Flow Manifold Research Articles

Automated flow‐rate meter for flow‐analysis systems

An automated flow-rate meter easy to construct and operate is described. This is controlled by a microcomputer connected to an analog/digital converter interface and by a control software. It uses two acrylic flow cells, each comprising a bicolor light-emitting diode and a phototransistor placed on opposite sides. The performance of this flow-rate meter was evaluated by applying it to three flow manifolds: one monosegmented flow titration system by binary sampling; one conventional monosegmented flow system, and one single-line FIA system. The FIA system flow rate was assessed by means of a Vanderslice's expression. The time range of measurement of the flow rates was of 3.5–19.5 seconds and relative errors of 0.2–2.6% as well as relative standard deviations from 0.4 to 3.1% were attained. The flow-rate meter allows one to optimize precision and velocity of measurements just by changing one of its parameters. Moreover, the flow-rate meter can be used with flow systems, therefore allowing one to perform on-line measurements, which facilitates a quick and effective control of the channels flow rate.© 1999 John Wiley & Sons, Inc. Lab Robotics and Automation 11: 97–104, 1999

Flow injection Fourier transform infrared determination of nicotine in tobacco.

A fully automated procedure is proposed for the Fourier transform infrared (FTIR) determination of nicotine in tobacco. The method is based on the on-line extraction of nicotine with CHCl3. Samples, weighed inside empty extraction cartridges, were humidified with NH3 and the cartridges were installed in a flow manifold in which they were extracted with 2 ml CHCl3 for 2 min, then 400 microliters of the extract were introduced into a micro-flow cell using a carrier of CHCl3 and the IR spectrum was registered continuously. The absorbance, in the wavenumber range 1334-1300 cm-1, was measured, obtaining a peak as a function of time. The area of this peak was interpolated on a calibration line established from standard solutions of nicotine in chloroform treated in the same way as samples. The method provided a limit of detection of 0.1 mg ml-1 nicotine, an RSD lower than 2% and a sampling frequency of the whole procedure of 6 h-1. Results obtained for natural samples of cut tobacco and cigar compared well with those obtained by a batch FTIR procedure, involving an off-line extraction with a total time of 16 min. However, for yellow tobacco cigarette, an on-line extraction time of 10 min was required to obtain a good recovery of nicotine.

Basic experimental studies on the operation of photoionization detectors

Commercially available and self-made photoionization detectors have been studied in a simple flow manifold without chromatographic column. The self-made detector allowed the independent variation of the detector volume, the electrode surface area and a selective irradiation of the anodes and cathodes. The photoionization of ethanol and acetone has been measured in hydrogen as carrier gas. All experimental results were consistent with a model based upon a photoionization proceeding in the adsorption layer of the electrodes as the main signal generating process. It has been shown that the photoionization of molecules in the gas phase plays only a marginal role.

Indirect determination of cyclamate by an on-line continuous precipitation-dissolution flow system

A continuous-flow procedure is proposed for the indirect determination of sodium cyclamate by an atomic absorption spectrometric method in artificial sweeteners mixtures and soft drinks. Sulfamic group is oxidized to sulfate and it is continuously precipited with lead ion in a flow manifold. The lead sulfate formed is retained on a filter, washed with diluted ethanol and dissolved in ammonium acetate for on-line atomic absorption determination of lead, the amount of which in the precipitate is proportional to that of cyclamate in the sample. The proposed method allows the determination of sodium cyclamate in the range 1–90 μg ml −1 with a relative standard deviation of 3.1% at a rate of ca. 35 samples per h. The 3 σ detection limit is 0.25 μg ml −1. The method is very selective, no compounds normally found in the analysed samples and other artificial sweeteners had any effect on the determination of cyclamate.

Glassy Trapping of Manifolds in Nonpotential Random Flows

We study the dynamics of polymers and elastic manifolds in non potential static random flows. We find that barriers are generated from combined effects of elasticity, disorder and thermal fluctuations. This leads to glassy trapping even in pure barrier-free divergenceless flows $v {f \to 0}{\sim} f^\phi$ ($\phi > 1$). The physics is described by a new RG fixed point at finite temperature. We compute the anomalous roughness $R \sim L^\zeta$ and dynamical $t\sim L^z$ exponents for directed and isotropic manifolds.

Flow injection systems for elemental soil analysis determinations

Flow injection analysis (FIA) is becoming an important automated procedure for the elemental analysis of agricultural and environmental samples. This paper reviews the application of the FIA technique for soil elemental analysis determinations, giving short descriptions of the required flow manifolds by highlighting some of their most important features.

Automated on-line separation–preconcentration system for inductively coupled plasma atomic emission spectrometry and its application to mercury determination

An automated separation–preconcentration system coupled to an inductively coupled plasma atomic emission spectrometer is described. The preconcentration step is performed on a chelating resin microcolumn [silica gel functionalized with 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide] placed in the injection valve of a simple flow manifold. The system was applied to the determination of mercury in sea-water and biological samples. The optimum experimental conditions were evaluated for the continuous preconcentration of mercury, the direct generation of mercury vapour and the final determination of this element by ICP-AES. The proposed method has a linear calibration range from 2 to at least 1000 ng ml–1 of mercury, with a detection limit of 1 ng ml–1 (S/N=3) and a throughput of 40 samples h–1, for a 6 ml sample volume. The accuracy of the method was examined by the analysis of certified reference materials and by determining the analyte content in spiked environmental waters. The results show sufficiently high recoveries.

Anodic Stripping Voltammetry Coupled On-Line with Inductively Coupled Plasma Mass Spectrometry: Optimization of a Thin-Layer Flow Cell System for Analyte Signal Enhancement

Parameters affecting analyte signal enhancement in anodic stripping voltammetry-inductively coupled plasma mass spectrometry (ASV-ICP-MS), using a thin-layer ASV cell and microconcentric nebulization (MCN), have been examined. Silver was used as a test analyte and was deposited at a glassy carbon working electrode. The MCN allowed use of solution flow rates that were beneficial to optimum electrolytic performance of the thin-layer cell. High analyte deposition efficiencies obtained with the thin-layer cell, combined with minimal sample consumption of the MCN, allowed substantial signal enhancement (>400 times higher than continuous nebulization level) to be obtained with 2-3 mL of sample and deposition times of less than 30 min. Signal enhancement was strongly influenced by the opposing effect of flow rate on the electrolytic deposition efficiency (deposition efficiency decreases with increasing flow rate) and on the quantity of analyte delivered to the cell (analyte mass throughput increases with increasing flow rate). Excellent linearity for stripping peak heights was demonstrated for a wide range of analyte deposition times and for peak heights and peak areas (r > 0.999) over a wide concentration range (25 ng/L-20 μg/L). Precision was good (RSD typically <3% for n = 3-6) except for a high Ag blank contributed to by corrosion of the counter electrode and by Ag diffusion from the reference electrode into the cell. Details of the flow manifold and ASV cells are discussed, along with relevant performance characteristics of the MCN.

Flow Injection Fourier Transform Infrared Determination of Caffeine in Soft Drinks

A fully automated procedure has been developed for FT-IR determination of caffeine in soft drinks. Samples are first degasified by filtration and then directly injected into a flow manifold and passed through a 100 mg C18 SPE cartridge, conditioned with methanol and water. After the cartridge has been cleaned with water, the caffeine is eluted with CHCl3 and stabilized with ethanol. The flow injection (FI) recording is obtained by measuring the absorbance at 1658 cm-1 with a baseline established at 1800 cm-1. Area values for the FI recording obtained between 0.4 and 1.4 min after sample injection are interpolated in the calibration graph of a series of aqueous standards of caffeine, which were loaded and eluted in the same way as the samples. Preliminary studies were carried out using off-line SPE and off-line elution and on-line extraction and on-line elution, and the parameters involved in both the retention and elution of caffeine in solid phase extraction cartridges were evaluated, together with the measurement conditions for FT-IR determination of caffeine in CHCl3 solutions and the flow injection parameters. The procedure developed provides a limit of detection of 10 μg mL-1 of caffeine for a sample injection of 1 mL, a sampling frequency of 30 h-1, and a relative standard deviation of 3.5% for eight independent measurements at a concentration level of 100 μg mL-1.

Determination of nanogram levels of zirconium by chelating ion exchange and on-line preconcentration in flow injection UV—visible spectrophotometry

Trace quantities of zirconium were preconcentrated on a series of chelating resins. The experimental conditions for preconcentration such as pH, time and metal ion concentration were optimized for the batch processes. Continuous flow manifolds were developed for the on-line preconcentration of zirconium using microcolumns containing chelating resins. Calibration plots were obtained with correlation coefficients of 0.9990 ± 0.0008. The determination of zirconium was performed using Xylenol Orange at 535 nm. Binary and ternary mixtures of zirconium, thorium and titanium did not show any cross-contamination during column chromatographic separation.

Lyapunov-type numbers and torus breakdown: numerical aspects and a case study

In this work we examine the breakdown mechanism for a 2-torus associated to a system of coupled oscillators. To this end, we rely on computation of the Lyapunov-type numbers, as defined by Fenichel in N. Fenichel, Persistence and smoothness of invariant manifolds for flows, Indiana Univ. Math. J. 21 (1971) 193–226. We give some general results on these numbers, and some specific constructive results for the case in which there is phase-locking on the torus. This is the situation for the system of coupled oscillators we consider, and it leads to great simplifications in the computation of the Lyapunov-type numbers.

Semi-on-line microwave-assisted digestion of shellfish tissue for the determination of selenium by electrothermal atomic absorption spectrometry

An electrothermal atomic absorption spectrometric method for the determination of selenium in shellfish tissue at the microgram per gram level, following digestion of the sample in a continuous system including a microwave oven, is proposed. In the presence of palladium, the pyrolysis temperature for selenium can be raised to 1100 °C, and the signal is increased to a greater extent than with other reported chemical modifiers. The proposed method allows the determination of selenium in the range 25–250 µg l–1(2.5–25 µg l–1 Se after 10-fold dilution in the flow manifold). The precision achieved, expressed as the relative standard deviation, was 6.8% for within-run assays and 12.5% for between-run assays. The flow system is characterized by its simplicity (no special device is needed to process evolved gases during sample digestion). Samples can be introduced into the system as slurries made from unlyophilised fresh shellfish tissue (there is no difference between the mean results for unlyophilised and lyophilised samples.)

The automatic kinetic spectrophotometric assay for laccase activity usingo-phenylenediamine

An automatic flow-injection stopped-flow kinetic spectrophotometric method for determination of laccase activity is proposed. It is based on the oxidation of o-phenylenediamine (1,2-diaminobenzene) catalyzed by laccase during the stopped-flow period, yielding 2,3-diaminophenazine, which is determined spectrophotometrically. The substrate solution (o-phenylenediamine) and Na2HPO4-HAc (pH 6.20) buffer with sample (laccase) are pumped into the flow manifold via two separated channels at the same flow velocity and merged in the flow-through cell, then stopped for measuring variation of absorbance at 420 nm with time at a constant temperature of 55°C. The linear range of the method is over 0-2 U, and the detection limitation is 0.012 U. The proposed method has been applied to the analysis of laccase activity of real samples at 30 samples per hour. © 1996 John Wiley & Sons, Inc.

A systematic study of heteroclinic cycles in dynamical systems with broken symmetries

Let X be a Banach space or a manifold and G a compact Lie group acting on X. We study G-equivariant (semi)flows on X in the context of forced symmetry breaking. After applying small symmetry breaking perturbations, certain generic invariant manifolds of the above flows persist slightly changed. We obtain necessary and sufficient conditions for the existence of heteroclinic cycles on the perturbed manifolds. Applications are given for the case G = SO(3).

Micelle enhanced spectrofluorimetric assay for laccase activity by a flow-injection stopped-flow technique

An automated flow-injection stopped-flow kinetic spectrofluorimetric method for determination of laccase activity is proposed. It is based on the oxidation of o-phenylenediamine (1,2-diaminobenzene) catalysed by laccase during the stopped-flow period, yielding 2,3-diaminophenazine, which is determined by a micelle enhanced spectrofluorimetric method in a non-ionic surfactant medium. The substrate solution with Brij-35 and the buffer with sample are pumped into the flow manifold at the same flow rate and merged in the flow cell, then stopped for measuring the fluorescence intensity ( λ ex = 425 nm, λ em = 530 nm) which increases with time, at a constant temperature of 46°C. The linear range of the method is 0.1–118 U l −1 with a detection limit of 0.07 U l −1, using a 5 min stopped-flow reaction time. The proposed method has been applied to the assay for laccase activity of real samples at 10 samples per h.

Determination of Michaelis-Menten and inhibitor constants by an open-closed flow injection approach (Application to the alkaline phosphatase/theophylline system)

An automatic method for the estimation of Michaelis-Menten and inhibitor constants in biochemical systems was developed using an unsegmented open-closed flow manifold, and the Lineweaver-Burk and Dixon plot methods. The methods were applied to both the determination of K m of the enzymatic reaction catalyzed by bovine alkaline phosphatase using 4-methylumbelliferone phosphate as substrate, and the determination of the K i constant from theophylline as an inhibitor of this biochemical system. The data treatment and comparative results are presented. The values obtained agree with those provided by a conventional method with the biocatalyst in solution.

Simultaneous Determination of Arsenic, Selenium, and Antimony in Environmental Samples by Hydride Generation for Inductively Coupled Plasma Atomic Emission Spectrometry

Abstract Total arsenic, selenium, and antimony are determined simultaneously by inductively coupled plasma atomic emission spectrometry (ICP AES) with hydride vapor generation. A1 g wet, 0.25 g dry, or 10 mL water sample is digested by 1 of 2 methods in a 10 mL volumetric culture tube on a programmed heating block by heating with nitric acid and then boiling in a mixture of sulfuric and perchloric acids. For soils, a 0.25 g sample is digested in a 10 mL volumetric culture tube with hydrochloric acid. After digestion, the sample is treated with additional hydrochloric acid. Arsenic, selenium, and antimony are reduced to their hydrides by sodium borohydride in a simplified continuous- flow manifold. A standard pneumatic nebulizer separates the gaseous hydrides (AsH3, SeH2, and SbH3), which are then quantitated by ICP AES at 193.696,196.026, and 231.147 nm, respectively. The detection limits for As, Se, and Sb are 0.55,1.0, and 0.41 μg/L, respectively. Recoveries from 10 matrixes are 65 to 109%; recovery ranges for As, Se, and Sb are 81–109,87–108, and 65–123%, respectively. The method demonstrates good accuracy and precision for environmental samples and is especially suited for analysis of small samples. It requires no additional apparatus for hydride generation or sample introduction.

Potentialities and limitations of mixing simulations

AbstractAs numerical simulations in mixing become pervasive, an analysis of errors becomes crucial. Purposely discretized examples with exact analytical solutions provide a reference point from which to judge the soundness of numerical solutions. Three types of errors are identified and examined: discretization, time integration, and round‐off, with emphasis on the first two. Theoretical derivations and numerical examples for 2‐D, steady (regular) and time‐periodic (chaotic) flows indicate that errors, in general, behave as material lines. In regular flows, their magnitude increases, on the average, with at most t2, while in chaotic flows it increases exponentially. Errors tend to align with the direction of the streamlines in regular flows and with manifolds in chaotic flows. As a result, even though exact and calculated trajectories diverge exponentially fast in chaotic flows, overall mixing patterns are reproduced, at least qualitatively, even when the velocity field is calculated using the main features of a line as it is deformed by the flow, although the error in its length may be more than 100%. It is concluded that accurate quantitative information, such as the location of periodic points or the length of a deformed line, can be obtained from numerical simulations. However, robust application of standard numerical analysis tools, such as mesh refinement, is necessary, which, in turn, can lead to nearly prohibitive computational costs.

Precipitation flow-injection method for the determination of saccharin in mixtures of sweeteners

An atomic absorption spectrometric method for the determination of sodium saccharin in commercially available mixtures of artificial sweeteners and pharmaceuticals by continuous precipitation with silver ion in a flow manifold is proposed. The silver saccharinate precipitate formed is retained on a filter, washed with diluted acetic acid and dissolved in ammonia for on-line atomic absorption determination of silver, the amount of which in the precipitate is proportional to that of saccharin in the sample. The proposed method allows the determination of sodium saccharin in the range 5–75 μg ml −1 with a relative standard deviation of 2.7% at a rate of ca. 20 samples h −1. The method is very selective; other sweeteners do not interfere, but chloride must be absent.

The effect of header shapes on the flow distribution in a manifold for electronic packaging applications

The present paper investigates the effects of header shapes and the Reynolds number on the flow distribution in a parallel flow manifold to be used in a liquid cooling module for electronic packaging. The flow distribution in the manifold greatly depends on the header shape and the Reynolds number. Of the three different headers (i.e., rectangular, triangular, and trapezoidal), the triangular header produces the best flow distribution regardless of the Reynolds number.