Development of solid-phase chemiluminescence immunoassays for digoxin comparing flow injection and sequential injection techniques.

The development of a competitive solid-phase immunoassay for digoxin making use of the acridinium chemiluminescence system is described. Two different instrumental approaches are compared. One is based on a continuous flow system using a peristaltic flow injection analysis pump; the other uses a new sequential injection technique. In both systems a flow cell, consisting of transparent PTFE tubing packed with immobilized antibodies, acts as an immunoreactor. The entire assay, including both the immunoreaction and the chemiluminescence reaction, takes place in this immunoreactor cell. Compared with the flow injection technique, the sequential injection mode showed higher precision, ranging from 2.16 to 5.5% RSD depending on concentration. The total assay time, including regeneration, is less than 8 min with the sequential injection technique. The detection limit for both techniques is in the low femtomole range.     

Infrared detection in flow analysis - developments and trends (review)

Flow analysis offers an inexpensive and versatile means for the automation of analytical procedures and hence it has been incorporated in many different techniques. However, the use of infrared detection in flow analysis systems is not common. Whereas Fourier transform infrared (FTIR) spectroscopic detection has been routinely used in gas chromatography (GC), its use for liquid chromatography, and now for flow analysis, flow injection analysis, or sequential injection analysis, is not frequent. The most prominent reasons are probably: (i) the strong absorption of most of the common solvents, specially water, (ii) the relative poor sensibility compared to UV–vis, fluorescence, etc. (iii) FTIR is normally not even considered a valuable detection technique, (iv) problems arising from obtaining adequate information from transient IR signals from the injected samples, and (v) only a few analytical chemist uses routinely the FTIR technique. This practice neglects that IR spectroscopy offers some unique features that now, using modern FTIR instrumentation, can be exploited in an advantageous manner. It is important to realize that each sample (analyte/matrix) represents a special and unique analytical problem; which defines the mode of operation and implementation of the IR technique. Flow analysis–IR techniques – as well as all techniques – has a number of shortcomings to solve these problems. In this article, most of these strategies such as the use of: baseline correction, derivative spectroscopy, stopped flow systems, reverse flow systems, multiparametric calibrations, etc., will be discussed. Additionally, recent developments in on-line gas phase generation–FTIR and hydride generation–FTIR spectrometry, as well as the principles of the HPLC–FTIR and capillary electrophoresis–FTIR hyphenation are also discussed. This review aims to provide an account of the state of the art, of these relatively new techniques. Its beginning, developments, applications and new trends, basically in the MID–IR, and by using transmission cells.     

Phosphorescence in liquid solutions: a promising detection principle in liquid chromatography and flow injection analysis

A new detection technique for liquid chromatography and flow injection analysis has been developed. The technique is based on the phosphorescence of biacetyl in various eluents. It can be applied in two modes, i.e. sensitized and quenched phosphorescence. Especially the latter is widely applicable for instance to non-absorbing compounds as measured in ion chromatography.     

Residual aqueous ozone determination by gas diffusion reverse flow injection analysis

A novel system based on reverse flow injection analysis with a gaseous diffusion step (GD-r-FIA) has been developed for the analysis of ozone. It includes an automatic microburet injection system. The ozone diffuses through a microporous membrane of polyvinylidene difluoride (PVDF) from the donor stream to the acceptor stream containing nitrite ions. The nitrite concentration in the acceptor solution decreases due to the ozone reduction reaction. In this way, a simple indirect measurement of the ozone concentration can be performed using the Griess–Ilosvay reaction for the nitrite ion. This correlates with the decrease in absorbance of the azoic dye formed with the ozone concentration in the donor stream. The system has been optimised by investigating the effect of the nitrite concentration in the acceptor stream on the diffusion flow. The optimum nitrite concentration was set at 0.250 ppm with a flow rate of 1.5 ml/min. The efficiency of the ozone diffusion through the membrane was only 4.4%. This affects the average sensitivity, which is low (0.0092±0.0012 AU/ppm), although the detection limit is similar to that obtained with other reported methods (0.03 ppm). The main advantage of the system reported here is that it has a linear range that is an order of magnitude broader than those observed for other GD-FIA systems. This is especially useful for continuous monitoring systems, since the residual ozone concentration is normally between 0.05 and 5.0 ppm. Additionally, using the reverse flow injection analysis (FIA) technique minimises chemical consumption and residue generation. Finally, the stability of the ozone solution and the repeatability and reproducibility of the method have been studied.     

Determination of palladium by flame atomic absorption spectrometry combined on-line with flow injection preconcentration using a micro-column packed with activated carbon fibre

The versatility of flow injection as a procedure for enhancing the performance of atomic spectrometry is demonstrated by the on-line separation and preconcentration of analyte ions of interest for methods employing atomic spectrometric measurements. In this paper, a sensitive method for the determination of palladium by flame atomic absorption spectrometry associated on-line with the flow injection technique has been developed. A flow system comprising a micro-column packed with activated carbon fibre was used for the concentration of palladium. In order to further enhance the performance of the analysis a new manifold with an additional column has been designed to increase the sensitivity by doubling the analytical signals. The method is sensitive and easily operating with a sampling rate of 15-20/h. The detection limit of this method is 0.3 ng/ml in standard solution and the precision is 3.9% relative standard deviation at 50 ng/ml. Recoveries of palladium in spiked solutions are 103-107%.     

反相流动注射胶束增敏化学发光分析法测定硝苯地平

基于胶束介质中硝苯地平对碱性鲁米诺-过氧化氢化学发光体系的增敏作用,结合反相流动注射技术,建立了流动注射化学发光分析法测定硝苯地平的新方法.硝苯地平浓度在3.5×10-10～4.0×10-8 g·mL-1范围内时,化学发光强度与硝苯地平的浓度呈良好的线性关系,其相对标准偏差为1.4%(n=11,c=3.5×10-9 g...     

Reverse dual phase gas diffusion flow injection analysis

A flow injection gas diffusion system for gas acceptor to liquid donor stream, reverse dual phase gas diffusion flow injection analysis, has been demonstrated. Feasibility was shown with a carbon dioxide chemistry. A series of methods was investigated for hydrazine determinations. Using bromthymol blue indicator and a Celgard 2500 membrane a detection limit of 0.01 ppm v/v hydrazine was observed.     

Some theoretical aspects of flow injection analysis

The injection and detection methods in flow injection analysis (f.i.a.) are theoretically described. Theory is developed for a simple flow model based on laminar flow without diffusion. The results lead to the conclusion that exact specifications for injection and detection devices in experimental f.i.a. are necessary. The influence of the sample volume is described in more detail with a systems analysis model of f.i.a. in which the tanks-in-series model is used for transport of the fluid. The theoretical and experimental results are in good agreement, thus the theory developed for sample injection in f.i.a. appears to be valid.     

Hyphenation of flow injection/sequential injection with chemical hydride/vapor generation atomic fluorescence spectrometry

The dominant role played by flow injection/sequential injection (FI/SI, including lab-on-valve, LOV) in automatic on-line sample pretreatments coupling to various detection techniques is amply demonstrated by the large number of publications it has given rise to. Among these, its hyphenation with hydride/vapor generation atomic fluorescence spectrometry (HG/VG-AFS) has become one of the most attractive sub-branches during the last years, attributed not only to the high sensitivity of this technique, but also to the superb separation capability of hydride/vapor forming elements from complex sample matrices. In addition, it also provides potentials for the speciation of the elements of interest.It is worth mentioning that quite a few novel developments of sample pretreatment have emerged recently, which attracted extensive attentions from the related fields of research. The aim of this mini-review is thus to illustrate the state-of-the-art progress of implementing flow injection/sequential injection and miniaturized lab-on-valve systems for on-line hydride/vapor generation separation and preconcentration of vapor forming elements followed with detection by atomic fluorescence spectrometry, within the period from 2004 up to now. Future perspectives in this field are also discussed.     

Multisyringe flow injection system for total inorganic selenium determination by hydride generation-atomic fluorescence spectrometry

A new multisyringe flow injection system for total inorganic selenium determination by hydride generation-atomic fluorescence spectrometry (HGAFS) has been proposed. The flow methodology is based on the simultaneous injection of sample in the acid media (50% HCl), a reducing sodium tetrahydroborate solution (0.18%) and a solution of hydrochloric acid (50%) which are dispensed into a gas-liquid separation cell by using a multisyringe burette coupled with one multiport selection valve. The usage of the time-based injection increases the sample throughput and provides precise known volumes of sample. The hydride of selenium is delivered into the flame of an atomic fluorescence spectrometer by means of an argon flow. A hydrogen flow has been used to support the flame.The technique can be applied over a wide range of concentrations of selenium between 0.1 and 3.5 μg l⁻¹ with good repeatability (relative standard deviation (R.S.D.) values 4.6-7% for 1 μg l⁻¹ of Se). The detection limit of the developed technique (3σ_b/S) was 0.01 μg l⁻¹. A sample throughput was 28 samples per hour (84 injections). The multisyringe technique has been validated by means of reference solid (sea lettuce) and water (hard drinking water) materials with good agreement with certified values. The analytical features were compared with those obtained by using of the commercial flow injection analysis (FIA) system. The proposed method provides a higher sampling frequency and a significant reduction of reagent and sample consumption in front the flow injection application.     

An overview on flow methods for the chemiluminescence determination of phosphorus

A review on the flow analysis of phosphorus with chemiluminescence detection is presented. A brief discussion of the chemiluminescence principles and applications is given. Particular emphasis is devoted to coupling different flow techniques (flow injection, sequential injection, multicommutation, multisyringe flow injection, multi-pumping) to chemiluminescence detection. Enzymatic and non-enzymatic methods, mostly applied to environmental samples, are summarized and compared in terms of application range, detection limits, flow configuration, repeatability and sampling rate.     

Electroanalytical flow measurements

A review based on 94 cited original papers describes recent achievements in application of different electrochemical detection in flow analysis, injection techniques of flow analysis, liquid chromatography and capillary electrophoresis.     

Determination of ascorbyl 6-palmitate in food matrices by amperometric flow injection analysis

In this paper a rapid method based on a FIA (flow injection analysis) system with amperometric detection for the evaluation of ascorbyl 6-palmitate in foods is described. The selectivity of the proposed method is related to the low anodic potential applied to the working glassy carbon electrode (+0.1 V vs. Ag/AgCl) that leaves out interferences from ascorbic acid and phenolic compounds. By flow injection analysis, under optimised conditions, the calibration curve was linear in the range 0-20 mg l(-1) and the detection limit was 0.2 mg l(-1).     

Determination of hydrogen peroxide in reactor moderator solutions by flow injection analysis

A flow injection analysis (FIA) method for the determination of hydrogen peroxide in reactor moderator water has been developed and installed at the Savannah River Site (SRS) Water Quality Laboratory. The mode of detection is amperometric and the technique has an analytical range of 0.10-2.50 mug/ml with a sampling rate of 40 samples/hour. The calibration curve is linear with a correlation coefficient of 0.999 and the relative standard deviation is at the 0.50% level for both 0.10- and 2.50-mug/ml standards. When the FIA procedure is compared to the manual method previously used at the SRS Water Quality Laboratory for hydrogen peroxide analysis, it demonstrates a minimum twenty minute reduction in analysis time per sample and the total liquid waste generated per sample analyzed is reduced by 95%.     

Development of an on-chip injector for microchip-based flow analyses using laminar flow

A new on-chip injector for microchip-based flow analyses has been designed and characterized. The microchip design utilizes separate laminar flow streams of buffer and sample that are brought into parallel contact for a distance of 300 microm. The buffer flow stream is first routed through a conventional 6-port injection valve fitted with a 5 microm i.d. sample loop. When the 6-port valve is actuated from load to inject for a given time, the on-chip buffer flow stream is constricted and the sample flow stream is pressurized into the buffer flow channel. Once the valve returns to the load state the separate laminar flow streams resume. Fluorescence detection was used to characterize the injector and it was found that 50 injections of a 100 microM fluorescein sample led to an average peak height of 174.32 +/- 2.05 AFU (RSD 1.18%) and average peak skew of 1.37 +/- 0.06. The injector was also interfaced with amperometric detection. Injections of catechol solutions ranging in concentration from 500 nM to 100 microM resulted in a linear response (sensitivity = 2.49 pA microM(-1), r(2) = 0.998) and a limit of detection of 155 nM (S/N = 3). Compared to an off-chip injection scheme, plug dilution, band broadening, and peak asymmetry are much reduced. Finally, the injection and subsequent lysis of an erythrocyte sample was demonstrated, with an injected plug of erythrocytes being lysed 5.72 +/- 0.15 s after injection into a flow stream containing sodium dodecyl sulfate (n = 10). The new injection scheme does not require complex valving mechanisms or high pressures and enables reproducible injections from a continuous sample flow stream in a manner where changes in analyte concentration can be monitored with high temporal resolution.     

The effects of solvent preoxidation on inhibited chemiluminescence of pyrogallol oxidation in flow injection analysis and liquid chromatography

A new extension of chemiluminescence technique using pre-oxidation of a carrier solvent before the conventional inhibited chemiluminescence detection is presented in this study. The method is based on the modification of the oxidation chemistry of pyrogallol upon contact with a flow stream consisting of an organic solvent in mixture with an aqueous solution of a soft oxidant. The final response was found to depend on the kind of solvent and the oxidant/pre-oxidant mixture employed for the oxidation of pyrogallol and the solvent, respectively. By selecting the appropriate combination two detection modalities with increased sensitivity can be achieved. The first is based on the enhancement of the analytes signal through intensification of their scavenging effect on pyrogallol oxidation and the second on the enhancement of signal above the emission induced during the pyrogallol oxidation. Various combinations of organic solvents, oxidizing and pre-oxidizing mixtures were examined for their response in inhibited chemiluminescence measurements yielding very interesting results. The analytical utility of this new technique to the improvement of previous analytical methods as well as to the development of new procedures employing flow injection analysis is demonstrated. Furthermore, the application of the proposed method in combination with liquid chromatographic analysis is also presented.     

Bioluminescent detection of insect pheromones using an enzyme-based flow injection analysis system

The combination of flow injection analysis with chemiluminescent detection is shown to provide extremely selective and sensitive detection of insect pheromones which possess an aldehyde moiety. The flow injection analysis system provides reproducible control of both the reaction chemistry and the sample introduction process. Microliter volume samples can be precisely handled and analyzed with this experimental configuration. The detection system is based on the luciferase-catalyzed oxidation of reduced flavin mononucleotide which occurs in the presence of aldehydes with carbon backbones of between 14 and 16 carbons. A limit of detection of 3 fmol of tetradecyl aldehyde is demonstrated and the system is shown to be insensitive to the presence of various organic solvents up to concentrations of approximately 10%. The key experimental variables which control sensitive detection of pheromone at the femtomole level with be investigated and discussed.     

示波流动注射分析

将流动注射技术应用于示波分析，建立了示波流动注射分析，即动态示波分析法。设计了适用于示波分析的流通池，提出电压反馈的示波新技术，研究了新方法的重现性、检测限及影响去极剂峰高的各种因素。实验表明：新方法重现性好、简便、快速、灵敏，为示波测定的实际应用提供了可行的途径。     

Internal standard in flow injection analysis with amperometric detection

In this work, we describe for the first time the use of the internal standard method in flow injection analysis (FIA) with amperometric detection. The method is based on the application of sequential potential pulses to the working electrode in an electrochemical flow cell. The sequence of potential pulses is selected in such a way that the analyte and internal standard compound are detected and monitored individually and independently at the same working electrode. This approach compensates for random errors associated with variations of flow rate, injection volume, ionic strength difference between standards and samples, and accidental insertion or formation of air bubbles in the carrier stream. In addition, this method can overcome the major drawback of amperometric detection using solid electrodes, which is gradual electrode passivation. To illustrate the potential of this method, the flow-injection amperometric detection of uric acid using [Fe(CN)₆]^3? as an internal standard (IS) is presented as an example.     

Photometric detection in flow analysis systems using integrated PEDDs

A novel inexpensive optical-sensing technique has been developed for colorimetric flow analysis. This sensing system employs two LEDs whereby one is used as the light source and the other as a light detector. The LED used as light detector is reverse biased with a 5-V supply so that the photocurrent generated by the incident light discharges the capacitance. Direct digital output is provided by a simple timer circuit that measures the time taken for this discharge process from 5 V (logic 1) to 1.7 V (logic 0).

This sensing concept has been applied in flow analysis by constructing an optical flow cell with a pair of LEDs. Calibration of the integrated optical flow cell using a dye resulted in a linear response that obeys the Beer–Lambert law. The flow rate, dynamic range, sensitivity and limits of detection were investigated. The system was also used for pH determination in the range of pH 2.5–6.8 using bromocresol green (BCG). The pK_a of BCG was successfully determined by this technique.