The Chromatogram Passed SST, but Can You Trust the Result? A Practical Guide for Pharmaceutical QC Analysts

Introduction

In a pharmaceutical quality control laboratory, passing system suitability testing (SST) is an important step before analysing samples by HPLC. It helps demonstrate that the chromatographic system is performing acceptably for the intended analytical procedure.

But here is a question every QC analyst should ask:

If system suitability passes, does that automatically mean the sample result is correct?

No. A passing SST result does not, by itself, prove that every sample result is accurate, that the sample was prepared correctly, or that the chromatogram has been interpreted properly.

Imagine that an analyst completes an assay of a finished pharmaceutical product. The standard injections meet the approved system suitability criteria. The chromatogram looks normal at first glance, and the calculated assay falls within the specification.

The analyst is ready to submit the result.

However, during the final review, another analyst notices that the sample peak area is unusually low compared with previous batches. The system suitability results are acceptable, but something does not look right.

Should the result be accepted simply because SST passed?

This is where scientific judgment, careful chromatogram review, and good documentation become important.

1. What Does Passing System Suitability Actually Tell Us?

System suitability testing checks whether the chromatographic system meets predefined performance requirements for the analytical procedure.

Depending on the approved method, SST parameters may include:

• Resolution between specified peaks
• Tailing factor or peak symmetry
• Theoretical plate count
• Repeatability of replicate standard injections
• Other method-specific performance criteria

For example, an approved assay method may require the standard injection results to meet a defined percentage relative standard deviation (RSD), together with specified limits for tailing factor and plate count.

If all applicable criteria are met, the system has demonstrated the required performance for those checks.

However, SST does not automatically verify every part of the analytical process.

It may not reveal that:

• The sample was weighed incorrectly.
• The extraction was incomplete.
• The sample solution was prepared using the wrong dilution.
• A sample vial was labelled incorrectly.
• The sample solution degraded before injection.
• An integration setting was inappropriate for a particular chromatogram.
• The analyst used an incorrect calculation factor.

Therefore, SST passing is necessary when required by the method, but it is not a substitute for reviewing the complete analytical result.

The analyst must assess the result in the context of the approved method, sample preparation, raw data, calculations, and applicable acceptance criteria.

2. A Practical QC Scenario: Everything Passed, but Something Looks Different

Consider this hypothetical situation.

A QC analyst is testing a batch of tablets using a validated HPLC assay method.

The system suitability results meet the approved requirements. Standard injections are consistent, and the chromatographic system shows acceptable performance.

The sample assay is also within the approved specification.

During the data review, the reviewer notices three things:

1. The sample peak area is noticeably lower than expected from the available batch or historical trend information.
2. The sample chromatogram has a small change in baseline shape compared with the usual pattern.
3. The sample preparation record contains a dilution entry that needs clarification.

None of these observations alone proves that the result is wrong. Historical differences can occur for legitimate reasons, and a baseline change may not affect the result.

However, together, they provide a reason to review the data more carefully.

The correct response is not to reject the result automatically. It is also not to approve it merely because SST passed.

The analyst or reviewer should determine whether the observations have a scientifically justified explanation and whether the approved procedure was followed.

3. Seven Things to Review Before Accepting an HPLC Result

3.1 Review the sample preparation record

Start with the preparation steps, not just the chromatogram.

Check the sample weight, standard weight, volumetric flask sizes, dilution factors, extraction procedure, filtration requirements, and any other method-specific instructions.

Ask yourself:

• Was the correct sample quantity taken?
• Was the correct diluent used?
• Were all dilution steps performed as written?
• Was the sample prepared within the method's required conditions?
• Were the correct calculations applied?

A small preparation error can affect the final assay even when the HPLC system performs properly.

For example, if an incorrect dilution factor is entered into the calculation, the reported assay may be wrong despite an acceptable chromatogram.

The review should be based on recorded evidence. Do not assume that a preparation step was completed correctly simply because the final result looks reasonable.

3.2 Compare the standard and sample chromatograms

A reviewer should assess whether the chromatograms are consistent with the approved analytical method.

Consider:

• Is the principal peak at the expected retention-time region?
• Is the peak shape consistent with the method's expectations?
• Is there any unexpected peak that requires assessment?
• Is the baseline stable enough for reliable integration?
• Is there evidence of a possible interference or unresolved peak?

Retention time alone does not establish identity. Identification should follow the approved method and any applicable system suitability or identification requirements.

Similarly, a peak that looks unusual is not automatically evidence of contamination or an incorrect result. The observation must be evaluated scientifically.

3.3 Review peak integration

Peak integration can have a direct effect on the reported result.

Review whether the integration follows the approved method and the laboratory's controlled procedures. Pay attention to the baseline placement, peak start and end points, shoulder peaks, and any manual integration changes.

A reviewer should ask:

• Was the peak integrated consistently with the approved procedure?
• Is the baseline placement scientifically justified?
• Was manual integration performed, if permitted, and properly documented?
• Is there an unexplained difference between the displayed peak and the calculated area?

Do not change integration parameters simply to make a result pass specification.

If an integration adjustment is justified, it must follow the applicable procedure, preserve the original data and audit trail where required, and be supported by a documented rationale.

A good chromatogram review explains why the integration is appropriate; it does not merely confirm that a number was generated.

3.4 Check the calculation and dilution factors

An acceptable chromatogram can still produce an incorrect reported assay if the calculation is wrong.

Review the applicable formula in the approved method and verify the actual values used.

Check the standard potency or assigned value, standard and sample weights, dilution factors, sample quantity, average tablet weight where applicable, and any moisture or other corrections required by the method.

Do not rely solely on a spreadsheet result or a previously saved calculation template.

Confirm that the formula is appropriate for the analytical procedure and that the entered values match the original records.

If a calculation error is identified, handle and document it under the laboratory's approved procedure. Do not overwrite or conceal the original result.

3.5 Review blanks and possible carryover

When relevant to the method, review blank injections and the sequence around the sample.

A blank may help identify unexpected signals, while the sequence may reveal a possible carryover concern following a concentrated standard or sample.

Questions to consider include:

• Does the blank meet the applicable method requirements?
• Is there an unexpected peak at a relevant retention time?
• Was the injection sequence performed as approved?
• Is there evidence that a previous injection could have affected a later result?

Not every blank signal indicates a problem. Its significance depends on the method, peak identity, response, location in the sequence, and applicable acceptance criteria.

Any suspected carryover should be evaluated according to the approved procedure rather than dismissed or assumed without evidence.

3.6 Review instrument sequence and raw data

The sequence table and original data can provide information that is not obvious from the final printed chromatogram.

Check sample identifiers, injection order, acquisition details, processing methods, and relevant instrument records.

Where applicable, review the audit trail for changes to processing parameters, reintegration, reprocessing, or other data modifications.

A reviewer should be able to trace the reported result back to the original analytical data and understand how it was generated.

For more information about reliable electronic records, see the existing article on OOS Investigation in the Pharmaceutical Industry when the result meets the definition of an out-of-specification result and requires investigation under the applicable procedure.

3.7 Compare with previous results carefully

Historical data can help identify unusual patterns, but a difference from previous batches does not automatically mean that a result is invalid.

Consider whether the comparison is appropriate. Review comparable batches, methods, sample matrices, instrument conditions, and relevant process information.

A trend may reveal a change that deserves attention even when individual results remain within specification.

However, do not create unofficial acceptance limits from historical averages. Use approved specifications, established procedures, and appropriately justified trending criteria.

4. What If Everything Looks Acceptable but the Result Still Seems Unusual?

Sometimes the review finds no clear error, but a result remains unusual.

The analyst should distinguish between an observation and a confirmed problem.

For example:

• Observation: The sample peak area is lower than the usual historical range.
• Possible explanations: A legitimate batch difference, a preparation issue, sample instability, or another analytical factor.
• Evidence needed: The preparation record, calculations, chromatogram, sequence data, relevant method requirements, and any additional justified investigation.

The reviewer should document the concern and follow the laboratory's approved process.

If the result meets the definition of OOS, the formal OOS procedure should be followed. If the concern is a possible deviation, data integrity issue, or another type of discrepancy, the relevant procedure should be applied.

Do not automatically classify every unusual result as OOS. Equally, do not avoid a required investigation simply because the numerical result falls within specification.

For additional guidance, see Root Cause Analysis in the Pharmaceutical Industry. Root cause analysis should be evidence-based and should not begin with an assumed explanation.

5. Should the Analyst Repeat the Test?

Repeating an analysis may sometimes be justified, but it should not be the automatic response to an unexpected result.

Before repeating the test, the analyst should establish why additional testing is needed and follow the approved procedure.

A scientifically justified repeat may be appropriate in circumstances permitted by the method and laboratory procedures. The reason, authorization where required, testing plan, and resulting data should be documented.

Repeated injections or preparations must not be used selectively to obtain a preferred result.

For example, if an initial assay result is unexpectedly low and a second test gives a passing result, the second result does not automatically invalidate the first one. Both results must be evaluated under the applicable investigation procedure.

The decision should be based on documented evidence, not pressure to release a batch or obtain a passing number.

6. How Should the QC Reviewer Document the Concern?

Good documentation should allow another qualified person to understand what was observed, what was reviewed, and why the final decision was reached.

A useful review record may include:

Review item	What to document
Observation	The specific chromatographic or analytical concern
Initial assessment	Why the observation may matter
Records reviewed	Sample preparation, raw data, calculations, sequence, and relevant records
Findings	Evidence supporting or excluding potential explanations
Action taken	Any action required under the applicable procedure
Conclusion	The scientific rationale for the result disposition

This is a general documentation framework, not a replacement for your company's approved forms or procedures.

Avoid statements such as “result okay” or “no issue found” when a more specific explanation is needed.

A stronger conclusion explains which records were reviewed, what the evidence showed, and why the result was considered acceptable or why further investigation was required.

7. A Simple Decision Checklist for Daily HPLC Review

Before approving an HPLC assay result, ask these questions:

• [ ] Did the required system suitability criteria pass?
• [ ] Was the approved analytical method followed?
• [ ] Are sample identity and preparation records correct?
• [ ] Are the chromatogram and peak integration scientifically acceptable?
• [ ] Are the calculation and dilution factors verified?
• [ ] Have relevant blanks, sequence information, and raw data been reviewed?
• [ ] Have unusual observations been assessed rather than ignored?
• [ ] Is the reported result traceable to the original data?
• [ ] Has any required deviation or investigation been handled according to procedure?
• [ ] Is the final decision supported by documented evidence?

A checklist supports consistency, but it does not replace scientific judgment or the requirements of the approved method.

8. Why This Matters for Pharmaceutical Quality

An HPLC result is more than a peak area or a percentage assay. It is the outcome of a complete analytical process involving sampling, preparation, instrumentation, processing, calculation, review, and documentation.

ICH Q2(R2) describes principles for validating analytical procedures, while ICH Q14 addresses science- and risk-based analytical procedure development. Both are useful references for understanding why analytical performance must be considered in the context of the intended procedure.

The US Food and Drug Administration's guidance on data integrity also emphasizes the importance of reliable and accurate data in pharmaceutical manufacturing and quality control.

For QC analysts, the practical lesson is straightforward: a result should be accepted because the evidence supports it—not merely because the instrument generated a number and the system suitability report passed.

Conclusion

Passing system suitability is an important part of HPLC analysis, but it is not the final proof that a sample result is correct.

A reliable QC analyst reviews the sample preparation, chromatogram, peak integration, calculations, sequence, raw data, and any unusual observations. When a concern is identified, the analyst follows the approved procedure and documents the scientific rationale for the decision.

The aim is not to find a problem in every chromatogram. It is to recognize when additional review is warranted and ensure that every reported result is defensible.

Remember: SST tells you whether the system met the specified suitability requirements. A complete data review helps determine whether the analytical result is adequately supported.

References

1. International Council for Harmonisation (ICH). ICH Q2(R2): Validation of Analytical Procedures — FDA guidance page.
2. International Council for Harmonisation (ICH). ICH Q14: Analytical Procedure Development — EMA guidance page.
3. US Food and Drug Administration (FDA). Data Integrity and Compliance With Drug CGMP: Questions and Answers.

This article is educational and does not replace the approved analytical method, applicable pharmacopoeial requirements, or your company's SOPs.