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.

41 recordsmedian 98.54 %spec 97.0 %

Laboratory	Reports	Gradient	MS resolution	Median purity %	Published bias (pp)	Bias-adjusted	Method suitability
Janoshik	19	30min	High	98.45	+0.00	98.45	ADEQUATE
PeptideMeter	8	28min	High	98.99	-0.05	99.04	ADEQUATE
Medutest	6 n=6	25min	Unit	98.96	+0.08	98.88	ADEQUATE
VendorInvestigate	3 n=3	32min	High	98.35	-0.11	98.46	ADEQUATE
Kestrel	3 n=3	15min	Unit	98.86	+0.24	98.62	ADEQUATE
Nordanalyt	2 n=2	35min	High	98.41, 98.98	+0.02	—	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.