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Highlights: [•] A micromethod was developed for quantification of 5-n-alkylresorcinols (5nARs). [•] The 5nARs react with a Fast Blue RR salt (FBRR) in an alkaline alcoholic medium. [•] Readings of new method are highly correlated (R 2 =0.99) with a Fast Blue B method. [•] Bland–Altman plot suggests that both methods can be interchangeably used. [•] The new micromethod saves time, reagents and solvents for quantification of 5nARs. [Copyright &y& Elsevier]

[Display omitted] • Alkylresorcinols as biomarkers of gluten intake. • DHCA as target analyte in urine samples. • FB-doped PDMS-TEOS membranes as colorimetric sensing devices. • UV-vis spectroscopic at 520 nm for screening negative/positive responses. • In-tube SPME-CapLC to confirm DHCA as biomarker of gluten in-take. Celiac disease is an immune-mediated systemic disorder elicited by gluten and related prolamines in genetically susceptible individuals. The current treatment is a strict and lifelong gluten-free diet. However, compliance with the gluten-free diet is not always adequate and many food products contain low concentrations of gluten. The determination of dietary transgressions is a challenge for patients, physicians and dietitians. Alkylresorcinols (AR) have been proposed as sensitive and specific biomarkers of gluten consumption. In this work silica–polymer composites doped with fast blue B reagent (FB) have been used to estimate alkylresorcinols in biological samples. The proposed colorimetric device was synthetized by immobilizing FB into polydimethylsiloxane-tetraethylortosilicate composite. The assay was based on the spontaneous release of FB to the solution containing AR (3,5-dihydroxyhydrocinnamic acid, DHCA) and the azocomplexe formation (520 nm). The response was evaluated with UV-vis spectroscopy and chromatography (in-tube SPME-Capillary LC-DAD) to isolate DHCA signal. The spectroscopic analysis can be used as a screening tool to differentiate positive and negative samples. Meanwhile, the chromatographic assay was necessary to isolate DHCA response in positive samples. LOD was 60 ng mL -1 by adding a SPE step. Precision provided adequate results (RSD < 15%). Preliminary studies in urine samples displayed successful results, showing DHCA can be used as biomarker of gluten intake. The here proposed methodology clearly simplifies the dietary transgression evaluation thanks to the development of a pre-screening tool before the chromatographic analysis. [ABSTRACT FROM AUTHOR]