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A kinetic process can sometimes be observed during a chromatographic separation. The chemical reaction is coupled with the rapid distribution of the reacting compounds between the mobile and stationary phases. The use of the pre‐equilibrium approximation enables the derivation of the rate law for the chemical reaction(s) taking place in the mobile and/or stationary phase. A simple procedure is proposed for writing down this rate equation. It can be applied to any on‐column reaction, whether reversible or irreversible. For first‐ or pseudo‐first‐order kinetics, integration of the rate equation gives an exponential function of concentration with respect to time. To demonstrate the application of the proposed method, the kinetics of the decomposition of murexide in a reversed‐phase C8 column was studied. Murexide decomposes through a fast reversible protonation process to give purpuric acid, which then decomposes irreversibly. The stopped‐flow HPLC technique was used to obtain the entire kinetic profile for the on‐column reaction. Additionally, the kinetics was measured off‐column using the same mobile phase. The values of the kinetic parameters obtained from the batch experiments enabled the determination of all kinetic parameters of the on‐column reaction using non‐linear least squares fitting of the derived rate equation. [ABSTRACT FROM AUTHOR]

Introduction: Phytochemical analysis of phenolic acids and flavonols poses a challenge, necessitating the development of an efficient separation method. This facilitates the quantification of these compounds, yielding valuable insights into their benefits. Objective: To develop a highly effective separation of phenolic acids and flavonols by capillary electrophoresis and ultraviolet (UV) detection through the modification of the capillary surface using 3‐aminopropyltriethoxysilane (APTES) at millimolar concentrations. Methods: The capillary surface is modified with 0.36 mM‐APTES solution. The electrolyte is 20.0 mM borate buffer (pH 9.0). Separation performance (plate number N, resolution Rs), stability, and reproducibility of the coating procedure are evaluated using the analysis of phenolic acids, rutin and quercetin. Results: The modified capillary provided efficient separation with plate numbers N ≥ 1.0 × 104 m−1 and resolution Rs ≥ 0.8 for all pairs of adjacent peaks of the separation of five selected phenolic acids, rutin, quercetin, caffeine and methylparaben (as internal standard). The precisions of the relative migration times for 17 consecutive analyses of samples over 3 h were 1% relative standard deviation (RSD) for rutin and 7% RSD for quercetin. The analysis of rutin and quercetin in 12 dietary supplement product samples only required a simple dilution step for sample preparation. Conclusion: A straightforward modification technique utilising millimolar concentrations of APTES resulted in highly efficient separation of phenolic acids, rutin and quercetin, accompanied by high precision and surface stability. The modified capillary proved successful in analysing rutin and quercetin content in dietary supplements. The analysis of phenolic acids and flavonols poses challenges, demanding the development of an effective separation technique. This study aimed to achieve separation using capillary electrophoresis and UV detection, achieved by modifying the capillary surface with APTES. The modified capillary demonstrated efficient separation with high plate numbers and resolution for diverse compounds. The method exhibited excellent stability and reproducibility. Analysis of rutin and quercetin in dietary supplement samples only required a simple sample dilution step. This approach provides an efficient method of phenolic acids and flavonols analysis conveniently. [ABSTRACT FROM AUTHOR]

This work presents the use of a transparent 'Cross Injection Analysis' (CIA) platform as a flow system for chemiluminescence (CL) measurements. The CL-CIA flow device incorporates introduction channels for samples and reagents, and the reaction and detection channels are in one acrylic unit. A photomultiplier tube placed above the reaction channel detects the emitted luminescence. The system was applied to the analysis of (i) Co(II) via the Co(II)-catalyzed H2O2-luminol reaction and (ii) paracetamol via its inhibitory effect on the catalytic activity of Fe(CN)63− on the H2O2-luminol reaction. A linear calibration was obtained for Co(II) in the range of 0.002 to 0.025 mg L−1 Co(II) (r2 = 0.9977) for the determination of Co(II) in water samples. The linear calibration obtained for the paracetamol was 10 to 200 mg L−1 (r2 = 0.9906) for the determination of pharmaceutical products. The sample throughput was 60 samples h−1. The precision was ≤4.2% RSD. The consumption of the samples and reagents was ca. 170 µL per analysis cycle. [ABSTRACT FROM AUTHOR]

AbstractAcrylamide, a probable human carcinogen present in heat-processed foods and environmental contaminants, requires sample extraction and preconcentration before chromatographic analysis. The method developed in this study employed derivatization with xanthydrol and dispersive liquid–liquid microextraction utilizing low-density anisole. Durian or potato chips were combined with deionized water, defatted with hexane, and subjected to precipitation of soluble carbohydrates and proteins using clarification reagents. Water samples were filtered through a membrane filter. Acrylamide was derivatized by introducing an acidic methanolic solution of xanthydrol at 50 °C. The derivatized acrylamide was extracted with 70 µL of anisole and vortexed, with the methanol from the xanthydrol solution serving as the disperser solvent. The anisole layer was analyzed using gas chromatography with both flame ionization and mass spectrometric detection. Linear calibration plots exhibited coefficients of determination >0.9997. The precision was measured at <10% RSD, and recoveries ranged from 84% to 107%. The quantitation limit varied from 2 to 10 µg kg−1 for processed chips and from 0.05 to 0.10 µg L−1 for water samples. Acrylamide was detected in all processed chip samples, with some concentrations exceeding the benchmark value of 750 μg kg−1. However, no acrylamide was identified in any of the water samples. [ABSTRACT FROM AUTHOR]

Introduction: Brassica vegetables contain high levels of indole compounds which have been found to provide health benefits, especially as cancer‐preventive agents. An efficient and rapid method using solvent extraction with capillary electrophoresis (CE) and ultraviolet (UV) detection was developed for the determination of four major indoles from four types of Brassica vegetables. Materials and Methods: Freeze‐dried samples of four Brassica vegetables, i.e. broccoli, cauliflower, Chinese cabbage and cabbage, were selected. Hence, 1 mL of the binary solvent dimethylformamide (DMF)–methanol, 4:1 (v/v), was used for sample extraction. The extracts were diluted with the running buffer and directly analysed using CE with UV detection of four indole compounds. Results: The binary solvent DMF–methanol, 4:1 (v/v) was selected from studies of the extraction efficiency of standard indoles spiked in ivy gourd (as the negative control sample) and using diphenylamine as the internal standard. Recovery was 80(±10)–120(±3)% for the four indoles: indole‐3‐carbinol (I3C), indole‐3‐acetonitrile (I3A), indole‐3‐acetic acid (IAA), and 3,3′‐diindolylmethane (DIM). For direct analysis suitable dilution of the extract with the running buffer was required. The linear range of the quantitation is 0.75–25.0 μg/mL, limit of detection (LOD) of 0.14–0.52 μg/mL and r2 > 0.998. The amount of indole in the Brassica vegetables are in the order I3C > > IAA, I3A > DIM. Conclusion: A rapid method for extraction and quantitation of four indoles in four Brassica vegetables using CE with UV detection was developed. It has the potential as an efficient technique for generating data for use in agricultural and nutritional studies. Rapidmeasurement of four indole compounds in Brassica vegetables using one milliliter of a binary organic solvent extract was achieved with capillary electrophoresis‐UV analysis. Freeze‐dried samples of four Brassica vegetables were prepared. An aliquot extract was diluted with the running buffer and directly analysed using CE‐UV detection for indole compounds. [ABSTRACT FROM AUTHOR]