Solid phase extraction-diffuse reflectance infrared Fourier transform spectroscopy method for the detection of low concentrations of methylene blue pigment in aqueous matrices using MCM-41

• MCM-41 has high affinity for MB separation with a q m of 370.4 mg/g at pH 7.0. • MB detection on MB-loaded MCM-41 was realized after the SPE experiments by DRIFTS . • The SPE-DRIFTS method has a detection limit of 0.10 % w/w MB/MCM-41. • Detection of MB was successfully applied in a real water sample. • The method proposed here avoiding the use of expensive and toxic solvents. The efficiency and high sensitivity of the combination between solid phase extraction (SPE) with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) as a method for the monitoring of emerging contaminants (ECs) in water, was evaluated and optimized through the detection of aqueous methylene blue (MB) at low concentrations using MCM-41 as solid active phase. Through the sol–gel route and post-synthetic treatments three mesoporous ordered silica with MCM-41 pores arrangement were synthesized and deeply characterized in order to determine the physicochemical properties of the mesoporous solid phases. One has silanol surface groups while the others feature a mixture of aminopropyl/silanol or methyl/silanol surface moieties. The batch separation experiments at pH = 7.0 ± 0.2 showed that the pristine and methylated MCM-41 solid phases had the highest affinities toward MB with removal efficiencies greater than 99 % for these samples, while the aminopropyl-modified MCM-41 retained only 32.5 %. MB detection by DRIFTS was done through the appearance of the absorption bands at 1488, 1390 and 1337 cm −1 associated with C–H and C S + bending vibrations, with a limit of detection of 0.10 % w/w MB/MCM-41. When applied the SPE-DRIFTS method the necessary w/w ratio (0.10 %) was reached when a distilled water MB solution of 0.01 mg/L was passed through the SPE cartridge filled with 50 mg of MCM-41 and using a flow rate of 1.5 ml/min. The MB detection limit was successfully evaluated in a real water sample extracted to from río Negro, Patagonia, Argentina . The method presented here features the advantage of avoiding the use of expensive and toxic solvents as well as extra handling steps which could interfere with the detection process. The findings here reported suggest great potential of MCM-41-based SPE step prior to DRIFTS for ECs detection.