What do HPLC peak-type codes (BB, VV, VB, BV, PV) mean on a peptide COA?
A reversed-phase HPLC peak table is the quantitative record of a chromatographic run. HPLC peak areas have long served as the direct readout of an assay in analytical biochemistry, which makes the integration rule as important as the detector response (DOI:10.1006/abio.1993.1102). On a peptide COA, the Type or Peak Type column is the chromatography data system's shorthand for that rule.
BB (baseline–baseline) means the peak starts and ends on a drawn baseline. For an isolated main peak that returns to baseline, BB is the expected code. The reported area is the integral between the start and stop ticks and the baseline segment that joins them.
VV (valley–valley) means the peak is fused to one or more neighbours. Integration starts and ends at valleys rather than at baseline, so area is sensitive to valley location. A main peak coded VV beside a large neighbour is a prompt to inspect chromatographic resolution rather than to accept the area-percent line uncritically.
VB and BV are mixed codes: one side sits on baseline and the other at a valley. VB usually indicates a baseline start and a valley end (a later fused related substance). BV is the reverse. These codes identify which shoulder is fused and which side still reaches baseline. PV, VP and other perpendicular-drop variants record a vertical cut from a valley to the baseline. Area on the main-peak side of the cut is assigned to the main peak and can raise main-peak area-percent relative to a tangent skim of the same trace.
Not every chromatography data system uses the same alphabet. Empower, Chromeleon, OpenLab and LabSolutions expose overlapping but not identical Type vocabularies. Complete laboratory peptide documentation therefore names the CDS, the processing method and the software version, not only the pump and detector model. If Type is printed without a legend, the chromatogram start and stop ticks and the baseline segments remain the independent check. For research lots, the main peak should carry an isolated-peak code on a method that returns to baseline before the next reportable peak; fused codes on the main peak should be explained; and every reportable related substance should carry a Type that matches the trace. A blank Type column leaves the COA incomplete as an experimental record.
How do drop, skim and rider-peak flags change area-percent on peptide COAs?
When two peaks share a valley, the chromatography data system must partition the valley area. That partition is a processing event, not a chemical property of the peptide. Reading a chromatogram as experimental material means asking what was measured and how it was reduced to a number, rather than accepting the headline figure (DOI:10.1002/asi.5090180408).
A perpendicular drop draws a vertical line from the valley to the baseline and assigns all area on each side of that line to the adjacent peak. If the main peak is large and the related substance is a small fused front or tail, drop usually gives the impurity less area than a tangent skim, because the slice under the valley is awarded to the larger peak. Main-peak area-percent rises; related-substance area-percent falls. The detector trace is unchanged.
A tangent or exponential skim constructs a baseline under the rider along a tangent or along an exponential decay of the parent peak. Area above the skim line is assigned to the impurity; area below remains with the parent. For a tailing main peak with a late rider, skim typically assigns more area to the impurity than a drop would, so main-peak area-percent falls. The same ultraviolet trace can therefore support two different purity statements depending only on the processing method.
Shoulder-detection thresholds decide whether an inflection is a peak at all. If the shoulder is not detected, no Type code appears and the area remains inside the main peak. A statement that no related substances exceed the reporting threshold is therefore a statement about processing as much as about the sample. For Australian research lots, confirm the reporting threshold printed on the COA; count inflections that look like shoulders; check whether each inflection has a row and a Type; note drop versus skim on every fused pair that includes the main peak; and recompute whether area-percent closes after solvent-front exclusion. A visual shoulder without a row is a documentation defect, not an analytical improvement. If the peak table lists manual or forced events, Type codes may no longer reflect the default method; the pack should record who authorised the event and whether the same event was applied to the bracketing standard.
How should laboratory peptide documentation link peak-type codes to the drawn baseline?
A COA is a document, and documents are misread when a summary sentence is treated as a substitute for the methods and results that support it. Structured reading—methods first, then results, then limitations—is as relevant to a certificate as to a journal article (DOI:10.5694/j.1326-5377.1992.tb137249.x). For HPLC, the methods are the processing parameters, the results are the peak table, and the chromatogram is the figure.
The drawn baseline is that figure. Start and stop ticks should coincide with the Type code. A BB peak whose ticks sit in the noise well above the apparent baseline is not BB in any practical sense. A VV peak whose ticks are not at the visible valleys has been processed with a different peak-width or threshold than the printout suggests.
Some methods allow a sloping baseline under a late-eluting cluster. A sloping BB under a tailing main peak reduces area relative to a horizontal baseline, yet the Type code may still print as BB. Laboratory peptide documentation should state whether the processing method uses a horizontal baseline, a peak-to-peak baseline, or a traditional lowest-point baseline.
If the valley between two peaks does not reach the blank baseline, a drop flag will cut through real analyte signal. The Type code looks decisive; the chemistry is still co-elution. Orthogonal mass-spectral traces in the same pack are the check—not a second reading of the same ultraviolet area-percent. Peak-type codes on the sample are uninterpretable without the blank. A BB peak at the solvent front that also appears in the blank should be excluded from area-percent, regardless of Type. Packs for Australian research lots should include the blank chromatogram, the sample chromatogram, and the processing-method identity so a reviewer can see whether solvent peaks were excluded before normalisation.
A practical concordance worksheet is peak label, retention time, Type, start time, stop time, baseline description, present in blank, and included in area-percent. Every row on the COA peak table should fill that worksheet. Request the integration-events report if the ticks are not printed. Do not promote the purity line over the figure, and do not treat a Type code as independent of the baseline that was actually drawn (DOI:10.5840/acpq199569241).
Which peak types belong on the system-suitability chromatogram versus the sample chromatogram?
System-suitability (SST) chromatograms exist to show that the method, column and detector were in a state capable of producing interpretable Type codes. If the SST main peak is itself VV or heavily skimmed, sample Type codes cannot be read as if the method had baseline resolution.
A well-resolved SST or reference-standard chromatogram should show the marker peak as BB (or the CDS equivalent), with tailing factor, plate count and, where a resolution mixture is used, resolution to the nearest marker meeting the method's printed limits. Those limits belong on the COA or in the attached SST table. Sample chromatograms may then be compared: if the sample main peak is BB and the SST was BB, Type codes are being used in their intended regime. If the sample is VV while the SST was BB, the sample has a fused related substance, an overload, or a column-history effect, and area-percent for that lot is method-limited.
Where a standard is run before and after the sample, Type codes on the two standards should match. A BB-to-VV change across the sequence suggests drift in retention, mobile-phase composition, or column surface, not a change in the peptide lot. Lot identity may still be locked by mass data, but the HPLC purity figure is sequence-position dependent and should be flagged in the batch record.
A blank after a concentrated standard should not present a BB main peak at the peptide retention time. If it does, sample area-percent is contaminated and Type codes on the sample are reading carryover plus analyte. Australian batch documentation should include that blank, not only the sample printout. When the COA includes a sample-versus-reference overlay, compare Type codes at shared retention times. A reference impurity coded BB that is absent in the sample is not a defect. A sample peak coded VV at a retention time where the reference is clean is a lot-specific fused peak and should appear in the related-substances table with a relative retention time.
Finding the SST page in a multi-file pack is a documentation-literacy task. Australian research groups already use structured workflows to find information in large documentation holdings (DOI:10.3897/tdwgproceedings.1.19941). Apply the same habit to a COA pack: contents list, SST chromatogram, blank, sample, peak table, processing method. If SST Type codes are omitted, the sample Type column has no control.
How do you lock HPLC peak-type codes to lot identity, vial labels and Australian batch records?
Peak-type codes are processing metadata. They become lot-traceability metadata only when they are bound to the same identifiers that appear on the vial, the packing list and the invoice.
The sample name in the CDS sequence, the COA lot number, the vial-label lot number and the packing-list lot number must be identical character-for-character, including prefix, hyphenation and check digits. A chromatogram labelled with an internal laboratory number must carry a cross-reference table to the commercial lot. If the Type column is copied from a representative vial onto a multi-vial order, the documentation pack should state that all vials share that lot and that the chromatogram is from a stated vial position.
The HPLC sequence should show blank, SST, sample and bracketing standard with vial positions. Peak-type codes for the sample row must come from that sample's data file, not from a template. CDS result identifiers printed on the COA allow a reviewer to request the original data file if Type codes look inconsistent with the trace.
For research material supplied from Australian stock, the dispatch record should repeat the lot number that sits on the COA header and in the chromatogram sample name. Tracked dispatch provides an independent timestamp; it does not replace batch documentation. The analytical pack—COA, chromatogram, peak table with Type codes, SST and blank—should be retrievable by lot after dispatch. Researchers comparing two lots should compare Type codes on the main peak and on the nearest related substance, not only the headline purity, because a BB lot and a VV lot are not analytically equivalent even if both print the same area-percent.
If a lot is reprocessed with a new integration method, Type codes can change without a new synthesis. Version control belongs on the COA: method identity, processing version, analysis date, reviewer. A second PDF with different Type codes and the same lot number is a documentation collision unless the revision history explains it. Type codes do not confirm sequence, counter-ion or water content. Identity still requires mass spectrometry and, where relevant, amino-acid analysis. Type codes only describe how chromatographic area was partitioned. Treating them as identity is a category error in reading results (DOI:10.7816/ulakbilge-05-15-06).
Apply this checklist to documented stock
You now have a practical way to read purity figures, method notes, and lot traceability. When you source materials, hold suppliers to that same checklist — ClaraScience issues batch documentation with every order and dispatches from Australian warehouses with Express tracked shipping.
Start with a retail order to review documentation end-to-end, or register for wholesale if you restock multiple compounds.
Frequently asked questions
What does BB mean in the HPLC Type column on a peptide COA?
BB means baseline-to-baseline integration: the peak starts and ends on the drawn baseline, and the reported area is the integral between those ticks. On research peptide lots it is the expected code for an isolated main peak that returns to baseline. Always confirm the ticks on the chromatogram match the code; a printed BB with ticks sitting in noise is not a true baseline-to-baseline result.
Why might the main peak be coded VV even when area-percent still looks large?
VV means valley-to-valley fusion with a neighbour. Area-percent can still print as a large number because most of the cluster is assigned to the main peak, especially if a perpendicular drop was used. The code is a resolution warning, not an analytical upgrade. Compare the sample with the SST chromatogram and inspect the nearest related-substance row before treating the lot as chromatographically isolated.
Do HPLC peak-type codes prove peptide identity?
No. Type codes describe only how chromatographic area was partitioned. Sequence and molecular mass still require mass spectrometry and, where used, orthogonal methods. A BB main peak at the expected retention time is consistent with identity only inside a defined retention window and only when the sample name matches the lot. Treat Type codes as processing metadata, not as a substitute for intact-mass confirmation.
What should an Australian research documentation pack include so Type codes can be checked?
At minimum: COA header with lot number, sample chromatogram with start and stop ticks, peak table with Type and area-percent, blank chromatogram, SST chromatogram, processing-method identity and CDS name, and a packing-list lot that matches the vial label. Tracked dispatch records should repeat that lot number. If ticks or Type legends are missing, request the CDS integration-events report.
How should multi-vial orders handle a single HPLC Type-code table?
The pack should state that all vials share one lot and identify which vial position was chromatographed. Type codes from a representative vial apply to that lot, not to untested separate lots. Sample name, COA lot, vial label and packing list must match character-for-character. If vials come from more than one lot, each lot needs its own chromatogram and Type column.
What is the difference between a drop flag and a skim flag on a peptide COA?
A drop flag cuts vertically from a valley to the baseline and usually assigns more of the shared area to the larger peak. A skim draws a tangent or exponential curve under a rider and assigns the area above that curve to the impurity. The detector trace can be identical while area-percent changes. Record which algorithm the processing method used.
References
- DOI:10.1006/abio.1993.1102 — The Direct Assay of Kinases and Acyl-CoA Synthetases by HPLC: Application to Nucleoside Diphosphate Kinase and Succinyl-CoA Synthetase — Analytical Biochemistry — 1993
- DOI:10.1002/asi.5090180408 — Suggestions on how to read experimental material in information science — American Documentation — 1967
- DOI:10.5694/j.1326-5377.1992.tb137249.x — 13. How to read a journal article — Medical Journal of Australia — 1992
- DOI:10.5840/acpq199569241 — How (Not) To Read Heidegger — American Catholic Philosophical Quarterly — 1995
- DOI:10.3897/tdwgproceedings.1.19941 — Documentation about Atlas of Living Australia tools: how to find information — Proceedings of TDWG — 2017
- DOI:10.7816/ulakbilge-05-15-06 — HOW TO BE READ PIAAC RESULTS FOR ADAPTATION TO NEW AGE? — Ulakbilge Dergisi — 2017
Research use only
This article is provided for laboratory research and educational purposes only. Products referenced are not for human or veterinary use. ClaraScience makes no therapeutic, medical, or efficacy claims, and nothing here constitutes medical advice.
