Table 2.

Number of reliable uncharacterized peaks detected using seven filtering conditions.

Filtering Order	Filtering Condition	Plasma	Urine
1	Number of peaks with S/N > 5 in the gathered QC samples	340	282
2	Number of peaks whose MTs and m/z’s do not match with those of known metabolites	276	202
3	Peaks that are detected in independently prepared QC samples (S/N > 5)	181	180
4	Pearson’s correlation coefficient (PCC) between amounts of samples and relative peak areas is above 0.3	115	153
5	Peaks that are not clustered with known peaks based on the differences in the migration times (dMTs) and the correlation between peak areas among the samples	99	145
6	Inferred fragment clusters based on the differences in the migration times (dMTs) and the correlation between peak areas among the samples	53	114
7	S/N of peak < 5 in the standard solution (labeled as All STD) which contains 278 and 240 standard compounds for cation and anion, respectively	35	74