. Which of the following is commonly used as a carrier gas in GLC?

• Oxygen
• Carbon dioxide
• Nitrogen
• Methane

17. Headspace GLC is the preferred method for analyzing:

• Volatile substances like ethanol in blood
• Non-volatile drugs like paracetamol
• Heavy metals in urine
• High molecular weight proteins

18. An advantage of TLC over GLC is its:

• Higher sensitivity and resolution
• Better suitability for quantitative analysis
• Simplicity, low cost, and ability to run multiple samples
• Ability to analyze thermally unstable compounds without derivatization

19. In a GLC analysis of a mixture, the compound that elutes first generally has the:

• Highest boiling point
• Lowest boiling point and/or weakest interaction with the stationary phase
• Highest molecular weight
• Greatest polarity

20. The plot of detector response versus time in GLC is called a:

• Spectrogram
• Chromatogram
• Zymogram
• Elution profile

21. Ninhydrin spray is used in TLC to specifically detect which class of compounds?

• Alkaloids
• Barbiturates
• Cannabinoids
• Amino acids and primary/secondary amines

22. In GLC, ‘temperature programming’ refers to systematically:

• Increasing the column temperature during a run
• Keeping the injector port at a constant high temperature
• Cooling the detector to improve sensitivity
• Maintaining the entire system at body temperature

23. What is the main purpose of the oven in a Gas Chromatograph?

• To house and control the temperature of the column
• To pre-heat the carrier gas
• To burn the sample after detection
• To cool the injector port

24. In toxicology, liquid-liquid extraction is a common sample preparation step before GLC to:

• Isolate the drug/toxin from the biological matrix
• Make the sample more volatile
• Directly inject blood into the GLC
• Sterilize the sample

25. A significant limitation of TLC as a standalone identification technique in forensic toxicology is its:

• High operational cost
• Requirement for large sample volumes
• Lower specificity compared to confirmatory methods like GC-MS
• Inability to separate polar compounds