Table 1.

Comparison of relative standard deviation of peak area for quality control samples across normalization approaches.¹

Normalization Approach	RPLC Data		HILIC Data
	Median RSD (IQR)	Peaks with RSD < 0.3, n (%)	Median RSD (IQR)	Peaks with RSD < 0.3, n (%)
Raw Data	0.23	9827/12,811	0.33	8271/18,977
	(0.16–0.29)	(76.7%)	(0.23–0.48)	(43.6%)
SVR	0.15	12,023/12,794	0.19	15,158/18,882
	(0.10–0.20)	(94.0%)	(0.13–0.27)	(80.3%)
SVR and Creatinine	0.18	11,744/12,794	0.20	15,104/18,882
	(0.15–0.23)	(91.8%)	(0.13–0.27)	(80.0%)
SVR and Specific Gravity	0.15	12,023/12,794	0.19	15,158/18,882
	(0.10–0.20)	(94.0%)	(0.13–0.27)	(80.3%)
SVR and PQN	0.08	12,667/12,794	0.11	18,106/18,882
	(0.05–0.11)	(99.0%)	(0.07–0.16)	(95.9%)

¹ SVR addresses analytical variability, while creatinine, specific gravity, and PQN address concentration variability. RPLC data represent hydrophobic metabolites, and HILIC data represent hydrophilic metabolites. Raw data has been processed using XCMS without any application of a normalization technique. Abbreviations: RPLC, reversed-phase liquid chromatography; HILIC, hydrophilic interaction chromatography; RSD, relative standard deviation; IQR, interquartile range; SVR, support vector regression; PQN, probabilistic quotient normalization.