Flow Diffusion Analysis

A novel method of valveless sample introduction in flow analysis systems called flow-diffusion analysis (FDA) is described Due to the reduction of mechanical parts, i e an injection valve is dispensable, the system becomes very simple and its transformation into the micro-scale should require less effort than the respective transfer of conventional flow-injection systems Additionally, due to the time based sampling, the method is more flexible in terms of sensitivity and linear range compared to established volume based methods... 

There are many potential advantages to kinetic methods of analysis, perhaps the most important of which is the ability to use chemical reactions that are slow to reach equilibrium. In this chapter we examine three techniques that rely on measurements made while the analytical system is under kinetic rather than thermodynamic control chemical kinetic techniques, in which the rate of a chemical reaction is measured radiochemical techniques, in which a radioactive element s rate of nuclear decay is measured and flow injection analysis, in which the analyte is injected into a continuously flowing carrier stream, where its mixing and reaction with reagents in the stream are controlled by the kinetic processes of convection and diffusion. 

Separation Modules Incorporating a separation module in the flow injection manifold allows separations, such as dialysis, gaseous diffusion, and liquid-liquid extraction, to be included in a flow injection analysis. Such separations are never complete, but are reproducible if the operating conditions are carefully controlled. 

Separation module for a flow Injection analysis using a semipermeable membrane for dialysis and gaseous diffusion. 

Willason and Johnson [53] have described a modified flow-injection analysis procedure for ammonia in seawater. Ammonium ions in the sample were converted to ammonia which diffused across a hydrophobic membrane and reacted with an acid-based indicator. Change in light transmittance of the acceptor steam produced by the ammonia was measured by a light emitting diode photometer. The automated method had a detection limit of 0.05 xmol/l and a sampling rate of 60 or more measurement per hour. 

Many transition metal complexes have been considered as synzymes for superoxide anion dismutation and activity as SOD mimics. The stability and toxicity of any metal complex intended for pharmaceutical application is of paramount concern, and the complex must also be determined to be truly catalytic for superoxide ion dismutation. Because the catalytic activity of SOD1, for instance, is essentially diffusion-controlled with rates of 2 x 1 () M 1 s 1, fast analytic techniques must be used to directly measure the decay of superoxide anion in testing complexes as SOD mimics. One needs to distinguish between the uncatalyzed stoichiometric decay of the superoxide anion (second-order kinetic behavior) and true catalytic SOD dismutation (first-order behavior with [O ] [synzyme] and many turnovers of SOD mimic catalytic behavior). Indirect detection methods such as those in which a steady-state concentration of superoxide anion is generated from a xanthine/xanthine oxidase system will not measure catalytic synzyme behavior but instead will evaluate the potential SOD mimic as a stoichiometric superoxide scavenger. Two methodologies, stopped-flow kinetic analysis and pulse radiolysis, are fast methods that will measure SOD mimic catalytic behavior. These methods are briefly described in reference 11 and in Section 3.7.2 of Chapter 3. 

Three electroviscous effects have been noted in the literature.27 The primary electroviscous effect refers to the enhanced energy dissipation due to the distortion of the diffuse layer from spherical symmetry during flow. The analysis for low diffuse layer potentials has been clearly reviewed by van de Ven28 and the result for the intrinsic viscosity with Ka—> oo is ... 

In this technique, which was developed in the 1970s, microlitre volumes of liquid sample are injected, at intervals, into a continuously flowing carrier stream which is not air-segmented. Various reagent streams are introduced as required and controlled mixing of reagents and sample occurs. The fact that flow injection analysis does not involve air-segmented streams makes it possible to include such separation steps as solvent extraction and gas diffusion. 

Gas-diffusion flow injection analysis is capable of detecting very low concentrations of chlorine dioxide in water (i.e., detection limit is 5 ppb). A chemiluminescence flow-through detector cell is used to measure the concentration chlorine dioxide as a function of chemiluminescence intensity. A gas diffusion membrane separates the donor stream from the detecting stream and removes ionic interferences from iron and manganese compounds, as well as from other oxychlorinated compounds, such as chlorate and chlorite (Hollowell et al. 1986 Saksa and Smart 1985). 

Hollowell DA, Gord JR, Gordon G, et al. 1986. Selective chlorine dioxide determination using gas-diffusion flow injection analysis with chemiluminescent detection. Anal Chem 58 1524-1527. 

Hollowell DA, Pacey GE, Gordon G. 1985. Selective determination of chlorine dioxide using gas diffusion flow injection analysis. Anal Chem 57 2851-2854. 

H. Mana and U. Spohn, Sensitive and Selective Flow Injection Analysis of Hydrogen Sulfite/Sulfur Dioxide by Fluorescence Detection with and without Membrane Separation by Gas Diffusion, Anal. Chem. 2001, 73, 3187. 

Tecator Ltd. [16] have described a flow injection analysis method for the determination of 0.2 -1.4 mg/1 (as NH3N) of ammonia nitrogen in soil samples extractable by 2 M potassium chloride. The soil suspension in 2 M potassium chloride is centrifuged and filtered and introduced into the flow injection system for the analysis of ammonia (and nitrate) one parameter at a time. Ammonia is determined by the gas diffusion principle, in which a PTFE membrane is mounted in the gas diffusion cell. 

Veenstra, T. T., Lammerink, T. S. J., van den Berg, A., Elwenspoek, M. C., Characterization method for a new diffusion mixer applicable in micro flow injection analysis systems, in Proceedings of the Micromechanics Europe (MNE)... 

Chen, H., Fang, Q., Yin, X.F., Fang, Z.L., A multiphase laminar flow diffusion chip with ion selective electrode detection. Micro Total Analysis Systems Proceedings pTAS 2002 symposium, 6th Nara, Japan, Nov. 3-7, 2002, 371-373. 

Fig. 19. Schematic design of a flow injection analysis (FIA) system. A selection valve (top) allows a selection between sample stream and standard(s). The selected specimen is pumped through an injection loop. Repeatedly, the injection valve is switched for a short while so that the contents of the loop are transported by the carrier stream into the dispersion/reaction manifold. In this manifold, any type of chemical or physical reaction can be implemented (e.g. by addition of other chemicals, passing through an enzyme column, dilution by another injection, diffusion through a membrane, liquid-liquid extraction, etc. not shown). On its way through the manifold, the original plug undergoes axial dispersion which results in the typical shape of the finally detected signal peak...

The stress at any point can be determined from the difference in the pressure at that location, P, and the average pressure, (P> (ie., a- = P — (P)). Scherer s analysis demonstrates stress at the surface of a plate as o- = o-y = X(,7ijl3Df, which is similar to that of the preceding anal5Tsis in its dependence on the flux,j, the flow diffusivity, Df, and Xq, but different in that the network viscosity, rj, replaces the mechanical properties of the ceramic green body (compare this result with equation 14.64). 

There have been several approaches to overcome the traditionally slow SEC separations, which are caused by the diffusion processes in SEC columns. Most of them are column-related (see High-Speed SEC Columns, Small Particle Technology, and Smaller SEC Column Dimensions ) one utilizes the column void volume (cf. Overlaid Injections ), while another replaces separation with simplified sample preparation (see Flow Injection Analysis ). Cloning existing methods and instrumentation is also reviewed with respect to the potential time gain (see Cloning of SEC Systems ). Benefits and limitations of each method are summarized in Table 1. 

Diffusion and dispersion are important mechanisms for the transport of chemicals. This chapter first addresses diffusion and dispersion in the single phase flow. Then it discusses the fractional flow curve analysis in the water/oil two-phase flow. Fractional flow curve analysis may not provide an accurate estimate of actual field flood performance, but it is a good tool for mechanism analysis. 

ADP AFP ab as ALAT AP ASAT ATP BQ BSA CEH CK CME COD con A CV d D E E EC ECME EDTA EIA /e FAD FET FIA G GOD G6P-DH HBg HCG adenosine diphosphate a-fetoprotein antibody antigen alanine aminotranferase alkaline phosphatase aspartate aminotransferase adenosine triphosphate benzoquinone bovine serum albumin cholesterol ester hydrolase creatine kinase chemically modified electrode cholesterol oxidase concanavalin A coefficient of variation (relative standard deviation) layer thickness diffusion coefficient enzyme potential Enzyme Classification enzyme-chemically modified electrode ethylene diamine tetraacetic acid enzyme immunoassay enzyme loading factor flavin adenine dinucleotide field effect transistor flow injection analysis amplification factor glucose oxidase glucose-6-phosphate dehydrogenase hepatitis B surface antigen human chorionic gonadotropin... 

Nielsen, D.R., J.W. Biggar, and J.M. Davidson. 1962. Experimental consideration of diffusion analysis in unsaturated flow problem. Soil Sci. Soc. Am. Proc. 26 107-111. 

D. Robinson, J.E. Anderson, J.-L. Lin, Measurement of diffusion coefficients of some indoles and ascorbic acid by flow injection analysis, J. Phys. Chem. 94 (1990) 1003. 

As the sample plug starts being pushed forward, axial diffusion is the main component of the dispersion process, due to the high concentration gradients at the sample/carrier stream interface. The hypothetical peak shape associated with the flowing sample is shown in Fig. 5.9b, which corresponds to the first theoretical Taylor solution [28,29] for the diffusive-convective equation (Eq. 3.4). Situations associated with Fig. 5.9a,b never occur in practice in flow injection analysis. 

The presence of artefacts in the analytical path, such as mixing chambers, tubing connections, de-bubblers and other chamber-like components, can also affect sample dispersion in flow injection analysis. The effects of a mixing chamber and the detector inner volume are discussed in 3.1.2.2 and 6.3.2, respectively. The presence of devices for liquid—liquid extraction and gas diffusion (or dialysis) alters dispersion, and is dealt with in Chapter 8. 

D. Betteridge, W.C. Cheng, E.L. Dagless, P. David, T.B. Goad, D.R. Deans, D.A. Newton, T.B. Pierce, An automated viscosimeter based on high-precision flow injection analysis. Part II. Measurement of viscosity and diffusion coefficients, Analyst 108 (1983) 17. 

D.C. Stone, J.F. Tyson, Flow cell and diffusion coefficient effects in flow injection analysis, Anal. Chim. Acta 179 (1986) 432. 

M. Ibrahim, Z. Gongwei, Z. Junjie, Determination of diffusion coefficients of proteins by flow injection analysis and its application to estimation of molecular masses of proteins, Instrum. Sci. Technol. 26 (1998) 333. 

G. Gerhardt, R.N. Adams, Determination of diffusion coefficients by flow injection analysis, Anal. Chem. 54 (1982) 2618. 

G.W. Zou, Z. Liu, C.X. Wang, Flow injection analysis methods for determination of diffusion coefficients, Anal. Chim. Acta 350 (1997) 359. 

W.A. Boyle, R.F. Buchholz, J.A. Neal, J.L. McCarthy, Flow-injection analysis estimation of diffusion coefficients of paucidisperse and polydisperse polymers such as polystyrene sulfonates, J. Appl. Polymer Sci. 42 (1991) 1969. 

The classical manifold architecture in Fig. 8.22, upper was exploited in the pioneering work incorporating GD in flow injection analysis for the spectrophotometric determination of total carbon dioxide in blood plasma [265]. Details of the separation unit are shown in Fig. 8.23, left. The donor stream with the sample zone was acidified and the released CO2 diffused through the membrane towards the acceptor stream, which was an alkaline cresol-red indicator solution. Analyte collection resulted in a transient lowering of the pfi of this stream and hence a transient modification to the monitored absorbance. The recorded peak height was proportional to the CO2 content in the injectate. 

C02 (total) Blood plasma GD UV—Vis 10—50 mmol I.1 Flow injection system original implementation of gas diffusion in flow injection analysis buffered cresol-red indicator solution as the acceptor stream [265]... 

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