Buffer streams

In preparative continuous free flow electrophoresis, continuous buffer and sample feed are introduced at one end of a thin, rectangular electrophoresis chamber. A schematic is presented in Fig. 11-5. The sample stream is usually introduced through a single port while buffer is introduced through several ports, essentially producing a buffer curtain . Because the buffer streams are introduced independently, it is fairly easy to establish a variety of gradients (e.g., pH, density, ionic strength) across the buffer curtain . 

The simplest design for an enzyme reactor is to merely have the substrate and enzyme in two merging buffer streams followed by a reaction delay coil (Fig. 12). The delay... 

Rinsing the sensor surface with buffer results in an irreversible dissociation, because all molecules which dissociate from immobilized protein are removed from the system by the buffer stream, allowing one to determine the rate constant of dissociation separately. 

Force/buffer stream used in washing steps is too strong... 

Transverse IEF was also conducted in a pressure-driven flow for BSA and soybean lectin separation on-chip [1040], Here, Pd electrodes were used (in preference to Au) because of the non-gassing character of Pd. In addition, the protein sample was sandwiched between two buffer streams and was prevented from direct contact with the channel wall (and hence the electrode), a process akin to hydrodynamic focusing [1040],... 

To illustrate this principle, we have chosen a lectin-glycoprotein system (130). The glycoenzymes glucose oxidase and peroxidase are bound to immobilized Concanavalin A or lentil lectin coupled to Sepharose. The immobilized lectin is packed in a small column inside a simple flow calorimeter. A continuous buffer stream (flowrate 0.75 mL/min) is pumped through a small column, at the outlet of which is placed a thermistor. This unit is well insulated from the surroundings. 

Other lactate analyzers use lactate oxidase (LOD). Clark et al. (1984b) use the enzyme in the YSI23L instrument (USA) as immobilized between a cellulose acetate membrane and a polycarbonate membrane, the latter serving to exclude high-molecular weight interferents. Lactate measurement in whole blood pipetted immediately after withdrawal into the phosphate buffer stream of the analyzer yielded the following correlation with values obtained with deproteinized blood (Weil et al., 1986) ... 

A well-defined volume of the gaseous sample is directed towards the flow manifold, where it interacts with a liquid medium, and the chem-iluminometric determination of nitrous acid in an indoor environment [18] is a good example. A calibrated vacuum pump aspirated the volume of air through a diffusion scrubber and the membrane-separated analyte was collected into a buffered stream that directed it towards an 8-port injection valve after passing a de-bubbler, the analyte zone was directed towards the detector. With this approach, a 120 pp tv detection limit was attained. The characteristics, potential and limitations of analytical procedures involving diffusion scrubbers and other devices for gas sampling aimed at in-line flow-based determinations have been discussed elsewhere [19]. 

Figure 4.17. Determination of the reaction rate constant for the oxidation of crotonic acid by potassium permanganate, (a) Manifold used (cf. Figs. 4.15c and 4.16). b, c) Absorbancetime response curves actually recorded. The values of the dispersion coefficient Da were obtained by dispersion experiments. All curves in each set of experiments were recorded consecutively from the same starting point (5 ), with an increasing delay time (td - 7, 8, 9, and 10 s, a-d and a -d ) with the stopped-flow period /s = 20 s (additionally, in each series a single run without stop is included), b) KMn04 (C° = 8.54 x lO"" M) in phosphate buffer in absence of crotonic acid, (c) KMn04 (Cli = 8.54 x lO"" M) in phosphate buffer, crotonic acid (C j = 2.10 x lO"" M) in phosphate buffer, stream B. (From Ref 838 by permission of the American Chemical Society).

In 1981, Meyerhoff and Fraticelli [35] appear to be the first to report on the coupling of a gas-diffusion separation system to a flow-through potentiometric detector. Ammonia was isolated from the donor stream containing the sample by penetrating a microporous membrane and collection in an acceptor buffer stream, and then determined selectively using a tubular nonactin p>olymer membrane electrode. The precision (<7% r.s.d.) and sample throughput (30 h ) of this early application was rather low. 

Figure 19.3 (a) White light image of hydrodynamic focusing of I PA by buffer streams. Fluorescence images of (b) DilClS in I PA stream and (c) CF in buffer streams [51]. 

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