Characterization of the absorption of histidine and lead by Juglan regia L., Platanus L., and Pinus nigra L. using high-performance liquid chromatography–mass spectrometry and inductively coupled plasma–mass spectrometry

High-performance liquid chromatography–mass spectrometry and inductively coupled plasma – mass spectrometry were used for the determination of histidine and lead in Juglan regia L., Platanus L., and Pinus nigra L. leaves from industrial areas including Gaziantep City and Bursa City, Turkey. Distilled water was used for the extraction of histidine from plant material at 90°C for 30 min. The flow rate of the mobile phase, fragmentation potential, injection volume, and column temperature were optimized to be 0.2 mL min^?1, 70 V, 15 µL, and 20°C for the determination of histidine. The concentrations of histidine were from 7–9 mg kg^?1 for Juglan regia L., 2–5 mg kg^?1 for Platanus L., and 1–7 mg kg^?1 for Pinus nigra L. The concentrations of Pb were from 1–42 mg kg^?1 for Juglan regia L., 1–4 mg kg^?1 for Platanus L., and 1–62 mg kg^?1 for Pinus nigra L.     

Spectrophotometric Determination of Silicon in Rice and Alloy Steel Samples

Abstract

In the medium of 0.128 mol/L nitric acid and 0.450 mol/L sulfuric acid, silicon(IV) and ammonium molybdate form molybdosilicate blue blue complex in the presence of ascorbic acid. The maximum absorption wavelength of the complex locates at 810 nm. The apparent molar absorptivity is ε_810 nm = 3.18 × 10⁴ L · mol^?1 · cm^?1. Beer's law is followed over the range of 0 ～ 1.0 µg/mLof silicon(IV). The present method has been successfully applied to the determination of silicon in rice and alloy steel samples.     

DETERMINATION OF FLAVONES IN LOPHATHERUM GRACILE BY LIQUID CHROMATOGRAPHY TANDEM MASS SPECTROMETRY

Lophatherum gracile Brongn. (L. gracile) has been used for food and medicine in China for thousands of years. Flavonoids are one of the main bioactive components of this herb. A reliable method was established using liquid chromatography with tandem mass spectrometry to determine the concentrations of seven flavonoids. The separation was performed using a C₁₈ column at 40°C and the mobile phase was a mixture of methanol and 0.3% formic acid (v/v) in water in gradient elution mode at a flow rate of 1 mL/min. Quantification was performed through tandem mass spectrometry with negative electrospray ionization and multiple reaction monitoring at m/z [M-H]^?. The method was validated using calibration curves, limits of detection and quantification, precision, repeatability, stability, and accuracy. Seven compounds in eleven samples were determined, and there were significant differences in the concentrations of isoorientin, swertiajaponin, afzelin, luteolin-7-O-β-D-glucoside, vitexin, isovitexin, and swertisin. The established method is suitable for quality control for the analysis of L. gracile, as well as to provide necessary information for the rational utilization of L. gracile resources.     

CATALYTIC KINETIC SPECTROPHOTOMETRIC DETERMINATION OF TRACE AMOUNTS OF ETHYLENEDIAMINETETRAACETIC ACID BASED ON ITS CATALYTIC EFFECT ON THE REACTION OF RHODAMINE B AND POTASSIUM DICHROMATE

A new method for the determination of trace ethylenediaminetetraacetic acid (EDTA) was developed using catalytic kinetic spectrophotometry based on the principle that in the medium of 0.10 mol/L sulfuric acid, trace EDTA has a catalytic effect on the oxidation of rhodamine B by potassium dichromate, and a suitable amount of 6.0 mol/L NaOH solution can inhibit the catalytic reaction. At the maximum absorption wavelength of 546 nm, the linear range for the determination of EDTA was shown over the concentration range 5.0 × 10^?5–7.0 × 10^?4 mol/L and the detection limit of this method for EDTA was 0.0501 mmol/L. The linear regression equation for the determination of EDTA and regression coefficient were ΔA = 512C (C: mol/L) + 0.0966, γ = 0.9993, respectively. The apparent activation energy of the catalytic reaction was 81.57 KJ/mol. The proposed method has been successfully applied to the determination of trace ethylenediaminetetraacetic acid in water and apple tinned foodstuff samples with satisfactory results. The relative standard deviation of 13 replicate determinations of EDTA was 1.15–2.37% and the recovery of the method was 99.90–102.7%, respectively. The determined results were in good agreement with that of established method Fe(III)-H₂O₂-bromothymol blue system inhibitory-kinetic spectrophotometry.     

DETERMINATION OF PICOMOLE CONCENTRATIONS OF ALUMINUM (III) IN HUMAN SALIVA AND URINE BY A LUMINOL-CARBOXYMETHYL CHITOSAN CHEMILUMINESCENCE SYSTEM

A luminol–carboxymethyl chitosan (CMCS) system was established using flow injection chemiluminescence (CL) based on the enhancing effect of CMCS on the luminol–dissolved oxygen reaction. The CL intensity was linear with the CMCS concentration ranging from 0.01–30.0 µM. Al(III) was shown to quench the CL of the luminol–CMCS reaction, and the decrease of CL intensity was linear with the logarithm of Al(III) concentration over the range from 10–1000 pM with a detection limit of 3.5 pM (3σ). At a flow rate of 2.0 mL min^?1, the analysis was performed within 30 s. The proposed CL method was successfully applied to the determination of picomole levels Al(III) in human saliva and urine after oral intake of two aluminum hydroxide tablets, with recoveries from 90.6–108.7% and relative standard deviations <3% (n = 5). The results indicated that the excreted Al(III) in saliva and urine reached its maximum values at 3 hr and 2 hr, and the total excretive ratio were 1.24 × 10^?3% and 3.45% in 6 hr and 12 hr, respectively. The elimination rate constant k and the half–life time t _1/2 in human saliva and urine were 0.3747 hr^?1, 1.8495 hr, 0.7132 hr^?1, and 0.9717 hr, respectively. The possible CL mechanism of the luminol–CMCS–Al(III) reaction is discussed.     

Determination of Lead in Spiked Seawater Samples by Electrothermal Atomic Absorption Spectrometry using Chemical Modifiers

Abstract

The determination of lead in spiked sodium chloride solution with 3.4% salinity and natural sea‐water samples by electrothermal atomic absorption spectrometry (ETAAS) with Zeeman‐effect background correction was investigated using neodymium, samarium, and erbium salts as modifiers with the addition of citric acid (CA) as a reducing agent. In order to demonstrate the high potential of rare earth metals in combination with citric acid, optimum pyrolysis temperature, atomization temperature, and optimum masses of neodymium, samarium, and erbium were found for the determination of lead. These modifiers were used for the determination of lead in sodium chloride solution with 3.4% salinity and in natural sea water samples by means of the calibration graphs prepared with pure analyte solutions.

The detection limits for lead spiked sample matrices were calculated with the 2σ criterion between 2.0 to 2.1 ng mL^?1 for neodymium and citric acid, between 5.3 to 7.4 ng mL^?1 for samarium and citric acid, and between 1.7 to 2.1 ng mL^?1 for erbium and citric acid and for a sample volume of 10 µL. The recoveries for lead spiked sea water samples were 97–102%, with neodymium and citric acid modifier and erbium and citric acid modifier. They were only 66–68% without modifier.     

PVC MATRIX MEMBRANE SENSORS FOR POTENTIOMETRIC DETERMINATION OF ARECOLINE

The construction and electrochemical response characteristics of Poly (vinyl chloride) (PVC) membrane sensors for arecoline HBr (AR) are described. The sensing membranes incorporate ion association complexes of (AR) cation and sodium tetraphenyl borate (NaTPB) (sensor 1) or phosphomolybdic acid (PMA) (sensor 2) or phosphotungstic acid (PTA) (sensor 3) as electroactive materials. The sensors display a fast, stable and near-Nernstian response over a relative wide AR concentration range (1 × 10^?2 – 4 × 10^?5 M) and (1 × 10^?2 to 5 × 10^?6 M), with cationic slopes of 52.5, 50.5 and 51.5 mV per concentration decade for sensor 1, 2, and 3, respectively over a pH range of 3.0–6.0. The sensors show good discrimination of AR from several inorganic and organic compounds. The direct determination of 1.5–2360.0 μg/ml of AR show an average recovery of 99.0, 98.5 and 99.5% and a mean relative standard deviation of 1.7, 1.6 and 1.5% at 200.0 μg/ml for sensor 1, 2 and 3 respectively. The proposed sensors have been applied for direct determination of AR in human saliva. The results obtained for determination of AR in saliva using the proposed method comparable favorably with those obtained using HPLC method.     

Characterization of the interaction between bovine serum albumin and doxycycline by chemiluminescence and molecular docking

The interaction of bovine serum albumin with doxycycline was investigated using chemiluminescence and molecular docking. Doxycycline at concentrations from 1.0 to 2.5 × 10³ pmol · L^?1 quenched the chemiluminescence from the luminol–bovine serum albumin system. The data were analyzed using a chemiluminescence mathematic model for protein–ligand interaction, log[(I₀ – I)/I] = logK + nlog[D]. The binding constant of bovine serum albumin with doxycycline was 3.36 × 10⁵ L · mol^?1 at 298 K with one binding site. The binding constant, enthalpy change, entropy change, and binding free energy change showed that the bonding of doxycycline to bovine serum albumin was spontaneous and enthalpy driven via hydrogen bonding and van der Waals forces. Further molecular docking analysis substantiated that doxycycline was well positioned in the pocket at the subdomain IIA (site I) of bovine serum albumin with a binding constant of 3.31 × 10⁵ L · mol^?1. Doxycycline served as both a hydrogen acceptor and donor and mainly interacted with the Arg217 residue through four hydrogen bonds with an average length of 2.55 Å. The chemiluminescence mechanism of doxycycline on luminol–bovine serum albumin system was evaluated, showing that a ternary complex of luminol–bovine serum albumin–doxycycline was formed with luminol and doxycycline at sites III and I of bovine serum albumin.     

Batch and Flow‐Injection Determination of Catecholamines Using Ion Selective Electrodes

Abstract

New epinephrine (EP), dopamine (DA), and L‐Dopa (LD) ion selective PVC membrane electrodes based on ion‐pairs of catecholamines with tetraphenylborate (TPhB) are prepared. In the present work, plastic membrane selective electrodes have been constructed. They are based on the incorporation of EP‐TPhB, DA‐TPhB, or LD‐TPhB ion exchangers in poly(vinylchloride) (PVC) membranes plasticized with di(2‐ethylhexyl)sebacate (DES). The electrodes show a near – Nernstian response in the concentration ranges: 1.0×10^?4—1.0×10^?2 mol/L (epinephrine), 5.0×10^?5–1.0×10^?2 mol/L (dopamine), and 5.0×10^?4–1.0×10^?2 mol/L (L‐Dopa). The electrodes selective for epinephrine and L‐Dopa are used as detectors in the flow injection system. The proposed methods allow determination of catecholamines in pharmaceutical preparations.     

Determination of methyl gallate in Bauhinia retusa extract by high-performance liquid and thin-layer chromatography

Two stability-indicating chromatographic methods are reported for the determination of methyl gallate in crude extracts of Bauhinia retusa. Separation by high performance thin layer chromatography was conducted on silica gel aluminum sheets using 9.5:0.5:0.2 (v/v/v) chloroform:methanol:acetic acid at 280 nm. The results from the 2–40 µg/band were used to prepare a linear calibration graph. The limits of detection and quantitation were 0.5 and 1.5 µg/band, respectively. The reverse phase high performance liquid chromatographic isolation of methyl gallate was performed at ambient temperature with an injection volume of 10 μL. The mobile phase consisted of 40:60 (v/v) methanol:0.1% ortho-phosphoric acid. The separation was performed at 1 mL/min using a detection wavelength of 280 nm. The calibration graph for methyl gallate was rectilinear from 0.02–40 µg/mL with limits of detection and quantitation of 0.004 and 0.010 µg/mL, respectively. For both methods, intra-day and inter-day precision were evaluated and the relative standard deviation was less than 2%, indicating good precision. The robustness was evaluated by making small and deliberate changes to appropriate parameters and the calculated relative standard deviation was less than 2%.The chromatographic methods were employed to determine methyl gallate in crude Bauhinia retusa extracts.     

A GREEN METHOD FOR THE DETERMINATION OF CHROMIUM(VI) AND IRON(III) IN WATER BY SEQUENTIAL INJECTION ANALYSIS AND SPECTROPHOTOMETRIC DETECTION

In this article, an organic-reagent-free method was described for the determination of Cr(VI) and Fe(III) by double-system double-wavelength sequential injection technique with a single sample injection. In this approach, the determination of Cr(VI) was based on the detection of a blue unstable intermediate compound resulting from the reaction of Cr(VI) with hydrogen peroxide, and the determination of Fe(III) was based on the color reaction of Fe(III) with thiocyanate in acidic medium. Sequential injection analysis (SIA) parameters, including spacer solution volume, aspiration order, aspiration volumes, flow rate, acid medium, solution acidity, and reagent concentrations, were optimized. The linear range for the determination was 3.0–60.0 μg mL^?1 for Cr(VI) and 1.0–40.0 μg mL^?1 for Fe(III), respectively. The limit of detection (LOD) was 0.6 μg mL^?1 for Cr(VI) and 0.2 μg mL^?1 for Fe(III), and the limit of quantitation (LOQ) was 2.0 μg mL^?1 for Cr(VI) and 0.67 μg mL^?1 for Fe(III). The total volume of the reagent consumed in each determination was only 0.11 mL. The proposed method was applied to the simultaneous determination of Cr(VI) and Fe(III) in electroplating wastewater and environmental waters. The results were in good agreement with those obtained by atomic absorption spectrometry. The recoveries were in the range of 97.5–101.1%.     

Determination of polydatin by gold nanoparticle-enhanced chemiluminescence of silver nitrate and luminol

A novel flow injection method for the determination of polydatin is reported based on the inhibition of silver nitrate, luminol, and gold nanoparticles chemiluminescence. Under the optimum condition, the decrease in chemiluminescence was proportional to the concentration of polydatin from 1.0 × 10^?8 to 1.0 × 10^?5 mol/L. The detection limit was 2.1 × 10^?9 mo1/L and the relative standard deviation was 2.1% for the determination of 1.0 × 10^?6 mol/L polydatin. This method was successfully employed for the determination of polydatin in Polygonum cuspidatum roots and human urine.     

Determination of benzimidazoles in pharmaceuticals and human serum by high-performance liquid chromatography

A liquid chromatographic method is described for the quantification of prednisolone, benzimidazoles, and preservatives using a C₁₈ analytical column as stationary phase. The mobile phase was 30:70 methanol:pH 2.5 phosphate buffer at a flow rate of 1.0 mL min^?1 with absorbance detection at 235 nm. The method was linear for concentrations ranged from 40–10,000 ng mL^?1. Low values of coefficient of variance were obtained when samples were analyzed as replicates. Excellent recovery values were recorded in commercial products and fortified samples. International Conference of Harmonization protocols were employed to perform comprehensive method validation. The reported method has applications for pharmaceutical and serum samples.     

DETERMINATION OF LEAD(II) BY FLOW-INJECTION ANALYSIS USING LUMINOL-POTASSIUM PERIODATE POST-CHEMILUMINESCENCE REACTION

The post-chemiluminescence (PCL) phenomenon arising from the potassium periodate–luminol reaction induced by lead(II) was investigated. A strong PCL signal was observed when lead(II) was injected into the mixture of potassium periodate and luminol in a flow-cell. The influencing factors on the PCL intensity of the system were investigated. Under the optimum experimental conditions, the present method allowed the determination of lead(II) in the concentration range of 1.0 × 10^?8 to 1.0 × 10^?5 mol/L and the detection limit for lead(II) was 2.3 × 10^?10 mol/L. The relative standard deviation was 3.2% for 11 replicate analyses of 1.0 × 10^?6 mol/L lead(II). Combined with cotton cellulose xanthate for separation, the proposed method was applied to the determination of lead(II) in real water samples with satisfactory results.     

Spectrofluorometric determination of ascorbic acid using thiamine and potassium ferricyanide

A simple and sensitive spectrofluorometry method for the determination of ascorbic acid was reported. In alkaline solution, the nonfluorescent thiamine was oxidized by potassium ferricyanide and formed the fluorescent thiochrome with an excitation maximum at 367?nm and an emission peak at 441?nm. However, the fluorescence intensity gradually decreased in the presence of ascorbic acid. The decreased fluorescence was linearly dependent under the optimum conditions with the concentration of ascorbic acid from 0.086–1.5?µmol?L^?1 with a correlation coefficient of 0.9996. The detection limit of 0.026?µmol?L^?1 was lower than many other methods. Additionally, the mechanism underlying the enhancement and quenching of this method was discussed. The protocol was used to determine ascorbic acid in tablets and juice with satisfactory results.     

Determination of carnosic acid and carnosol in Rosmarinus officinalis L. by high-performance capillary electrophoresis

Carnosol and carnosic acid in Rosmarinus officinalis L. were separated by high-performance capillary electrophoresis using a 50?cm capillary, a 12?mmol/L 80:20 pH 9.9 borax:methanol buffer using 25?kV of applied voltage at 30°C with detection at 280?nm. Rosmarinus officinalis L. was extracted with methanol with ultrasound at 170?W and 50?kHz for 20?min. The precision, repeatability, and recovery of the method were evaluated. The calibration relationships for carnosol and carnosic acid were y?=?2.331x?+?5.92 from 0.01 to 0.160?mg/mL and y?=?7.980x?+?4.32 from 0.005 to 0.080?mg/mL, respectively. The established method allows the separation and quantification of carnosic acid and carnosol in R. officinalis from various locations in China.     

INHIBITIVE KINETIC SPECTROPHOTOMETRIC DETERMINATION OF PROTEIN

A novel inhibitive kinetic spectrophotometric method for the determination of protein is proposed based on the principle that serum albumin (SA) has an inhibitive effect on the oxidation discoloring of p-acetylchlorophosphonazo (CPApA) by potassium periodate in the medium of 4.0 × 10^?4 mol/L H₂SO₄ at 100°C. The maximum absorption peak of SA – CPApA – KIO₄ system is located at 550 nm. The absorbance difference (ΔA) is linearly related with the concentration of SA over the range of 0.80–7.50 µg/mL at the wavelength and fitted the equation: ΔA = 0.064C (C: µg/mL) – 0.0173, with a correlation coefficient γ = 0.9973. The detection limit of the method was 0.30 μg/mL. The method was successfully used to determine protein content in milk and milk powder samples and the determined results were in good agreement with those of tribromoarsenazo spectrophotometry. The relative standard deviation for 13 replicate determinations of the method was 3.64–3.76%. The standard addition recovery of the method was 99.50–101.6%.     

Mechanical and tribological properties of Cr–Nb double-glow plasma coatings deposited on Ti–Al alloy

Double-glow plasma (DGP) coatings are recommended for metallic components to mitigate the damage induced by complex working conditions in previous studies. In this paper, Nb-rich (Cr–Nb₄) and Cr-rich (Cr₄–Nb) -alloyed layers were formed onto the Ti–Al substrate via a DGP process to enhance its wear resistance. Scratch and Nano-indentation tests were used to evaluate the mechanical properties of the coatings. The tribological behaviour of the coatings were investigated using a pin-on-disc tribometer by rubbing against the GCr15 ball. Results from surface analysis techniques showed that the coatings mainly comprised Cr, Nb and Cr₂–Nb phases, and were well bonded to the substrate. The hardness of the Cr–Nb₄ coating was 11.61GPa and the Cr₄–Nb coating was 9.66 GPa which all higher than that of the uncoated Ti–Al which was 5.65 GPa. However, the critical load of the Cr₄–Nb coating ~21.64 was higher than that of the Cr–Nb₄ coating ~17.6. And the specific wear rate of Cr–Nb₄ coating, Cr₄–Nb coating and uncoated Ti–Al were 3.54 × 10^?4, 0.01 × 10^?4 and 1.53 × 10^?4mm³ N^?1 m^?1_, respectively. The low-wear mechanism of the coatings is discussed in detail in this paper.     

Comparison of some physical techniques for detection of spoilage in apple juice inoculated with Saccharomyces cerevisiae: Optical and photothermal methods

Abstract

Several physical techniques were used to study the extent of spoilage in apple juice deliberately inoculated with yeast (concentration of Saccharomyces cerevisiae ranged from 25 cells mL^?1 to 2.5 × 10⁶ cells mL^?1, respectively) and their performance compared in terms of detection limit achieved. The optical methods used in this investigation rely on the measurement of either absorption [as is the case for classical spectrophotometry (SP) and the so called optothermal window (OW), a variant of a photothermal method], or scattering [examples are turbidimetry (TB), laser scattering (SC), and laser speckle fluctuation (SF)]. It is shown that the presence of yeast increases both optical absorption and scattering. The most favorable detection limit (25 cells mL^?1) and a highest (nearly 10⁴) dynamic range, combined with a good linearity, were obtained with the experimental set‐up for SC. In addition, the extent of correlation between different methods was determined using two markedly different reference substances, i.e., (i) the mixture of apple and blackcurrant juices, representing a strongly absorbing sample, and (ii) diluted (dilution factor of 10³) milk as a strong scatterer. Finally, one has monitored the progress of a spontaneous spoilage process in the inoculated juices stored at 5°C under aerobic conditions.     

Flow Injection Chemiluminescence Analysis of Diphenhydramine Hydrochloride and Chlorpheniramine Maleate

Abstract

A new chemiluminescence (CL) method, using flow injection, is described for the determination of diphenhydramine hydrochloride and chlorpheniramine maleate. The method is based on the restraining effects on the CL reaction of luminol‐potassium ferricyanide in alkaline solutions. The various experimental parameters affecting the chemiluminescence intensity were studied carefully and incorporated into the procedure. The method allows the determination of 1.0–100 µg mL^?1 diphenhydramine hydrochloride and 0.1–10.0 µg mL^?1 chlorpheniramine maleate. The detection limits of the method are 0.3 µg mL^?1 for diphenhydramine hydrochloride and 0.02 µg mL^?1 for chlorpheniramine maleate. The method was successfully applied to the determination of diphenhydramine hydrochloride and chlorpheniramine maleate in pharmaceutical preparations.