Flow injection methods dialysis

One example of a flow injection method coupled to an HPLC separation can be found for the determination of tartaric acid (Figure 17.1d). In this method, a dialysis unit was used for sample preparation, the injected sample was dialyzed, and a small portion (20 J,L) of the dialyzed sample was injected into the high-pressure eluent stream followed by analyte separation on a C18 column and UV-Vis detection (photodiode array... 

In continuous flow methods, the sample is inserted into a flowing stream, where a number of operations can be performed before it is transported to a flow-through detector. Hence, these systems behave as automated analyzers in that they can perform not only sample processing operations but also the final measurement step. Such sample processing operations as reagent addition, dilution, incubation, mixing, dialysis, extraction, and many others can be implemented between the point of sample introduction and detection. There are two different types of continuous flow systems segmented flow analyzers and flow injection analyzers. 

The analysis of Al in biological samples requires considerable sensitivity. The methods of choice are ETAAS and ICP-AES, due to sensitivity, simplicity and low cost after instrument acquisition. Water and dialysis fluid samples containing 0.7% HNO3 are stable at —20°C for many months (Taylor et al. 1994). Flow injection analysis has been applied to Al determination in beverages, parenteral solutions, water, and digested biological tissues (Coedo et al. 

With a method in hand for routinely constructing cytochrome c oxidase modified electrodes that exhibited direct electron transfer between the electrode and the oxidase, amperometry was used to detect reduced cytochrome c in solution at the oxidase-modified electrodes in a flow injection analysis format [69]. The dialysis cell was equipped with a wall jet inlet to direct cytochrome c solution past the oxidase-modified electrodes. Figure 12 shows the current response for three sequential reduced cytochrome c injections. Control experiments conducted at bilayer modified electrodes containing no oxidase showed current responses that are about 2% of those shown in Figure 12. This response may be due to changes in electrode capacitance and/or cytochrome c reacting at bilayer defect sites on the electrode. QCM measurements showed that no cytochrome c incorporated into the bilayer. However, cytochrome c was electrostatically held at the surface of the bilayer membrane at lower ionic strength [69]. 

Bunpeng, R, S. Lapanantnoppakhun, and J. Jakmunee. 2008. Flow injection amperometric method with dialysis sample pretreatment for determination of ascorbic acid. Chiang Mai J. Sci. 35 345-354. 

However, the use of air bubbles has some disadvantages. Thus, their high compressibility results in pulsation their injection and subsequent removal complicates the operational design and their presence reduces the efficiency of separation techniques, e.g. dialysis, liquid—liquid extraction, hinders the implementation of stopped-flow methods and precludes miniaturization in many cases. 

The FIA system is defined as an automated method of an analytical procedure in which a liquid sample is injected into a continuous carrier flow, and this mixture is driven to the detection cell. During transport, the sample is subjected to several operations such as dilution, incubation, mixing, and dialysis (Ruzicka and Hansen, 1988). The monose-gmented FIA is a kind of flow system in which the sample is transported between two air bubbles, but the flow is not continuous and the bubbles need to be purged before they enter the detection cell (Calatayud, 1996). The most sophisticated FIA manifolds are those based upon computer-controlled automated systems, such as SIA and MSFIA (Magalhaes et ah, 2009). 

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