Flow-injection manifolds

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. 

Finally, FIA is an attractive technique with respect to demands on time, cost, and equipment. When employed for automated analyses, FIA provides for very high sampling rates. Most analyses can be operated with sampling rates of 20-120 samples/h, but rates as high as 1700 samples/h have been realized. Because the volume of the flow injection manifold is small, typically less than 2 mb, consumption of reagents is substantially less than with conventional methods. This can lead to a significant decrease in the cost per analysis. Flow injection analysis requires additional equipment, beyond that used for similar conventional methods of analysis, which adds to the expense of the analysis. On the other hand, flow injection analyzers can be assembled from equipment already available in many laboratories. 

Zhang et al. [44] determined penicillamine via a FIA system. A 50 pL sample was injected into an aqueous carrier stream of a flow injection manifold and mixed with... 

Flow injection methodologies are highly suitable for implementing CL analyses using low-pressure continuous mixing. There are many reported applications of this type including immobilized reactants [13] or enzymes [14], One recent example is the flow injection manifold used for the determination of poly-... 

Figure 12 General flow injection manifold used for the simultaneous determination of (a) organic species involved in enzymatic reactions and (b) inorganic ions, using a reduction column both with CL detection. IV, injection valve.

A simple flow injection manifold for CL measurements is depicted in Figure 2. 

The flow cell is the most important component of a flow injection manifold for CL measurements since maximum radiation should be generated while the solution is flowing in front of the detector. Other attributes of the flow cell are the small dead volume of the cell to allow fast and effective washing between injections... 

Fig. 13.9 Schematic diagram of a single-channel flow injection manifold, showing the transient nature of the signal output. (-) Liquid flow (...) data flow.

Flow-injection and continuous-flow systems are very similar. The major differences are outhned here. Continuous-flow systems are characterized by a relatively long start-up time prior to instrument stabilization, whereas the flow-injection approach requires little more time than that needed to stabilize the detector output. Tubing diameters on a flow-injection manifold are usually much smaller and the samples are injected into the flow line rather than aspirated. No wash cycle is employed in the flow-injection regime, since the sample is a discrete slug. Flow rates in continuous-flow manifolds are often larger than in the flow-injection regime. 

Various methods ofachieving preconcentration have been applied, including Hquid -hquid extraction, precipitation, immobihzation and electrodeposition. Most of these have been adapted to a flow-injection format for which retention on an immobihzed reagent appears attractive. Sohd, sihca-based preconcentration media are easily handled [30-37], whereas resin-based materials tend to swell and may break up. Resins can be modified [38] by adsorption of a chelating agent to prevent this. Sohds are easily incorporated into flow-injection manifolds as small columns [33, 34, 36, 39, 40] 8-quinolinol immobilized on porous glass has often been used [33, 34, 36]. The flow-injection technique provides reproducible and easy sample handhng, and the manifolds are easily interfaced with flame atomic absorption spectrometers. 

The complexity of die flow injection manifold required by the three approaches was very similar. All of them necessitated electronic interfaces to control the propulsion and injection systems through the microcomputer in approaches I and II, and the injection and switching valves in manifold III. A passive electronic interface was also required in all three manifolds in order to acquire data fi om the biosensor/detection system. 

Figure 3.10 — Flow manifolds for implementation of flow-through biosensors. (A) Flow injection merging-zones manifold for the bioluminescence detennination of ATP. ATP standards (30 fiL) and luciferin (30 fiL) are injected into the buffered carrier streams, each pumped at 0.7 mL/min and synchronously merged 12.5 cm downstream. Distance from merging point to immobilized enzyme coil, 2.2 cm. (Reproduced from [59] with permission of Elsevier Science Publishers). (B) Completely continuous flow manifold for the determination of NADH. (Reproduced from [71] with permission of the Royal Society of Chemistry). (C) Segmented-flow manifold for the determination of L-(+)-lactate. (Reproduced from [65] with permission of Marcel Dekker, Inc.). (D) Single-channel flow injection manifold with immobilized reagent for the detennination of glucose. (Reproduced from [77] with permission of Elsevier Science Publishers).

Figure 3.14 — (A) Flow injection system for the determination of glucose in the presence of interfering compounds. (Reproduced from [92] with permission of Elsevier Science Publishers). (B) Flow injection manifold for the simultaneous determination of sucrose and glucose. (Reproduced from [93] with permission of the American Chemical Society).

Integrated optical immunosensors. A flow-cell containing an affinity reagent can be flexible enough for implementation of all the steps involved in an immunoassay provided it is used in a flexible flow injection manifold that can be adapted as required. 

The above-described two-layer flow-cell was used for the determination of anions based on a quenching phenomenon. Table 3.4 gives the determination limits obtained by using various quenchers and a flow injection manifold in which the cell was inserted. The poor selectivity of quenching can be overcome by using a continuous separation technique e.g. HPLC), as in the determination of the anilines listed in Table 3.4. 

The flow injection manifold shown in Fig. 5.5.A, which includes a probe-type fluorimetric biosensor accommodated in a thermostated flow-cell at 35°C, was used for the determination of L-glutamate in foods and... 

Figure 5.5 — Flow-through biosensor for the determination of L-glutamate. (A) Flow injection manifold. (B) Sensing microzone of the probe sensor (optrode), incorporated in the flow-cell (FTC). P pump IV injection valve MC mixing chamber AD air damper BFB bifurcated fibre bimdle LS light source PMT photomultiplier R recorder GLU L-glutamate 0-Glu 2-oxoglutarate E enzyme layer I optical insulator S sensing layer PS polyester support. For details, see text. (Adapted from [6] with permission of Elsevier Science Publishers).

Figure 5.19 — Flow-through biochemical sensor based on the twofold immobilization of the catalyst (urease) and reagent (an acid-base azo dye) in the sensing microzone for the determination of urea in kidney dialysate. (A) Sensing microzone held in a microcircuit. (B) Valveless flow injection manifold. P pumps T timer S sample W waste. For details, see text. (Reproduced from [57] with permission of Elsevier Science Publishers).

Urea in kidney dialysate can be determined by immobilizing urease (via silylation or with glutaraldehyde as binder) on commercially available acid-base cellulose pads the process has to be modified slightly in order not to alter the dye contained in the pads [57]. The stopped-flow technique assures the required sensitivity for the enzymatic reaction, which takes 30-60 s. Synchronization of the peristaltic pumps PI and P2 in the valveless impulse-response flow injection manifold depicted in Fig. 5.19.B by means of a timer enables kinetic measurements [62]. Following a comprehensive study of the effect of hydrodynamic and (bio)chemical variables, the sensor was optimized for monitoring urea in real biological samples. A similar system was used for the determination of penicillin by penicillinase-catalysed hydrolysis. The enzyme was immobilized on acid-base cellulose strips via bovine serum albumin similarly as in enzyme electrodes [63], even though the above-described procedure would have been equally effective. 

Flow injection manifold for coupling with atomic spectrometry. The column can be used for preconcentration, matrix removal or chromatography. 

For these techniques, a dissolved sample is usually employed in the analysis to form a liquid spray which is delivered to an atomiser e.g. a flame or electrically generated plasma). Concerning optical spectrometry, techniques based on photon absorption, photon emission and fluorescence will be described (Section 1.2), while for mass spectrometry (MS) particular attention will be paid to the use of an inductively coupled plasma (TCP) as the atomisation/ionisation source (Section 1.3). The use of on-line coupled systems to the above liquid analysis techniques such as flow injection manifolds and chromatographic systems will be dealt with in Section 1.4 because they have become commonplace in most laboratories, opening up new opportunities for sample handling and pretreatment and also to obtain element-specific molecular information. 

The experimental design evaluated the factors influencing a flow-injection manifold including an ultrasound-assisted step... 

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