How to Read a BTLabs Batch Report

A batch report is the only document that allows you to verify whether the vial contains what is stated on the label. Yet it is usually a PDF that no one opens, because it is unclear what you are looking at. Below is an explanation of what the components of a BTLabs report mean, how to link the report to the vial in your hand, and where the limits of the document lie.

Two measurements, two questions

A BTLabs report contains two types of analyses, and it is worthwhile keeping them apart. HPLC, high-performance liquid chromatography, separates the sample into its components and measures the size of each fraction. That yields the purity figure: what percentage of what is in the vial is the intended substance.

The identity measurement answers a different question: is it the correct substance? On current BTLabs reports, this is performed using FTIR, a form of infrared spectroscopy. The spectrum of the sample must display the characteristic absorption bands of the peptide. Many other laboratories use mass spectrometry for this purpose, which measures the mass of the molecule and compares it to the theoretical mass. How to read such a mass spectrum, including expected and measured mass, can be found in Purity, HPLC, and mass spectrometry.

These two types of measurements are not interchangeable. A sample can be 99% pure and still contain the wrong compound: in that case, 99% of what is inside is a single substance, just not the substance you were looking for. A purity value without an accompanying identity measurement therefore says less than it appears.

The report header: which vial was tested

At the top are the details that link the report to a specific sample. Read these first, because everything below them applies only to that sample.

• Report #: the report number from BTLabs itself. You use this number to verify the report with the lab.
• Lot Number: the lot number of the batch. This number should match the label on the vial you have in hand.
• BT Sample ID: the lab's internal sample code.
• Testing material and Labeled as: the name of the substance as submitted and as stated on the label.
• Labeled Peptide Content: the amount of peptide stated on the label, for example 5 mg.
• Tested and Date: when the measurement was performed and when the report was issued.
• Visual Description: the appearance of the vial upon receipt: powder, label, and cap.

If the lot number does not match, you are looking at the report of a different batch, which reveals nothing about your material. This is why our reports on Lab reports are searchable by lot number rather than solely by substance name. You start with the number on the glass.

The test table, line by line

The core of the report is a table with four columns: the test, the method, the specification, and the measured outcome. The method column refers to a chapter of the United States Pharmacopeia (USP): the standard method used for testing.

• General Appearance: a visual inspection. The specification is, for example, "white powder", and the result indicates whether the sample conforms to it.
• Mass: the weight of the content as received.
• FTIR Identification and Composition Analysis: the identity measurement. The result confirms whether the spectrum matches the peptide and sometimes notes whether excipients or bulking agents are present in the powder.
• HPLC Purity: the purity in percent, alongside the specification, for example at least 98%.
• HPLC Potency Assay: the content determination (assay). The actual amount of peptide present in the vial in milligrams, both as an absolute value and as a percentage of the label claim. The specification is typically between 90 and 110% of the label value.
• Peptide-to-Excipients Ratio: the ratio between peptide and excipients in the powder.

Purity and potency (assay) are often conflated, but they are distinct figures. Purity indicates what fraction of the peptide material is the intended substance. Potency indicates how much of that substance is present in the vial. A sample can be 99% pure and still contain fewer milligrams than stated on the label. For example, if it states 4.9 mg against a 5 mg label claim, that represents 98% of the label value.

The excipient ratio explains why a powder can weigh more than the peptide quantity itself. When calculating the concentration of a stock solution, one calculates using the measured peptide content, not the weight of the powder. The reconstitution guide describes how to dissolve a lyophilisate.

What an HPLC chromatogram shows

A chromatogram is a plot displaying time on the horizontal axis and signal intensity on the vertical axis. Each substance eluting from the column produces a peak. The point at which the apex of a peak appears is called the retention time. The intended compound is typically the largest peak, and purity is the area of that peak divided by the total area of all peaks. A review by Mant et al. (2007) describes reversed-phase HPLC as the standard technique for the analysis of synthetic peptides.

Small secondary peaks are normal. What one wants to observe is a narrow, symmetrical main peak and negligible remaining peaks. A broad or split main peak, or a shoulder on the flank, indicates a mixture that the column does not cleanly resolve. Minor peaks immediately adjacent to the main peak are often related peptides: variants missing an amino acid, an oxidized side chain, or another degradation product. The review article by D'Hondt et al. (2014) systematically lists these types of related impurities. Why such variants arise during synthesis can be read in What are peptides.

Verifying the report yourself

BTLabs provides its own verification portal (verify.btlabtesting.com) where you enter the Report # and retrieve the report directly from the laboratory, without seller intervention. The entire premise of third-party analysis is lost if one must take the supplier's word that this third party exists.

A practical sequence:

1. Read the lot number on the vial's label.
2. Search for the corresponding report by lot number on Lab reports.
3. Note the Report # and check it on the BTLabs verification portal, or follow the verification link on the report.
4. Compare substance name, labeled content, and lot number across the report, the verification result, and the vial.

Research demonstrates that this is not an unnecessary step. Verbeke et al. (2015) examined synthetic peptides sold as having at least 95% purity. Fewer than half met that purity level in their independent analysis, and in one sample, the main component possessed a different structure than the intended peptide. Their conclusion was that researchers should not rely blindly on supplier certificates.

What a report does not state

A batch report pertains to the contents of a vial. It makes no statements about what that substance does or about usage. It is a certificate of analysis, not a package insert or usage guidance. BTLabs notes this explicitly: the report provides no information regarding particulate matter, microbial contamination, or endotoxins, and the results apply solely to the tested sample as received.

The report characterizes the dry powder at the time of testing. How stable the peptide remains after opening or dissolution falls outside the scope of the document; this is addressed in Storing peptides.

Counterions also largely remain unaddressed. Synthetic peptides are frequently supplied as salts following purification, for example with trifluoroacetate (TFA). HPLC purity evaluates peptide peaks, not counterion salts. For in vitro research, this can be relevant: Cornish et al. (1999) observed that TFA in low concentrations inhibited the proliferation of osteoblasts and chondrocytes in cell culture.

Frequently asked questions

Why are there multiple numbers on the report?

The Report # is used for verification with the laboratory. The Lot Number identifies the batch and must match the label on your vial. The BT Sample ID is the internal sample identifier assigned by the lab.

Is 98% purity sufficient?

This depends on the research question. The report states the specification and the measured value. The remaining percentage usually consists of related peptides whose exact identity is not detailed on the report; in sensitive cell models, this may be relevant.

What is the difference between purity and potency?

Purity is the proportion of the intended substance within the peptide material. Potency (assay) is the amount of peptide in milligrams present in the vial, compared to the label.

Does the report provide information about sterility?

No. Sterility, endotoxins, and particulate matter are not measured unless tested separately and explicitly noted on the report.

References

1. Verbeke F, Wynendaele E, Braet S, D'Hondt M, De Spiegeleer B. Quality evaluation of synthetic quorum sensing peptides used in R&D. Journal of Pharmaceutical Analysis, 2015. https://pubmed.ncbi.nlm.nih.gov/29403929/
2. D'Hondt M, et al. Related impurities in peptide medicines. Journal of Pharmaceutical and Biomedical Analysis, 2014. https://pubmed.ncbi.nlm.nih.gov/25044089/
3. Mant CT, et al. HPLC analysis and purification of peptides. Methods in Molecular Biology, 2007. https://pubmed.ncbi.nlm.nih.gov/18604941/
4. Cornish J, et al. Trifluoroacetate, a contaminant in purified proteins, inhibits proliferation of osteoblasts and chondrocytes. American Journal of Physiology - Endocrinology and Metabolism, 1999. https://pubmed.ncbi.nlm.nih.gov/10567002/