Ascorbic Acid Vitamin Research Articles

Amperometric sensor based on carbon nanotube, ionic liquid, and polyaspartic acid for ascorbic acid determination

AbstractAn amperometric sensor for ascorbic acid determination has been developed by modifying the surface of a glassy carbon electrode (GCE) with polyaspartic acid (PolyAsp), carboxylated multi‐walled carbon nanotube (c‐MWCNT), and ionic liquid (IL, 1‐butyl‐3‐methylimidazolium hexafluorophosphate). The amount of each modification material on the surface was optimized in order to achieve good analytical performance. The operating conditions of c‐MWCNT−IL/PolyAsp/GCE were optimized. The performance characteristics of c‐MWCNT−IL/PolyAsp/GCE were investigated at optimum pH (8.0) and optimum potential (+0.20 V), and the sensor responded linearly to ascorbic acid between 5.3–2766.3 μM with a sensitivity of 19.64 μA mM−1 and detection limit of 3.0 μM. Determination of ascorbic acid in vitamin C tablet, vitamin C injection solution, and orange juice was successfully performed with the presented sensor and the recovery values were found between 98.9% and 101.6%.

Efficient Estimation of ascorbic acid in vitamin C tablets enabled by phase-transfer strategy

In this paper, we introduced a novel phase-transfer strategy tailored for the efficient batch detection of ascorbic acid in vitamin C tablets. This method entailed the reaction between ascorbic acid and an excess of potassium permanganate. Subsequent reaction of the residual potassium permanganate with sodium oxalate in an acidic medium led to the generation of carbon dioxide. The quantification of the produced carbon dioxide was achieved using headspace GC, enabling the indirect measurement of ascorbic acid. The obtained findings revealed that the headspace method exhibited satisfied precision with a relative standard deviation of less than 2.11 % and high sensitivity with a limit of quantitation of 0.27 μmol. These results firmly establish the reliability of this innovative approach for determining ascorbic acid. In addition, the highly automated feature of headspace method significantly enhances the efficiency of batch sample detection and reduces the errors caused by human operation. Thus, the adoption of the transformed phase strategy has demonstrated its effectiveness in assessing ascorbic acid, especially for large-scale sample analysis in industrial applications, owing to its efficiency, precision, and sensitivity.

Iron modified hydrogen-bonded organic framework as fluorescent sensor for ascorbic acid detection

Herein, iron modified hydrogen-bonded organic framework (Fe-HOF) was successfully prepared by introducing the yellow-green fluorescent ligand 2,5-dihydroxyterephthalic acid into HOF and then modifying Fe3+. A simple turn-on fluorescence strategy is proposed for the detection of ascorbic acid (AA) based on Fe-HOF. Fe3+ could effectively quench fluorescence emission of HOF. In the presence of AA, Fe3+ was reduced to Fe2+, which led to the fluorescence recovery of HOF, thus realizing the fluorescence quantitative detection of AA. These fluorescence responsive behaviors of Fe-HOF ensure fluorescence assay of AA within 0.5 − 8 μM, along with a limit of detection (LOD) of 0.14 μM. The sensing platform could realize the rapid detection of ascorbic acid in vitamin C pills, tablets and beverages in the detection of ascorbic acid with good recoveries.

Selective fluorescence detection of acetylsalicylic acid, succinic acid and ascorbic acid based on a responsive lanthanide metal fluorescent coordination polymer.

A fluorescent sensor for highly selective and ultrasensitive detection of acetylsalicylic acid (ASA), succinic acid (SA), and ascorbic acid (AA) was reported. The water-soluble fluorescent ligand salicylic acid (Sal) was generated through catalyzing ASA by the hydrolase activity of zeolitic-imidazolate framework-8 (ZIF-8) or natural esterase (Est). The Sal can coordinate with 2-methylimidazole (2-MIm) and Ln(III) to form a fluorescent lanthanide coordination polymer (LCP), which has a fluorescence emission peak with the maximum wavelength at 412 nm (the excitation wavelength at 300 nm). Therefore, the detection of ASA can be achieved through the fluorescence intensity changes of LCPs in the system, which has comparable sensitivity and good selectivity (linear range of 0.031-1.00 mM and LODs of 11.72 and 3.22 μM) as compared to a direct reaction between Est/ZIF-8 and ASA for detecting ASA (linear range of 0.05-1.20 mM and limits of detection (LODs) of 4.43 and 4.58 μM). Furthermore, upon the addition of SA and AA, the fluorescence intensity of the reaction system can be enhanced and weakened through changing the energy resonance transfer pathways and affecting the enzymatic reaction process, respectively, realizing their sensitive and selective fluorescence detection. The established fluorescent sensors can work well in a wide linear range of SA concentrations from 0 to 2.50 mM (Est-based reaction system) and 0 to 1.50 mM (ZIF-8-based reaction system) with the LODs of 0.032 and 0.028 mM, respectively. The linear ranges of AA concentrations are from 0.0078 to 0.25 mM (Est-based reaction system) and 0.0078 to 0.13 mM (ZIF-8-based reaction system) with the LODs of 2.54 and 3.80 μM, respectively. The established sensors were successfully used in the detection of SA in rabbit plasma, with a recovery of 84.0%-98.7%. Additionally, the contents of ASA in Aspirin Enteric-Coated tablets and AA in vitamin C tablets were also determined by the developed methods.

N/S-GQDs/KMnO4 hybrid as a colorimetric and fluorescent dual-signal readout probe for sensitive and selective detection of ascorbic acid

A nitrogen and sulfur co-doped graphene quantum dots (N/S-GQDs) and permanganate was employed to prepare a N/S-GQDs/KMnO4 dual-signal readout colorimetric and fluorescent probe for sensitive detection of ascorbic acid (AA). In the detection system, the addition of KMnO4 quenched significantly the fluorescence (FL) of N/S-GQDs, meanwhile, the transparent aqueous dispersion of N/S-GQDs changed into yellow–brown with new absorption peak (maximum absorption at 338 nm). Interestingly, introduction of AA into the N/S-GQDs/KMnO4 system could recover the quenched fluorescence and result in a decrease in the absorbance (at 338 nm) of the test solution in a concentration dependent manner, and hence demonstrated the potential practical use of the sensing system for AA detection. Based on various spectroscopic studies, it has been concluded that the static as well as inner filter effect was the main quenching mechanisms in the detection system. The dual-response sensor showed linear response in the concentration range between 0.01 and 30 µM with the limit of detection (LOD) of 8.3 nM and 100 nM, respectively, for the fluorescent and colorimetric detections. In addition, the proposed detection system has been successfully applied to the detection of AA in vitamin C tablets. Moreover, the proposed detection strategy is convenient and fast, prevents complex and tedious probe preparation procedure, and capable of visual detection of AA.

Single-atom Fe nanozymes with excellent oxidase-like and laccase-like activity for colorimetric detection of ascorbic acid and hydroquinone.

Although traditional Fe-based nanozymes have shown great potential, generally only a small proportion of the Fe atoms on the catalyst's surface are used. Herein, we synthesized single-atom Fe on N-doped graphene nanosheets (Fe-CNG) with high atom utilization efficiency and a unique coordination structure. Active oxygen species including superoxide radicals (O2•-) and singlet oxygen (1O2) were efficiently generated from the interaction of the Fe-CNG with dissolved oxygen in acidic conditions. The Fe-CNG nanozymes were found to display enhanced oxidase-like and laccase-like activity, with Vmax of 2.07 × 10-7M∙S-1 and 4.54 × 10-8M∙S-1 and Km of 0.324mM and 0.082mM, respectively, which is mainly due to Fe active centers coordinating with O and N atoms simultaneously. The oxidase-like performance of the Fe-CNG can be effectively inhibited by ascorbic acid (AA) or hydroquinone (HQ), which can directly obstruct the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). Therefore, a direct and sensitive colorimetric method for the detection of AA and HQ activity was established, which exhibited good linear detection and limit of detection (LOD) of 0.048μM and 0.025μM, respectively. Moreover, a colorimetric method based on the Fe-CNG catalyst was fabricated for detecting the concentration of AA in vitamin C. Therefore, this work offers a new method for preparing a single-atom catalyst (SAC) nanozyme and a promising strategy for detecting AA and HQ.

New findings on ligand series used as SARS-CoV-2 virus inhibitors within the frameworks of molecular docking, molecular quantum similarity and chemical reactivity indices

Background The severe acute respiratory syndrome coronavirus (SARS-CoV)-2 virus causes an infectious illness named coronavirus disease 2019 (COVID-19). SARS-CoV is a positive-sense single-stranded RNA virus from the Betacoronavirus genus. The SARS-CoV-2 RNA-dependent RNA polymerase (RdRp) has an important role in the viral life cycle and its active site is a very accessible region, thus a potential therapeutic approach may be to target this region to study the inhibition of viral replication. Various preexisting drugs have been proposed for the treatment of COVID-19 and the use of existing antiviral agents may reduce the time and cost of new drug discoveries, but the efficacy of these drugs is limited. Therefore, the aim of the present study was to evaluate a number of ligands used as SARS-CoV-2 virus inhibitors to determine the suitability of them for potential COVID-19 treatment. Methods In this study, we selected a series of ligands used as SARS-CoV-2 virus inhibitors such as: abacavir, acyclovir, amprenavir, ascorbic acid vitamin C, azithromycin, baloxavir, boceprevir, cholecalciferol vitamin D, cidofovir, edoxudine, emtricitabine, hydroxychloroquine and remdesivir. These ligands were analyzed using molecular docking, molecular quantum similarity, and chemical reactivity indices defined within a conceptual density functional theory framework. Results The analysis of molecular quantum similarity indices on inhibitors showed a high number of differences from a structural point of view. However, they are quite similar in their electronic density, obtaining the highest values in the electronic similarity index. Global and local chemical reactivity indices were analyzed. Conclusions These studies allowed for the identification of the main stabilizing interactions using the crystal structure of SARS-CoV-2 RdRp. The molecular quantum similarity and chemical reactivity descriptors provide novel insights into these ligands that can be used in the design of new COVID-19 treatments.

Dual signal AA detection based on fluorescence and local surface plasmon resonance absorption technology

The core/shell Au@MnO2 nanoparticles (Au@MnO2 NPs) were prepared and characterized by UV–vis spectrum, transmission electron microscopy (TEM) and X-ray photoelectron spectrum (XPS). It was found that MnO2 in the shell of Au@MnO2 NPs could oxidize thiamine (VB1) into blue fluorescent thiochrome (TC). The reduction of MnO2 in the shell layer could lead to a decrease of Au@MnO2 NPs size along with a blue shift of the localized surface plasmon resonance (LSPR) peak. Once ascorbic acid (AA) was introduced, MnO2 in the shell was rapidly reduced to Mn2+ ions. Accordingly, the oxidation of VB1 was inhibited and the fluorescence of TC was weakened. Based on these phenomena, we have established a dual signal method for AA determination with the help of UV–vis and fluorescence spectrophotometer. Under the optimum conditions, the LSPR absorption peak shift (Δλ) of Au@MnO2 NPs and the decrease in fluorescence of TC correlated well with AA concentration ranging from 0.75 to 17.5 μM. The detection limits of LSPR absorption assay and fluorescence assay were 0.18 and 0.47 μM, respectively. More importantly, this dual-signal detection method has been used for the determination of AA in vitamin C tablets with high accuracy and precision, indicating its promising potential applications.

Highly efficient determination of trace ascorbic acid in vitamin C tablets by boronate affinity-modified magnetic metal–organic frameworks

Ascorbic acid (AA) plays an important role in many life processes. The chronic nutritional deficiency of AA will lead to the symptoms of scurvy. Therefore, the sensitive quantitative detection of AA is most important in the pharmaceutical analysis, food industry and diagnostic application. In this study, a dual-functional magnetic metal–organic frameworks (Fe3O4@SiO2@UiO-PBA) nanoparticles was synthesized by modifying phenylboronic acid to the surface of magnetic UiO-66-NH2 via postsynthetic modification for selectively and sensitively florescent detection of AA. Due to the abundant amino groups and grafted phenylboronic acid, the proposed nanoparticles have the dual properties of hydrophilicity and boronate affinity. Under optimum conditions, the obtained Fe3O4@SiO2@UiO-PBA nanoparticles can detect AA within 30 s, and has a good linear relationship with the concentration of AA in the range of 5.0–60 μM with a detection limit of 2.5 μM (S/N = 3). In addition, the prepared Fe3O4@SiO2@UiO-PBA nanoparticles showed excellent selectivity and great potential application in the highly efficient determination of trace AA in vitamin C tablets. These results indicated that a convenient method was proposed to develop fluorescent probes for rapid and sensitive detection of trace AA in real samples.

Hierarchical N-doped porous carbon scaffold Cu/Co-oxide with enhanced electrochemical sensing properties for the detection of glucose in beverages and ascorbic acid in vitamin C tablets

This research focuses on the development of a highly efficient electrocatalyst, CuxO/NPC@Co3O4/NPC-10–7, for detecting glucose and ascorbic acid. In a 0.1 M NaOH solution, the modified electrode exhibits a sensitivity of 3314.29 μA mM−1 cm−2 for glucose detection. The linear range for ascorbic acid sensing is 0.5 μM − 23.332 mM, with a detection limit as low as 0.24 μM. In a 0.1 M PBS solution, the linear range for ascorbic acid detection extends to 43.328 mM, which represents the best performance reported to date by chronoamperometry. Moreover, the electrode demonstrates high accuracy, with a recovery rate of 96.80 % − 103.60 % for glucose detection and a recovery rate of 95.25 % − 104.83 % for ascorbic acid detection. These results suggest that the CuxO/NPC@Co3O4/NPC-10–7 modified electrode shows significant potential for practical applications in food detection.

New findings on ligand series used as SARS-CoV-2 virus inhibitors within the frameworks of molecular docking, molecular quantum similarity and chemical reactivity indices

Background: The severe acute respiratory syndrome coronavirus (SARS-CoV)-2 virus causes an infectious illness named coronavirus disease 2019 (COVID-19). SARS-CoV is a positive-sense single-stranded RNA virus from the Betacoronavirus genus. The SARS-CoV-2 RNA-dependent RNA polymerase (RdRp) has an important role in the viral life cycle and its active site is a very accessible region, thus a potential therapeutic approach may be to target this region to study the inhibition of viral replication. Various preexisting drugs have been proposed for the treatment of COVID-19 and the use of existing antiviral agents may reduce the time and cost of new drug discoveries, but the efficacy of these drugs is limited. Therefore, the aim of the present study was to evaluate a number of ligands used as SARS-CoV-2 virus inhibitors to determine the suitability of them for potential COVID-19 treatment. Methods: In this study, we selected a series of ligands used as SARS-CoV-2 virus inhibitors such as: abacavir, acyclovir, amprenavir, ascorbic acid vitamin C, azithromycin, baloxavir, boceprevir, cholecalciferol vitamin D, cidofovir, edoxudine, emtricitabine, hydroxychloroquine and remdesivir. These ligands were analyzed using molecular docking, molecular quantum similarity, and chemical reactivity indices defined within a conceptual density functional theory framework. Results: The analysis of molecular quantum similarity indices on inhibitors showed a high number of differences from a structural point of view. However, they are quite similar in their electronic density, obtaining the highest values in the electronic similarity index. Global and local chemical reactivity indices were analyzed. Conclusions: These studies allowed for the identification of the main stabilizing interactions using the crystal structure of SARS-CoV-2 RdRp. The molecular quantum similarity and chemical reactivity descriptors provide novel insights into these ligands that can be used in the design of new COVID-19 treatments.

Dual-functional lanthanide-MOF probe nanocomposite based on hydroxyapatite nanowires as fluorescent sensor for ascorbic acid.

Adual-functional lanthanide-MOF nanocomposite probewas designed and constructed for the detection of ascorbic acid (AA). The magnetically functionalized hydroxyapatite nanowires are selected as the carriers and simultaneously loaded with ciprofloxacin (CIP) and terbium metal organic framework to form the internal reference fluorescence probe nanocomposite (Fe3O4-HAPNWs-Tb/MOF-CIP). This dual-functional lanthanide-MOF probe not only combines the respectively unique fluorescence properties of lanthanide MOFs and CIP, but also takes full advantage of the rapid separation properties of the magnetic component. Structural and spectroscopic characterization results have demonstrated the successful synthesis of probe material and the fluorescence mechanism. At a suitable excitation wavelength (295nm), the probe can simultaneously emit characteristic fluorescence of CIP (445nm) and Tb3+ (543nm). In the presence of AA, the ratio of I543/I445 decreases rapidly with increasing of AA concentration. The linear range of determinationis 0.3-40μM with a detection limit of 20.4nM. Thecontents of AA in vitamin C tablets and four fruit juice samples were detected by the composite probe. The spiked recoveries ranged from 82.6 to 104.2% with relative standard deviations (RSD) less than 2.1%, revealing the practical application value of the developed sensor in healthcare and food fields. A novel internal reference fluorescence sensor (Fe O -HAPNWs-Tb/MOF-CIP) was constructed for detecting ascorbic acid by solvothermal and self-assembly techniques, showing excellent selectivity and sensitivity based on the different responses of Tb/MOF and CIP to the target.

Facile and sustainable synthesis of sodium lignosulfonate derived carbon quantum dots for the detection of total Mn and ascorbic acid

A fluorescent nanoprobe based on sodium lignosulfonate derived carbon quantum dots (SLS-CQDs) was fabricated through a facile and sustainable one-step hydrothermal treatment. The obtained SLS-CQDs had excellent fluorescence properties and were applied to detect total Mn and ascorbic acid (AA). The fluorescence of SLS-CQDs could be effectively quenched by Mn based on a static quenching process and recovered by the addition of AA. An “on–off-on” fluorescent nanoprobe was established to determine total Mn and AA with the detection limits of 6.9 µg/L and 0.65 µM with the corresponding linear ranges of 0.25–2.25, 5–25 mg/L, and 5–110 µM, respectively. This nanoprobe could accurately detect total Mn in surface water and AA in Vitamin C effervescent tablet samples. The proposed method is simple and can be performed easily, indicating that SLS-CQDs might be used in environmental monitoring, food and drug testing.

Cerium/polyacrylic acid modified porphyrin metal-organic framework as fluorescence and photothermal sensor for ascorbic acid measurement

A fluorescence and photothermal dual-signal assay was developed for the determination of ascorbic acid (AA). Cerium/polyacrylic acid modified porphyrin metal-organic frameworks (PCN-224@PAA-Ce MOFs) exhibit oxidase-like activity and can effectively oxidize 3,3 ′, 5,5 ′-tetramethylbenzidine (TMB) from colorless substrates to blue substrates (oxTMB). The absorption spectrum of oxTMB overlaps with the emission spectrum of PCN-224@PAA-Ce, resulting in quenching of fluorescence emission of PCN-224@PAA-Ce. oxTMB, as an excellent photothermal agent, converts the optical signal into the thermal signal (temperature increasing) driven by 808 nm laser. In the presence of AA, the blue oxTMB was reduced to colorless TMB, which led to the fluorescence recovery of PCN-224@PAA-Ce and at the same time, the photothermal signal was changed with the temperature decreasing under the driving of 808 nm laser. The detection limits (LOD) of fluorescence/photothermal dual-mode AA sensor strategies were as low as 0.73 μM and 1.4 μM, respectively. Rapid analysis of ascorbic acid was accomplished with the present procedure, AA in vitamin C tablets and human serum samples were validated.

New findings on ligand series used as SARS-CoV-2 virus inhibitors within the frameworks of molecular docking, molecular quantum similarity and chemical reactivity indices

Background: The severe acute respiratory syndrome coronavirus (SARS-CoV)-2 virus causes an infectious illness named coronavirus disease 2019 (COVID-19). SARS-CoV is a positive-sense single-stranded RNA virus from the Betacoronavirus genus. The SARS-CoV-2 RNA-dependent RNA polymerase (RdRp) has an important role in the viral life cycle and its active site is a very accessible region, thus a potential therapeutic approach may be to target this region to study the inhibition of viral replication. Various preexisting drugs have been proposed for the treatment of COVID-19 and the use of existing antiviral agents may reduce the time and cost of new drug discoveries, but the efficacy of these drugs is limited. Therefore, the aim of the present study was to evaluate a number of ligands used as SARS-CoV-2 virus inhibitors to determine the suitability of them for potential COVID-19 treatment. Methods: In this study, we selected a series of ligands used as SARS-CoV-2 virus inhibitors such as: abacavir, acyclovir, amprenavir, ascorbic acid vitamin C, azithromycin, baloxavir, boceprevir, cholecalciferol vitamin D, cidofovir, edoxudine, emtricitabine, hydroxychloroquine and remdesivir. These ligands were analyzed using molecular docking, molecular quantum similarity, and chemical reactivity indices defined within a conceptual density functional theory framework. Results: The analysis of molecular quantum similarity indices on inhibitors showed a high number of differences from a structural point of view. However, they are quite similar in their electronic density, obtaining the highest values in the electronic similarity index. Global and local chemical reactivity indices were analyzed. Conclusions: These studies allowed for the identification of the main stabilizing interactions using the crystal structure of SARS-CoV-2 RdRp. The molecular quantum similarity and chemical reactivity descriptors provide novel insights into these ligands that can be used in the design of new COVID-19 treatments.

Ascorbic Acid Sensor Based on CdS QDs@PDA Fluorescence Resonance Energy Transfer

An ascorbic acid (AA) sensor was constructed based on the fluorescence resonance energy transfer (FRET) between CdS quantum dots (CdS QDs) and polydopamine (PDA) to detect trace AA sensitively. FRET occurred due to the broad absorption spectrum of PDA completely overlapped with the narrow emission spectrum of CdS QDs. The fluorescence of CdS QDs was quenched and in the “off” state. When AA was present, the conversion of DA to PDA was hindered and the FRET disappeared, resulting in the fluorescence of CdS QDs in an “on” state. Importantly, the degree of fluorescence recovery of CdS QDs displayed a desirable linear correlation with the concentration of AA in the range of 5.0–100.0 μmol/L, the linear equation is , and the detection limit is 1.16 μmol/L (S/N = 3, n = 9). There was almost no interference with common amino acid, glucose and biological sulfhydryl small molecules to AA. Trace amount of AA in vitamin C tablets were determined and satisfactory results were obtained; the recoveries were observed to be 98.01–100.7%.

A novel nonenzymatic ascorbic acid electrochemical sensor based on gold nanoparticals-chicken egg white-copper phosphate-graphene oxide hybrid nanoflowers

Au-CEW-Cu3(PO4)2-GO nanoflowers (HNFs), which were assembled of gold nanoparticals (Au NPs), chicken egg white (CEW), copper phosphate (Cu3(PO4)2) and graphene oxide (GO) together to form a flower-like organic/inorganic hybrid nanocomposite, were synthesized through a simple and gentle one-pot co-precipitation method. The prepared samples were well characterized by scanning electron microscope, transmission electron microscope, energy dispersive x-ray spectrometer, x-ray diffraction and Raman spectrometer. The prepared Au-CEW-Cu3(PO4)2-GO HNFs was used to modify glassy carbon electrode to fabricate an electrochemical sensor for detection of ascorbic acid (AA). The electrochemical test results show that the linear range of the developed sensor is 8–300 μM and the detection limit is 2.67 μM (S/N = 3). While this sensor displays high sensitivity of 6.01 × 10–3 μA μM−1 cm−2 and low detection potential of 35 mV due to the combination of the high conductivity of Au NPs, the larger specific surface area of GO and the intrinsic electrocatalytic activity of CEW-Cu3(PO4)2 HNFs. Moreover, the Au-CEW-Cu3(PO4)2-GO HNFs-based sensor was successfully developed for application in electrochemical detection of AA in vitamin C tablets.

A novel ascorbic acid ratiometric fluorescent sensor based on ZnCdS quantum dots embedded molecularly imprinted polymer and silica-coated CdTeS quantum dots

Ascorbic acid (AA) is involved in many important biological processes in the body whose determination is of great value for the diagnosis and treatment of diseases. We constructed a novel ratiometric fluorescence sensor for specific recognition and sensitive ratiometric determination of AA. In this sensor, CdTeS quantum dots coated silica shell (CdTeS QDs@SiO2) to act as a reference and offer a built-in correction for environmental factors. ZnCdS quantum dots were encapsulated in a three-dimensional network imprinted polymer (ZnCdS QDs@MIP) to provide response signal. The fluorescence emission of ZnCdS QDs@MIP was selectively quenched in the presence of AA, and a good linear model was fitted based on the fluorescence intensity ratios of ZnCdS QDs@MIP and CdTeS QDs@SiO2 (F530/F705) and the concentrations of AA in the range of 1–500 μM with a detection limit of 0.78 μM. The reliability of the proposed sensor in the real samples analysis was investigated through the detection of AA in vitamin C tablets and satisfactory results were obtained.

Molecularly imprinted electrochemical sensor for ascorbic acid determination based on MXene modified electrode

Molecularly imprinted electrochemical sensor for ascorbic acid (AA) detection was prepared based on MXene modified glassy carbon electrode (MIPs/MXene/GCE). MXene with layered structure was synthesized by chemical etching method and the o-phenylenediamine (o-PD) polymer was electrochemically polymerized onto MXene modified electrode surface. With the binding of AA molecules onto electrode, the current response of the sensor was decreased. Under the optimized experimental conditions, the current response change of the sensor was in linear with the concentration of AA in the range from 0.5 μM to 10 μM with detection limit of 0.27 μM. The sensor has good selectivity, which was applied to the determination of AA in vitamin C tablets.

Combining In-Tip Reaction and Infrared Thermal Imaging for Fast and Portable Enthalpimetric Analysis.

In this work, the in-tip thermal infrared enthalpimetry (in-tip TIE) method is proposed for fast enthalpimetric analysis. In this method, the reactions inside the tips of a multichannel pipette were combined with temperature monitoring by an infrared camera. The filter paper was used inside the tips to retain reagents as solutions (wetted paper mode) or as solids (dried paper mode) to perform neutralization, redox, or precipitation reactions. The dried reagents inside the tips were obtained by oven drying a solution retained in the filter paper. The determination of the total acidity of the vinegar, ascorbic acid in vitamin C tablets, and chloride in soy sauces and saline inhalation solutions was performed as examples of the application of the proposed method. The agreement with reference methods ranged from 98 to 107%. The use of reagents dried inside the tip was feasible, leading to a simple aspiration of sample solution within the 12 tips of the pipette to perform a rapid analysis (1 min). Therefore, up to 720 measurements in 1 h were feasible for in-tip TIE over up to 12 measurements for the reference methods. Moreover, miniaturization reduced reagent consumption and residue generation. For example, for in-tip TIE, only 3.6 mL of residues was generated (n = 12) over 60-240 mL in reference methods (n = 3). Contrarily to other TIE methods, no microplates or stirring was required, opening possibilities for field analysis since the multichannel pipette and the infrared camera are both operated with batteries.