Micellar catalysis in flow injection systems: the nitrosation reaction.

The use of aqueous micellar carrier streams in flow injection is shown to catalyse on-line reactions and thereby improve the sensitivity relative to non-micellar systems. The effect of several different micellar systems on the nitrosation reaction of N,N-diethylaniline in acidic solution was investigated. The mechanism of the micellar enhancement is discussed and the sensitivities of the method in both aqueous and micellar media are compared. The presence of the cationic surfactant, cetyltrimethylammonium bromide, is shown to improve the sensitivity of the analysis. The effect of the micellar solution on the dispersion characteristics of the system was also studied. The greater viscosity of the micellar phase increases dispersion for non-reacting systems, but when monitoring a reaction product the increased reaction rate can counteract this and the micellar carrier can show less over-all dispersion than the aqueous carrier.     

Micellar-catalyzed reactions for flow-injection systems : Determination of pyridoxal

The advantages of applying the solubilization and catalytic properties of aqueous micelle solutions to reactions taking place in flow-injection systems are demonstrated. The reaction of pyridoxal (a B₆ vitamin) with cyanide was investigated in both aqueous and micellar cetyltrimethylammonium bromide (CTAB) solution. Higher sensitivities and lower limits of detection were obtained for the micellar carrier, with the pseudo-first-order reaction rate increasing by a factor of two in 0.05 M CTAB relative to water carrier. Because the micellar aggregates also increase fluorescence quantum yields, use of fluorescence detection gave further signal enhancement, with the limit of detection lowered by a factor of three. Measurement of dispersion in the two systems was also investigated and compared. A new method of characterizing dispersion in flow-injection systems, based on moment analysis of exponentially modified Gaussian peak shapes, is described.     

Fluorescent behavior of B-phycoerythrin in microemulsions of aerosol OT/water/isooctane

Taking advantage of its unusual fluorescent properties, the incorporation of B-phycoerythrin (B-PE) in aerosol OT (AOT, sodium bis-(2-ethylhexyl) sulphosuccinate)/water/isooctane microemulsions was investigated by following their steady-state and time-resolved fluorescence as a function of the water-to-surfactant molar ratio, w(0). The fluorescent intensity at 575 nm increased continuously with increasing water content, saturating at a w(0) around 35 and staying practically constant at w(0)> or =40. The steady-state anisotropy showed an initial increase with increasing water content until w(0)=23 and then decreased strongly, staying practically constant when w(0)> or =40. The values of the fluorescent parameters, anisotropy and fluorescent intensity, were unchanged when the water content of the system increased in the range between w(0)=40 to 50. This implies the effective incorporation of B-PE in the microemulsion droplets with w(0)> or =40, as well as the equilibrium of the dispersion at these water/surfactant ratios, since higher water content does not affect the main surrounding microenvironment of the protein. The overall incorporation in the microemulsion droplets caused minor spectroscopic changes with respect to biliprotein in aqueous solution of 20 mM sodium phosphate buffer, pH 7.0, such as a blue absorption shift of 3 nm and an emission shift of 1.5 nm, as well as a slight increase in excitation anisotropy spectrum mainly caused by a decrease in protein mobility. Therefore, there are no important interactions between the chromophores and the AOT sulfonate head groups. Emission intensity decays followed complex kinetics in both aqueous and dispersion media. The stability with time and temperature of the biliprotein in the microemulsion was higher than in the aqueous solution. All the results can be explained in terms of B-PE inclusion in the water droplets of AOT microemulsions where the protein has similar configuration and conformation to that in aqueous solution but with the chromophores more protected.     

Monitoring the removal of carbonate from alkali metal hydroxide solutions using gas diffusion flow injection

Monitoring the removal of carbonate from alkali metal hydroxide (MOH, M = K, Na) solutions with calcium oxide (CaO) was studied using a newly developed method for the determination of trace amounts of total carbonate (TC) in alkaline solutions based on a flow injection (FI) technique coupled with a gas diffusion system. The optimized conditions of the FI system were as follows: the flow rate of each carrier, reaction solution (H2SO4) and receptor solution (Cresol Red, pH 8.9) was 0.25 ml min(-1), the sample size was 0.1 ml and the concentration of H2SO4 in the reaction solution was 0.09 M. The limit of detection of TC by the proposed method was 4 x 10(-7) M. The removal efficiency of carbonate was affected by the amount of CaO added, the shaking time of the solutions and the concentration of MOH. For 1 M NaOH and KOH solution, the removal efficiency of carbonate was about 99% and the concentration of residual carbonate was 4 x 10(-5) and 1.2 X 10(-4) M, respectively, when the amount of CaO added was 2 g l(-1) and the shaking time was 16 h.     

Factors affecting the detection limit of a flow- injection spectrophotometric procedure

Design criteria for manifolds to obtain adequated sensitivity and freedom from certain types of noise are discussed. For the determination of chloride by the mercury(II) thiocynate method, the mergin-streams manifold, needed to eliminated negative peaks at low concentrations and refractive index effects, increased the baseline noise because of inefficient mixing at the confluence point. Packed-bed reactors and single-bead-string reactors (SBSR) significantly improved the baseline noise. Refractive index effects caused by sample concentration gradients were eliminated by the injection of large volumes (>500 μl), so that the detector could view a homogeneous central part of the sample zone. This approach maximises the signal because the dispersion is governed only by the relative flow rates of the carrier and reagent streams. The detection limits for chloride were improved to 40 ng l^?1 in aqueous solutions of low ionic strength and to 1.3 mg l^?1 in 5.25% (w/v) potassium sulphate.     

Design of the Fluoride Ion-Selective Electrode as Tubular Detector for Flow Injection Analysis

ABSTRACT

Design of the fluoride ion-selective electrode (FISE) as the tubular detector used in the flow injection analysis (FIA) has been described. Among other things, this design makes it possible to use various internal contacts. The effect of pH on peak height and detection limit in the pH range from 2.8 to 8.0 has been examined. The effect of flow rate and sample injection volume on peak height and range of linear response has also been examined. The flow rates range from 0.56 mL/min to 4.05 mL/min, while the injection volumes are 100 and 200 μL. The optimum conditions are carrier solution (0.1 M KNO₃ buffer pH 4 and 10^-6 M NaF), flow rate 1.54 mL/min and sample injection volume 100 μL.

Applicability of the FISE as the tubular detector in determination of Fe(III)-ions and AI(III)-ions by flow infection analysis has been examined at pH values of 2.8 and 3.4.     

Increasing Solid Content in Latexes of Polyacrylamide Nanoparticles Made by Semi-continuous Inverse Heterophase Polymerization

The synthesis of polyacrylamide nanoparticles by semi-continuous inverse heterophase polymerization as a function of feeding rate of monomer aqueous solution is reported here. In this process, a concentrated acrylamide aqueous solution is dosed semi-continuously at various rates over an AOT-toluene solution containing the initiator. Our results indicate that particle size and the viscosimetric molar masses diminish as the dosing rate is slowed down and that smaller particles, as well as lower molar masses, are obtained compared to those produced by batch and semi-continuous microemulsion polymerizations, employing the same concentration of surfactant. Moreover, higher polymer/surfactant ratios are higher compared to those obtained in batch microemulsion polymerization and similar or slightly higher than that in semi-continuous microemulsion polymerization.     

单磺化酞菁镓在水、微乳液中的解聚反应动力学研究

本文研究了单磺化酞菁镓（ＳＰｃＧａ）在水、微乳液（ＴｒｉｔｏｎＸ－１００－壬烷－正戊醇－水）中的二聚现象和解聚反应动力学，测定了二聚平衡常数ＫＤ和解聚速率常数ｋ。结果表明：ＳＰｃＧａ的解聚反应速率与ＳＰｃＧａ的单体浓度ＣＭ和双体浓度ＣＤ的关系为：Ｖ＝ｋ１ＣＤ－ｋ２ＣＭ２     

Electric field-induced mobilisation of multiphase solution systems based on the nitration of benzene in a micro reactor

This paper describes the electric field-induced flow characteristics of multiphase solutions in a micro reactor device using the nitration of benzene as a model process. Photolithographic and wet etching techniques were used to fabricate the micro reactor (channels, 200 microns id, 100 microns deep) in a borosilicate glass substrate. The results focus specifically on the flow parameters of reagents/reactants (i.e., voltage, solution concentration and pH ranges and current-voltage relationships) used in this study. The benzene was introduced and mobilised by electroosmotic flow (EOF), as a microemulsion using an appropriate surfactant (sodium dodecyl sulfate), whilst the nitronium ions, produced in situ from mixed H2SO4-HNO3 (the nitrating agent), underwent electrophoretic-induced (electrokinetic) mobility. A co-surfactant, butan-1-ol, was used owing to (a) its relative solubility in the aqueous surfactant solution, (b) its ability to aid the solubilization of benzene, (c) the provision of a water-rich (oil-in-water) rather than oil-rich (water-in-oil) microemulsion system and (d) its lack of significant adverse effects on the EOF. The optimum conditions used for the nitration of benzene within the micro reactor were a run of the microemulsion as main reagent stream, then three 30 s segmented injections of mixed acid, with a 5 s push of the microemulsion into the system after each injection, and then a 60 s stopped-flow reaction time before driving reaction product segments to a collection reservoir.     

Capillary batch injection analysis and capillary flow injection analysis with electrochemical detection: a comparative study of both methods

Capillary batch injection analysis (CBIA) and capillary flow injection analysis (CFIA) in combination with electrochemical detection as well as optical detection methods were studied and compared with respect to their performance. Despite the differences in technical equipment both techniques share the same idea of reproducible transport and washout of nanolitre samples over sensing surfaces. Thus the same electrochemical flow cell can be used for both CBIA and CFIA. The amperometric and potentiometric CBIA responses were studied under various experimental conditions in order to optimise the CBIA set-up. In particular, the density of the sample solution relative to that of the cell electrolyte had a remarkable effect on the hydrodynamic characteristics of CBIA. Dispersion in CFIA was investigated using on column UV-detection for electroosmotic flow (EOF) conditions as well as for gravity flow conditions. It is demonstrated for a 75 μm capillary that the relative band broadening of the sample plug under gravity flow is only about twice as large as under EOF. Furthermore, dispersion in a system that involves a chemical reaction between the sample and the carrier solution, namely CrO₇ ^2– and Fe²⁺ has been investigated by amperometric detection and exploited for the determination of dichromate microsamples.     

Flow Injection Analysis of Mercury/Cold Vapor Atomic Fluorescence Spectrophotometry

Abstract

A new flow injection system for the determination of mercury by the cold vapor atomic fluorescence method is described. A sample solution (64 μ1) is injected into a stream of 0.1 M hydrochloric acid, which is mixed with a stream of 3% tin (II) chloride solution in a mixing joint. The combined stream is carried through a reaction coil for reduction of Hg (II) to Hg (0) and subsequently introduced into a specially designed gas-liquid separation vessel. Then the vaporized mercury is swept into a flow type fluorescence cell with a continuous flow of argon after removal of water in the gas phase through a condenser. Mercury is excited with an electrodeless discharge lamp as a source and the mercury fluorescence at both 184.9 and 253.7 nm is measured with a solar-blind photomultiplier. This method allows about 35 determinations of mercury in aqueous samples per hour. The calibration curve is linear over the 0–20 ppb range of mercury. The limit of detection (S/N = 3) is 0.008 ng (0.12 ppb × 64 μ1) and the coefficient of variation is below 1% for the 1–20 ppb solutions (n=10).     

Spectropotometric Determination of Cyanide by Flow Injection Analysis

Abstract

The flow injection technique is shown to provide fast, reliable, and sensitive determination of cyanide. Spectrophotometric detection in the ultraviolet region at 267 nm was used for measuring the absorbance of tetracyanonickelate (II) complex ion. The nickel carrier stream and the sample solutions were buffered at pH 10 (ammoniacal buffer). The method has a detection limit of 0.2 ppm cyanide. At a sampling rate of 90 samples per hour, with 60 μl sample injections, high reproducibility of measurements was achieved, with about 1% relative standard deviation. The effects of sample volume, flow rate, coil length, and anions interference on the FIA-spectrophotometeric signals are reported.     

Mössbauer spectroscopy of liquid SnCl4 solutions trapped in a rigid microemulsion

A rigid microemulsion was prepared containing submicroscopic droplets of liquid aqueous tin tetrachloride solution. Recoilless-ray resonance absorption (the Mössbauer effect] was achieved in this system, indicating that the organic dispersion medium of the microemulsion behaved as a carrier, enhancing the Debye-Waller factor for the quasiliquid phase of the system. The Mössbauer spectra reflected the presence of two types of tin(IV) in the cavities of the microemulsion: SnCl₄ species situated in the bulk solution and on the cavity wall, respectively.     

On-line collection/concentration and detection of sulfur dioxide in air by flow-injection spectrophotometry coupled with a chromatomembrane cell.

A simple and rapid procedure for SO2 determination in air was developed by using a flow injection analysis (FIA) system coupled with a 3-hole chromatomembrane cell (CMC). The CMC was applied for the on-line collection/concentration of SO2 from air into a solution of 2 g l(-1) triethanolamine (TEA) solution as an absorbing solution: SO2 was converted to SO3(2-) in the alkaline absorbing solution. The solution containing absorbed SO2 was introduced into the carrier stream of the FIA system. The amount of SO3(2-) in the absorbing solution was measured by spectrophotometry with a mixed reagent of pararosaniline and formaldehyde, and was converted to the concentration of SO2 in the air sample. A calibration graph prepared by using standard sodium sulfite aqueous solutions was adopted for the determination of SO3(2-) in the absorbing solution. The SO2 concentration in indoor air examined was found to be 22.7 +/- 0.2 ppbv using 20 ml of air sample with the air flow rate of 5 ml min(-1), where the relative standard deviation was 1.7%. The detection limit for aqueous solutions and air samples were 6.9 x 10(-8) M and 0.48 ppbv, respectively. The measuring time for one sample was about 10 min when a 20 ml air sample was used. The interferences from common anionic species, formaldehyde and acetaldehyde, were also examined.     

A simple flow injection spectrophotometric determination of nitrite based on its reaction with thiourea.

A simple flow injection spectrophotometric method for the determination of nitrite is described. Nitrite injected into the flow system reacts with thiourea in acidic medium and the generated thiocyanate ion reacts with Fe(III) in the reagent solution to produce a highly colored product. The influences of chemical and physical parameters including reagent concentrations, sample volume injected, flow rates of the carrier and reagent solutions, reaction coil length and reaction temperature, were studied and optimum values of these parameters were established. Under the optimum conditions, the calibration curve for nitrite was linear over the concentration range 0.36 - 90 microg ml(-1) without preconcentration and over the range 3.8 - 500 ng ml(-1) with a simple online preconcentration step using an anion exchange column. The corresponding detection limits were 0.36 micro ml(-1) and 3.8 ng ml(-1), respectively. Up to 25 samples can be analyzed per hour, with an average relative standard deviation of < or = 1.2%. Interferences by various foreign ions were studied and the method was applied to the determination of nitrite in water and spiked water samples.     

Aqueous Flow Injection Analysis with Fourier Transform Infrared Detection

Abstract

The combination of the automated sample handling capabilities of flow injection analysis combined with detection by attenuated total reflection infrared spectroscopy is presented. This automated system is used to quantitate aliphatic esters, such as dioctylsulfosuccinate, in aqueous solutions at the mg levels. Fairly high reproducibility, 1 to 5%, at a rate of at least 25 samples per hour is possible.     

On-line concentration sample stacking coupled with water-in-oil microemulsion electrokinetic chromatography

This study describes for the first time, the ability of a normal stacking mode (NSM) on-line concentration step coupled with water-in-oil (W/O) microemulsion electrokinetic chromatography (MEEKC), using six common penicillin antibiotics (oxacillin, penicillin V, penicillin G, nafcillin, ampicillin, and amoxicillin) as test analytes. Optimization of penicillin separation in the conventional W/O MEEKC system demonstrated that change in the type and concentration of the oil phase (1-butanol) and column temperature had a pronounced effect on the separation. With the subsequent development of the NSM coupled with W/O MEEKC, improved separation and detection sensitivities were observed when an organic solvent plug (1-propanol; 1.04 cm) was placed between the W/O microemulsion and the sample solutions. This could be attributed to the solution viscosity difference between the aqueous sample zone and the organic solvent plug causing the penicillin to be stacked in this 1-propanol plug. The optimal NSM W/O MEEKC provided about 12-fold increase in detection sensitivity compared with conventional sample injection (50 mbar, 3 s). Finally, this proposed method was successfully applied in the analyses of several food samples (porcine organs) spiked with penicillin.     

Study of Injection Angle and Carrier Gas Flow Rate Effects on Particles In-Flight Characteristics in Plasma Spray Process: Modeling and Experiments

This paper investigates the influence of particle injection angle on particle in-flight behaviors and characteristics at different primary and carrier gas flow rates through an integrated modeling and experimental approach. Particle in-flight status such as temperature, velocity, size and their distribution are analyzed to examine particle’s melting status before impact. Results from the experiments and numerical simulations both show that, when carrier gas flow rate is fixed, a small injection angle favors the particle melting and flattening. This behavior is independent of primary and secondary gas flow rates, spray distance and carrier gas flow rate. When both carrier gas flow and injection angle vary, a high carrier gas flow rate and a small injection angle are recommended for high particle temperature and velocity.     

Optimisation of a Flow Injection System with a Piezoelectric Quartz Crystal Detector for the Determination of Inorganic Mercury

ABSTRACT

A new method combining flow injection methodology with quartz crystal microbalance (QCM) detection is proposed for inorganic mercury analysis. A modified simplex method is used in order to maximise the observed analytical signals (crystal frequency decrease). Six parameters were optimised: the concentration of the acidic carrier solution, the lengths of the sample loop and mixing coil, and the flow rates of the sample carrier, the reductant stream (SnCl₂), and the carrier of the mercury vapour (N₂). An increase of 18% in the signal of the centroid of the calibration line was achieved, as well as an increase in the sensitivity from 290 Hz μg^? to 313 Hz μg^?. Following the proposed procedure, detection limits of 47 μg L^? of inorganic mercury were found for sample volumes of 0.5 mL.     

Capillary batch injection analysis and capillary flow injection analysis with electrochemical detection: a comparative study of both methods

Capillary batch injection analysis (CBIA) and capillary flow injection analysis (CFIA) in combination with electrochemical detection as well as optical detection methods were studied and compared with respect to their performance. Despite the differences in technical equipment both techniques share the same idea of reproducible transport and washout of nanolitre samples over sensing surfaces. Thus the same electrochemical flow cell can be used for both CBIA and CFIA. The amperometric and potentiometric CBIA responses were studied under various experimental conditions in order to optimise the CBIA set-up. In particular, the density of the sample solution relative to that of the cell electrolyte had a remarkable effect on the hydrodynamic characteristics of CBIA. Dispersion in CFIA was investigated using on column UV-detection for electroosmotic flow (EOF) conditions as well as for gravity flow conditions. It is demonstrated for a 75 μm capillary that the relative band broadening of the sample plug under gravity flow is only about twice as large as under EOF. Furthermore, dispersion in a system that involves a chemical reaction between the sample and the carrier solution, namely CrO₇ ^2– and Fe²⁺ has been investigated by amperometric detection and exploited for the determination of dichromate microsamples. Received: 28 November 1997 / Revised: 23 February 1998 / Accepted: 26 February 1998