Flow injection systems detectors

Solvent extraction offers unique advantages among separation techniques. A system based on extraction into a polymer [poly(vinyl chloride)] as solvent was examined here because of possible advantages in speedy simplicity, sample size, solvent handlingy etc.f especially when coupled with flow injection and an amperometric detector. Solutes examined included salicylic acid and 8-hydroxy quinoline. The apparatus typically consisted of 0.8-mm i.d. X 170-cm coiled tubing that could be connected directly to the injection loop of a flow-injection amperometric detector system containing a nickel oxide electrode. 

The continuous-stream flow-injection system (Figure 2) consisted of a gravity-feed electrolyte reservoir, a sample injection valve (Rheodyne, Model 50) fitted with a 30 /xL-sample loop, and a flow-through electrochemical detector cell. The channel diameter of the Teflon tubing for the stream was 0.8 mm. The tubing length from injector to detector was 10 cm. 

Burguera, J.L., Burguera, M. Flow injection systems for on-line sample dissolution/decom-position. In Sanz-Medel, A. (ed.) Flow Analysis with Atomic Spectrometric Detectors, pp. 135-149. Elsevier, Amsterdam (1999)... 

H.L. Pardue, P. Jager, Kinetic treatment of unsegmented flow systems. Part 3. Flow injection system with gradient chamber evaluated with a linearly responding detector, Anal. Chim. Acta 179 (1986) 169. 

This strategy was also exploited for the determination of alcoholic strength in beverages [103]. As the proposed flow injection system included an LED-based detector, the Schlieren signal was increased due to the poor collimation of the incident radiation beam. About 120 samples were run per hour, and precise results (r.s.d. = 3.4%) were obtained. 

T. Yamane, E. Goto, A flow injection system for the simultaneous determination of two components in a single injection and with a single detector, Anal. Sd. 5 (1989) 221. 

The feasibility of using a portable flow injection system for the in situ monitoring of river water was demonstrated by the design and deployment of a field instrument with spectrophotometric detection for the determination of phosphate [4], Solid-state technology (LED source and photodiode detector) was used to construct a compact, battery-operated analyser that could operate without maintenance for several weeks, yielding reliable, pseudo-continuous results. The monitor was further applied to the determination of nitrate [5] and ammonium [6] in river waters. Details of the instrumentation were also reported [7,8]. 

FIGURE 8.14 Flow diagram of a flow injection system with wetting film extraction. S = sample C = aqueous carrier stream Org = organic solvent Ec = extraction coiled reactor SP = solvent added for single phase establishment Me — mixing coiled reactor D = detector. For details, see text. 

Thiabendazole Natural waters Nylon powder Room-temperature phosphorescence 4.5 ng mL 1 Flow injection system solid phase at the detector (optode) [518]... 

Zinc Synthetic solutions Electrodialysis UV-Vis 100 nmol L-1 Flow injection system electrodialysis for reagent addition via a cellulose membrane LED detector [289]... 

In-line filtration without a filtering element is also feasible. To this end, a three-dimensional reactor [299], also called a knitted or knotted reactor (see 6.2.3.4), can be used, as emphasised in the landmark article reporting the flow injection determination of lead in blood and bovine liver by flame atomic absorption spectrometry [300]. The analyte was co-precipitated the complex formed was retained on the inner walls of a knitted reactor and then released by isobutyl methyl ketone and transported to the detector. Interference from iron(III) at high concentrations was circumvented, sensitivity was markedly improved and precise results were obtained. This innovation was recently exploited to remove organic selenium and determine the speciation of inorganic selenium in a flow-injection system with atomic fluorescence spectrometric detection [301]. 

Immunoassay is a very sensitive technique that can be applied in environmental chemistry and food chemistry, and is very often used in clinical chemistry. By inclusion of immunoassay in the flow injection system, precise control of reaction times can be achieved compatibility with any heterogeneous or homogeneous format, and detector, good accuracy, and reproducibility are assured the analysis time decreases and the analytical process becomes more flexible.243... 

Y. Hirai, N. Yoza, and S. Ohashi, Flow Injection System as a Post-Column Reaction Detector for High-Performance Liquid Chromatography of Phos-phinate, Phosphonate and Orthophosphate. J. Chromatogr,. 206 (1981) 501. 

K. W. Pratt and D. C. Johnson, The Vibrating Wire Electrode as am Am-perometric Detector for Flow Injection Systems. Anal. Chim. Acta, 148 (1983) 87. 

Flow injection is a method using on-line discrimination chemical reactions. Direct selective preconcentration is performed on microcolumns, the analytes being concentrated up to three to four orders of magnitude and injected into the detector. Usually as separation techniques ion-exchange, liquid-liquid extraction, gas diffusion are used. Flow injection systems are connected either to ETA AS or ICP-AES detection systems. These methods have been used for determinations of redox species such as Crflll)/ Cr(IV), Fe(II)/Fe(III), As(III)/As(V), Se(IV)/Se(VI) in soil extracts and water samples. 

The manifold of the flow-injection system was similar to that proposed in our previous study (Asan et al., 2003). The peristaltic pump was used for propelling the reagent carrier solution at a flow-rate of 1 mL min i. Samples were injected into the reagent carrier solution, soon load the reaction coil. The reaction zone containing the complex was moving towards the flow-through spectrophotometric detector cell in which the presence of iron(III)-DPA-4-SA complex was selectively monitored, and the absorbance of the complex at 410 nm was continuously recorded. 

As in the previous work, the flow injection system consisted of a Cole Parmer Mas-terflex peristaltic pump, Rheodyne 7125 injector, Bioanalytical System (BAS) TL-5A flow through electrochemical cell and either an IBM EC/230 or a BAS CV 37 potentiostat. These instruments respectively are designed for use with an electrochemical detector for liquid chromatography and for low current measurements such as with ultramicroelectrodes. A pulse dampener was also included in the flow system. 

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