Sensitive determination of endogenous hexanal and heptanal in urine by hollow-fiber liquid-phase microextraction prior to capillary electrophoresis with amperometric detection

Hexanal (Hex) and heptanal (Hep) in human blood have been regarded as potential biomarkers of lung cancer. In this work, a hollow-fiber liquid-phase microextraction (HF-LPME) method has been developed for the preconcentration of these trace aldehydes in urine samples. After derivatization with an electroactive compound 2-thiobarbituric acid, these two non-electroactive aldehydes were converted to electroactive adducts, therefore detectable by capillary zone electrophoresis with amperometric detection (CZE-AD) approach. Experimental conditions of derivatization, extraction, electrophoretic separation and detection were optimized. Under the optimum conditions, the enrichment factors for Hex and Hep could reach 320 and 355, respectively. The limits of detection for Hex and Hep were 2.7 and 0.97 nM, respectively; the average recoveries were in the range of 61–95% and relative standard deviation (RSD) values less than 8.5%. The present method has been applied to quantitative analysis of two biomarkers in human urine in lieu of blood samples, and the assay results showed that the contents of Hex (0.99–6.7 μM) and Hep (2.5–6.4 μM) found in the urine sample of the lung cancer patients were significantly higher than those in the healthy volunteers, liver cancer patients, as well as diabetics. The proposed HF-LPME/CZE-AD method may provide a potential alternative for early non-invasive diagnosis of lung cancer disease.