Quantitative measurement of 4-hydroxy-3-methoxymandelic and homovanillic acids in plasma using capillary gas chromatography-mass spectrometry and stable isotope dilution: Preliminary data

Determination of homovanillic acid (HVA) in human plasma by HPLC with coulometric detection and a new SPE procedure

A sensitive high-performance liquid chromatographic method has been developed for the determination of homovanillic acid (HVA), the main metabolite of dopamine, in human plasma. Analyses were carried out on a reversed-phase column (C8, 250 mm x 4.6 mm i.d., 5 microm) using a mobile phase composed of 10% methanol and 90% aqueous citrate buffer, containing octanesulfonic acid and EDTA at pH 4.8. Coulometric detection was used, setting the guard cell at +0.100 V, the first analytical cell at -0.200 V and the second analytical cell at +0.500 V. A careful solid-phase extraction procedure, based on strong anion exchange (SAX) cartridges (100 mg, 1 mL), was implemented for the pre-treatment of plasma samples. Extraction yield was satisfactory, being the mean value 98.0%. The calibration curve was linear over the concentration range of 0.2-25.0 ng mL(-1) of homovanillic acid. The limit of quantitation (LOQ) was 0.2 ng mL(-1) and the limit of detection (LOD) was 0.1 ng mL(-1). The method was successfully applied to plasma samples from former alcohol, cocaine and heroin addicts. Results were satisfactory in terms of precision and accuracy. Hence, the method is suitable for the determination of homovanillic acid in human plasma.

The secretion of ibuprofen metabolites interferes with the capillary chromatography of urinary homovanillic acid and 4-hydroxy-3-methoxymandelic acid in neuroblastoma diagnosis

Neuroblastoma is the most common extracranial solid tumor in children. Abnormal secretion of catecholamines in tissues and body fluids allows for the differential diagnosis of neuroblastoma from other neoplasms and its distinction from non-neoplastic inflammatory diseases. This is achieved by assaying homovanillic acid and 4-hydroxy-3-methoxymandelic acid, the catabolites of catecholamine metabolism. In the course of an evaluation of children with suspected neuroblastoma, homovanillic acid and 4-hydroxy-3-methoxymandelic acid were analyzed in urine samples by capillary gas chromatography with flame ionization detection after extraction and derivatization of these compounds as trimethylsilyl derivatives. In three urine samples a significant increase in biogenic amines was observed, but these results were not confirmed by thin-layer chromatography. Patient history revealed that these children had been treated with ibuprofen, an analgesic and anti-inflammatory drug. To verify how ibuprofen or its metabolites may have interfered with capillary gas chromatography with flame ionization detection, we analyzed the same samples by capillary gas chromatography-mass spectrometry. In urine samples from patients on the drug, the presence of a peak identified as the trimethylsilyl ester of hydroxyibuprofen, which had the same retention time as 4-hydroxy-3-methoxymandelic acid, was found to interfere with the capillary gas chromatography with flame ionization detection analysis of the metabolite. This interference must be taken into account during the laboratory diagnosis of neuroblastoma.