Flow-Injection Chemiluminescence Method for Sensitive Determination of Ascorbic Acid in Fruit Juices and Pharmaceutical Samples Using a Luminol-Cetyltrimethylammonium Chloride Reversed Micelle System

Dual-template molecularly surface imprinted polymer on fluorescent metal-organic frameworks functionalized with carbon dots for ascorbic acid and uric acid detection

In this work, dual-template molecularly imprinted polymer surfaces imprinted on blue fluorescent Cr-based MOF (Cr-MOF) functionalized with yellow emissive carbon dots (Y-CDs) were prepared using l-ascorbic acid (AA) and uric acid (UA) as templates for simultaneous selective recognition of AA and UA. The as-prepared nanocomposite probe (Y-CDs/Cr-MOF@MIP) contains two recognition site cavities and emits a dual well-resolved fluorescence spectra when excited at 390 nm; blue emission (λ_em 450 nm) is due to Cr-MOF, and yellow emission (λ_em 560 nm) is due to Y-CDs. The yellow fluorescence emission of Y-CDs was quenched upon the addition of ascorbic acid, while Cr-MOF's emission remained unaffected. In the same way, the blue fluorescence emission of the Cr-MOFs was quenched in the presence of uric acid, while the yellow emission remained constant. Both emissions were quenched in a sample containing both AA and UA. This can be exploited to design a dual-template biosensor to detect UA and AA simultaneously. The Y-CDs/Cr-MOF@MIP sensor displayed a dynamic linear response for AA in the range 25.0 µM - 425.0 µM with a detection limit of 1.30 µM, and for UA in the range 25.0 µM - 425.0 µM with a detection limit of 1.10 µM. The dual-target probe Y-CDs/Cr-MOF@MIP was highly selective and sensitive for the detection of UA and AA in human urine samples due to the selectivity of the two recognition sites.

Influencing Factors for Determining the Crystallinity of Native Cellulose by X-ray Diffraction

Full width at half maximum (FWHM) of diffraction peaks of native cellulose is larger than 1°. The diffraction peaks of the crystalline phase largely coincide with those of the amorphous phase of cellulose, leading to the low resolution. Therefore, when calculating the crystallinity of natural cellulose by fitting the peaks, only relying on the single evaluation factor of Rwp (R-weighted Pattern) may lead to great randomicity of calculation results. Due to the special crystal structure of natural cellulose and the characteristics of crystallinity determination by peak separation method, the XRD Rietveld fitting method is adopted to determine the crystallinity of native cellulose. Through limiting the convergence conditions of fitting functions, we firstly discuss the effects of peak shape functions, scanning range, and the positions of amorphous peaks on crystallinity determination, which helps to reduce the randomness of XRD in solving crystallinity of cellulose and improve the precision of calculation. Then, three evaluation indexes (Rwp, FWHM, and RSD) are used to evaluate the rationality of crystallinity calculation results. Moreover, the reproducibility and precision of the crystallinity of three kinds of natural cellulose are tested under the optimized conditions. At the same time, the optimized fitting method is adopted to calculate the content of cellulose I and II, which can be used to guide the selection of alkali concentration and alkali treatment time in the spinning process of native cellulose.

Development of an Optode Detector for Determination of Anionic Surfactants by Flow Injection Analysis

A flow-injection analysis (FIA) method for assaying an anionic surfactant (AS) using AS optode detector was demonstrated. The optode membrane consists of 2-nitrophenyl octyl ether as a plasticizer, lactone form rhodamine B (L-RB) and poly(vinyl chloride). The linear response concentration range of the AS optode to AS was 20 - 100 μmol dm^-3 in the FIA system. The sampling rate for an AS ion (40 μmol dm^-3 sodium dodecylbenzenesulfonate) in the proposed FIA system was ca. 5 samples h^-1. The AS level in commercially available laundry detergents by the proposed FIA system was determined.

Core-shell Au@Pt Nanoparticles Catalyzed Luminol Chemiluminescence for Sensitive Detection of Thiocyanate

In this study, core-shell Au@Pt nanoparticles (Au@Pt NPs) with peroxidase catalytic activity were synthesized by the seed-mediated method, and were used to catalyze the reaction of luminol-H₂O₂ to enhance the chemiluminescence (CL) intensity. It was found that thiocyanate (SCN^-) can effectively inhibit the catalytic activity of Au@Pt NPs. Based on this phenomenon, a method to detect SCN^- by using the Au@Pt NPs-catalytic luminol-H₂O₂ CL system was established, which has an ultra-low detection limit and an ultra-wide linear range, as well as the advantages of being simple and having low-cost and convenient operation. The research mechanism indicated that SCN^- could be adsorbed on the surface of Au@Pt NPs and occupies the active sites of Pt nanostructures, which led to a decrease in the amount of Pt⁰ and a loss of the excellent catalytic activity of Au@Pt NPs. After optimizing the experimental conditions, this assay for detecting SCN^- exhibited a good linear range from 5 to 180 nM, and the low detection limit was 2.9 nM. In addition, this approach has been successfully applied to the detection of SCN^- in tap-water samples, which has practical application value and embodies good development prospects.

Simultaneous quantification of peroxidase and ascorbic acid in biosamples with an automatic system based on a Fe(iii)/methylthymol blue-carbon dot simulative enzyme

Simultaneous and automatic quantification of peroxidase and ascorbic acid based on one reaction system and application of a carbon dot simulative enzyme.

Lansoprazole Determination in Pharmaceutical Formulations by Flow Injection Coupled with Acidic KMnO4-Quinine Chemiluminescence System

A simple and rapid flow injection chemiluminescence (FI-CL) method based on the reaction of potassium permanganate (KMnO₄) and quinine was established for the determination of lansoprazole in pharmaceutical formulations. A linear calibration curve was achieved over the range from 0.01 to 20.0 mg L^-1 LNP (R² = 0.9997 (n = 8); RSD = 1.1 - 3.7% (n = 4)) with a limit of detection of 3.0 × 10^-3 mg L^-1 (S/N = 3) and injection throughput of 150 h^-1. By applying the Student t-test (calculated t-test value: t = 1.059907664, and tabulated t-distributed (95%) = 2.200985) it was found that the proposed method and reported spectrophotometric method were not significantly different. The LNP was efficiently extracted and the recovery of LNP from the spiked pharmaceutical formulations was in the range of 91.0 - 105.9% (%RSD = 1.6 - 3.6, n = 4). No significant interference activity was detected from the excipients commonly found in the drug samples analyzed. The possible chemiluminescence emission mechanism is discussed briefly.

Surfactant enhanced flow injection chemiluminescence method for vitamin D3 determination in pharmaceutical formulations

A flow injection based chemiluminescence process has been reported for vitamin D₃ determination without using especial chemiluminescence reagent. Vitamin D₃ shows enhancement on the CL intensity of diperiodatocuprate(III) with surfactant (Triton X-100) solution. The calibration curve was found to be linear over the concentration range 0.01-40 mg/L (R² = 0.9997, n = 8) tested. A limit of detection (S/N = 3), limit of quantification (S/N = 10) and sample injection throughput of 2.5 × 10^-3, 8.3 × 10^-3 mg/L and 150 h^-1 respectively were obtained. Various experimental variables were tested to get most suitable response, e.g., the concentrations of reagents, and their flow rates, sample injection volume and photomultiplier tube voltage. The effect of potential interferences was also examined. Vitamin D₃ determination was successfully carried out in pharmaceutical formulations. The recoveries from the formulations were obtained in the range of 96 ± 4-108 ± 2%. The reaction mechanism discussion for diperiodatocuprate(III) complex-Triton X-100-vitamin D₃ was also included.