Mixing coil

Reduction of nitrate is achieved by the use of a mixing coil containing copperised cadmium wire. Spectrophotometric evaluation of the nitrite produced is achieved by the use of sulfanilamide N( 1 naphthyl) ethylene diamine hydrochloride system. 

The great boost of analytical CL appeared soon after the discovery of flow injection analysis (FTA) by Ruzicka and Hansen [3], The speed with which the solutions of reagents can be supplied to the detector proved to be the best for CL reactions. Various mixing coils were investigated and this was the beginning of an avalanche of research on CL [4],... 

Figure 3 CL detection systems in combination with HPLC. P, pump I, injector C, column M, mixing tee D, detector RC, reaction coil MC, mixing coil RE, recorder E, eluent R, reagent W, waste IMER, immobilized enzyme reactor.

The pump provides constant flow and no compressible air segments are present in the system. As a result the residence time of the sample in the system is absolutely constant. As it moves towards the detector the sample is mixed with both carrier and reagent. The degree of dispersion (or dilution) of the sample can be controlled by varying a number of factors, such as sample volume, length and diameter of mixing coils and flow rates. 

Automation in derivatization has led to the development of pre-colnmn and post-column HPLC techniqnes. In post-column derivatization, the separated components elnting from the colnmn are derivatized on-line in a heated mixing coil prior to entering the detector. Pre-column derivatization can be performed in many autosamplers or automated liquid handlers. 

A typical extraction manifold is shown in Figure 13.2. The sample is introduced by aspiration or injection into an aqueous carrier that is segmented with an organic solvent and is then transported into a mixing coil where extraction takes place. Phase separation occurs in a membrane phase separator where the organic phase permeates through the Teflon membrane. A portion of one of the phases is led through a flow cell and an on-line detector is used to monitor the analyte content. The back-extraction mode in which the analyte is returned to a suitable aqueous phase is also sometimes used. The fundamentals of liquid liquid extraction for FIA [169,172] and applications of the technique [174 179] have been discussed. Preconcentration factors achieved in FIA (usually 2-5) are considerably smaller than in batch extraction, so FI extraction is used more commonly for the removal of matrix interferences. 

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.

Solvent extraction can be automated in continuous-flow analysis. For both conventional AutoAnalyzer and flow-injection techniques, analytical methods have been devised incorporating a solvent extraction step. In these methods, a peristaltic pump dehvers the hquid streams, and these are mixed in a mixing coil, often filled with glass ballotini the phases are subsequently separated in a simple separator which allows the aqueous and organic phases to stratify. One or both of these phases can then be resampled into the analyser manifold for further reaction and/or measurement. The sample-to-extractant ratio can be varied within the limits normally applying to such operations, but the maximum concentration factor consistent with good operation is normally about 3 1. 

Carrier-gas is transferred from the column through a heated metal capillary, which minimizes the dead volume at the end of the column and prevents condensation of the column effluent prior to its entry into the scrubbing unit. The tube carrying the liquid stream is joined to the gas stream tube, at a T-junction that is joined to the mixing coil by a glass-to-metal seal. Furfural is transferred from the gas stream into the liquid stream and the colour develops the two phases are then separated by the debubbling unit and the liquid stream is re-sampled through the flow cell of the colorimeter. A Technicon peristaltic... 

The outflow end of the pump tubing is connected directly to the components of the chemistry module. This module consists mainly of connectors and glass mixing coils. Proprietary modules are available, of course, but it is perfectly feasible to assemble the necessary components on a plastic tray fitted with four legs. Pump tubing and connectors are available from many suppliers. Apart from the OEMs, sources include ... 

Figure 4.14 — (A) Flow injection system for the preconcentration and determination of copper P peristaltic pumps A 0.5 M HNOj B sample q = 2.5 mL/min) C water (jq = 0.5 mL/min) E 1 M NaNOj/O.l M NaAcO, pH 5.4 q = 0.5 mL/min F 1 M NaAcO/2 x 10 M Cu pH 5.0 (9 = 1.0 mL/min) 3-5 valves ISE copper ion-selective electrode W waste I and II 2 and 3 mL of chelating ion exchanger for purification III 100 fil of chelating ion exchanger for metal ion preconcentration. (B) Scheme of the flow system for the determination of halides A 4 M HAcO/1 M NaCl/0.57 ppm F B 1 M NaOH/0.5 M NaCl C, mixing coil (1 m x 0.5 mm ID PTFE tube) Cj stainless-steel tube (5 cm x 0.5 mm ID) ISE ion-selective electrode R recorder. (Reproduced from [128] and [129] with permission of Elsevier Science Publishers and the Royal Society of Chemistry, respectively).

Figure 7.1. Flow diagram of the system for determination of manganese. P peristaltic pump S injection port R reaction coil (length 30 cm) M mixing coil (length 60 cm) and W waste. The numbers in the pump are the flow rates in ml/min of the carrier, reduction, reagent, neutralisation and masking streams, which correspond to (a), (b), (c), (d) and (e), respectively. The distances S-C and C-B are approximately 2 cm. From [29]...

The reaction occurs rapidly at room temperature and is complete by the time the stream exits from the second of the two mixing coils and enters the colorimeter. 

The pre-column derivatization shown in Figure 6 involves ion-pairing reactions carried out on some alkaloids. Gfeller, et al (3) formed the ion pairs with picric acid in the mixing coils, then extracted them into chloroform. Detection was at 330 nm. 

The glucose-sensitive FET ctm be applied to an in vitro blood assay, using a semiautomated flow appatratus (50). Figure 22 shows a schematic illustration of the apparatus. Human blood plasma is sucked up into the sample loop (SL) and then sent to the 30-pL sensor cell (SC) via the mixing coil (MC) and defoaming... 

Fig. 22. Schematic structure of flow apparatus P, pump SC, sensor cell SL, sample loop V, valve MC, mixing coil D, deforming device B and WB, washing solution S, sample solution. (Reproduced from Nakako et al. (50), with permission.)...

Fig. 3.9 Scheme of typical flow system I, II, III, IV solutions (e.g., sample, standard, reagents), PI and P2 pumps, Z valve, MP sample preparation module, M mixing coil, DET detection system... 

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