Two-dimensional isotachophoresis for the analysis of homovanillic acid and vanillylmandelic acid in urine for cancer therapy monitoring

Homovanillic acid (HVA) and vanillylmandelic acid (VMA) are routinely analyzed by HPLC with electrochemical detection after solid phase extraction for the diagnosis of neuroblastoma and phaechromocytoma. The aim of our study was to investigate whether these compounds can be determined without sample preparation using capillary isotachophoresis (ITP). For this purpose we used a commercially available instrument with two coupled capillary columns. HVA and VMA could be easily separated by ITP-ITP analysis at pH 3.4; the LODs were in the lower mu mol center dot L-1 range using conductivity detection. ITP calibration curves in spiked urine samples showed good linear correlation. However, although good correlation with HPLC analysis was also found, the ITP-ITP values were elevated compared to the HPLC values due to underlying matrix compounds in the respective zones.