Flow injection analysis sensitive detectors

A sensitive method for the flow injection analysis of Cu + is based on its ability to catalyze the oxidation of di-2-pyridyl ketone hydrazone (DPKH) by atmospheric oxygen. The product of the reaction is fluorescent and can be used to generate a signal when using a fluorometer as a detector. The yield of the reaction is at a maximum when the solution is made basic with NaOH. The fluorescence, however, is greatest in the presence of HCl. Sketch an FIA manifold that will be appropriate for this analysis. 

Because of its advantages (high sensitivity and selectivity, low cost and miniaturization) amperometric detection has been frequently used in flow injection analysis (FIA) and RP-HPLC. However, it has been established that the peak area (detector response) considerably depends on the flow rate. A general approach has been proposed to predict the effect of flow rate on the peak area in FIA and RP-HPLC. The general form of the correlation describing the flow in a parallel plate cell with short rectangular electrodes is... 

Sometimes it is not necessary to use the selectivity of a chromatographic technique. Sensitive analysis can sometimes be achieved with selective detection in flow injection analysis (FIA). Whilst some of the detectors described below may be appropriate in themselves in favourable cases, in most cases more sophisticated detection regimes are necessary, such as post-injection derivatisation of the analyte. Strategies involving some of the derivatisation methods outlined in Section 4.9.2 may be considered. 

Future developments that may facilitate ocean measurements from vessels or buoys include miniaturization of chromatographic equipment (so less solvent is needed per analysis), new solvent transport systems, such as electrokinetic transport, to reduce power requirements on the pumps, and more sensitive detectors for liquid chromatography. Certain combinations of very short columns and flow injection analysis are also promising for real-time studies. 

Flow-injection analysis is a versatile technique to evaluate the performance of a detector system. CHEMFETs may have an advantage over ISEs because of their small size and fast response times. We have tested our K+-sensitive CHEMFETs in a wall-jet cell with a platinum (pseudo-)reference electrode. One CHEMFET was contineously exposed to 0.1 M NaCl and the other to a carrier stream of 0.1 M NaCl in which various KC1 concentrations in 0.1 M NaCl were injected. The linear response of 56 mV per decade was observed for concentrations of KC1 above 5 x 10"5 M (Figure 9). When we used this FIA cell (Figure 10) for determination of K+ activities in human serum and urine samples, excellent correlations between our results and activities determined by flame photometry were obtained (Figure 11). 

Decristoforo G and Danielsson B 1984 Flow injection analysis with enzyme thermistor detector for automated detection of -lactams Anal. Chem. 56 263-8 Danielsson B, Mattiasson B and Mosbach K 1981 Enzyme thermistor devices and their analytical applications Appl. Biochem. Bioeng. 3 97-143 Mattiasson B and Danielsson B 1982 Calorimetric analysis of sugars and sugar derivatives with aid of an enzyme thermistor Carbohydr. Res. 102 273-82 Kirstein D, Danielsson B, Scheller F and Mosbach K 1989 Highly sensitive enzyme thermistor determination of ADP and ATP by multiple recycling enzyme systems Biosensors 4 231-9... 

T. Yao, Flow Injection Analysis for Cholinesterase in Blood Serum by Use of a Choline-Sensitive Electrode as an Amperometric Detector. Anal. Chim. Acta, 153 (1983) 169. 

Fig. 20. Electrochemical detectors used in FIA (flow-injection analysis) according to the geometry of the system. The sensitive parts of the electrodes are marked by bold lines.

A second obvious area of application is in continuous flow analysis or flow injection analysis systems, in which the immobilized molecules form reactors that can be readily inserted and replaced in a flow analysis manifold. The physical form of the enzymes varies widely packed-bed reactors are often used, but open-tube wall reactors and membrane reactors have also been investigated. A principal advantage of all such systems is that they can use all the optical or electrochemical detectors routinely used in flow analysis. However, the problems of producing stable and robust immobilized enzyme reactors have proved more intractable than many researchers hoped, and other advances (e.g.. the use of more sensitive detectors, improved availability of low-cost soluble enzymes) have minimized the advantages of using solid phase enzymes. 

A rotating enzyme-immobilized reactor and a flat pH electrode were incorporated into a sealed cell for use under continuous-flow/stopped-flow (SF) operation for the rapid determination of penicillins G and V in tablets and injectables [50]. A co-immobilization in a rotating bioreactor and amperometric detector resulted in a sensitive system for determination of succinylcholine and acetylcholine in pharmaceutical preparations [51]. A tandem system incorporating two rotating bioreactors into a continuous-flow/SF sample/reagentprocessing setup was apphed for the determination of alkaline phosphatase activity in serum samples [52]. By functional combination of the SF and flow-injection analysis (FIA), an automated micro apparatus was constructed resulting in significant reduction of the injection volumes of enzyme and substrate [53]. SF/continuous flow methods were apphed to acquire kinetic information also [54, 55]. 

Flow injection analysis Uses existing equipment, saves eluent No separation, limited time gain, not applicable for copolymers/blends, requires molar mass, sensitive detectors, only primary information (cone., M, rV), needs method change, needs special software Samples difficult to separate Utilize existing instruments... 

We have developed a new voltammetric method using a quinone reagent [5]. Based on the voltammetry of quinone and acids, we assembled an electrochemical detector for measuring acid concentration at a given potential. The flow injection analysis with electrochemical detection (FIA-ECD) method we developed is preferable, as it is a simpler, more sensitive, and rapid method for acid determination. This chapter assesses this method for determining the acid content in foods and beverages. 

Electrodes modified by eiectrodeposited 3-methylPT can be used as chemical sensors for organic and especially biological interesting molecules. The modified surfaces catalyze the oxidation of several compounds (e.g. ferrocyanide, catechol, ascorbic acid, hydroquinone, dopamine, epinephrine, acetaminophene, p-aminophenol, and reduced nicotinamide adenine dinucleotide). The sensitivity of these polymer-coated electrodes is 4 to 10 times higher than pure electrodes of platinum. Binary and also ternary mixtures can also be analyzed these electrodes are also suitable as an amperometric detector for flow injection analysis [211, 212]. 

An amperometric sensor for amino acids based on flow injection analysis (FIA) and using microelectrodes (10 pm diameter) primarily of P(Py) doped with sulfonate dopants such as tosylate and 3-sulfobenzoate was demonstrated by Akhtar et al. [823, 824]. Linear response was demonstrated for analytes such as aspartic acid and glutamic acid over the concentration range 7.5 X 10 to lO" with sensitivities in the region of 1.5 nC-M and detection limits of ca. 10 M. These authors also showed the use of a pattern recognition technique using the responses of six detector electrodes. Fig. 17-11 shows typical response of one of their sensors. 

Yao T. (1983) Flow injection analysis for cholinesterase in blood serum by use of a choline-sensitive electrode as an amperometric detector. Anal. Chim. Acta, 153, 169-174. 

This approach will not be practical for some time to come. The fundamental properties of surfactants (micelle formation, enrichment at interfaces) mean that the activity of a surfactant will usually differ from its absolute concentration (1). Just as serious is the technical problem that current surfactant-selective electrodes suffer from response which varies with their past and recent history they are also sensitive to the concentration of nonsurfactant ions. The result is that quantitative applications use electrodes not in direct measurements relating potential to concentration, but as indicators of the end point of a titration. In this latter application, it is not important that the electrode potential be exactly reproducible, but only that the potential change sharply as the surfactant concentration changes. For the titration of an anionic surfactant with a cationic surfactant, the electrode used for end point detection can be chosen to respond to either surfactant. Because of the drift in electrode potential, titrations must be conducted to an inflection in the titration curve rather than to a specific millivolt value. Details of the potentiometric titration methods can be found earlier in this chapter. The electrodes have also been demonstrated as detectors for flow injection analysis. 

SEC measurements were made using a Waters Alliance 2690 separation module with a 410 differential refractometer. Typical chromatographic conditions were 30°C, a 0.5-ml/min flow rate, and a detector sensitivity at 4 with a sample injection volume of 80 fil, respectively, for a sample concentration of 0.075%. All or a combination of PEO standards at 0.05% concentration each were used to generate a linear first-order polynomial fit for each run throughout this work. Polymer Laboratories Caliber GPC/SEC software version 6.0 was used for all SEC collection, analysis, and molecular weight distribution overlays. 

Procedure (See Chromatography, Appendix IIA.) Use a gas chromatograph equipped with a flame-ionization detector and a 4-m x 2-mm (id) stainless-steel column, or equivalent, packed with 15%, by weight, methyl trifluoropropyl silicone (DCFS 1265, or QF-1, or OV-210, or SP-2401) stationary phase on 80- to 100-mesh Gas Chrom R, or the equivalent. Condition a newly packed column at 120° and with a 30-mL/ min helium flow for at least 2 h (preferably overnight) before it is attached to the detector. For analysis, maintain the column isothermally at 105° the injection port and detector at 250° the carrier gas flow rate at 11 mL/min with fuel gas flows optimized for the gas chromatograph and detector in use. Change the experimental conditions as necessary for optimal resolution and sensitivity. The signal-to-noise ratio should be at least 10 1. 

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... 

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