Controlling impurities in pharmaceutical substances is a critical function of quality control, directly impacting the safety and efficacy of medicines. For B.Pharm students, a deep understanding of the various sources of impurities and the principles behind pharmacopoeial limit tests is fundamental. This quiz covers the origins of impurities and the specific methodologies for the limit tests of chloride, sulphate, iron, arsenic, lead, and heavy metals.
- Limit tests are designed to:
- Precisely quantify the amount of impurity
- Identify and control small quantities of impurities
- Determine the active ingredient’s potency
- Identify the drug’s functional groups
- The limit test for chlorides is based on the reaction of soluble chlorides with:
- Barium chloride
- Silver nitrate
- Nitric acid
- Ammonia solution
- In the limit test for chlorides, the opalescence produced is due to the formation of:
- Silver chloride
- Barium sulphate
- Ferrous thioglycollate
- Lead sulphide
- The Gutzeit apparatus is used for the limit test of which impurity?
- Iron
- Lead
- Chloride
- Arsenic
- The limit test for iron relies on the formation of a purple color with which reagent?
- Citric acid
- Ammonia
- Thioglycollic acid
- Hydrochloric acid
- In the limit test for sulphates, the turbidity is produced by the formation of:
- Barium chloride
- Barium sulphate
- Lead sulphate
- Sodium sulphate
- Why is dilute nitric acid added in the limit test for chlorides?
- To act as a catalyst
- To provide an alkaline medium
- To prevent the precipitation of other acid radicals like phosphate
- To develop the color
- Which of the following can be a source of impurities in a pharmaceutical substance?
- Raw materials
- Manufacturing process
- Storage conditions
- All of the above
- The limit test for arsenic is based on the conversion of arsenic into which gas?
- Arsenic trioxide
- Arsine gas (AsH₃)
- Arsenic pentoxide
- Arsenous acid
- In the limit test for heavy metals, the precipitate formed is typically a:
- Sulphate
- Chloride
- Sulphide
- Nitrate
- What is the role of citric acid in the limit test for iron?
- To act as an oxidizing agent
- To form a colored complex with iron
- To prevent the precipitation of iron by ammonia
- To provide an acidic medium
- The opalescence or turbidity in a limit test is compared with a:
- Blank solution
- Standard solution
- Test solution from a different batch
- Solvent
- Why is dilute hydrochloric acid added in the limit test for sulphates?
- To make the solution alkaline
- To prevent the precipitation of other acid radicals like sulphite and phosphate
- To increase the solubility of barium sulphate
- To act as a catalyst
- The stain produced on the mercuric chloride paper in the arsenic limit test is:
- Blue
- Yellow
- Green
- Purple
- The limit test for lead is based on the reaction of lead with:
- Thioglycollic acid
- Potassium cyanide
- Dithizone
- Silver nitrate
- Impurities that arise from the vessels and equipment used during manufacturing are a type of impurity from the:
- Raw materials
- Manufacturing process
- Storage conditions
- Formulation process
- A modified limit test is sometimes required for:
- Highly pure substances
- Colored substances
- Volatile substances
- Gaseous substances
- In the limit test for sulphates, barium chloride reagent contains a small amount of ______ to stabilize the turbidity.
- Ethanol
- Potassium sulphate
- Glycerin
- Hydrochloric acid
- The official book that prescribes the standards and limit tests for impurities is the:
- Dictionary
- Pharmacopoeia
- Formulary
- Textbook
- Which reagent is used to precipitate heavy metals as sulphides in the limit test?
- Hydrogen sulphide or Sodium sulphide
- Hydrogen chloride
- Nitric acid
- Ammonium chloride
- In the arsenic limit test, what is the role of stannous chloride?
- To act as an oxidizing agent
- To ensure the complete reduction of arsenic to arsine gas
- To produce the color
- To absorb the gas
- The Nessler’s cylinders used for limit tests are matched flat-bottomed tubes made of:
- Plastic
- Porcelain
- Glass
- Metal
- If the opalescence in the test solution is less than the standard solution in the chloride limit test, the sample:
- Passes the test
- Fails the test
- Needs to be re-tested
- Is of high purity
- Which of the following is an example of an impurity arising from atmospheric contamination?
- Unreacted starting material
- Carbon dioxide
- A catalyst
- A solvent
- The principle of the limit test for lead is:
- Precipitation
- Color comparison of a complex
- Gas formation
- Turbidity measurement
- The purple color in the limit test for iron is due to the formation of:
- Ferric thioglycollate
- Ferrous thioglycollate
- Ferrous hydroxide
- Ferric citrate
- Why is the observation in limit tests made by viewing the Nessler’s cylinders vertically?
- It is more convenient.
- To observe the color or turbidity against a white or black background through a greater depth of liquid.
- To prevent the escape of gas.
- To measure the volume accurately.
- In the limit test for heavy metals, the color of the sulphide precipitate is generally:
- White
- Yellow
- Brownish/Black
- Blue
- Reagents used during the manufacturing process can be a source of impurity if they are not:
- Completely removed from the final product
- Highly colored
- Volatile
- Expensive
- What is the function of potassium iodide in the Gutzeit test for arsenic?
- To act as a reducing agent
- To act as an oxidizing agent
- To absorb moisture
- To form a complex
- The limit test for sulphate is essentially a test for:
- Solubility
- Precipitation
- Turbidity comparison
- Color comparison
- An impurity can be defined as any substance in a pharmaceutical product that is not the:
- Excipient
- Solvent
- Active pharmaceutical ingredient (API) or an intended excipient
- Coloring agent
- The reaction in the limit test for chloride is a(n) ______ reaction.
- oxidation
- reduction
- precipitation
- hydrolysis
- To ensure a fair comparison in limit tests, the standard and test solutions must have the same:
- Volume
- Temperature
- Concentration of reagents
- All of the above
- The purpose of a limit test is to ensure that the amount of impurity is:
- Completely absent
- Below a certain specified limit
- Exactly equal to the standard
- Above a certain specified limit
- Which of the following is NOT a source of impurities?
- Method of manufacture
- Storage conditions
- Perfectly pure raw materials
- Atmospheric contamination
- The limit test for iron is carried out in a medium made alkaline by:
- Sodium hydroxide
- Ammonia
- Potassium carbonate
- Calcium hydroxide
- The principle of the limit test for heavy metals is the reaction between heavy metal ions and:
- Sulphide ions in an acidic medium
- Sulphide ions in an alkaline medium
- Chloride ions
- Nitrate ions
- In the limit test for arsenic, zinc and HCl are used to produce:
- Arsine gas
- Nascent hydrogen for reduction
- A colored complex
- An acidic environment
- A modified limit test for sulphates might be necessary if the substance is:
- An acid
- A base
- Highly soluble in water
- Alkaline and needs to be neutralized
- The term “opalescence” is associated with the limit test for:
- Sulphates
- Iron
- Chlorides
- Arsenic
- Impurities can affect a drug’s:
- Therapeutic efficacy
- Safety
- Stability
- All of the above
- The standard used in the limit test for lead is a dilute solution of:
- Lead nitrate
- Lead chloride
- Lead sulphate
- Lead acetate
- Which apparatus is essential for performing limit tests by visual comparison?
- Beaker
- Conical flask
- Nessler’s cylinder
- Volumetric flask
- What is the purpose of the cotton plug soaked in lead acetate in the Gutzeit apparatus?
- To absorb excess acid fumes
- To trap any hydrogen sulphide gas that may be produced
- To catalyze the reaction
- To detect the end of the reaction
- If the test solution produces less color than the standard solution in the limit test for iron, the sample:
- Fails the test
- Passes the test
- Is impure
- Requires re-testing
- The limit test for sulphate is based on a comparison of:
- Color
- Opalescence
- Turbidity
- Fluorescence
- An impurity resulting from the breakdown of the drug substance itself during storage is a:
- Manufacturing impurity
- Raw material impurity
- Degradation product
- Contaminant
- In the limit test for heavy metals, the pH is adjusted to around 3.5 using:
- Acetic acid and ammonia
- Hydrochloric acid
- A phosphate buffer
- An acetate buffer
- The overall principle of a limit test is to:
- Confirm the absence of impurities
- Ensure that unavoidable impurities are within acceptable safety limits
- Quantify all impurities present
- Identify the chemical structure of impurities
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
Mail- Sachin@pharmacyfreak.com