AssayIndex
Acceptance specification

Melanocortin-receptor peptides

Cyclic and linear melanocortin agonists, plus the kisspeptin decapeptide. 5 compounds in this class, 509 records.

5 compounds509 recordspurity spec 98.5 %observed median 99.28 %
Section 1

The specification

ParameterLimitWhere the limit came from
Purity by RP-HPLC≥ 98.5 % areaSet at the 19.1 th percentile of observed results for this class — low enough that ordinary material passes, high enough that a genuinely poor lot does not. Reviewed each quarter and last moved in 2025-Q1.
Water by Karl Fischer≤ 8.0 %Lyophilised peptides routinely carry 2–6 % residual water. The limit sits above the normal range and below the point at which water displaces enough cake mass to move the recovered-mass figure by more than the label tolerance.
Counter-ion≤ 10.0 %Derived from the stoichiometric maximum for a fully-protonated peptide of this class's typical basic-residue count, plus a margin. Above it, the salt is either non-stoichiometric or the cake contains free acid.
Bacterial endotoxin≤ 5.0 EU/mgAn index convention chosen so that the figure is comparable across records. It is not a pharmacopoeial limit: a real limit is dose-dependent and is computed per use from the K/M ratio. The endotoxin calculator does that calculation.
Mass accuracy± 15 ppmAchievable accuracy depends on mass. This class's limit reflects both the instrument capability and the mass differences that must be resolved within it — see mass-accuracy calibration.
Section 2

Compounds in this class

Per-compound thresholds override the class default where the chemistry requires it. Where a compound row differs from the class row above, the compound row wins.

CompoundMonoisotopic DaPurity specWaterCounter-ionppmRecordsObserved median
Melanotan II1023.540298.58.010.01518699.24
PT-141 (Bremelanotide)1024.524298.58.010.01520099.31
Afamelanotide1645.847498.08.010.0155399.28
Setmelanotide1116.470098.08.010.0150n<3
Kisspeptin-101301.630098.58.010.0157099.27
Section 3

What actually fails, and how often

A specification nobody fails is not a specification. These are the failure rates the thresholds above produce on the records the index holds.

ParameterLimitRecords outsideRate
Purity≥ 98.5 % area9218.07%
Water≤ 8.0 %10.20%
Counter-ion≤ 10.0 %00.00%
Endotoxin≤ 5.0 EU/mg20.39%
Mass accuracy± 15 ppm101.96%
0397811792.093.094.095.096.097.098.099.0100.092.00–92.25 %: n=092.25–92.50 %: n=092.50–92.75 %: n=092.75–93.00 %: n=093.00–93.25 %: n=093.25–93.50 %: n=093.50–93.75 %: n=093.75–94.00 %: n=094.00–94.25 %: n=094.25–94.50 %: n=094.50–94.75 %: n=094.75–95.00 %: n=095.00–95.25 %: n=095.25–95.50 %: n=095.50–95.75 %: n=095.75–96.00 %: n=096.00–96.25 %: n=096.25–96.50 %: n=096.50–96.75 %: n=096.75–97.00 %: n=197.00–97.25 %: n=197.25–97.50 %: n=197.50–97.75 %: n=897.75–98.00 %: n=1598.00–98.25 %: n=2698.25–98.50 %: n=4598.50–98.75 %: n=4298.75–99.00 %: n=3599.00–99.25 %: n=7199.25–99.50 %: n=6699.50–99.75 %: n=6199.75–100.00 %: n=137median 99.28 Purity (% area) Reports
Figure. Class-wide purity distribution with the acceptance specification drawn as a solid vertical and the observed median dashed. The area to the left of the solid line is the failure rate. A specification sitting deep in the left tail is doing its job; one sitting in the body of the distribution is measuring the population rather than screening it.