Showing papers on "Buffer solution published in 2019"
TL;DR: The main objective of this study is to develop novel electrochemical sensors for more sensitive and selective detection of FFA and to propose its oxidation mechanism.
72 citations
TL;DR: The B:CNW electrode was selected for the determination of paracetamol in the artificial urine sample using differential pulse voltammetry method, obtaining the calculated limit of detection on the level of 0.08006 µM.
49 citations
TL;DR: The stoichiometry of tannic acid with iron ions was tested in buffer solution by the mole ratio method and the result suggests that the complex ratio of tANNic acid to Fe(III) is 1 : 1 and toFe(II) 3:1 in the carbonate buffer solution, and the complex ratios of iron-tannic complexes are 1‷:‷1 at pH 2.2.
Abstract: UV-Vis absorption spectra of tannic acid were gained at pH 1.0∼9.0. Due to the pH value dependence of complex, the stoichiometry of tannic acid with iron ions was tested in buffer solution by the mole ratio method. The result suggests that the complex ratio of tannic acid to Fe(III) is 1 : 1 and to Fe(II) 3 : 1 in the carbonate buffer solution, and the complex ratio of iron-tannic complexes is 1 : 1 at pH 2.2. Due to the different color changes of tannic acid with iron ions in the coordination reactions, a tannic acid test paper was designed. The concentrations of Fe(III) more than 5.000 × 10−6 mol/L and the concentrations of Fe(II) more than 1.000 × 10−5 mol/L in aqueous solution can be detected by this test paper.
48 citations
TL;DR: Its biological application to detect the endogenous GSH was further proved by the HepG2 cell fluorescence image test and the minimum detection limit was distinctly below the physiological concentration of GSH in live cells.
33 citations
TL;DR: A simple, one-step approach to prepare a low-cost and binder free MoS2-pencil graphite electrode for the electrochemical oxidation of DNA nucleobases i.e., guanine (G) and adenine (A) in physiological pH buffer solution is reported.
33 citations
TL;DR: A simple and new chromogenic azo-azomethine chemosensor N'-(5-((2,4-dichloro- phenyl) diazenyl)-2-hydroxylbenzylidene) picolinohydrazide (L) has been synthesized as an effective colorimetric sensor for cyanide ion.
32 citations
TL;DR: A fluorescent enhancenment probe (1) derived from pyrene-containing Schiff base was developed and synthesized for the detection of Ag+ and Cu2+ in aqueous solutions.
Abstract: A fluorescent enhancenment probe (1) derived from pyrene-containing Schiff base was developed and synthesized for the detection of Ag+ and Cu2+ in aqueous solutions. In THF–HEPES buffer solution (20.0 mM HEPES, 1:9, v/v, pH 7.4), probe 1 shows a highly selective and sensitive fluorescent enhancement recognition of Ag+ with a binding ratio of 1:1 (probe 1: Ag+) and a detection limit of 4.8 nM. In THF–HEPES buffer solution (20.0 mM HEPES, 3:7, v/v, pH 7.4), probe 1 shows a highly selective and sensitive fluorescent enhancement recognition to Cu2+ with a binding ratio of 1:2 (probe 1: Cu2+) and a detection limit of 4.2 nM. Further invesitgation with NMR and UV–vis experiments indicates that the different fluorescent recognition to Ag+ and Cu2+ are due to different binding modes of 1-Ag+ and 1-Cu2+ in different solutions.
31 citations
TL;DR: In this paper, the authors introduced a new electrode comprising silver decorated multiwall carbon nanotube (Ag-MWCNT) as the sensing element for voltammetric investigation of anticancer drug Epirubicin (EP) in human whole blood, urine and injection.
Abstract: Here, we introduce a new electrode comprising silver decorated multiwall carbon nanotube (Ag-MWCNT) as the sensing element for voltammetric investigation of anticancer drug Epirubicin (EP) in human whole blood, urine and injection. Field emission scanning electron microscopy (FE-SEM), TEM, EDX and XRD methods were used to study the surface structure and topography of the modified electrode. We used electrochemical impedance spectroscopy (EIS) as a powerful tool to analyze the electrochemical properties of the new electrode. This modified electrode was applied for investigation of EP by cyclic voltammetry (CV) and square wave voltammetry (SWV) in an acetate buffer solution as a suitable supporting electrolyte (pH 1.5 - 6.8). The CV of EP in the potential range of -1.0 to 1.0 V showed reversible redox peaks that were dependent on pH. We optimized the conditions needed for practical application of the new electrochemical sensor, for which the redox peak current at pH 4.7 was linearly proportional to the concentration of EP in the range of 0.003 - 0.25 μM with a detection limit of 1.0 × 10-3 μM (RSD
31 citations
TL;DR: In this paper, a two-stage arsenic precipitation process was proposed, which consists of formation of scorodite at lower pH followed by precipitation of arsenical ferrihydrite at higher pH.
30 citations
TL;DR: This study shows that albumins act as both reducing agents and protective corona of AuNPs, and proves that the albumin is involved in the first step of Au(III) reduction.
Abstract: The formation and growth of gold nanoparticles (AuNPs) were investigated in pH 7 buffer solution of bovine serum albumin (BSA) at room temperature. The processes were monitored by UV-Vis, circular dichroism, Raman and electron paramagnetic resonance (EPR) spectroscopies. TEM microscopy and dynamic light scattering (DLS) measurements were used to evidence changes in particle size during nanoparticle formation and growth. The formation of AuNPs at pH 7 in the absence of BSA was not observed, which proves that the albumin is involved in the first step of Au(III) reduction. Changes in the EPR spectral features of two spin probes, CAT16 and DIS3, with affinity for BSA and AuNPs, respectively, allowed us to monitor the particle growth and to demonstrate the protective role of BSA for AuNPs. The size of AuNPs formed in BSA solution increases slowly with time, resulting in nanoparticles of different morphologies, as revealed by TEM. Raman spectra of BSA indicate the interaction of albumin with AuNPs through sulfur-containing amino acid residues. This study shows that albumins act as both reducing agents and protective corona of AuNPs.
29 citations
TL;DR: A kind of pH-sensitive polymer, poly(styrene- co-maleic anhydride-acrylic acid) (PS-MAn-AA)-based hybrid enzyme reactor based on porous polymer membrane fabrication established a platform for enzyme efficiency adjusting and displayed excellent stability and reusability of the proposed pH-PPM.
Abstract: The challenge for polymeric enzyme reactors at present is to selectively control the enzymolysis rate in complex conditions. Additionally, the fabrication methodology is hindered by complex processes, especially for achieving diverse stimuli responsiveness and functions. Here, we reported a kind of pH-sensitive polymer, poly(styrene- co-maleic anhydride-acrylic acid) (PS-MAn-AA)-based hybrid enzyme reactor. It comprised magnetic nanoparticles and a pH-sensitive PS-MAn-AA porous polymer membrane made by breath figure method. The enzyme l-asparaginase (l-ASNase) could covalently bond on the surface of the pH-sensitive porous polymer membrane (pH-PPM), and the resultant enzyme reactor was characterized by Fourier transform infrared spectroscopy and vibrating sample magnetometer. The apparent Michaelis-Menten constants ( Km and Vmax) of the l-ASNase enzyme reactor at different pH values were determined by a chiral ligand-exchange capillary electrophoresis method with l-asparagine as the substrate. The Vmax value of the l-ASNase enzyme reactor (0.67 mM/min) was almost 3-fold of that of the free l-ASNase (0.23 mM/min) at pH 8.2. Its ability to precisely control the enzymolysis rate in complex conditions is triggered primarily by the pH of the buffer solution, allowing controlled enzymatic reactions and displaying excellent stability and reusability of the proposed pH-PPM. This strategy for porous polymer membrane enzyme reactor fabrication has established a platform for enzyme efficiency adjusting. These valve-like distinguished features highlight the outstanding potential of stimuli-responsive enzyme reactor applied for enzyme immobilization and enzyme-related disease treatment.
TL;DR: In this paper, a new fluorescent sensor was designed and synthesized based on imidazo[2,1-b]thiazole and 2-hydroxy-1-naphthaldehyde, which could be used to detect Al3+ in methanol buffer solution and detect Zn2+ in ethanol buffer solution with detection limits of 1.45 × 10−7 M and 1.29× 10−8 M, respectively.
Abstract: (E)-N′-((2-Hydroxynaphthalen-1-yl)methylene)imidazo[2,1-b]thiazole-6-carbohydrazide (X), a new fluorescent sensor, was designed and synthesized based on imidazo[2,1-b]thiazole and 2-hydroxy-1-naphthaldehyde, which could be used to detect Al3+ in methanol buffer solution and detect Zn2+ in ethanol buffer solution with detection limits of 1.45 × 10−7 M and 1.29 × 10−8 M, respectively. X showed high sensitivity and selectivity towards Al3+ and Zn2+ in the presence of other metal ions. The fluorescence intensity of X was reversible even after six cycles with the sequentially alternative addition of metal ions (Al3+ and Zn2+) and PPi, showing an efficient “off–on–off” fluorescence behavior. The complexation ratio of X to Al3+ and Zn2+ was 1 : 1, which was proved by mass spectrometry and the B–H equation. The binding mode and sensing mechanism of X with metal ions (Al3+ and Zn2+) were verified by DFT/TDDFT calculations using Gaussian 09 based on the B3LYP/6-31G(d) basis set.
TL;DR: The results indicate that biological buffering solutions need to be carefully considered when evaluating IONP catalytic activity and their potential toxicological effects since under physiological conditions of pH, salinity and buffering species, the peroxidase-like activity of IONPs is dramatically reduced.
Abstract: Iron oxide nanoparticles (IONPs) are frequently used in biomedical applications due to their magnetic properties and putative chemical stability. Nevertheless, their well-known ability to mimic some features of the peroxidase enzyme activity under specific conditions of pH and temperature could lead to the formation of potentially harmful free radical species. In addition to the intrinsic enzyme-like activity of IONPs, the buffer solution is an important external factor that can alter dramatically the IONP activity because the buffer species can interact with the surface of the particles. In our study, IONP activity was evaluated in different buffering solutions under different experimental conditions and predominant free radical species were measured by electron paramagnetic resonance using the spin-trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO). The formation kinetics of the reactive oxygen species were studied by UV-visible spectroscopy with TMB and DAB peroxidase substrates. We found that the highest catalytic oxidation of peroxidase substrates and free radical generation were achieved in acetate buffer, while phosphate buffer inhibited the peroxidase-like activity of IONPs in a concentration dependent manner. When emulating the physiological conditions, a lower catalytic activity was observed at pH 7.4 when compared to that at pH 5.0. Also, in phosphate buffered saline (PBS), we observed an enhancement in the peroxidase substrate oxidation rate that was not accompanied by an increase in DMPO/adduct formation which could be related to a non-specific oxidation catalyzed by the chloride ion. Similar observations were found after the addition of a bicarbonate to HEPES buffer. TMB oxidation did not occur when the reaction was conducted with free iron ions from metal salts with the same concentration of the IONPs (0.33 Fe2+ and 0.66 Fe3+). However, we observed even higher catalytic activities than those when doubling the IONP concentration when they are combined with the free iron salts. These results indicate that biological buffering solutions need to be carefully considered when evaluating IONP catalytic activity and their potential toxicological effects since under physiological conditions of pH, salinity and buffering species, the peroxidase-like activity of IONPs is dramatically reduced.
TL;DR: In this paper, a voltammetric sensor was developed using a nitrogen-doped porous carbon and nitrogen-depleted graphene nanocomposite modified glassy carbon electrode for the simultaneous determination of dopamine (DA), uric acid (UA) and ascorbic acid(AA).
Abstract: A voltammetric sensor was developed using a nitrogen-doped porous carbon and nitrogen-doped graphene nanocomposite modified glassy carbon electrode for the simultaneous determination of dopamine (DA), uric acid (UA) and ascorbic acid (AA). Detailed characteristics of the nanocomposites were investigated by SEM, TEM, XPS, XRD and FT-IR. Experimental conditions such as accumulation time, accumulation potential and buffer solution pH were optimized. The sensor demonstrated a linear plot of 0.01–15.0 mmol L−1 for AA, 0.08–350.0 μmol L−1 for DA, and 0.5–100.0 μmol L−1 for UA, with detection limits of 1.99 μmol L−1, 0.011 μmol L−1 and 0.088 μmol L−1, respectively. The established method exhibited excellent reproducibility, anti-interference and stability, and it was applied to DA, UA and AA determination in real urine samples with recoveries between 100.2% and 102.0%.
TL;DR: This study presents a green analytical method for palladium determination by slotted quartz tube flame atomic absorption spectrometry (SQT-FAAS) following switchable liquid–liquid microextraction (SLLME).
Abstract: This study presents a green analytical method for palladium determination by slotted quartz tube flame atomic absorption spectrometry (SQT-FAAS) following switchable liquid–liquid microextraction (SLLME). Efficient extraction of palladium was facilitated by complexation with a Schiff base ligand, synthesized specifically for this study. A three-stage thorough optimization procedure was carried out to boost the absorbance output of palladium. Complex formation was the first stage, and parameters evaluated included buffer solution pH and amount, concentration of ligand, and mixing period. The amount of switchable solvent and concentration and amount of sodium hydroxide and acid amount were optimized in the second stage. Optimization of sample and fuel flow rates and SQT parameters completed the third stage of optimization, and all optimum parameters were used to determine analytical performance of the method. The method had a broad linear dynamic range, and the calibration plots showed good linearity with R2 values greater than 0.9991. The limits of detection and quantification of the SLLME-SQT-FAAS method were 15 and 50 μg/L, respectively. The precision of the method, expressed as percent relative standard deviation, was below 9.0% for all measurements. Spiked recovery results performed for a palladium electroplating bath solution gave poor results when quantified against aqueous calibration standards. Matrix matching was therefore used to improve recovery results which ranged between 97 and 105% for four different spike concentrations.
TL;DR: In the method reported here, swellable pH-sensitive polymer particles are deposited on the interior surface of a silica hollow bottle resonator and sigmoid shaped titration curves similar to those obtained using turbidity to monitor refractive index changes of the particles as a function of pH are monitored.
TL;DR: The analytical application of detecting the concentration of acetic acid in vinegar was investigated and the detection values were found similar to the reference values, fully demonstrating a good linear relationship between the logarithm of the relative fluorescence intensity ratio of the CDs and the pH value of the system.
Abstract: New carbon dots (CDs) were prepared by a microwave method using m-trihydroxybenzene and dilute sulphuric acid as raw materials. The as-prepared CDs exhibited excellent water solubility and photoluminesence properties. The optimum excitation and emission wavelengths of the new CDs were at 365 nm and 465 nm, respectively. The fluorescence of the new CDs experienced remarkable changes in the presence of Britton-Robinson (BR) buffer solution with different pH values under 4°C after reacting for 70 min. In addition, a linear relationship between the logarithm of the relative fluorescence intensity ratio [lg(IF /IFo )] of CDs and the pH values of the sensing system ranging 1.81-5.72 was obtained, with a correlation coefficient of 0.9933. Thus, a sensitive and simple method to detect the pH value of solution was developed. Furthermore, the analytical application of detecting the concentration of acetic acid in vinegar was investigated. The detection values were found similar to the reference values, fully demonstrating a good linear relationship between the logarithm of the relative fluorescence intensity ratio of the CDs and the pH value of the system. Hence, the method could be used to detect the concentration of acetic acid in vinegar.
TL;DR: In this paper, the transformation of DNIC with thiourea ligands in an aqueous buffer solution at neutral pH and in the presence of reduced glutathione (GSH) has been studied.
TL;DR: In this article, the stability constants (lgKc) and thermodynamic parameters of complex formation (ΔcG, ΔcH and ΔcS) have been calculated and presented in a table.
TL;DR: A novel fluorescent probe made of BINOL and coumarin shows highly enantioselective fluorescence enhancement in the presence of an amino acid with a very small difference between the two enantiomers, allowing the determination of both concentration and enantiomeric composition of amino acids.
TL;DR: In this paper, an alternative electron transfer (AET) process by dissolving the glucose oxidase (GOX) enzyme in the electrolyte instead of direct immobilization on the electrode's surface to demonstrate better performance of glucose sensing was proposed.
Abstract: Here, we demonstrate efficient electrochemical detection of glucose in blood serum using CdS nanoribbons coated indium Tin Oxide (ITO) electrode. Main appeal of this work is to establish an alternative electron transfer (AET) process by dissolving the glucose oxidase (GOX) enzyme in the electrolyte instead of direct immobilization on the electrode’s surface to demonstrate better performance of glucose sensing. In this context, we developed an experimental strategy through amperometric detection of hydrogen peroxide (H2O2) which is an intermediate reaction product of glucose oxidation by GOX present in the buffer solution. Therefore, we separately performed electrochemical detection of H2O2 by CdS nanoribbons in buffer solution followed by glucose detection with the same electrode by dissolving GOX in the buffer solution. The linear range of amperometric current measured with the same concentration of both H2O2 and glucose overlaps with each other which clearly proves that electrocatalytic reduction of both the analytes occur at the same rate on the CdS surface. Our studies reveal that dissolved GOX in buffer solution have a better performance than the GOX immobilized electrode. Furthermore, chronoamperometric detection of glucose in actual blood serum sample was performed and our results show even better performance than the commercially available glucometer.
TL;DR: In this paper, a new film containing poly(amido amine) dendrimer, silver nanoparticles and multi-walled carbon nanotubes composite with poly(neutral red) was prepared on a paraffin wax impregnated graphite electrode.
Abstract: A new film containing poly(amido amine) dendrimer, silver nanoparticles and multi-walled carbon nanotubes composite with poly(neutral red) was prepared on a paraffin wax impregnated graphite electrode. The PAMAM / AgNPs–MWCNT / PNR film exhibited promising electrocatalytic oxidation of ascorbic acid (AA) in acetate buffer solution of pH 4.0. The PAMAM / AgNPs–MWCNT / PNR film-modified electrode enhanced the sensitivity of detection of AA. The PAMAM / AgNPs–MWCNT / PNR film-modified electrode was characterized by cyclic voltammetry, chronoamperometry, hydrodynamic voltammetry (HDV) and difference pulse voltammetry. These experiments confirmed the electrocatalytic oxidation of AA by PAMAM / AgNPs–MWCNT / PNR film-modified electrode. The PAMAM / AgNPs–MWCNT / PNR-modified electrode has been found to possess good electrocatalytic activity towards AA oxidation which has been observed at a lower oxidation potential of around 0.26 V with a higher current response. The electrochemical oxidation of AA by PAMAM / AgNPs–MWCNT / PNR-modified electrode involved a two proton and two electron process. A linear relationship between the catalytic current and AA concentration was obtained in the range from 0.16 to 2500
$$\upmu $$
M with a detection limit of 0.053
$$\upmu $$
M.
TL;DR: McDougall's buffer provides both better conditions for in vitro fiber digestion and greater precision in digestibility estimates, and is recommended over Kansas buffer.
Abstract: The aim of this study was to compare the in vitro digestibility of dry matter (IVDMD) and neutral detergent fiber (IVNDFD) using 2 buffer solutions with or without urea addition. The study was comprised of 2 separate experiments. In both experiments, the treatments were composed of Kansas or McDougall's buffer solutions with or without urea addition, according to a 2 × 2 factorial arrangement. In Exp. I, the IVDMD and IVNDFD of 25 forages and 25 concentrates were evaluated. Samples were incubated for 48 h using an artificial fermenter and nonwoven textile filter bags (100 g/m2). In this experiment, the repeatability and discriminatory power among samples were calculated within forage or concentrate samples, for each treatment. In Exp. II, Tifton hay and ground corn samples were incubated for 48 h. The pH and ammonia nitrogen (NH3-N) concentration were measured after 0, 3, 6, 12, 18, 24, and 48 h of incubation. In Exp. I, the interaction between buffer solution and urea addition impacted the IVDMD and IVNDFD of forages (P 0.05). However, greater IVDMD and IVNDFD were observed for McDougall's buffer (P < 0.05), while urea addition increased IVDMD and IVFDFD estimates (P < 0.05) regardless of buffer solution used. In general, repeatability of the digestibility was better using McDougall's buffer and improved when urea was added. Urea addition also decreased the discriminatory power among samples for both buffers. In Exp. II, a buffer solution × urea addition × incubation time interaction was detected (P < 0.05) for pH and NH3-N in both Tifton hay and ground corn. Kansas buffer exhibited lower pH values with a greater decrease observed throughout incubation time when compared to McDougall's buffer. The use of Kansas buffer with urea addition was the only treatment exhibiting NH3-N accumulation throughout incubation. In conclusion, McDougall's buffer provides both better conditions for in vitro fiber digestion and greater precision in digestibility estimates, and is recommended over Kansas buffer. In spite of urea addition increases the precision of in vitro digestibility estimates, it decreases discriminatory power among samples.
TL;DR: In this article, a novel tetrabromobisphenol A (TBBPA) sensor was fabricated based on a CTAB-capped gold nanoparticle (AuNPs)-thio-β-cyclodextrin (SH-β)-CD)/graphene oxide modified glassy carbon electrode (GCE).
Abstract: In this study, a novel tetrabromobisphenol A (TBBPA) sensor was fabricated based on a CTAB-capped gold nanoparticle (AuNPs)-thio-β-cyclodextrin (SH-β-CD)/graphene oxide modified glassy carbon electrode (GCE). The peak current of TBBPA was dramatically enhanced by the AuNPs with a diameter of 6.2 nm on the modified electrodes compared with the other sized particles (10.1 or 16.1 nm). To further improve the electrochemical performance of the modified electrode, the influence of pH of the buffer solution and the accumulation time on the determination were investigated. The optimum pH and accumulation time were 7.0 and 180 s, respectively. The developed sensor exhibited good reproducibility, and excellent sensitivity and selectivity, showing a low detection limit (1.2 × 10−9 mol L−1) and a linear range from 1.5 × 10−8 to 7 × 10−6 mol L−1. In addition, a possible oxidization mechanism of TBBPA was also discussed. Finally, this sensor was successfully applied to detect TBBPA in water samples, and the results were consistent with those acquired by high-performance liquid chromatography.
TL;DR: A simple and stable pH sensor based on an extended-gate field-effect transistor (EGFET) is demonstrated using electron-beam deposited Al₂O₃ as a pH sensing layer and the pH detection accuracy is improved by using the reference electrode with a KCl electrolyte.
Abstract: A simple and stable pH sensor based on an extended-gate field-effect transistor (EGFET) is demonstrated using electron-beam deposited Al₂O₃ as a pH sensing layer. The threshold voltage of the EGFET is modulated by different pH values of the buffer solution. A control experiment with a bare Au electrode confirms that the stable pH sensing response with linearity and reproducibility originates from the Al2O3 sensing layer. The minimum area of the pH sensing layer is estimated by considering that the different sizes of the sensing layer are easily modeled with different values of external capacitors connected to the readout transistor. The study verifies that the pH detection accuracy is improved by using the reference electrode with a KCl electrolyte.
TL;DR: Changing the buffer solution from pH 8 to pH 6, pH-responsive membrane with dual size-exclusion property could be used to purify monoclonal antibody sustainably without chromatography polishing steps.
TL;DR: In this paper, a carboxyl-functionalized graphene SGFET was used for anodization in Carmody buffer solution at pH 7 and showed that the original structure of graphene was conserved.
TL;DR: The method has been successfully applied to extract morpholinium cations from spiked water samples of Songhua River, Hulan River, East Lake, and Mopanshan Reservoir in China and provides a new approach for monitoring ionic liquids in environmental water.
Abstract: An ion chromatography and solid-phase extraction method has been applied for the separation and detection of morpholinium cations in environmental water samples. The water samples were purified and enriched by a UF-SCX sulfonic acid extraction column and eluted with 0.5 mol L−1 phosphoric acid/sodium dihydrogen phosphate buffer solution/55% methanol. The target compounds were separated on a carboxylic acid cation exchange column with 5.0 mmol L−1 methane sulfonic acid/2% acetonitrile as the mobile phase and direct conductivity detection. The method has been successfully applied to extract morpholinium cations from spiked water samples of Songhua River, Hulan River, East Lake, and Mopanshan Reservoir in China with the recoveries ranging from 75.0% to 98.3%. The relative standard deviations of intraday precision and interday precision are 2.1% and 5.9% or less, respectively. Using this method it is possible to preconcentrate water samples to 0.01–0.04 mg L−1. The results show that the method is applicable to detection of morpholinium ionic liquid cations in environmental water samples and provides a new approach for monitoring ionic liquids in environmental water.
TL;DR: In this article, compound classes of transformation products from aqueous and solid phase photodegradation of 2,4,6-trinitrotoluene (TNT) have been identified by liquid and solid state 13C and 15N NMR.
Abstract: Photolysis is one of the main transformation pathways for 2,4,6-trinitrotoluene (TNT) released into the environment. Upon exposure to sunlight, TNT is known to undergo both oxidation and reduction reactions with release of nitrite, nitrate, and ammonium ions, followed by condensation reactions of the oxidation and reduction products. In this study, compound classes of transformation products from the aqueous and solid phase photodegradation of 2,4,6-trinitrotoluene (TNT) have been identified by liquid and solid state 13C and 15N NMR. Aqueous phase experiments were performed on saturated solutions of T15NT in deionized water, natural pond water (pH = 8.3, DOC = 3.0 mg/L), pH 8.0 buffer solution, and in the presence of Suwannee River Natural Organic Matter (SRNOM; pH = 3.7), using a Pyrex-filtered medium pressure mercury lamp. Natural sunlight irradiations were performed on TNT in the solid phase and dissolved in the pond water. In deionized water, carboxylic acid, aldehyde, aromatic amine, primary amide, azoxy, nitrosophenol, and azo compounds were formed. 15N NMR spectra exhibited major peaks centered at 128 to 138 ppm, which are in the range of phenylhydroxylamine and secondary amide nitrogens. The secondary amides are proposed to represent benzanilides, which would arise from photochemical rearrangement of nitrones formed from the condensation of benzaldehyde and phenylhydroxylamine derivatives of TNT. The same compound classes were formed from sunlight irradiation of TNT in the solid phase. Whereas carboxylic acids, aldehydes, aromatic amines, phenylhydroxylamines, and amides were also formed from irradiation of TNT in pond water and in pH 8 buffer solution, azoxy and azo compound formation was inhibited. Solid state 15N NMR spectra of photolysates from the lamp irradiation of unlabeled 2,6-dinitrotoluene in deionized water also demonstrated the formation of aromatic amine, phenylhydroxylamine/ 2° amide, azoxy, and azo nitrogens.
TL;DR: A simple capillary electrophoresis (CE) method that using β-cyclodextrin (β-CD) as buffer modifier has been developed for the detection of ten amino acids of jujube from five different geographical origins.
Abstract: A simple capillary electrophoresis (CE) method that using β-cyclodextrin (β-CD) as buffer modifier has been developed for the detection of ten amino acids of jujube from five different geographical origins. The CE methodology was optimized through the variation of type, pH and concentration of the buffer solution, concentration of the additive β-CD, applied voltage, injection time and wavelength of the UV detection. It was found that the best separation of ten kinds of amino acids was achieved within less than 6 min under the optimum separation conditions: 50 mmol L-1 pH 9.5 borate-phosphate buffer with 5.0 mmol L-1 β-CD, 15 kV applied voltage, 25 °C column temperature, 210 nm detection wavelength, and 5 s injection time. This method showed good repeatability with RSD values of 1.4-3.4% for peak area, and 1.4-4.7% for migration time, when β-CD was used as buffer modifier. Under the optimum conditions, the method has been successfully applied to the detection of actual jujube samples, which also verifies the effectiveness and practicability of the method. Recovery of real samples was in ranging of 90%-105%, which proved the feasibility of the method. It also proved that the method was successfully applied to the quantitative analysis of amino acids of interest in plant samples.