Analytical standards

What the tests actually measure.

Purity, identity, content and stability are four different questions answered by four different measurements. Most of the confusion in this field comes from treating them as one.

Research use only. Every compound described on this site is supplied and handled strictly for in vitro laboratory research. Not for human or veterinary use. Not for consumption. Nothing here is medical advice, and nothing here describes how any compound should be administered to a person or an animal. Written for laboratories and researchers working in Canada. Health Canada does not authorise these compounds for human use.
01 · Purity

Reversed-phase HPLC

High-performance liquid chromatography separates a sample by how strongly each component binds to a non-polar stationary phase. The sample is pushed through a packed column under pressure while the solvent composition changes on a gradient; components elute at different times and a detector records absorbance as they pass.

What it gives you

The area of the main peak as a percentage of total peak area — conventionally reported at 214 nm, where the peptide bond itself absorbs.

What it does not give you

Identity. HPLC shows that the sample is predominantly one substance. It is silent on which substance that is.

What to look for

Column type, gradient, detection wavelength, and the chromatogram itself. A number without these is unverifiable.

02 · Identity

Mass spectrometry

Mass spectrometry ionises the sample and measures mass-to-charge ratio, giving the molecular mass of what is actually present. Compared against the theoretical mass calculated from the sequence, it confirms — or refutes — that the molecule is the one named on the label.

Why it is the important one

A sample can be 99% pure and be entirely the wrong compound. Purity and identity are independent measurements and only one of them is routinely published.

Where it matters most

Between structurally similar molecules. PT-141 and Melanotan II differ by a single amidation — about 1 Da. HPLC will not reliably separate them. Mass spec will.

What to look for

Observed mass, theoretical mass, and the difference between them stated explicitly.

03 · Content

Net peptide content

The most commonly omitted figure on a certificate, and the one that most often explains a discrepancy. A lyophilised peptide is not pure peptide by mass — it carries trifluoroacetate or acetate counterions bound to basic residues, plus residual water. A vial labelled 10 mg can be 99% pure by HPLC and still contain meaningfully less than 10 mg of peptide.

Net content is determined separately, typically by amino acid analysis or nitrogen determination. Where it is not stated, the labelled mass is gross mass and should be read as such.

04 · Stability

Cold chain and why lyophilisation exists

Peptides degrade by hydrolysis, oxidation and deamidation — all of which need water, oxygen or both. Freeze-drying removes the water, which is why research peptides ship as a powder rather than a solution.

Lyophilised

Stable for extended periods at −20 °C, desiccated and protected from light. This is the storage state referenced throughout the compound reference.

Reconstituted

Stability drops sharply once in solution. Refrigerated, and measured in weeks rather than months, with wide variation between compounds.

Particularly sensitive

Sequences containing cysteine (oxidation and disulfide scrambling), methionine (oxidation), and asparagine-glycine motifs (deamidation).

05 · Handling

Laboratory handling notes

Equilibrate first

Allow a vial to reach room temperature before opening. Opening a cold vial draws in ambient moisture that condenses onto the powder.

Reconstitution arithmetic

Concentration is mass divided by volume. 5 mg into 2 mL gives 2.5 mg/mL. Direct the solvent down the vial wall rather than onto the cake.

Do not shake

Agitation at an air–liquid interface denatures peptides. Swirl gently and allow time to dissolve.

Surface adsorption

Cationic peptides such as LL-37 adsorb to glass and standard plastics at low concentrations. Low-bind labware is standard practice.

Aliquot once

Repeated freeze–thaw cycling is a leading cause of measurable degradation. Divide into single-use aliquots at first reconstitution.

Label everything

Compound, lot, concentration, solvent and date of reconstitution. An unlabelled aliquot is an unusable aliquot.

06 · In practice

Reading a certificate you have been handed

Four questions, in order. If the first two cannot be answered from the document itself, the rest do not matter.

Question 1

Which batch is this?

Find the lot number and check it against the vial. No match, no evidence.

Question 2

Who ran it, and when?

A named laboratory and a date. An unnamed lab is an unfalsifiable claim.

Question 3

Purity by what method?

HPLC with stated conditions, and ideally the chromatogram. A bare percentage is not a result.

Question 4

Was identity confirmed?

Observed mass against theoretical mass. If this section is absent, the certificate establishes purity and nothing else.

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