A high performance liquid chromatography (HPLC) and an isotachophoresis (ITP) separation method were compared in a study of human urine specimens collected from unexposed individuals, which were added with m-methylhippuric-acid (MHA), a xylene (1330207) metabolite, ranging from 0.39 to 25 millimoles per liter. A paired t-test failed to show any significant differences between the two methods, with a correlation coefficient of 0.997. Recovery was linear with respect to added MHA, except at the highest concentrations. The average recovery of urinary MHA amounted to 102 percent for HPLC and 99 percent for ITP, and was not affected by low concentrations of MHA. The MHA quantitation limits (estimated twice the limits of detection) were 0.2 millimoles per liter by both methods. The authors state that in other studies with urine from exposed individuals, quantitation limits have ranged from 0.2 to 0.8 millimoles per liter, depending on the interfering agents present in the urine samples. The authors conclude that the two methods are complementary and give identical data, and that HPLC presents the advantage of being able to separate the ortho isomer, while ITP does not.