Solid sampling coupled to flame furnace atomic absorption spectrometry for Mn and Ni determination in petroleum coke

A solid sampling flame furnace atomic absorption spectrometry (SS-FF-AAS) system was developed for Mn and Ni determination in petroleum coke. The proposed system for solid sampling was a quartz cell with two perpendicular tubes (T-shaped tubes), positioned above the burner. Manganese and Ni determination was made using an atomic absorption spectrometer with deuterium background corrector, air-acetylene flame and a single slit burner. Powdered samples of coke were introduced as pellets (up to 62 mg) into the quartz cell with a movable hollow quartz piston. When the sample pellet reached the end of quartz cell (T-connection), in the presence of a constant oxygen flow, it quickly burned and the combustion products were transferred to the upper slit tube where the atomic absorption process occurs. Calibration was possible using aqueous reference solutions applied directly on high purity graphite pellets. Results obtained for Mn and Ni using the proposed SS-FF-AAS system were compared to those obtained by inductively coupled plasma optical emission spectrometry (ICP OES) and inductively coupled plasma mass spectrometry (ICP-MS) after sample decomposition by high pressure microwave assisted acid digestion and also by microwave induced combustion. Agreement better than 96% was obtained for both methods employing a previous step of sample digestion (ICP OES and ICP-MS) and by SS-FF-AAS. Accuracy was evaluated using certified reference materials and also recovery tests. The relative standard deviation was lower than 9% for both analytes. The characteristic mass was 18.3 and 14.7 ng and the limit of detection was 0.6 and 0.8 µg g^− 1 for Mn and Ni, respectively. The proposed SS-FF-AAS system can be applied for Mn and Ni determination in petroleum coke, combining a relatively high sample throughput (9 determinations per h), and a suitable precision and accuracy.     

Development of a simple combining apparatus to perform a magnetic stirring-assisted dispersive liquid–liquid microextraction and its application for the analysis of carbamate and organophosphorus pesticides in tea drinks

This study introduced a simple combining apparatus for performing a magnetic stirring-assisted dispersive liquid–liquid microextraction (MSA-DLLME) for the detection of trace carbamate and organophosphorus pesticides in tea drinks coupled with high performance liquid chromatography. The simple combining apparatus was made up of a sample vial and a cut plastic dropper. The bulb end of the cut plastic dropper was inserted into the neck of the sample vial and the open tip end of the plastic dropper was then cut to an appropriate length. The combining apparatus made was then used to perform the MSA-DLLME. In this experiment, 1-octanol was injected into the tea drink sample solution and the extraction process accelerated by magnetic agitation. The sample solution turned clear and separated into two layers after leaving it alone for several minutes. The cut plastic dropper was gently put down into the sample vial, and then the liquid level of the sample solution elevated up to the tip of the plastic dropper for the collection of low-density extractant. Finally, the collected extractant was drawn out by a microsyringe and injected into the high performance liquid chromatography-diode-array detector for analysis. A series of extraction parameters were investigated and optimized. Under the most favorable conditions, high enrichment factors were obtained for carbofuran, carbaryl and isocarbophos (between 130 and 185). The limits of detection (S/N = 3) were in the range of 0.13–0.61 μg L⁻¹, and the relative standard deviation varied below 7.8% (n = 5). Additionally, good recoveries were obtained between 79.4% and 114.4% in the three tea drinks. The simple combining apparatus utilized in this MSA-DLLME method was shown to be economical, fast, and convenient for the collection of low density extractant.     

Automated measurement of permeation and dissolution of propranolol HCl tablets using sequential injection analysis

Aim of this study was to automate sampling and quantification of the previously described apparatus for combined determination of dissolution and permeation through Caco-2 monolayer by means of sequential injection analysis (SIA). Native fluorescence of propranolol HCl in Krebs-Ringer buffer (KRB) was used for quantification. Sampling was done at three different locations within the apparatus at a high sampling frequency (approximately 60 h⁻¹). Injection volume delivered to the fluorescence detector was 50 μL for permeation monitoring and 25 μL for dissolution monitoring. Linear regression for 50 μL injection yielded a detection limit calculated as 0.04 μg mL⁻¹ of propranolol HCl in KRB (R² > 0.999). However, linearity for dissolution monitoring was not given for the complete range of concentrations and first order polynomial calibration was established (R² > 0.9999). To conclude, the SIA system was able to monitor simultaneously dissolution and permeation of the immediate release propranolol HCl tablets and the authors succeeded in automating the apparatus for combined measurement of dissolution and permeation. In addition, the obtained data was consistent with data obtained by manual sampling followed by HPLC analysis.     

Experimental densities,vapor pressures,and critical point,and a fundamental equation of state for dimethyl ether

Densities, vapor pressures, and the critical point were measured for dimethyl ether, thus, filling several gaps in the thermodynamic data for this compound. Densities were measured with a computer-controlled high temperature, high-pressure vibrating-tube densimeter system in the sub- and supercritical states. The densities were measured at temperatures from 273 to 523 K and pressures up to 40 MPa (417 data points), for which densities between 62 and 745 kg/m³ were covered. The uncertainty (where the uncertainties can be considered as estimates of a combined expanded uncertainty with a coverage factor of 2) in density measurement was estimated to be no greater than 0.1% in the liquid and compressed supercritical states. Near the critical temperature and pressure, the uncertainty increases to 1%. Using a variable volume apparatus with a sapphire tube, vapor pressures and critical data were determined. Vapor pressures were measured between 264 and 194 kPa up to near the critical point with an uncertainty of 0.1 kPa. The critical point was determined visually with an uncertainty of 1% for the critical volume, 0.1 K for the critical temperature, and 5 kPa for the critical pressure. The new vapor pressures and compressed liquid densities were correlated with the simple TRIDEN model. The new data along with the available literature data were used to develop a first fundamental Helmholtz energy equation of state for dimethyl ether, valid from 131.65 to 525 K and for pressures up to 40 MPa. The uncertainty in the equation of state for density ranges from 0.1% in the liquid to 1% near the critical point. The uncertainty in calculated heat capacities is 2%, and the uncertainty in vapor pressure is 0.25% at temperatures above 200 K. Although the equation presented here is an interim equation, it represents the best currently available.     

Chemiluminescence from singlet oxygen that was detected at two wavelengths and effects of biomolecules on it

We developed the detection apparatus that equipped with the two-photomultiplier tubes for chemiluminescence from singlet oxygen. Singlet oxygen was generated with reaction between sodium hypochlorite and hydrogen peroxide. The chemiluminescence from singlet oxygen, the dimol light emission (ca. 634 nm) and the monomol light emission (ca. 1270 nm), was observed simultaneously for the same reaction cell. The effects of sodium azide as an antioxidant, human serum albumin, and α-amino acids on the chemiluminescence based on the both emissions were examined; the observed chemiluminescence could provide direct information with regard to the reaction between singlet oxygen and antioxidant/biomolecules. The apparent rate constants for quenching singlet oxygen in the presence of human serum albumin were calculated to be ca. 3.3 × 10⁹ and ca. 8.8 × 10⁸ M⁻¹ s⁻¹ for the dimol and monomol light emissions, respectively, under the present conditions. The chemiluminescence intensities of the dimol emission decreased in the presence of His, Asp, Phe, Ser, and Tyr, and that of the monomol decreased in the presence of Cys and Trp. The chemiluminescence observed in the presence of biomolcules was discussed together with the reactivities of sodium hypochlorite and hydrogen peroxide to biomolecules.     

A new isopiestic apparatus for the determination of osmotic coefficients

A new isopiestic apparatus has been designed and constructed following several criteria. It consists mainly of several small sample cups for holding small quantities of reference standard solutions, and a big sample cup for a bigger quantity of a test solution. Using this apparatus, experiments on NaOH solutions have been performed. The experimental procedure, the consistency among the samples in equilibrium, the equilibration process, and the determined osmotic coefficients of NaOH solutions are discussed. The apparatus is found to ensure a consistent temperature among the samples in equilibrium, meeting the experimental requirements for samples of molalities less than 0.05 mol · kg⁻¹. Inside the apparatus, the temperature can reach the desired uniform temperature within less than 0.5 d. In the experiments, the equilibration process is essentially determined by changes in the reference standard solutions in the small cups. Thus the apparatus is not only reliable and stable, but is also suitable for experiments on solutions of viscous, complex and unstable solutes. The equilibration time of the experiments is fast, which is practical for samples of molalities less than 0.05 mol · kg⁻¹. Moreover, with the new apparatus it is easy to determine the end point of the equilibration.     

New isothermal vapor–liquid equilibria for the CO2 + n-nonane,and CO2 + n-undecane systems

Experimental vapor–liquid equilibria (VLE) for the CO₂ + n-nonane and CO₂ + n-undecane systems were obtained by using a 100-cm³ high-pressure titanium cell up to 20 MPa at four temperatures (315, 344, 373, and 418 K). The apparatus is based on the static-analytic method; which allows fast determination of the coexistence curve. For the CO₂ + n-nonane system, good agreement was found between the experimental data and those reported in literature. No literature data were available for the CO₂ + n-undecane system at high temperature and pressure. Experimental data were correlated with the Peng–Robinson equation of state using the classical and the Wong–Sandler mixing rules.     

New analytic apparatus for experimental determination of vapor–liquid equilibria and saturation densities

A new experimental apparatus for performing simultaneous determination of high-pressure vapor–liquid equilibria (VLE) and saturated densities was developed in this work. The experimental methodology was verified by measuring these properties for the carbon dioxide + 1-propanol and carbon dioxide + 2-propanol systems from 313 to 363 K. The apparatus is based on the static-analytic method for VLE determinations and was slightly modified by coupling a vibrating U-tube densitometer to obtain saturated densities for both vapor and liquid phases. VLE measurements agreed with previous literature data and were correlated with the Peng–Robinson equation of state coupled to the Wong–Sandler mixing rules. Saturation densities at temperatures above 313 K have not been published up to now.     

Scaling up of high-speed countercurrent chromatographic apparatus with three columns connected in series for rapid preparation of (−)-epicatechin

In the present study, compact high-speed countercurrent chromatographic apparatus was constructed with three columns connected in series. Two sets of columns were prepared from 10 mm and 12 mm I.D. tubing to form 12 L and 15 L capacities, respectively. Performance of these columns was compared for the separation of (−)-epicatechin gallate (ECG) from a tea extract by flash countercurrent chromatography (FCCC). In each separation, 200 g of the tea extract in 1600 mL of mobile phase was loaded onto the column. The 12 L column gave 7.5 L (35 g of ECG) and the 15 L column gave 9 L (40 g of ECG) of ECG solution without impurities. The ECG solution was directly hydrolyzed by tannase into (−)-epicatechin. The hydrolysate was purified by flash chromatography on AB-8 macroporous resin to give 52 g of EC (purity 99.1%). This scaled up apparatus could be used for the industrial separation of natural products.     

An analytical application of the electrocatalysis of the iodate reduction at tungsten oxide films

Films of non-stoichiometric tungsten oxides have been deposited onto glassy carbon surfaces by electrodeposition from acidic W(VI) solutions and the chemical stability of these oxides was investigated by using the electrochemical quartz crystal microbalance. At these modified surfaces, rotating disc electrode voltammetric experiments indicated that iodate is electrocatalytically reduced in a mass-transport controlled process. The influence of the film thickness on the response to iodate was investigated and the results indicated a linear relationship between catalytic current and film thickness for relatively thin oxide layers. The modified electrode was employed successfully as an amperometric sensor for iodate in a flow injection apparatus. The linear response of the developed method is extended from 5 μmol L⁻¹ to 5 mmol L⁻¹ iodate with a limit of detection (signal-to-noise = 3) of 1.2 μmol L⁻¹. The repeatability of the method for 41 injections of a 1 mmol L⁻¹ iodate solution was 0.8% and the throughput was determined as 123 h⁻¹. Interference from other oxidant anions such as nitrate and nitrite was not noticeable, whereas bromate and chlorate interfere at slight levels. The method was used in the determination of the iodate content in table salt samples.     

Spectrophotometric and spectrodensitometric determination of Clopidogrel Bisulfate with kinetic study of its alkaline degradation

Four sensitive, selective and precise stability-indicating methods for the determination of Clopidogrel Bisulfate (CLP) in presence of its alkaline degradate and in pharmaceutical formulations were developed and validated. Method A is a second derivative (D²) spectrophotometric one, which allows the determination of CLP in presence of its alkaline degradate at 219.6, 270.6, 274.2 and 278.4 nm (corresponding to zero-crossing of the degradate) over a concentration range of 4-37 μg mL⁻¹ with mean percentage recoveries 99.81 ± 0.893, 99.72 ± 0.668, 99.88 ± 0.526 and 100.46 ± 0.646, respectively. CLP can be determined in the presence of up to 65% of its degradate. D² method was used to study the kinetic of CLP alkaline degradation that was found to follow a first-order reaction. The t_1/2 was 6.42 h while K (reaction rate constant) was 0.1080 mol/h. Method B is the first derivative of the ratio spectra (DD¹) spectrophotometric method, by measuring the peak amplitude at 217.6 and 229.4 nm using acetonitrile and CLP can be determined in the presence of up to 70% of its degradate. The linearity range was 5-38 μg mL⁻¹ with mean percentage recoveries 99.88 ± 0.909 and 99.70 ± 0.952, respectively. Method C based on the determination of CLP by the bivariate calibration depending on simple mathematic algorithm which provides simplicity and rapidity. The method depends on quantitative evaluation of the absorbance at 210 and 225 nm over a concentration range 5-38 μg mL⁻¹ with mean percentage recovery 99.27 ± 1.115. CLP can be determined in the presence of up to 70% of its degradate. Method D is a TLC-densitometric one, where CLP was separated from its degradate on silica gel plates using hexane:methanol:ethyl acetate (8.7:1:0.3, v/v/v) as a developing system. This method depends on quantitative densitometric evaluation of thin layer chromatogram of CLP at 248 nm over a concentration range of 0.6-3 μg/band with mean percentage recovery 99.97 ± 1.161. CLP can be determined in the presence of up to 90% of its alkaline degradate. The selectivity of the proposed methods was checked using laboratory prepared mixtures. The proposed methods have been successfully applied to the analysis of CLP in pharmaceutical dosage forms without interference from other dosage form additives and the results were statistically compared with the official method.     

Investigation of organic phase biosensor for measuring glucose in flow injection analysis system

The aim of our present work was to develop a flow-through measuring apparatus for the determination of glucose content as model system in organic media and to compare the properties of the biosensor in organic and in aqueous solutions. Glucose oxidase (GOx) enzyme was immobilized on a natural protein membrane in a thin-layer enzyme cell, made of Teflon. The enzyme cell was connected into a flow injection analyzer (FIA) system with an amperometric detector. After optimizing the system the optimal flow rate was found at 0.8 ml min⁻¹. In this case 50-60 samples were measured per hour. Adding ferrocene monocarboxylic acid (FMCA) to acetonitrile and to 2-propanol the optimal concentration was 5 mg l⁻¹, while in the case of tetrabutylammonium-p-toluenesulfonate (TBATS) the optima were 2.7 and 8.0 mg l⁻¹, respectively. With 6% buffer in acetonitrile containing FMCA more than 100 samples could be measured with the enzyme cell without any loss of activity. Measuring the hydrogen peroxide content produced in 2-propanol, the optimal concentration of buffer solution was at about 20%. The linear measuring range was 0-0.5 mM glucose in acetonitrile and 0-1.0 mM in 2-propanol.Glucose concentration of oily food samples was measured and compared with results obtained by the reference UV-photometric method. The correlation between the results measured by the two methods was very good with correlation coefficient (r) as high as 0.976.     

A methodology for the determination of reductive sulphur in optical and technical glass

This paper describes an analytical method for the determination of reductive sulphur (S(IV), S(-II)) in glass. The glass sample is dissolved in hydrofluoric/hydrochloric acid mixture and the sulphur is separated via distillation in an apparatus made of polyfluoralkoxyethylene (PFA). The distilled hydrogen sulphide is trapped in buffered boric acid-zinc acetate solution and subsequently determined after conversion to an ethylene blue dye. The range of the method lies within a range of 2-1200 μg g⁻¹ reductive sulphur. The quantification limit for reductive sulphur is 2 μg g⁻¹.Different analysed glass types show either no detectable reductive sulphur or up to 30% of the total sulphur content reductive sulphur. The inter-laboratory standard deviation shown by a round robin test performed is excellent (±4 μg g⁻¹; average 59 μg g⁻¹). Sources of error of the methodology are discussed.     

Determination of mercury by intermittent flow electrochemical cold vapor generation coupled to atomic fluorescence spectrometry

A novel method for determination of mercury was developed using an intermittent flow electrochemical cold vapor generation coupled to atomic fluorescence spectrometry (IF-ECVG-AFS). The mercury vapor was generated on the surface of glassy carbon cathode in the flow cell. The operating conditions for the electrochemical generation of mercury vapor were investigated in detail, and the interferences from various ions were evaluated. Under the optimized conditions, no evident memory effects of mercury were observed. The calibration curve was linear up to 5 μg L⁻¹ Hg at 0.54 A cm⁻². A detection limit of 1.2 ng L⁻¹ Hg and a relative standard deviation of 1.8% for 1 μg L⁻¹ Hg were obtained. The accuracy of method was verified by the determination of mercury in the certified reference human hair. The ECVG avoided the use of reductants, thereby greatly reducing the contamination sources. In addition, the manifold of IF-ECVG-AFS was simple and amenable to automation.     

Spectrophotometric determination of zinc and copper in a multi-syringe flow injection analysis system using a liquid waveguide capillary cell: application to natural waters

This work exploits a multi-syringe injection analysis (MSFIA) system coupled with a long liquid waveguide capillary cell for the spectrophotometric determination of zinc and copper in waters. A liquid waveguide capillary cell (1.0 m pathlength, 550 μm i.d. and 250 μL internal volume) was used to enhance the sensitivity of the detection. The determination for both ions is based on a colorimetric reaction with zincon at different pH values. The developed methodology compares favourably with other previously described procedures, as it allows to reach low detection limits for both cations (LODs of 0.1 and 2 μg L⁻¹, for copper and zinc, respectively), without the need for any pre-concentration step. The system also provided a linear response up to 100 μg L⁻¹ with a high throughput (43 h⁻¹) and low reagent consumption and effluent production. The developed work was applied to natural waters and three certified reference water samples.     

Time-based multisyringe flow injection system for the spectrofluorimetric determination of aluminium

A time-based multisyringe flow injection procedure with spectrofluorimetric detection is proposed in this paper for the determination of aluminium in drinking water. The flow methodology is based on the simultaneous or sequential injection of sample and chelating reagent (viz. 8-hydroxyquinoline-5-sulphonic acid) plugs using a multicommutation approach so that three successive injections may be performed with a sole displacement of the piston driver bar of the burette. Thus, an injection throughput as high as 154 h⁻¹ is achieved by sampling a 182 μl sample zone. In order to enhance the luminescence, the reaction is carried out in micellar medium using hexadecyltrimethylammonium chloride as surfactant. The influence of geometric and hydrodynamic variables as well as several parameters such as multicommutation timing, ligand and surfactant concentration and reagent pH was assessed.Under the selected working conditions, a linear dynamic range from 10 to 500 μg l⁻¹ Al(III), a 3σ detection limit of 0.5 μg l⁻¹ and a coefficient of variation of 0.6% at the 30 μg l⁻¹ level were obtained. The analytical features were compared with those reported in previous flow injection and sequential injection methods. The multisyringe technique was successfully applied to the determination of aluminium in drinking water at low mineralisation levels, validating the results by inductively coupled plasma atomic emission spectrometry.     

Studies on the pervaporation membrane of permeation water from methanol/water mixture

This investigation was performed to find if the nanometer SiO₂ added in the membranes can improve the pervaperation performance of the membranes. Acrylic acid (AA) and acrylonitrile (AN) were synthesized by solution polymerization with and without nanometer SiO₂. The copolymer solution was made into main body of the membranes, then composited with the polyvinyl alcohol (PVA) acetal membranes, to make the three-layer sandwich composite pervaporation membranes. The structure and the performance of the membranes were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry (TG), dynamic themomechanical analysis apparatus (DMA) and mechanical property testing. Pervaporation experiments were carried out using these membranes to separate the mixtures of methanol/water over the complete concentration range 70–98%, and results showed that the selectivity of the membranes with nanometer SiO₂ had notable improvement. For the 98% mixture at 60 °C, the separate factor is up to 1458, which is improved more than 10 times compared to the membranes without nanometer SiO₂, the permeate flux is up to 325 g/(m² h). For the 70% mixture at 70 °C, the separate factor arrived at 12, the permeate flux is up to 7097 g/(m² h), which is improved more than 14 times compared to membranes without nanometer SiO₂. It was concluded that the pervaperation performance of the membranes can improve greatly by nanometer SiO₂.     

Flow injection analysis of ethyl xanthate by in-line dialysis and UV spectrophotometric detection

A simple and sensitive spectrophotometric flow method for determination of low concentrations of the flotation collector O-ethyldithiocarbonate (ethyl xanthate, CH₃CH₂-O-CS₂⁻) in solutions is described. The method is based on ethyl xanthate detection at 301 nm in medium of NaOH 50 mmol L⁻¹. By injection of 200 μL of sample, the analytical method shows linear response for the ethyl xanthate concentration from 0.5 up to 500 μmol L⁻¹. Successive injections of 4 μmol L⁻¹ ethyl xanthate (n = 23) show a coefficient of variation lower than 0.6%, denoting high repeatability. The detection limit is 0.3 μmol L⁻¹. At a flow rate of 2.0 mL min⁻¹, a frequency of 120 injections/h of ethyl xanthate can be attained. By introduction of a tangential dialysis cell in the FIA system, the manual sample filtration step with 0.22 μm filter was eliminated and the residual interference of suspended material, was completely overcome even for unfiltered sludge suspension samples, an important advantage that compensates for the frequency reduction to 25 injections/h elevation and detection limit elevation to 2 μmol L⁻¹, still outreaching for many applications. Potential applications of the method embrace the at line determination of ethyl xanthate in the ore processing industry, control of the concentration at its optimal level during the flotation process, as well as monitoring of residues in the effluents.     

Investigation on Ochratoxin A stability using different extraction techniques

The stability of Ochratoxin A during its extraction using different extraction techniques has been evaluated. Microwave-assisted extraction and pressurised liquid extraction, in addition to two other reference methods of extraction, i.e. ultrasound-assisted and magnetic stirring-assisted extraction, were evaluated. The effect of extraction temperature using the cited techniques was checked.The results show that Ochratoxin A can be extracted using microwave-assisted extraction at temperatures up to 150 °C without degradation. Pressurised liquid extraction can be used at temperatures up to 100 °C, for extraction times of less than 30 min. Further, both ultrasound-assisted extraction and magnetic stirring extraction can be applied at temperatures up to 65 °C.High-performance liquid chromatography combined with fluorescence detection using a Chromolith RP-18e column at a flow rate of 5 mL min⁻¹ was used to quantify the Ochratoxin A. The retention time for the Ochratoxin A was 1.3 min. The limits of detection (LOD) and of quantification (LOQ) were 0.03 and 0.10 μg L⁻¹, respectively.     

Fast transient infrared studies in material science: development of a novel low dead-volume, high temperature DRIFTS cell

A prototype DRIFTS flow reaction chamber was designed and developed in order to find analytical application in the study of heterogeneous catalysts operating at high temperatures under fast transient gas feed conditions. Minimisation of dead-volumes allows gas replacement in 8-10 s at 10 mL min⁻¹ total flow. To overcome problems related to the reactivity of the cell walls under alternating oxidizing/reducing gases, the cell was built with Inconel 600™, which was tested to be very inert even at high temperatures. The sample holder, which was developed to closely resemble a micro plug-flow reactor, poses some problems in terms of heat transfer to the outer body of the cell (limiting then the maximum reachable temperature) and of the correct measurement of the actual sample temperature. These problems were solved with a careful re-design of the upper part of the cell. The second prototype thus derived is able to reach temperatures up to 803 K and allows gas replacement in less than 4 s at 10 mL min⁻¹. The cell is inserted in a MCT-FT-IR, which allows to collect high quality spectra with a 1 s time-resolution. The downstream flow can be analysed by a quadrupole mass spectrometer equipped with an enclosed source and by a commercial GC. The performances of this prototype cell are presented showing some tests carried out with ceria-zirconia (Ce_xZr_1−xO₂) catalysts for CO abatement under real operando conditions.