Cross-section

NAD+ 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 NAD+, with a class minimum gradient of 15 min, the method is a live explanation.

44 recordsmedian 99.28 %spec 97.0 %

Laboratory	Reports	Gradient	MS resolution	Median purity %	Published bias (pp)	Bias-adjusted	Method suitability
Janoshik	21	30min	High	99.37	+0.00	99.37	ADEQUATE
Nordanalyt	7 n=7	35min	High	99.47	+0.02	99.45	ADEQUATE
VendorInvestigate	6 n=6	32min	High	98.37	-0.11	98.48	ADEQUATE
PeptideMeter	4 n=4	28min	High	98.33	-0.05	98.38	ADEQUATE
Medutest	4 n=4	25min	Unit	99.23	+0.08	99.16	ADEQUATE
Kestrel	2 n=2	15min	Unit	98.28, 98.06	+0.24	—	ADEQUATE

Figure. NAD+ 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.