CWEA Laboratory Analyst Grade 3 Quality Control Exam with
Questions and Answers/Plus a Rationale Updated 2026 A+/Instant
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Table of Contents
•
1. Quality Assurance and Quality Control Principles
•
2. Calibration and Instrument Performance
•
3. Blanks, Duplicates, Spikes, and Laboratory Control Samples
•
4. Method Detection Limits and Quantitation Limits
•
5. Accuracy, Precision, Bias, and Statistical QC
•
6. Control Charts and Trend Analysis
•
7. Analytical Batches and QC Acceptance
•
8. Sample Handling, Preservation, and Integrity
•
9. Standards, Reagents, and Reference Materials
•
10. Data Review, Corrective Action, and Reporting
•
11. Proficiency Testing and Demonstration of Capability
•
12. Documentation, Audits, and Quality-System Compliance
, 1. A wastewater laboratory obtains an LCS recovery of 72% for an analyte with an
established acceptance range of 80–120%. The associated environmental samples
otherwise produce plausible results. What is the most defensible action?
A. Report all sample results because the environmental samples are plausible
B. Widen the LCS limits after reviewing the sample results
C. Investigate the failed LCS and determine the impact on the associated batch
before reporting
D. Delete the LCS result from the final data package
Answer: C [Investigate the failed LCS and determine the impact on the associated batch
before reporting]
Rationale: A failed LCS indicates that the analytical process may not have demonstrated
acceptable accuracy for the batch, so the laboratory must evaluate the failure and its impact
before reporting; simply accepting plausible samples, changing limits post hoc, or deleting
QC data compromises data validity.
2. During an ICP analysis, the initial calibration meets the laboratory's criteria, but the
continuing calibration verification at the end of the sequence is outside the
established acceptance range. What should the analyst do first?
A. Average the beginning and ending calibration results
B. Follow the method-specific CCV failure procedure and determine which results
are affected
C. Recalibrate only if sample results appear unusual
D. Substitute the initial calibration value for the CCV
Answer: B [Follow the method-specific CCV failure procedure and determine which results
are affected]
Rationale: A CCV verifies ongoing calibration performance, and a failure requires
documented evaluation and corrective action; averaging calibration checks or ignoring a
failure does not establish instrument control.
3. A laboratory analyst notices that three consecutive LCS recoveries are 116%, 118%,
and 119%, all technically within a 120% upper limit. What is the best quality-control
interpretation?
A. The results are automatically unacceptable
B. No review is necessary because every result passed
C. The pattern should be evaluated for a developing positive bias or trend
D. The acceptance range should immediately be narrowed
Answer: C [The pattern should be evaluated for a developing positive bias or trend]
Rationale: Statistical QC uses trends and patterns in addition to individual acceptance limits,
so repeated near-limit results can indicate emerging bias even when each result individually
passes; changing limits without evidence is inappropriate.
, 4. A laboratory receives a sample with a missing collection time even though holding-
time compliance depends on that information. What is the strongest QC response?
A. Estimate the collection time from the laboratory receipt time
B. Use the average collection time from previous samples
C. Document the deficiency and resolve sample acceptance or reporting according
to the laboratory's documented procedure
D. Report the result without qualification
Answer: C [Document the deficiency and resolve sample acceptance or reporting according
to the laboratory's documented procedure]
Rationale: Sample acceptance must be based on documented requirements and traceable
information rather than assumptions; reconstructing missing information without support
can invalidate holding-time determinations.
5. A matrix spike recovery is 58%, while the LCS recovery is 96% and the method blank
is acceptable. Which conclusion is most appropriate?
A. The entire analytical batch automatically fails
B. The instrument calibration must have failed
C. The low matrix-spike recovery may indicate matrix effects and should be
evaluated according to method requirements
D. The LCS result must be discarded
Answer: C [The low matrix-spike recovery may indicate matrix effects and should be
evaluated according to method requirements]
Rationale: An acceptable LCS with poor matrix-spike recovery can indicate sample-specific
matrix effects rather than general method failure; matrix-spike results assess performance in
the actual sample matrix and should be interpreted according to the applicable method.
6. Two duplicate wastewater results are 18.0 mg/L and 20.0 mg/L, with an established
RPD limit of 15%. What is the best conclusion?
A. The duplicate automatically passes because both results are close numerically
B. The duplicate fails because the RPD is approximately 10.5%, so the duplicate
actually passes
C. The duplicate fails because the absolute difference is 2.0 mg/L
D. Precision cannot be evaluated from duplicates
Answer: B [The duplicate fails because the RPD is approximately 10.5%, so the duplicate
actually passes]
Rationale: RPD is calculated as the absolute difference divided by the mean multiplied by
100, giving approximately 10.5%, which is below 15%; absolute difference alone is not the
specified acceptance statistic.
7. A laboratory's method blank contains an analyte at a concentration above the
laboratory's established blank acceptance criterion. What is the most appropriate
, response?
A. Subtract the blank concentration from every sample
B. Investigate the source of contamination and evaluate its effect on associated
samples
C. Report the samples because blanks are informational only
D. Replace the blank with a new result without documenting the failure
Answer: B [Investigate the source of contamination and evaluate its effect on associated
samples]
Rationale: A contaminated method blank can demonstrate contamination introduced during
preparation or analysis and may affect associated sample results; undocumented subtraction
or replacement does not correct the underlying QC problem.
8. An analyst prepares a calibration standard using a stock solution whose expiration
date has passed. What is the primary concern?
A. The standard concentration is guaranteed to be unchanged
B. The standard's validity and traceability are no longer assured under the
laboratory's established control system
C. Only the instrument response is affected
D. Expiration dates apply only to biological samples
Answer: B [The standard's validity and traceability are no longer assured under the
laboratory's established control system]
Rationale: Standards must be appropriately controlled, documented, and within established
validity periods unless a documented extension or verification procedure applies; otherwise
analytical traceability is compromised.
9. A laboratory wants to demonstrate that a newly assigned analyst can consistently
perform a wastewater method before analyzing compliance samples independently.
Which QC activity is most directly applicable?
A. Method blank analysis only
B. Documented demonstration of capability
C. Client complaint review
D. Instrument preventive maintenance
Answer: B [Documented demonstration of capability]
Rationale: Demonstration of capability establishes that an analyst can perform the method
successfully before independent routine testing; a blank or maintenance record does not
demonstrate analyst competence.
10. During review, an analyst discovers that a pipette calibration was overdue when
several samples were prepared. What is the most appropriate quality-system action?
A. Ignore the issue if sample results appear reasonable
B. Change the preparation dates
Questions and Answers/Plus a Rationale Updated 2026 A+/Instant
Download PDF
Table of Contents
•
1. Quality Assurance and Quality Control Principles
•
2. Calibration and Instrument Performance
•
3. Blanks, Duplicates, Spikes, and Laboratory Control Samples
•
4. Method Detection Limits and Quantitation Limits
•
5. Accuracy, Precision, Bias, and Statistical QC
•
6. Control Charts and Trend Analysis
•
7. Analytical Batches and QC Acceptance
•
8. Sample Handling, Preservation, and Integrity
•
9. Standards, Reagents, and Reference Materials
•
10. Data Review, Corrective Action, and Reporting
•
11. Proficiency Testing and Demonstration of Capability
•
12. Documentation, Audits, and Quality-System Compliance
, 1. A wastewater laboratory obtains an LCS recovery of 72% for an analyte with an
established acceptance range of 80–120%. The associated environmental samples
otherwise produce plausible results. What is the most defensible action?
A. Report all sample results because the environmental samples are plausible
B. Widen the LCS limits after reviewing the sample results
C. Investigate the failed LCS and determine the impact on the associated batch
before reporting
D. Delete the LCS result from the final data package
Answer: C [Investigate the failed LCS and determine the impact on the associated batch
before reporting]
Rationale: A failed LCS indicates that the analytical process may not have demonstrated
acceptable accuracy for the batch, so the laboratory must evaluate the failure and its impact
before reporting; simply accepting plausible samples, changing limits post hoc, or deleting
QC data compromises data validity.
2. During an ICP analysis, the initial calibration meets the laboratory's criteria, but the
continuing calibration verification at the end of the sequence is outside the
established acceptance range. What should the analyst do first?
A. Average the beginning and ending calibration results
B. Follow the method-specific CCV failure procedure and determine which results
are affected
C. Recalibrate only if sample results appear unusual
D. Substitute the initial calibration value for the CCV
Answer: B [Follow the method-specific CCV failure procedure and determine which results
are affected]
Rationale: A CCV verifies ongoing calibration performance, and a failure requires
documented evaluation and corrective action; averaging calibration checks or ignoring a
failure does not establish instrument control.
3. A laboratory analyst notices that three consecutive LCS recoveries are 116%, 118%,
and 119%, all technically within a 120% upper limit. What is the best quality-control
interpretation?
A. The results are automatically unacceptable
B. No review is necessary because every result passed
C. The pattern should be evaluated for a developing positive bias or trend
D. The acceptance range should immediately be narrowed
Answer: C [The pattern should be evaluated for a developing positive bias or trend]
Rationale: Statistical QC uses trends and patterns in addition to individual acceptance limits,
so repeated near-limit results can indicate emerging bias even when each result individually
passes; changing limits without evidence is inappropriate.
, 4. A laboratory receives a sample with a missing collection time even though holding-
time compliance depends on that information. What is the strongest QC response?
A. Estimate the collection time from the laboratory receipt time
B. Use the average collection time from previous samples
C. Document the deficiency and resolve sample acceptance or reporting according
to the laboratory's documented procedure
D. Report the result without qualification
Answer: C [Document the deficiency and resolve sample acceptance or reporting according
to the laboratory's documented procedure]
Rationale: Sample acceptance must be based on documented requirements and traceable
information rather than assumptions; reconstructing missing information without support
can invalidate holding-time determinations.
5. A matrix spike recovery is 58%, while the LCS recovery is 96% and the method blank
is acceptable. Which conclusion is most appropriate?
A. The entire analytical batch automatically fails
B. The instrument calibration must have failed
C. The low matrix-spike recovery may indicate matrix effects and should be
evaluated according to method requirements
D. The LCS result must be discarded
Answer: C [The low matrix-spike recovery may indicate matrix effects and should be
evaluated according to method requirements]
Rationale: An acceptable LCS with poor matrix-spike recovery can indicate sample-specific
matrix effects rather than general method failure; matrix-spike results assess performance in
the actual sample matrix and should be interpreted according to the applicable method.
6. Two duplicate wastewater results are 18.0 mg/L and 20.0 mg/L, with an established
RPD limit of 15%. What is the best conclusion?
A. The duplicate automatically passes because both results are close numerically
B. The duplicate fails because the RPD is approximately 10.5%, so the duplicate
actually passes
C. The duplicate fails because the absolute difference is 2.0 mg/L
D. Precision cannot be evaluated from duplicates
Answer: B [The duplicate fails because the RPD is approximately 10.5%, so the duplicate
actually passes]
Rationale: RPD is calculated as the absolute difference divided by the mean multiplied by
100, giving approximately 10.5%, which is below 15%; absolute difference alone is not the
specified acceptance statistic.
7. A laboratory's method blank contains an analyte at a concentration above the
laboratory's established blank acceptance criterion. What is the most appropriate
, response?
A. Subtract the blank concentration from every sample
B. Investigate the source of contamination and evaluate its effect on associated
samples
C. Report the samples because blanks are informational only
D. Replace the blank with a new result without documenting the failure
Answer: B [Investigate the source of contamination and evaluate its effect on associated
samples]
Rationale: A contaminated method blank can demonstrate contamination introduced during
preparation or analysis and may affect associated sample results; undocumented subtraction
or replacement does not correct the underlying QC problem.
8. An analyst prepares a calibration standard using a stock solution whose expiration
date has passed. What is the primary concern?
A. The standard concentration is guaranteed to be unchanged
B. The standard's validity and traceability are no longer assured under the
laboratory's established control system
C. Only the instrument response is affected
D. Expiration dates apply only to biological samples
Answer: B [The standard's validity and traceability are no longer assured under the
laboratory's established control system]
Rationale: Standards must be appropriately controlled, documented, and within established
validity periods unless a documented extension or verification procedure applies; otherwise
analytical traceability is compromised.
9. A laboratory wants to demonstrate that a newly assigned analyst can consistently
perform a wastewater method before analyzing compliance samples independently.
Which QC activity is most directly applicable?
A. Method blank analysis only
B. Documented demonstration of capability
C. Client complaint review
D. Instrument preventive maintenance
Answer: B [Documented demonstration of capability]
Rationale: Demonstration of capability establishes that an analyst can perform the method
successfully before independent routine testing; a blank or maintenance record does not
demonstrate analyst competence.
10. During review, an analyst discovers that a pipette calibration was overdue when
several samples were prepared. What is the most appropriate quality-system action?
A. Ignore the issue if sample results appear reasonable
B. Change the preparation dates
