Selective determination of 3,5-dihydroxycinnamic acid in urine samples as gluten intake biomarker: high-performance thin-layer chromatography combined with colorimetric detection.

The determination of biomarkers is a significant field of analytical chemistry research under continuous evolution that contributes to enhance diagnostics and enable more personalized medicine. Celiac disease is a systemic autoimmune disorder caused by the ingestion of gluten (Glu) proteins found in various cereals. Currently, the only effective way to prevent and manage potential complications is through a strict gluten-free diet (GFD). However, both intentional and unintentional dietary transgressions can occur, often leading to persistent symptoms and ineffective treatment. In this scenario, the development of analytical strategies to detect biomarkers of gluten intake and monitor adherence to a GFD is of significant interest. Herein, we present an analytical strategy based on high-performance thin-layer chromatography (HPTLC) combined with colorimetric detection to estimate 3,5-dihydroxycinnamic acid (3,5-DHCA) as selective biomarker of Glu intake in urine. The approach combined Fast Blue (FB)-doped polydimethylsiloxane (PDMS) membrane with colorimetric HPTLC (RP-C18) giving rise to a selective method to isolate 3,5-DHCA response in urine samples. Detection by visual inspection, image analysis, and spectroscopic response was evaluated and compared. Analytical parameters were estimated showing a good sensitivity (limit of detection (LOD) ≤ 0.8 mg L^-1) and precision, relative standard deviation (RSD) values < 7%. Analysis of urine samples of celiac patients and control patients was performed, and recovery studies showed satisfactory values (R > 80%). The preliminary results indicated correlation between Glu intake and positive 3,5-DHCA responses. This study demonstrated that FB-doped PDMS membranes-HPTLC is a promising tool for detecting dietary transgressions to the GFD by visual inspection, and subsequent quantitative analysis by image analysis and spectroscopic techniques. Hence, the proposed analytical method contributes to the advance of knowledge about celiac disease, which still remains an important challenge to our society.