Cross-section

GHK-Cu by laboratory

The same compound measured by different laboratories on different gradients. Where the medians differ, the question is whether the material differed or the method did — and for GHK-Cu, with a class minimum gradient of 15 min, the method is a live explanation.

72 recordsmedian 98.56 %spec 97.0 %

Laboratory	Reports	Gradient	MS resolution	Median purity %	Published bias (pp)	Bias-adjusted	Method suitability
Janoshik	28	30min	High	98.53	+0.00	98.53	ADEQUATE
PeptideMeter	17	28min	High	98.48	-0.05	98.53	ADEQUATE
Medutest	10	25min	Unit	98.63	+0.08	98.55	ADEQUATE
VendorInvestigate	6 n=6	32min	High	98.56	-0.11	98.67	ADEQUATE
Kestrel	6 n=6	15min	Unit	98.73	+0.24	98.49	ADEQUATE
Nordanalyt	5 n=5	35min	High	98.65	+0.02	98.63	ADEQUATE

Figure. GHK-Cu purity by contributing laboratory. Any offset between rows has two possible sources — a real difference in the material each laboratory happened to receive, and the laboratory's own bias — and this figure cannot separate them. The paired analysis that can is on inter-lab agreement.