Flow-injection analysis reproducibility

Separation Modules Incorporating a separation module in the flow injection manifold allows separations, such as dialysis, gaseous diffusion, and liquid-liquid extraction, to be included in a flow injection analysis. Such separations are never complete, but are reproducible if the operating conditions are carefully controlled. 

The accuracy and precision of FIA are comparable to that obtained by conventional methods of analysis. The precision of a flow injection analysis is influenced by variables that are not encountered in conventional methods, including the stability of the flow rate and the reproducibility of the sample s injection. In addition, results from FIA may be more susceptible to temperature variations. These variables, therefore, must be carefully controlled. 

The determination of lead in blood is the most widespread clinical use of ASV The technique is attractive because it is rapid, simple and reproducible A recent advance is to couple ASV to flow injection analysis in order to automate the process so that smaller samples and shorter analysis time can be achieved Lead is also routinely determined in bonemeal meant for human consumption by ASV Both lead and cadmium are determined in agricultural crops by ASV... 

Sample preparation, injection, calibration, and data collection, must be automated for process analysis. Methods used for flow injection analysis (FLA) are also useful for reliable sampling for process LC systems.1 Dynamic dilution is a technique that is used extensively in FIA.13 In this technique, sample from a loop or slot of a valve is diluted as it is transferred to a HPLC injection valve for analysis. As the diluted sample plug passes through the HPLC valve it is switched and the sample is injected onto the HPLC column for separation. The sample transfer time typically is determined with a refractive index detector and valve switching, which can be controlled by an integrator or computer. The transfer time is very reproducible. Calibration is typically done by external standardization using normalization by response factor. Internal standardization has also been used. To detect upsets or for process optimization, absolute numbers are not always needed. An alternative to... 

MWNTs favored the detection of insecticide from 1.5 to 80 nM with a detection limit of InM at an inhibition of 10% (Fig. 2.7). Bucur et al. [58] employed two kinds of AChE, wild type Drosophila melanogaster and a mutant E69W, for the pesticide detection using flow injection analysis. Mutant AChE showed lower detection limit (1 X 10-7 M) than the wild type (1 X 10 6 M) for omethoate. An amperometric FIA biosensor was reported by immobilizing OPH on aminopropyl control pore glass beads [27], The amperometric response of the biosensor was linear up to 120 and 140 pM for paraoxon and methyl-parathion, respectively, with a detection limit of 20 nM (for both the pesticides). Neufeld et al. [59] reported a sensitive, rapid, small, and inexpensive amperometric microflow injection electrochemical biosensor for the identification and quantification of dimethyl 2,2 -dichlorovinyl phosphate (DDVP) on the spot. The electrochemical cell was made up of a screen-printed electrode covered with an enzymatic membrane and combined with a flow cell and computer-controlled potentiostat. Potassium hexacyanoferrate (III) was used as mediator to generate very sharp, rapid, and reproducible electric signals. Other reports on pesticide biosensors could be found in review [17],... 

A more recent development is a technique known as flow injection analysis, in which a discrete volume of a liquid sample is injected into a carrier stream. Reagents required for the development of the analytical property of the analyte, e g. colour developing reagents for spectrophotometry, are already present in the stream. The stream then flows straight to the detector and the technique depends upon the controlled and reproducible dispersion of the sample as it passes through the reaction zone. Thus the reaction does not necessarily need to develop to completion,... 

Coupling CPE to flow injection analysis (FIA) has also been exploited in both on-line and off-line configurations [73, 84]. The use of FIA to introduce the SRP into various analytical devices facilitates the dissolution of the SRP in small volumes (increased preconcentration factor), alleviating reproducibility problems [73]. 

Flow injection analysis is a continuous flow method in which highly precise sample volumes are introduced into a stream using segmented or unsegmented flow. The method must be accurate, precise and reproducible before it can be considered as a useful technique and the following test proves that this technique does meet all the requirements. Tyson [3], carried out several studies involving flow injection techniques and atomic spectroscopy with considerable success. 

More recently, it was demonstrated that the thermistor approach could be used to monitor specific interactions of fluoride ions with silica-packed columns in the flow injection mode. A thermometric method for detection of fluoride [56] was developed that relies on the specific interaction of fluoride with hydroxyapatite. The detection principle is based on the measurement of the enthalpy change upon adsorption of fluoride onto ceramic hydroxyapatite, by temperature monitoring with a thermistor-based flow injection calorimeter. The detection limit for fluoride was 0.1 ppm, which is in the same range as that of a commercial ion-selective electrode. The method could be applied to fluoride in aqueous solution as well as in cosmetic preparations. The system yielded highly reproducible results over at least 6 months, without the need of replacing or regenerating the ceramic hydroxyapatite column. The ease of operation of thermal sensing and the ability to couple the system to flow injection analysis provided a versatile, low-cost, and rapid detection method for fluoride. 

Spectrophotometry is a technique most frequently applied in flow injection analysis, mainly owing to the easy coupling of the two methods, and good reproducibility of the measuring conditions. Practically all rapid reactions suitable for use in spectrophotometric determinations may be utilized under conditions of flow injection analysis. FIA coupled with spectrophotometry is a rapid (several dozens of determinations per hour) and sufficiently precise analytical technique [50-54]. 

Flow analysis has often been referred to as an analytical technique, but this is not strictly true, as it is an advanced procedure for carrying out automated chemical assays. The cornerstone features inherent to flow injection analysis, namely sample insertion, controlled dispersion and reproducible timing [5], are considered here in a broader context, in order to encompass the different modes of flow analysers. 

One can then infer that flow injection analysis relies on three cornerstone features sample injection, controlled dispersion and reproducible timing [50]. A typical flow injection analyser and the related recorder output are shown in Fig. 2.7. 

Flow injection analysis offers many attractive features to biosensor analysis. The reproducibility and the speed are two dominant characteristics when combining FIA with proper sampling and sample handling. It can be used for both enzyme-based assays and immunochemical binding assays. 

FIG. 9 Background-corrected three-dimensional spectra of flow-injection analysis peaks of horseradish peroxidase (HRP) at = 0.550, 0.715, and 0.850 V versus Ag/AgCl. HRP, 3.2 X 10 M (10 /xL) K2lrCl6 in reservoir, 6.8 x 10 M total flow rate, 0.5 mL min . The inset shows (A) a peak-top total spectrum and (B) a background spectrum at = —0.850 V, where the difference between the two spectra is very small. Even in such a case, reproducible background spectra are obtained. (From Ref. 25.)... 

Figure 5 Flow injection systems used to determine benzophe-none-3 (2-hydroxy-4-methoxybenzophenone or oxybenzone) in sunscreen creams (A) flow injection analysis (FIA) (B) sequential injection analysis (SIA). Reagents (1), (2), (12), (14) peristaltic pump (3) merging point (4) injection valve (5) reaction coil (6) flow cell (7) ethanol (8) autoburette with syringe (9) holding coil (10) eight-channel selector valve (11) sample or standard solutions (13). (Reproduced from Chisvert A, Salvador A, Pascual-Martf MC, and March JG (2001) Fresenius Journal of Analytical Chemistry 369 684-689.)...

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