Liquid-liquid microextraction in a multicommuted flow system for direct spectrophotometric determination of iodine value in biodiesel

Chip-Based Spectrofluorimetric Determination of Iodine in a Multi-Syringe Flow Platform with and without In-Line Digestion-Application to Salt, Pharmaceuticals, and Algae Samples

In this work, a flow-based spectrofluorimetric method for iodine determination was developed. The system consisted of a miniaturized chip-based flow manifold for solutions handling and with integrated spectrofluorimetric detection. A multi-syringe module was used as a liquid driver. Iodide was quantified from its catalytic effect on the redox reaction between Ce(IV) and As(III), based on the Sandell–Kolthoff reaction. The method was applied for the determination of iodine in salt, pharmaceuticals, supplement pills, and seaweed samples without off-line pre-treatment. An in-line oxidation process, aided by UV radiation, was implemented to analyse some samples (supplement pills and seaweed samples) to eliminate interferences and release iodine from organo-iodine compounds. This feature, combined with the fluorometric reaction, makes this method simpler, faster, and more sensitive than the classic approach of the Sandell–Kolthoff reaction. The method allowed iodine to be determined within a range of 0.20–4.0 µmol L⁻¹, with or without the in-line UV digestion, with a limit of detection of 0.028 µmol L⁻¹ and 0.025 µmol L⁻¹, respectively.

Multi-energy calibration to circumvent matrix effects in the determination of biodiesel quality parameters by UV-Vis spectrophotometry

Biodiesel is a sustainable fuel, which consists of a mixture of fatty acid alkyl esters obtained by the transesterification of vegetable oils or animal fats. Due to the diversity of raw materials used in its production, the biofuel can show significant differences in its physicochemical properties, which causes severe matrix effects in biodiesel analysis. In this work, a calibration strategy recently proposed for atomic spectrometry, named multi-energy calibration (MEC), was evaluated as a tool to circumvent matrix effects in molecular spectrometry. The strategy yielded more accurate results in the spectrophotometric determination of the iodine value and free glycerol in biodiesel produced from different raw materials (root mean square error of prediction, RMSEP, values of 6.0 and 8.0, respectively), than both external standard calibration (EC, RMSEP as high as 45.6) and the standard additions method (SAM, RMSEP as high as 25.3). Moreover, results agreed with those obtained by the reference procedures at the 95% confidence level, which was not observed for EC (free glycerol determination) and SAM (iodine value determination). Coefficients of variation (n = 8) and limits of detection (99.7% confidence level) were, respectively, estimated at 1.7% and 5 g I₂/100 g iodine value and 3.0% and 10 mg kg^-1 free glycerol in biodiesel, which are comparable to or better than those achieved using previously proposed procedures. Thus, MEC is a viable alternative for biodiesel quality control, with outstanding minimization of matrix effects, simplicity, practicality, and environmental friendliness.