Cross-section

L-Glutathione (reduced) 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 L-Glutathione (reduced), with a class minimum gradient of 15 min, the method is a live explanation.

122 recordsmedian 99.00 %spec 98.5 %

Laboratory	Reports	Gradient	MS resolution	Median purity %	Published bias (pp)	Bias-adjusted	Method suitability
Janoshik	59	30min	High	99.07	+0.00	99.07	ADEQUATE
Medutest	23	25min	Unit	99.08	+0.08	99.00	ADEQUATE
PeptideMeter	20	28min	High	98.78	-0.05	98.83	ADEQUATE
VendorInvestigate	8	32min	High	98.78	-0.11	98.89	ADEQUATE
Nordanalyt	6 n=6	35min	High	98.64	+0.02	98.62	ADEQUATE
Kestrel	6 n=6	15min	Unit	99.34	+0.24	99.11	ADEQUATE

Figure. L-Glutathione (reduced) 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.