Raw data and chromatograms: what to ask a lab for

To review a chromatographic result, ask the lab for original instrument files, a processed chromatogram, a peak table, the method, sample records, and quality-control results. Raw data and chromatograms: what to ask a lab for depends on whether the goal is a basic check, an independent review, or formal records.

Key takeaways

• Request the instrument's original files as well as readable exports.
• Get the method, sample sequence, sample identifiers, and run date.
• Ask how the lab set peak boundaries and changed the processing.
• Request actual control results and the limits used to judge them.
• Match the file package to the depth and purpose of your review.
• Agree on access, record retention, and change tracking before formal work begins.

Know the difference between raw data and results

Raw data include the signals recorded by the instrument during a run; reconstructing the result also requires the associated settings, sample sequence, metadata, processing history, and audit trail. A report shows selected results, while a processed chromatogram plots the signal over time and a peak table lists measured peaks and values.

Ask for all three: original instrument data, the processed chromatogram, and the peak table. A PDF or image can show the final view, but it cannot replace the files needed to review how that view was made.

Request the reported values alongside records that tie each value to a sample identifier and analysis. Without those links, a clear number may be hard to match to the run that produced it.

The lab-testing page is useful for reviewing lot-level records. It provides batch reports for purity and pH and keeps older reports published.

For the meaning and parts of a certificate, see how to read a certificate of analysis. A certificate summarizes findings, while the instrument files and processing records show more of the path to those findings.

Request files that let you retrace the analysis

A complete package should let a reviewer connect an instrument signal to a sample and then to a reported value. Ask for the original instrument data file and a common export, such as a table file, so the values can be reviewed in other tools.

Many labs use a chromatography data system, which is software that stores, processes, and displays instrument runs. Ask for the software name and version, plus a viewer or clear export steps if the original files need that system to open.

Request the analytical method, which is the written procedure used for the test, and the sample sequence, which lists the samples in run order. Also ask for sample identifiers and the run date, so each result can be placed in the right test sequence.

Ask for metadata, or file details such as instrument settings, file times, and processing dates. These details help explain when the signal was recorded and which settings shaped the displayed result.

For a fuller reconstruction, ask for sample-preparation records, the acquisition method actually applied, calibration or check-standard records, and the processing method or version used. The written procedure alone may not show which settings were applied to a particular sequence. Match these records to the sample and run, and ask for any revised report linked to its processing history.

For records that connect a sample to its lot, see lot trace and certificate records.

• Original instrument files in the format created by the instrument.
• A readable export of the signal or peak data.
• The software name, version, and file-opening steps.
• The method, sequence, sample identifiers, and run date.
• Settings, file times, and other relevant metadata.

This comparison is an example of variation, not a universal target or evidence that one integration setting is correct. The method, signal, and predefined processing rules matter; the percentage alone cannot establish whether peaks were integrated appropriately.

Ask how peaks became reported values

Peak integration is the software's choice of where a peak starts and ends, and how it calculates the area under that peak. Ask for the integration settings because different boundaries can change the measured area. A higher integration rate is not automatically better: review representative peaks against the method's rules, especially where peaks overlap or the baseline is unclear.

Request the record of any manual change, including who made it, when it was made, and why. Ask whether the data were processed again, too. Reprocessing means calculating results again from stored instrument signals, and the change record should link each version to the value in the report.

Retention time is the time when a peak appears during a run. Peak area is the space beneath the peak on the plot. Both can help compare runs, but their meaning depends on the method and settings used.

Ask for the audit trail, a record of who changed data or settings and when. It helps a reviewer see whether a reported value came from the first processing or a later change.

With method Y, Site A auto-integrates 80% of peaks; other sites auto-integrate 30%.

Source: LCGC International

Get quality checks with the sample results

Ask for the actual results from blanks, controls, and repeat samples, rather than a statement that checks were done. A blank, such as an extraction blank, goes through the preparation steps without the target material. A positive control contains known material that should give an expected result.

Request the pass limits and the run's results against them. A number is easier to judge when the lab shows the rule it used to decide whether the method worked as planned.

Ask for the specific criteria, not just a pass statement. For example, the method may require a blank to stay below its stated threshold, a control or calibration check to fall within a validated interval, and repeat preparations to agree within a pre-set tolerance. Run criteria may also cover retention-time windows, peak shape or resolution, baseline stability, and check-standard response. Compare each required result with its own criterion, check that controls are tied to the run, and ask how any failure or omitted check was investigated. Limits should be set for the method and sample before results are judged, not chosen after a run to make it pass.

Ask how the lab checked for carryover, which is material from one sample affecting the next sample. Also ask what action followed a failed check, so the record shows how the lab handled a run that missed its limits.

Keep the quality-control records tied to the same run and sample identifiers as the reported results. The independent testing and certification information is relevant when reviewing what tests and quality records a lab reports.

The lab-testing page says an independent lab tests every batch for purity and pH. HPLC is a method that separates parts of a sample as liquid passes through a column under pressure.

Ask what the method can and cannot show

Ask what the analytical method measures and what it does not measure. Different methods answer different questions, so a clear result for one feature does not prove every other feature of a sample.

Ask how the lab checked accuracy, repeatability, and working range for that sample type. Accuracy concerns closeness to a known value, repeatability concerns how closely repeated tests agree, and working range is the span where the method gives useful results.

Request the smallest amount the method can detect and the smallest amount it can measure reliably. These limits are not always the same. The lab should explain which limit applies to the reported result.

If accreditation matters, ask which exact tests and methods fall within its scope. Accreditation is formal recognition of a lab's competence for named work, and it may cover some tests but not all of them.

The pattern described here assumes results come from a stable, approximately normal process; it will not fit every control series. Skew, trends, shifts, or dependent repeated results can change the pattern. Use the lab's documented control-chart rules and investigate unusual patterns rather than treating the band as a stand-alone pass limit.

Match the data package to your review

For a basic review, request the report, chromatogram, peak table, method, and sample identifiers together. This set provides the result and the main details needed to place it in context.

For an independent review, also ask for original instrument files, processing settings, quality-control results, and the change history. Include the software details and a usable export, so the reviewer can open and assess the files.

For work with formal record rules, agree on file access, retention, and change tracking before the analysis starts. State which records must remain available and how long the lab will keep them.

Ask the lab to list which records it can provide and how each file connects to the reported result. A clear link from sample to run, signal, processing step, and final value makes later review more direct.

A written request can be brief and specific: "Please provide the original instrument files, processed chromatogram, peak table, method, sample sequence, identifiers, run date, metadata, quality-control results, integration settings, and change history. Please include the software name and version, a readable export, and the record that links each result to its sample."

What questions do labs often get about chromatograms?

How do you read a gas chromatogram?

Read the horizontal axis as time and the vertical axis as detector response. Compare traces only when the column, temperature program, and detector settings match, since those settings shape the pattern.

Can two substances have the same retention time?

Yes. Two substances can leave the column at similar times and form a single overlapping peak. A second method, such as mass spectrometry, which separates charged particles by mass, can help distinguish them.

Does a larger peak always mean there is more of a substance?

No. A detector can respond differently to different substances, and a signal can exceed its useful range. The lab needs a suitable calibration to connect peak size with the amount measured.

What can a noisy or uneven baseline mean?

It can point to background signal, unstable instrument conditions, or a sample or solvent issue. Comparing the run with a blank can help show whether the pattern also appears without the sample.

How long should a lab keep chromatographic data?

There is no single retention period that fits every project. The required period depends on the record rules and agreement that apply, so set it in writing before the work begins.

For related topics, see How Readypep Works, Products, Research use only, Shipping, Why ReadyPep, Manufacturer-distributor split explained, Faq, Blog, Cold Chain In Transit, and Pre Filled Pens Versus Vials.

Conclusion

Raw data and chromatograms: what to ask a lab for comes down to files and records that connect the sample to the reported value. Request the instrument files, processed views, method, sample details, quality checks, and change history, then match the package to the review you need.