Stopped-flow injection analysis. The influence of diffusion on dispersion of normal and reverse flow injection

A relationship is derived to enable the comparison of the dispersion heights of normal and reverse flow injection analysis (FIA). A single channel flow system is employed in the absence of a chemical reaction. The stopped-flow injection method is used to probe the influence of molecular diffusion on the overall dispersion of normal and reverse FIA, which appeared to demonstrate fundamentally different diffusion behaviors. Small discrepancies are observed between the dispersion heights, which are enhanced by the stopped-flow period, especially when unmatched matrix ionic compositions of the indicator and counter solutions were involved. For these conditions, the diffusion flux rate is enhanced considerably, displaying a peak, in addition to the transient, for both methods. The influence of diffusion on the dispersion characteristics of normal and reverse FIA is discussed theoretically. Diffusion in the proposed model is postulated to oppose dispersion by convection. The latter initiates concentration gradients in the injection zone and propagates it with flow time over the dispersion zone profile. The diffusion flux then reacts in order to confine the indicator dispersion for normal FIA and to enhance it for reverse FIA. This model is consistent with the experimental results and accounts for most of the phenomena encountered. Probably owing to the influence of secondary flow phenomena, the use of coiled tubes has suppressed the effects of diffusion on the overall dispersion behavior.Part of the experimental work was performed at IMI Institute for Research and Development, Haifa, Israel.     

可更新表面分析技术进展

概述了流动注射及顺序注射可更新表面分析技术及仪器的进展。介绍了该技术原理、仪器系统、流通池等方面的新发展以及在传感器、免疫分析、生物配位作用检测、酶反应检测、细胞功能检测等领域的应用。参考文献32篇。     

Novel Simultaneous Determination of Calcium and Magnesium Based on Flow Injection Gradient Titration

A novel approach based on flow injection gradient titration is proposed for the simultaneous spectrophotometric determination of Ca and Mg based on parameters of a single signal. Two reagents, calmagite and EDTA, are used to perform the determinations. Calmagite is introduced into a sample to form complexes with the analytes and the solutions are introduced into the holding coil of a sequential injection system in the sequence: carrier, air, sample, EDTA, and sample. In the system, EDTA replaces calmagite to form more stable complexes in turn with Ca and Mg. Next, the flow is reversed and the mixture is directed to the detector where the signal is measured at 680?nm. The signal consists of two parts: a short plateau (the signal for the sum of absorbance of complexes of Ca and Mg with calmagite) and a peak (the signal corresponding to titration of both complexes using EDTA). The absorbance values measured at the plateau and appropriately measured peak width were applied to determine analytes using two-component calibration. The method was verified for the determination of analytes in synthetic samples and in a certified reference material of surface water. Using the developed method, Mg and Ca were determined within the concentration ranges of 0.5–5.0 and 1.0–10.0?mg?L^?1, with precision better than 2.2 and 4.2% (relative standard deviation) and accuracy of 7.0 and 6.8% (relative error). The detection limits were 0.1 and 0.3?mg?L^?1 for Mg and Ca, respectively. The method was applied to analysis of mineral water samples.     

Reversed flow injection and sandwich sequential injection methods for the spectrophotometric determination of copper(II) with cuprizone

Two new flow methods, flow injection analysis (FIA) and sequential injection analysis (SIA), for the spectrophotometric determination of Cu(II) in water at trace levels have been developed and optimised. Both methods are based on the reaction with oxalic acid bis(cyclohexylidene hydrazide) (cuprizone) in alkaline media. The two procedures have been developed for the final aim to compare their performances and to offer new rapid heavy metals analysis tools, avoiding the use of extraction steps. A detailed study of the physico-chemical parameters affecting the systems performances has been carried out. The reversed FIA and sandwich SIA approaches offered the best sensitivity. In both cases, an extremely good linearity has been obtained within the range 0.06-4 μg ml⁻¹ (correlation coefficient r=0.9999), whereas the observed detection limits were 0.013 and 0.004 μg ml⁻¹, for FIA and SIA, respectively. Furthermore, due to the great similarity of the diffusion zones in the reaction slugs, our approach offers the opportunity to compare the two methods in analogous conditions. This SIA method, besides keeping its typical reagent saving features, offered analytical performances equivalent to those of FIA. To obtain these results, an original “stop-flow like” method was successfully employed in the SIA approach. Both methods were validated by analysis of real water samples, after copper addition, and certified reference samples of fortified and waste waters.     

An environmental friendly method for the automatic determination of hypochlorite in commercial products using multisyringe flow injection analysis

A multisyringe flow injection analysis system was used for the determination of hypochlorite in cleaning agents, by measurement of the native absorbance of hypochlorite at 292 nm. The methodology was based on the selective decomposition of hypochlorite by a cobalt oxide catalyst giving chloride and oxygen. The difference of the absorbance of the sample before and after its pass through a cobalt oxide column was selected as analytical signal. As no further reagent was required this work can be considered as a contribution to environmental friendly analytical chemistry. The entire analytical procedure, including in-line sample dilution in three steps was automated by first, dilution in a stirred miniature vessel, second by dispersion and third by in-line addition of water using multisyringe flow injection technique. The dynamic concentration range was 0.04-0.78 g L⁻¹ (relative standard deviation lower than 3%), where the extension of the hypochlorite decomposition was of 90 ± 4%. The proposed method was successfully applied to the analysis of commercial cleaning products. The accuracy of the method was established by iodometric titration.     

A multisyringe flow-through sequential extraction system for on-line monitoring of orthophosphate in soils and sediments

A fully automated flow-through microcolumn fractionation system with on-line post-extraction derivatization is proposed for monitoring of orthophosphate in solid samples of environmental relevance. The system integrates dynamic sequential extraction using 1.0 mol l⁻¹ NH₄Cl, 0.1 mol l⁻¹ NaOH and 0.5 mol l⁻¹ HCl as extractants according to the Hieltjes-Lijklema (HL) scheme for fractionation of phosphorus associated with different geological phases, and on-line processing of the extracts via the Molybdenum Blue (MB) reaction by exploiting multisyringe flow injection as the interface between the solid containing microcolumn and the flow-through detector. The proposed flow assembly, capitalizing on the features of the multicommutation concept, implies several advantages as compared to fractionation analysis in the batch mode in terms of saving of extractants and MB reagents, shortening of the operational times from days to hours, highly temporal resolution of the leaching process and the capability for immediate decision for stopping or proceeding with the ongoing extraction. Very importantly, accurate determination of the various orthophosphate pools is ensured by minimization of the hydrolysis of extracted organic phosphorus and condensed inorganic phosphates within the time frame of the assay. The potential of the novel system for accommodation of the harmonized protocol from the Standards, Measurement and Testing (SMT) Program of the Commission of the European Communities for inorganic phosphorus fractionation was also addressed. Under the optimized conditions, the lowest detectable concentration at the 3σ level was ≤0.02 mg P l⁻¹ for both the HL and SMT schemes regardless of the extracting media. The repeatability of the MB assay was better than 2.5% and the dynamic linear range extended up to 7.0 mg P l⁻¹ in NH₄Cl and NaOH media and 15 mg P l⁻¹ whenever HCl is utilized as extractant for both the HL and SMT protocols.     

Determination of Sulfaguanidine in Food and Veterinary Pharmaceuticals by Flow Injection Analysis with Spectrophotometric Detection

This work proposes a flow injection analysis system for sulfaguanidine determination in pharmaceutical and food samples. The method was based on the reaction of sulfaguanidine with nitronium ion to produce a colored complex whose absorbance was measured at 545?nm. The flow injection analysis system’s significant parameters were checked by a fractional factorial design 2^7–2 and optimization by a Doehlert matrix. The flow injection analysis system shows optimum values at 0.28, 2.00, and 0.11% (w/v) for N-naphtil ethylenediamine, ammonium sulfamate, and sodium nitrite concentrations, respectively. The possible interferents present in pharmaceutical and food samples were assessed by a multivariate technique and depicted on probability charts, indicating no significant interferences at the 95% level of confidence interval. The method showed detection and quantification limits of 0.012 and 0.039?mg?L^?1, an analytical frequency of 30 readings h^?1 and precision always lower than 5.0% expressed as the relative standard deviation. The obtained results were in accordance with those obtained by high-performance liquid chromatography.     

Capillary Electrophoresis as a Monitoring Tool for Flow Composition Determination

Flow analysis is the science of performing quantitative analytical chemistry in flowing streams. Because of its efficiency and speed of analysis, capillary electrophoresis (CE) is a prospective method for the monitoring of a flow composition withdrawn from various processes (e.g., occurring in bioreactors, fermentations, enzymatic assays, and microdialysis samples). However, interfacing CE to a various flow of interest requires further study. In this paper, several ingenious approaches on interfacing flow from various chemical or bioprocesses to a capillary electrophoresis instrument are reviewed. Most of these interfaces can be described as computer-controlled autosamplers. Even though most of the described interfaces waste too many samples, many interesting and important applications of the devices are reported. However, the lack of commercially available devices prevents the wide application of CE for flow analysis. On the contrary, this fact opens up a potential avenue for future research in the field of flow sampling by CE.     

Flow/sequential injection sample treatment coupled to capillary electrophoresis. A review

Various flow sample handling approaches coupled to capillary electrophoresis (CE) are reviewed, covering the research in this field in the 12 years since the milestone year of 1997, when practical interfaces to on-line couple flow injection (FI) and capillary electrophoresis were first developed independently by two research groups. Some previous attempts are also presented. Since 1997 a plethora of ingenious coupled systems have been developed. Although several reviews are available on various aspects of the topic, we have opted for a comprehensive overview of all FI-CE systems, as well as related and similar systems. This coupling has thus also led to the development of systems based on hybrids between the classical and microchip approaches. Truly microchip FI-CE systems are also included in this review.The developed systems have been used for various sample treatments, including on-line membrane-assisted sample treatment, column-based preconcentration, on-line derivatization and monitoring, to name just a few. The utility of coupling flow sampling to CE has been demonstrated in various practical applications that are discussed in detail. The current state-of-the-art and foreseeable future developments are also discussed.     

Highly sensitive gas-diffusion sequential injection analysis based on flow manipulation

The present paper describes approaches utilizing the powerful flow manipulation capabilities of sequential injection analysis (SIA) to substantially improve the efficiency of gas-diffusion separation compared to its traditional implementation in flow injection analysis (FIA). Ammonia, ethylamine, diethylamine and triethylamine were used as model analytes in this study. Eleven flow manipulation approaches involving continuous flow, stop-flow, oscillating flow, and the introduction of air bubbles to separate the sample zone from the donor solution were tested. Improvement in sensitivity compared to traditional gas-diffusion FIA exceeding one order of magnitude was achieved. It was observed that this improvement increased with the molecular size of the analyte.     

Flow injection chemiluminescent detection of trace Co(II) with dibromoalizarin violet-H2O2-CTMAB system

Chemiluminescence was observed when dibromoalizarin violet was oxidized with hydrogen peroxide in alkaline solution. Trace amounts of Co (II) catalysed this CL reaction strongly, especially in the presence of the cationic surfactant cetyltrimethylammonium bromide, and the CL intensity was proportional to the concentration of Co(II). A flow injection system with CL detection was established to investigate this CL system. The optimum conditions for this CL reaction were investigated in detail, and the optimized flow injection parameters were determined by the modified simplex method. A CL analytical method for determination of ultratrace amounts of Co (II) was developed with a detection limit of 4 pg/mL. It was used for analysis of natural water samples, and the results compare very well with those from GFAAS. A possible mechanism for this CL reaction is proposed on the basis of studying CL spectra, absorption spectra, fluorescent spectra and HMO treatment for the reagent molecule. The effects of various types of surfactants on CL reaction are also discussed.     

Flow analysis based on a pulsed flow of solution: theory, instrumentation and applications

The increased demands placed on solution propulsion by programmed flow systems, such as sequential injection analysis, lab-on-value technology, bead injection and multi-commutation, has highlighted the inability of many conventional pumps to generate a smooth, consistent flow. A number of researchers have examined ways to overcome the inadvertent, uncontrolled pulsation caused by the mechanical aciton of peristaltic pumps. In contrast, we have developed instruments that exploit the characteristics of a reproducible pulsed flow of solution. In this paper, we discuss our instrumental approaches and some applications that have benefited from the use of a reproducible pulsed flow rather than the traditional linear flow approach. To place our approach in the context of the continuously developing field of flow analysis, an overview of other programmed flow systems is also presented.     

Multisyringe Flow Injection Potentialities for Hyphenation with Different Types of Separation Techniques

The advantages of combining flow techniques with separation techniques are noteworthy. Flow-based methods are excellent tools for automating analytical procedures owing to their speed of analysis, reagent and sample saving ability, versatility, and inexpensive equipment. However, flow-based methods alone do not allow the separation of several analytes in a mixture. On the other hand, separation techniques (viz., chromatographic separations, capillary electrophoresis), widely used in analytical research due to high selectivity, require more expensive instrumentation. Thus, the combination of both techniques achieved the required selectivity with a more versatile, automated and, in some cases, low-cost methodology.

Multisyringe flow injection evidences interesting features with the utilization of the aforementioned combination of methods. Its potential for hyphenation with different separation techniques have been recently explored and are depicted in the present paper.     

Determination of Ethanol in Alcoholic Drinks: Flow Injection Analysis with Amperometric Detection Versus Portable Raman Spectrometer

A flow injection analysis with integrated amperometric alcohol dehydrogenase biosensor and a handheld Mira‐DS Raman spectrometer have been compared for the determination of ethanol in different samples of alcoholic drinks. The biosensor was constructed from the commercial screen‐printed carbon electrode as amperometric transducer and covered by a thin layer comprising alcohol dehydrogenase, reduced single‐layer graphene oxide, rhodium(IV) dioxide, and glutaraldehyde. Both assemblies were tested on analysis of plum brandy, white rum, vodka, white and red wines, strong dark beer, and non‐alcoholic beer. The two principally different analytical methods were critically compared and some limitations found, especially in case of analysis of red wine and beers. Finally, some future improvements of both analytical tools under test outlined.     

Calibration by the gradient ratio-standard addition method in flow injection flame atomic absorption spectrometry

A calibration method has been developed which is realised in the flow injection analysis (FIA) by the gradient technique. According to this method two transient peaks, one for a sample and the other for a sample with standard addition, are recorded and compared point by point in the entire defined time range. The analytical result is estimated on the basis of information gained about the local analyte concentrations in the sample zone. The method allows the results to be reliable when both the non-linear calibration dependence and the interference effect occur. As an example, calcium in synthetic samples containing silicon, phosphate, aluminium, vanadium and titanium, and also in iron ore sample, were determined by flame atomic absorption spectrometry (FAAS). It has been proved, that the method can be effective in overcoming even extremely strong interferences, providing analytical results with average accuracy equal to ca. 5% and with precision 2–3 times inferior to that obtained by conventional FI calibration.     

Chiral analysis by mass spectrometry using the kinetic method in flow systems

Chiral analysis is an important task of analytical chemistry. Besides separation techniques, mass spectrometry can be applied in this field. One mass spectrometric approach is based on Cooks' kinetic method. The method was successfully applied in a static system in which the concentration of the analyte as well as the chiral selector solution was constant during the experiment. The application of the kinetic method in dynamic systems (changing concentration of analyte) is presented. Such systems allow the speeding up of the analytical process (flow injection analysis (FIA)) or the use of the kinetic method for chiral detection after liquid chromatographic separation.The influence of the concentration of the components of the chiral selector solution as well as its flow rate on the recognition of enantiomers was evaluated. A new procedure for correction for the differences between ratio of enantiomers in the liquid phase and their observed ratio in the gas phase is also described. A significant improvement in accuracy using this procedure was achieved. Applicability of the method was demonstrated in the analysis of amino acids using FIA as well as HPLC/MS. After an achiral separation of leucine and isoleucine, chiral mass spectrometric detection was successfully used for enantiomeric recognition.     

Electrochemically assisted injection – a new approach for hyphenation of electrochemistry with capillary-based separation systems

A new concept based on the electrochemical conversion of analyte species during the injection into capillary flow systems is presented. This approach is termed electrochemically assisted injection (EAI). In a specially designed injection cell containing the analyte solution a conversion efficiency of about 83% can be achieved. Potassium octacyanotungstate(IV) served as a model compound for the analytical characterisation of EAI applying capillary flow injection analysis with double-pulse amperometric detection. Capillary electrophoresis experiments were performed using EAI to study the electrochemical oxidation of various ferrocene derivatives in acetonitrile solution. The electropherograms recorded with UV detection show separated signals for the ferrocene compounds and their oxidation products. The migration behaviour and the stability of ferrocenium cations and other reaction products were investigated.     

Design of the Fluoride Ion-Selective Electrode as Tubular Detector for Flow Injection Analysis

ABSTRACT

Design of the fluoride ion-selective electrode (FISE) as the tubular detector used in the flow injection analysis (FIA) has been described. Among other things, this design makes it possible to use various internal contacts. The effect of pH on peak height and detection limit in the pH range from 2.8 to 8.0 has been examined. The effect of flow rate and sample injection volume on peak height and range of linear response has also been examined. The flow rates range from 0.56 mL/min to 4.05 mL/min, while the injection volumes are 100 and 200 μL. The optimum conditions are carrier solution (0.1 M KNO₃ buffer pH 4 and 10^-6 M NaF), flow rate 1.54 mL/min and sample injection volume 100 μL.

Applicability of the FISE as the tubular detector in determination of Fe(III)-ions and AI(III)-ions by flow infection analysis has been examined at pH values of 2.8 and 3.4.