Sources of errors in analytical procedures MCQs With Answer

Sources of errors in analytical procedures MCQs With Answer

This concise introduction explains common sources of errors in analytical procedures relevant to B. Pharm students. It covers key concepts such as systematic error, random error, gross error, bias, precision, accuracy, calibration, instrument drift, sampling, sample preparation, contamination, matrix effects, operator error, and environmental influences (temperature, humidity). Understanding these error sources helps in method validation, troubleshooting, improving sensitivity, specificity, and ensuring reliable assay results in pharmaceutical analysis. Practical steps—standardization, proper pipetting, use of blanks, and routine maintenance—minimize errors. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which type of error causes consistent deviation from the true value and affects accuracy?

• Random error
• Systematic error
• Gross error
• Sampling error

Correct Answer: Systematic error

Q2. Which source of error is most commonly caused by improper pipetting technique?

• Instrument drift
• Operator error
• Matrix effect
• Calibration error

Correct Answer: Operator error

Q3. What is the primary characteristic of random error in analytical measurements?

• It shifts all results by a fixed amount
• It is unpredictable and affects precision
• It only occurs during calibration
• It can be completely eliminated by averaging

Correct Answer: It is unpredictable and affects precision

Q4. Which of the following is a gross error?

• Small instrument noise
• Contamination leading to a wildly incorrect result
• Systematic bias from standard impurity
• Normal matrix variability

Correct Answer: Contamination leading to a wildly incorrect result

Q5. Calibration errors mostly lead to which analytical problem?

• Reduced method sensitivity
• Increased random scatter
• Systematic bias in reported concentrations
• Improved accuracy

Correct Answer: Systematic bias in reported concentrations

Q6. Which environmental factor can cause instrument drift and affect reproducibility?

• Operator’s skill level
• Ambient temperature fluctuations
• Sample viscosity only
• Color of the laboratory walls

Correct Answer: Ambient temperature fluctuations

Q7. Matrix effects in analytical procedures refer to:

• Errors from using incorrect units
• Interferences from sample components affecting measurement
• Queue of samples awaiting analysis
• Only instrumental baseline noise

Correct Answer: Interferences from sample components affecting measurement

Q8. Which practice best reduces random error in replicate measurements?

• Using contaminated reagents
• Averaging multiple independent measurements
• Changing the method during analysis
• Ignoring outliers without assessment

Correct Answer: Averaging multiple independent measurements

Q9. Which quality control tool helps detect systematic errors over time?

• Blank sample only
• Control chart (Shewhart chart)
• Single calibration check once a year
• Random spot checks

Correct Answer: Control chart (Shewhart chart)

Q10. Contamination of reagents most directly affects which analytical attribute?

• Precision only
• Accuracy and trueness
• Linear range expansion
• Instrument calibration schedule

Correct Answer: Accuracy and trueness

Q11. In method validation, which error source is evaluated by recovery studies?

• Instrumental noise
• Trueness and matrix interference
• Analyst fatigue
• Pipette calibration only

Correct Answer: Trueness and matrix interference

Q12. Which action is most effective to minimize volumetric error when preparing standards?

• Use visibly dirty glassware
• Pre-rinse glassware with solvent and use calibrated volumetric flasks
• Estimate volumes by eye
• Use different pipettes for each transfer without calibration

Correct Answer: Pre-rinse glassware with solvent and use calibrated volumetric flasks

Q13. Baseline noise in an instrument typically contributes to:

• Systematic bias only
• Random error and reduced sensitivity
• Improved accuracy
• Elimination of matrix effects

Correct Answer: Random error and reduced sensitivity

Q14. Which type of blank helps identify contamination introduced during sample preparation?

• Method blank
• Instrument blank only
• Calibration blank that is never processed
• Standard solution

Correct Answer: Method blank

Q15. Drift in instrument response over time is best checked by:

• Running a single calibration at the start of the day
• Periodic analysis of calibration check standards during the run
• Changing operators frequently
• Using unverified reagents

Correct Answer: Periodic analysis of calibration check standards during the run

Q16. Which error source is most specifically related to incorrect standard purity?

• Random error due to noise
• Systematic bias from calibration standards
• Environmental humidity only
• Operator transcription error

Correct Answer: Systematic bias from calibration standards

Q17. Which of the following indicates poor precision?

• Results with high variability (high relative standard deviation)
• Results consistently near the true value
• Single measurement matching expected value
• Low background noise

Correct Answer: Results with high variability (high relative standard deviation)

Q18. Cross-contamination between samples can be minimized by:

• Re-using the same pipette tip for all samples
• Using disposable tips and proper cleaning procedures
• Skipping blank samples
• Always diluting samples with contaminated solvent

Correct Answer: Using disposable tips and proper cleaning procedures

Q19. What is the consequence of using expired reagents in an assay?

• No impact if the instrument is calibrated
• Potential systematic errors and reduced assay reliability
• Only increases precision
• Improves method selectivity

Correct Answer: Potential systematic errors and reduced assay reliability

Q20. Which parameter specifically assesses the closeness of measured values to the true value?

• Precision
• Trueness (or accuracy)
• Resolution
• Throughput

Correct Answer: Trueness (or accuracy)

Q21. Why is replication important when identifying random error?

• It eliminates systematic bias completely
• It allows estimation of variability and computation of standard deviation
• It replaces the need for calibration
• It ensures operator error persists

Correct Answer: It allows estimation of variability and computation of standard deviation

Q22. Which practice helps detect matrix interferences in an assay?

• Using only water as a solvent for all samples
• Performing standard addition experiments
• Running fewer calibration points
• Analyzing one sample without replicates

Correct Answer: Performing standard addition experiments

Q23. What does limit of detection (LOD) relate to in terms of error?

• The maximum concentration that causes systematic error
• The lowest analyte level distinguishable from background noise
• A measure of operator competence
• Only relevant to chromatography columns

Correct Answer: The lowest analyte level distinguishable from background noise

Q24. Transcription errors in recording results are classified as:

• Instrumental random error
• Human or clerical errors leading to gross or systematic mistakes
• Type of matrix effect
• Part of method validation criteria

Correct Answer: Human or clerical errors leading to gross or systematic mistakes

Q25. Which step in sample preparation commonly introduces variability if not standardized?

• Consistent vortexing, filtration, and dilution procedures
• Using identical containers for all samples
• Ignoring sample homogeneity
• Standardizing temperature and time of processing

Correct Answer: Ignoring sample homogeneity

Q26. How does poor instrument maintenance contribute to analytical errors?

• It only affects laboratory aesthetics
• It can cause baseline instabilities, drift, and increased random error
• It guarantees better precision
• It reduces need for calibration

Correct Answer: It can cause baseline instabilities, drift, and increased random error

Q27. Interference from co-eluting substances in chromatography is an example of:

• Sampling error only
• Specificity/selectivity problem causing systematic bias
• Improved method trueness
• Instrumental precision enhancement

Correct Answer: Specificity/selectivity problem causing systematic bias

Q28. Which control helps confirm the absence of contamination introduced during analysis?

• Calibration curve only
• Reagent blank or procedural blank
• Control chart without blanks
• Standard addition without blanks

Correct Answer: Reagent blank or procedural blank

Q29. Reproducibility between different laboratories is most affected by:

• Universal operator skill levels
• Differences in method implementation, instruments, and standards
• Using the same batch of filter paper only
• Laboratory décor

Correct Answer: Differences in method implementation, instruments, and standards

Q30. Which corrective action addresses a persistent systematic bias revealed by quality control samples?

• Ignore the bias and continue
• Investigate calibration, standards, method, and instrument performance and recalibrate or repair as needed
• Reduce the number of QC samples
• Only increase sample throughput

Correct Answer: Investigate calibration, standards, method, and instrument performance and recalibrate or repair as needed

G S Sachin

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