Delay coil

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... 

In some applications, additional components acting as reactors for specific chemical pretreatment are incorporated within the flow manifold. Typical examples are ion-exchange microcolumns for preconcentration of the analyte or removal of interferences and redox reactors, which are used either to convert the analyte into a more suitable oxidation state or to produce online an unstable reagent. Typical examples of online pretreatment are given in Table 2. Apart from these sophisticated reactors, a simple and frequently used reactor is a delay coil (see also Fig. 4), which may be formed by knitting a segment of the transfer line. This coil allows slow CL reactions to proceed extensively and enter into the flow cell at the time required for maximum radiation. The position of the reactors within the manifold is either before or after the injection port depending on the application. 

A continuously operating peristaltic pump dehvers samples, standard solutions and reagents to the analytical system. A colour reaction then takes place in a heating hath or time delay coil, allowing reactions up to 10 minutes to go to completion. 

The alkaloids pass through the dialysis membrane from the pH 4 buffered sulphuric acid extract donor stream into a pH 9 buffered aniline recipient stream. They are then reacted with cyanogen bromide to produce a yellow colour, the absorbance of which is measured at 460 nm after passage through a suitable delay coil to allow the full colour intensity to develop. 

Fig. 3.6 Manifold diagram of nicotine alkaloids AutoAnalyser. Mixing coils, dialyser and delay coil are housed in a purpose built, light-tight controlled temperature bath.

Figure 4.16 — Schematic diagram of a split-stream FI system used for the determination of glutamine in bioreactor media C de-ionized water carrier stream R buffer diluent reagent stream S sample injection point L delay coils CPG controlled pore glass enzyme reactor ISE ammonium ion-selective membrane electrode W waste. (Reproduced from [139] with permission of the American Chemical Society).

FIGURE 7.2 Didactic representation (upper) and flow diagram (lower) of a typical single-line flow system with merging zones. S = sample R — reagent C — carrier stream LS/ Lr = sampling loops IC = injector-commutator RD = delay coiled reactor Rc = main coiled reactor D = detector shaded area = alternative IC position solid arrows = sites where pumping is applied. 

Delay coils are generally glass coils. Their number and length is determined by the time required to achieve the desired reaction after addition of all reagents. 

The calculation of the delay coils required for the determination of phosphate may serve as an example. 

Standard glass coils (see Fig. 10-10) have a volume of about 170/iL per loop, which results in a delay of 1 min per 14 turns of delay coil (standard coil length) for a total flow rate (sample + reagent + air) of 2.45mL/min, i.e., 49 coil loops (21 respectively) are required as the delay coil. 

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