Microconduits

McKelvie, I. D. Cardwell, T. J. Cattrall, R. W. A Microconduit Flow Injection Analysis Demonstration Using a 35-mm Slide Projector, /. Chem. Educ. 1990, 67, 262-263. Directions are provided for constructing a small-scale FIA system that can be used to demonstrate the features of flow injection analysis. For another example see Grudpan, K. Thanasarn, T. Overhead Projector Injection Analysis, Anal. Proc. 1993, 30, 10-12. 

Ruzicka, J. Plow Injection Analysis Prom Test Tube to Integrated Microconduits, Anal Chem. 1983, 55, 1040A-1053A. 

Figure 3.37 — (A) Optosensor with fibrous flow-through structure on the surface of which a pH indicator is covalentiy bound C Carrier stream d thickness of indicator-containing celiuiose pad r reflector o opticai fibre. (B) Integrated microconduit for measurement of pH comprising injection valve and optosensor S sample solution, PI and P2 tubes leading to the peristaltic pumps W waste tube. (Reproduced from [262] with permission of Elsevier Science Publishers).

Dialysis units provided highly efficient means for increasing selectivity in a dynamic system by placement in front of a lithium-selective electrode constructed by incorporating 14-crown-4 ether 3-dodecyl-3 -methyl-1,5,8,12-tetraoxacyclotetradecane into a PVC membrane that was in turn positioned in a microconduit circuit by deposition on platinum, silver or copper wires. The circuit was used to analyse undiluted blood serum samples by flow injection analysis with the aid of an on-line coupled dialysis membrane. For this purpose, a volume of 200 pL of sample was injected into a de-ionized water carrier (donor) stream and a 7 mM tetraborate buffer of pH 9.2 was... 

Figure 4.17 — (A) Exploded view of a tubular flow-cell integrated microconduit system. I Ag/AgCl inner reference electrode M sensitive membrane S internal reference solution. (B) Detail of the integrated microconduit shown within the dotted lines in C. (C) Integrated-microconduit FI manifold for potentiometric measurements C carrier stream R reference electrode solution P pump V injection valve I indicator electrode R reference electrode I pulse inhibitor G ground W waste. (Reproduced from [140] with permission of Pergamon Press).

Future directions for FIA include improved methods for determining concentrations in FIA (i9, 20), an advanced modular system using fiber optics or ion-selective field-effect transistors in the detectors (20), and a system of solid microconduits for handling the solutions (20). These developments suggest even greater reductions in the size and cost of automated chemical analyses. 

J. Ruzicka, Flow injection analysis. From test tube to integrated microconduits, Anal. Chem. 55 (1983) 1040A. 

I.D. McKelvie, T.J. Cardwell, R.W. Cattral, A microconduit flow-injection analysis demonstration using a 35-mm slide projector, J. Chem. Edu. 67 (1990) 262. 

One of the first prototypes involved the use of integrated microconduits [104]. The flow channels, the injection device and the outlet to the detector were mechanically engraved into a flat PVC block using channels with a cross sectional area of 0.8 mm2 and covered with a flat plate glued on top of the machined block. The system was operated with a conventional peristaltic pump. A similar system, but using a piston pump, was proposed in the 1990 s [105]. 

J. Ruzicka, E.H. Flansen, Integrated microconduits for flow injection analysis, Anal. Chim. Acta 161 (1984) 1. 

B. Cetin, H. Yuncu, and S. Kakac, Gaseous flow in microconduits with viscous dissipation, International Journal of Transport Phenomena 8, 297-315 (2006). 

In order to achieve chaotic advection in 3-D, steady flow in a geometry that has certain complexity created by 3-D microconduits can be used. When all the conduits lay in the same plane such as the zigzag and square-wave microconduit, the S5mimetry of the flow field is preserved, and chaotic... 

One of the best interfaces between sensor cells and FIA streams has been reported by Ruzicka and Hansen (1985) and Petersson et al (1986). In both cases the concept of microconduits is powerfully demonstrated. A microconduit is a reduced-size FIA system. Early in the theoretical development of FIA, it was clear that a decrease in size was advantageous. The dispersion coefficient is lowered, the mixing is faster, and the manifold can be placed on a small 2 in by 4 in Plexiglass block. In fact all components of the FIA system with the exception of the pumps can be on the Plexiglass block. 

Petersson B, Hansen E and Ruzicka J 1986 Enzymic assay by flow injection analysis with detection by chemiluminescence determination of glucose, creatinine, free cholesterol and lactic acid using an integrated FIA microconduit Anal. Lett. 19 649-65 Ruzicka J and Hansen E 1975 Row injection analysis. Part I. A new concept of fast continuous flow analysis Anal. Chim. Acta 78 145-57... 

Lab-on-valve (LOV) is a development of FI A whereby a microchannel chip (microconduit) is combined with a switching valve. It is a type of pTAS system. The function of the... 

As with other analytical techniques, there is a trend in FIA towards significant reductions In size, which ultimately result in considerable advantages. In this way miniaturized FIA In its two versions was conceived capillary FIA and integrated microconduits. 

The coiled tube has so far been the most frequent geometric form of the FIA microreactor. However, it is useful to review all channel geometries (Fig. 2.8). These are straight tube (A), coiled tube (5), mixing chamber (C), single-bead string reactor (D), 3-D or knitted reactor (E)y and imprinted meander (cf. microconduits Section 4.12) or combinations of these geometries. 

To summarize, the three scaling factors are the dispersion coefficient D, the residence time t, and the dispersion factor Pi/2 = SmlVr- These factors were used for optimization of the design of integrated microconduits [608] (Section 4.12). 

The reaction rate was measured in the FIA microconduit shown in Fig. 4.16, the manifold and readouts being rendered in Fig. 4.17, showing the absorbance-time response curves for reaction rate measurement of the oxidation of crotonic acid by permanganate. By taking the readouts at different delay times td, corresponding to different values of the dispersion coefficient Da, with and without the presence of crotonic acid, it was possible to calculate the reaction rate constant. 

Figure 4.40. (a) Manifold and b) microconduit incorporating an ion-exchange column as used for preconcentration of metal ions. The sample, injected into the carrier stream C, is mixed with buffer B to adjust pH before entering the column filled with Chelex-IOO (volume 150 (xL). Metal ions are retained on the column and are subsequently eluted countercurrently by a small zone of eluent (E, acid) pumped by pump P2. As the two pumps are operated sequentially, the eluted sample is carried to detector D (atomic absorption spectrophotom-. eter). The manifold components within the boxed area are those contained within the microconduit. 

Figure 4.48. (Left) Calibration run for lactic acid in the concentration range 0-10 mg/dL using the FIA microconduit system depicted in Fig. 4.47. (Right) Calibration graph for the lactic acid standards shown at the left.

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