On-line sorptive preconcentration platform incorporating a readily exchangeable Oasis HLB extraction micro-cartridge for trace cadmium and lead determination by flow injection-flame atomic absorption spectrometry

A simple, sensitive and inexpensive flow injection solid phase extraction (SPE) system was developed for automatic determination of trace level concentrations of metals. The potentials of this novel scheme, coupled to flame atomic absorption spectrometry (FAAS), were demonstrated for trace cadmium and lead determination in environmental water samples. The method was based on on-line chelate complex formation of target species with ammonium diethyldithiophosphate (DDTP), retention onto the surface of reversed-phase poly(divinylbenzene-N-vinylpyrrolidone) co-polymeric beads (Oasis HLB) and elution with methanol prior to atomization. A special PVC adapter was designed for easy and rapid replacement of the commercially available SPE cartridge. All main chemical and hydrodynamic parameters affecting the complex formation, sorption and elution of the analyte were optimized thoroughly. Moreover, the effect of potential interfering species occurring in environmental samples was also explored.For 90 s preconcentration time, enhancement factors of 155 and 180, detection limits (3s) of 0.09 μg L^− 1 and 0.9 μg L^− 1 and relative standard deviations (R.S.D.) of 2.9% (at 4.0 μg L^− 1) and 2.6% (at 20.0 μg L^− 1) were obtained for cadmium and lead, respectively, with a sample throughput of 24 h^− 1. The measurement trueness of the developed method was evaluated by analyzing a certified reference material and spiked environmental water samples. The proposed method is well suited to detect the target elements at concentration levels below the maximum allowed concentrations endorsed by the European Framework Directive (2008/105/EC) in inland and coastal waters.     

On Yau's problem of evolving one curve to another: Convex case

A revised Yau's Curvature Difference Flow is considered to deform one convex curve $X_0$ to another one $\stackrel{?}{X}$. It is proved that this flow exists globally on time interval $[0,+\infty )$ and the evolving curve, preserving its convexity and bounded area A, converges to a fixed limiting curve $X_{\infty }$ (congruent to $\sqrt{A/\stackrel{?}{A}}\stackrel{?}{X}$) as time tends to infinity, where $\stackrel{?}{A}$ is the area bounded by the target curve $\stackrel{?}{X}$.     

Determination of sibutramine with a new sensor based on luminol electrochemiluminescence

A flow injection electrochemiluminescence (FI-ECL) analysis method for the determination of sibutramine in the presence of luminol was studied under conventional cyclic voltammetry in alkaline Na₂CO₃-NaHCO₃ buffer solution (pH 8.0-12.0). This method is based on the enhanced ECL of luminol-sibutramine. Meanwhile, in order to overcome the drawbacks of conventional cells, a FI cell was designed, which is reusable and has a great improvement in sensitivity and selectivity for ECL analysis. Under the optimal experimental conditions, the enhanced ECL intensity was linearly related to the concentration of sibutramine in the range 1.0×10⁻⁸-1.0×10⁻⁶ g mL⁻¹ with a detection limit of 2.48×10⁻⁹ g mL⁻¹ and a correlation coefficient (R) of 0.9995. The relative standard deviation (RSD) for 1.0×10⁻⁷ g mL⁻¹ samples was 2.1% (n=11). The possible mechanism discussed. The proposed FI-ECL method has been successfully applied to the determination of sibutramine in diet pill samples.     

Fluorimetric detector and sensor for flow analysis made of light emitting diodes

Two compact optoelectronic fluorimetric devices operating according to the paired-emitter-detector-diode concept have been developed. The fluorimetric detector, fabricated of three light emitting diodes only, has been applied for the development of fluorimetric optosensor by further integration with sensing solid phase. In these investigations as a model analyte and as a model sensing layer useful for solid phase spectrometry, riboflavin and C18-silica have been chosen, respectively. Both developed analytical devices have been applied for non-stationary fluorimetric measurements performed under conditions of flow injection analysis. The presented flow-through detector and sensor operating under given flow conditions offer riboflavin determination in mg L⁻¹ and μg L⁻¹ ranges of concentration, respectively.     

Dissolution Testing and Potentiometric Assay of Sertraline Hydrochloride in Batch and FIA Conditions

An electrochemical polyvinyl chloride membrane sensor for sertraline (Ser) was prepared based on the ion associate of sertraline with phosphotungstic acid. The sensor was fully characterized in terms of its membrane composition, life span, effect of soaking, pH, interferences, and temperature and exhibited an average Nernestian response (61.6 ± 0.9 mV/decade) in the concentration range of 1.0 × 10^?2 –5.0 × 10^?5 M. Sertraline was assayed potentiometrically in its pure solutions and pharmaceutical preparations using the developed electrode under batch and flow injection conditions and the recovery values ranged from 93.44–101.12%, with a relative standard deviation of 0.53–1.27%.

The sensor was successfully applied to the determination of the dissolution profile study of (Ser) tablets and the results were validated by comparison with spectrophotometric assays according to the quality control unit of the tablets pharmaceutical company producers. The results obtained from the proposed electrode were statistically analyzed and compared to a reported method. No significant difference was observed regarding both accuracy and precision.     

Modified split-potential model for modeling the effect of DBD plasma actuators in high altitude flow control

Surface DBD plasma actuators are novel means of actively controlling flow. They have shown promising ability in reducing drag, postponing transition from laminar to turbulent flow, suppression of separation, noise reduction and enhancement of mixing in different applications. The CFD simulation of the effect of plasma actuator in such kind of applications could provide more information, and insight, for optimization and design of close looped flow control systems. However, the fluid models for simulating the formation of the plasma and its effect are computationally expensive such that, although they provide more detailed information about the physics related to the formation plasma, they are still not viable to be used in large scale CFD simulations. In this paper, we present the modified version of a simpler model that predicts the thrust generated by the plasma actuator with acceptable accuracy and can be easily incorporated in CFD calculations. This model is also free of empirical fitting parameters, being based on pure flow physics scaling.     

尿碘的流动在线消化催化光度法测定

将尿样消化引入ＦＩＡ流路，并与催化光度法相结合，建立了尿碘的流动在线消化催化光度法，从而实现了尿碘的快速自动测定。本法分析速度１３０／ｈ，检测范围宽达４０～１６００μｇ／ＬＩ＾－，重现性好，实际尿样测定ＲＳＤ≤６．９％（ｎ＝８），方法具有创新和实用性，对尿碘的快速准确定值及碘缺乏病的防治有重要意义。     

Novel Sensors for Batch and Flow Injection Analysis of Histamine Based on Crown Ethers

Six types of histamine potentiometric sensors are developed. They are based on using dibenzo‐30‐crown‐10 (DB30C10) with potassium tetrakis(p‐chlorophenyl)borate lipophilic additive (Type I), dibenzo‐30‐crown‐10 without additive (Type II), dibenzo‐24‐crown‐8 (DB24C8) with the same additive (Type III), dibenzo‐24‐crown‐8 without additive (Type IV), dibenzo‐18‐crown‐6 with the additive (Type V) and dibenzo‐18‐crown‐6 without additive (Type VI) as neutral carriers for histamine. Sensors based on dibenzo‐30‐crown‐10 with (PTp‐C1PB) lipophilic additive (Type I) and dibenzo‐30‐crown‐10 without additive (Type II) show good response. The other sensors Types III–VI show poor response in terms of calibration range and slope.     

Optical study of a light diaphragm rupture process in an expansion tube

Abstract. Rupture of a light cellophane diaphragm in an expansion tube has been studied by an optical method. The influence of the light diaphragm on test flow generation has long been recognised, however the diaphragm rupture mechanism is less well known. It has been previously postulated that the diaphragm ruptures around its periphery due to the dynamic pressure loading of the shock wave, with the diaphragm material at some stage being removed from the flow to allow the shock to accelerate to the measured speeds downstream. The images obtained in this series of experiments are the first to show the mechanism of diaphragm rupture and mass removal in an expansion tube. A light diaphragm was impulsively loaded via a shock wave and a series of images was recorded holographically throughout the rupture process, showing gradual destruction of the diaphragm. Features such as the diaphragm material, the interface between gases, and a reflected shock were clearly visualised. Both qualitative and quantitative aspects of the rupture dynamics were derived from the images and compared with existing one-dimensional theory. Received 10 April 1999 / Accepted 17 April 2000     

A study of the parameters affecting the accuracy of the total pore blocking method

We report on a study wherein we investigate the different factors affecting the accuracy of the total pore blocking method to determine the interstitial volume of reversed-phase packed bed columns. Octane, nonane, decane and dodecane were all found to be suitable blocking agents, whereas heptane already dissolves too well in the applied fully aqueous buffers. The method of moments needs to be used to accurately determine the elution times, and a proper correction for the frit volume is needed. Failing to do so can lead to errors on the observed interstitial volume of the order of 2% or more. It has also been shown that the application of a high flow rate or a high pressure does not force the blocking agent out of the mesopores of the particles. The only potential source of loss of blocking agent is dissolution into the mobile phase (even though this is a buffered fully aqueous solution). This effect however only becomes significant after the elution of 400 geometrical column volumes, i.e., orders more than needed for a regular total pore blocking experiment.