99% pure is not 10 mg: purity, quantity and identity are three different numbers

Open a research peptide product page and the number you will see is a purity: 99.2%, 99.7%, ">99%". It is a real measurement and a useful one. It is also the answer to a question you may not have asked. Purity tells you how clean the material is. It does not tell you how much of it there is. A pen can be 99.5% pure and contain half the peptide on the label, and the purity figure would not flicker. Underdosing, the most common complaint in every buyers' forum, lives in a different number, and that number is the one most pages leave out.

Three attributes, three tests

The international guideline that defines how biological and peptide products are specified — ICH Q6B, adopted by the European and UK regulators — separates the properties of a product into distinct attributes, and three of them are what a buyer needs:

• Identity: is this the molecule the label names? Confirmed by mass spectrometry, which measures the molecular mass and compares it to the theoretical mass of the named compound. A pass here means "this is tirzepatide" and nothing more.
• Purity: of the peptide material present, what fraction is the intended molecule rather than related impurities — truncated sequences, oxidised forms, deletion products? Measured by HPLC as a percentage of chromatogram area. What the number does and does not mean.
• Quantity: how much of the molecule is actually there? For a lyophilised vial, milligrams per vial against the label. For a solution, a concentration in mg/ml, which with the fill volume gives the content per pen.

The guideline is explicit that quantity, expressed in mass, is a physicochemical measure of content and is distinct from purity. They are different questions with different methods, and a specification that has one without the other is incomplete.

Why purity cannot see underdosing

Purity by HPLC is a ratio of peak areas. The instrument separates the components of the sample, the detector records each as a peak, and purity is the main peak's area divided by the total. Halve the amount of sample injected and every peak halves together; the ratio does not move. That is the property that makes purity a good measure of cleanliness and a useless measure of amount. A 99% figure is compatible with 10 mg in the vial, or 5 mg, or 1 mg.

Quantity needs something purity does not: a reference. The lab runs a known amount of a certified standard of the same peptide, compares the response, and calculates the mass in the sample. It is a separate measurement, with its own calibration and its own uncertainty, and a report that has done it will show a figure in milligrams or mg/ml. A report that has not will show only a percentage.

What underdosing looks like on a report

Forum "testing results" threads for research peptides have, for years, reported the same pattern: purity in the high nineties and content well under label. The reasons are prosaic. Fill accuracy on cheap equipment. Peptide bought by the gram and vialled by eye. A manufacturer's certificate that quotes the purity of the bulk powder before it was ever weighed into vials. None of these touch purity. All of them show up in quantity.

The community's rule of thumb, repeated across those threads, is roughly that content should be within ten percent of the label and purity should not be below about 98%. Whatever threshold you use, the point is that you need the content number to apply it.

How to read both on a Biovanta report

Our independent reports publish both figures, per batch, and the testing page sets them beside the manufacturer's certificate:

• The current Retatrutide 40 mg batch, R40-20260203, was independently measured at 98.86% purity and 17.90 mg/ml.
• The current Tirzepatide 40 mg batch, Ti40-20260508, at 99.59% purity and 17.72 mg/ml.

Purity tells you the material is clean. The mg/ml figure, multiplied by the fill volume of the pen, tells you how much is in it against the 40 mg on the label. Both are the lab's numbers, transcribed as the lab wrote them, with the verification key so you can read the original. For a blend such as Glow, the report shows the content of each peptide in mg/ml and no purity percentage at all, for a reason explained in its own article.

The question to ask any vendor

Not "is it tested?" but "what was the measured content?" A vendor who tests per batch and publishes quantity has answered the question underdosing raises. A vendor who publishes a purity percentage and nothing else has told you the material is clean, which is worth knowing, and has left the question you actually had unanswered. Products are supplied strictly for in-vitro laboratory research.