A reliable and simple method for the assay of neuroendocrine tumor markers in human urine by solid-phase microextraction-gas chromatography-triple quadrupole mass spectrometry

Homovanillic acid (HVA), vanylmandelic acid (VMA), and 5-hydroxyindoleacetic acid (5-HIAA) are the metabolites of some catecholamines such as epinephrine, nor-epinephrine, dopamine and serotonin and their quantification is used in the diagnosis and management of patients with neurocrine tumors. A novel approach in the assay of these biomarkers in human urine samples by solid phase microextraction (SPME) combined with gas chromatography-triple quadrupole mass spectrometry (GC-QqQ-MS) is presented. A preliminary derivatization with ethyl chloroformate/ethanol was used and the corresponding derivatives were then extracted by SPME in immersion mode. The performance of five SPME fibers and three chloroformates were evaluated in univariate mode and the best results were obtained using the polyacrylate fiber and ethyl chloroformate. The variables affecting the efficiency of SPME analysis were optimized by the multivariate approach of "Experimental design" and, in particular, a central composite design (CCD) was applied. The optimum working conditions in terms of response values were achieved by performing analysis at room temperature with addition of NaCl (9.5%) and with an extraction time of 25.8 min. Identification and quantification of analytes were carried out by using a gas chromatography-triple quadrupole mass spectrometry (GC-QqQ MS) system in multiple reaction monitoring (MRM) acquisition. An evaluation of all analytical parameters shows that the proposed method provides satisfactory results. Very good linearities were, in fact, achieved in the tested calibration ranges with correlation coefficient values >0.99 for all the analytes and accuracies and RSDs calculated for between-run and tested at concentrations of 1, 10, and 80 mg L-1 were ranging from 91.3% to 106.6%, and from 0.5 to 8.9%, respectively. Moreover, the LOD values obtained can be considered very satisfactory (1.3, 0.046 and 24.3 mu g L-1 for HVA, VMA and 5-HIAA, respectively). The developed protocol represents, therefore, a simple, rapid and selective tool for assaying these acidic biomarkers in urine samples for neuroendocrine cancer diagnosis. (C) 2012 Elsevier B.V. All rights reserved. OI sindona, giovanni/0000-0002-5623-5795; NACCARATO, Attilio/0000-0001-5799-5369; Tagarelli, Antonio/0000-0002-8811-1631