Table II.

Molecules used as internal standards.

Name	CAS no.	Concentration
L-2-chlorophenylalanine	103616-89-3	1 µg/ml
(2H3)-L-Carnitine HCl	350818-62-1	1 µg/ml
4-Fluoro-L-α-phenylglycine	19883-57-9	1 µg/ml
L-Phenylalanine (2–13C, 99%)	63-91-2	1 µg/ml
(2H5)-Hippuric acid	53518-98-2	1 µg/ml
(2H5)-Kynurenic acid	350820-13-2	1 µg/ml
(2H5)-Phenoxy acetic acid	154492-74-7	1 µg/ml

A 10-µl 100-ppm mixture of each internal standard was added to 100 µl 70% methanol-water extract.