Table 2.

Metabolite recovery of the compounds in the spiking mixture (containing pure, known standard concentrations of different class compounds) indicated for each method. The compounds are grouped per class.

Spiking compound	Method 1 (original in-house)			Method 2 (acetonitrile addition)			Method 3 (two-step derivatization)			Method 4 (combined methods 2 & 3)			Method 5 (direct analysis)
	Pre-spike average	Post-spike average	% Recovery	Pre-spike average	Post-spike average	% Recovery	Pre-spike average	Post-spike average	% Recovery	Pre-spike average	Post-spike average	% Recovery	Pre-spike average	Post-spike average	% Recovery
4-Aminobutyric acid (GABA)	0.00	0.74	0.00	0.00	0.95	0.00	0.00	0.84	0.00	0.00	0.23	0.00	0.11	0.35	30.46
L-Alanine	0.00	3.06	0.00	0.00	4.01	0.00	0.00	3.70	0.00	0.00	1.79	0.00	1.85	3.01	61.35
L-Leucine	0.00	1.54	0.00	0.00	0.18	0.00	0.00	1.47	0.00	0.00	0.23	0.00	0.45	0.99	45.66
L-Tryptophan	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.01	0.00
L-Tyrosine	0.00	0.28	0.00	0.00	0.24	0.00	0.00	0.37	0.00	0.00	0.17	0.00	0.00	0.03	0.00
L-Phenylalanine	0.00	0.53	0.00	0.00	0.65	0.39	0.09	0.78	11.94	0.03	0.45	6.15	0.21	0.24	86.55
Ascorbic acid	0.00	0.02	0.00	0.00	0.04	0.00	0.00	0.09	0.00	0.00	0.01	0.00	0.09	0.11	86.49
Citric acid	0.57	0.79	72.25	1.02	1.24	82.56	0.59	0.89	65.61	0.90	0.69	130.81	1.63	1.38	118.12
Succinic acid	0.11	0.13	82.33	0.13	0.15	85.62	0.11	0.14	80.08	0.10	0.12	79.05	0.16	0.21	78.77
Palmitic acid	0.14	0.21	67.57	0.38	0.21	181.00	0.17	0.34	50.67	0.12	0.18	67.16	0.09	0.13	69.28
Average recovery			22.22			34.96			20.83			28.32			57.67