Indirect ultraviolet determination of silver with nickelocyanide ion by flow injection analysis

A flow-injection method for the ultraviolet spectrophotometric determination of silver, based on its reaction with nickelocyanide ion, Ni(CN)²⁻₄, in ammoniacal buffer medium (pH 10) and subsequent measurement of the decrease in the absorption of the Ni(CN)²⁻₄ complex at 275 nm is described. The calibration graph is linear in the range 10–400 μm silver. At a sampling rate of about 60 samples h⁻¹ with 35 μl sample injections, precision was about 1% relative standard deviation. The proposed method was successfully applied to the determination of silver in some common silver minerals.     

基于碘离子选择性电极的流动注射分析系统构建

碘硫(IS)热化学循环分解水是目前最有前景的核能制氢技术.在IS循环研究中,I-浓度的在线分析对于实现过程反应条件的监测控制以及进行有关反应动力学研究非常重要.以碘离子选择性电极为检测器,针对IS循环物料组成体系组装了一套流动注射分析系统,考察了样品温度、氢离子浓度、离子强度等因素对电极性能的影响,对FLA装置的栽流流...     

Flow injection method for the determination of silver concentration in drinking water for spacecrafts

A flow injection method has been developed for determination of silver. The method is based on a reduction reaction with sodium borohydride which leads to the formation of a colloidal species which is monitored at a wavelength of 390 nm.The reaction variables flow rate, sodium borohydride concentration and pH, which affect sensitivity, were investigated and their effects were established using a two-levels, three-factor experimental design. Further optimization of manifold variables (reaction coil and injection volume) allowed us to determine silver in the range 0.050-5.0 mg L⁻¹ with a minimum detectable concentration of 0.050 mg L⁻¹. Silver is added, as biocide, to drinking water for spacecrafts. The chemical species of silver, present in this kind of sample, were characterized by a procedure based on the selective retention of Ag⁺ onto a 2.2.2. cryptand based substrate followed by determination of the non-bound and bound (after elution) Ag⁺ by the FIA method. The method optimized was applied to a drinking water sample provided for the launch with the Automated Transfer Vehicle (ATV) module Jule Verne to the International Space Station (March 9, 2008).     

Carbon paste electrode modified with silver thimerosal for the potentiometric flow injection analysis of silver(I)

The utility of carbon paste electrode modified with silver ethylmercurythiosalicylate (silver thimerosal) in both static mode and flow injection analysis (FIA) is demonstrated. The electrode was fully characterized in terms of composition, response time, thermal stability, usable pH and ionic strength ranges. It has been shown that diisononyl phthalate (DINP) acts as more suitable solvent mediator for preparation of the electrode, which exhibits linear response range to Ag(I) extending from 5.0 × 10⁻⁷ to 1.0 × 10⁻³ M with detection limit of 2.5 × 10⁻⁷ M and Nernstian slope of 59.3 ± 1.0 mV/decade. The proposed chemically modified carbon paste electrode shows a very good selectivity for Ag(I) over a wide variety of metal ions and successfully used for the determination of the silver content of silver sulphadiazine (burning cream) and developed radiological films. The electrode was also used as an indicator electrode in the potentiometric titration of thiopental and thimerosal with AgNO₃.     

Continuous flow and flow injection stripping voltammetric determination of silver(I), mercury(II), and bismuth(III) at a bulk modified graphite tube electrode

The epoxy-impregnated graphite tube electrode bulk modified with 2-mercaptobenzoxazole, employed in a wall-jet configuration, was found to be useful for the continuous flow and flow injection stripping voltammetric determinations of Ag^I, Hg^II and Bi^III. For continuous flow, detection limits for Ag^I, Hg^II and Bi^III were 1.8 × 10⁻¹⁰ M, 1.9 × 10⁻⁹ M and 9.5 × 10⁻⁹ M, respectively (10 min accumulation, S/N = 3). Precisions for 5.00 × 10⁻⁹ M Ag^I, 1.00 × 10⁻⁸ M Hg^II and 1.00 × 10⁻⁷ M Bi^III were 10.5%, 5.77 % and 7.90% (relative standard deviations, n = 6), respectively. In the case of flow injection stripping, with a 500 μL injection loop, detection limits of 0.59 ng, 2.0 ng and 120 ng were obtained for Ag^I, Hg^II and Bi^III, respectively (S/N = 3). Selected metal ions, inorganic and organic substances were investigated for interferences. The electrode was tested with a certified sample and then applied to the determinations of the metal ions in a urine and a sea-water sample.     

Solid-phase iodine as an oxidant in flow injection analysis: determination of ascorbic acid in pharmaceuticals and foods by background correction

A flow injection analysis (FIA)-background correction method comprising two solid-phase reactors and spectrophotometry for determination of ascorbic acid (AsA) is proposed. A polyethylene mini-column filled with solid iodine (30% m/m suspended on silica gel beads), reactor 1, and other column filled only with silica gel, reactor 2, which are then incorporated in a flow system so that solid iodine reagent in reactor 1 is affected as the sample passes through the column. The sample blank is produced by the oxidation of the AsA by iodine to form dehydroascorbic acid, insensitive to ultraviolet at 267 nm. AsA in samples is determined after injected in reactor 2; the difference in two analytical signal observed is related to amount of AsA. The linear range of the system is up to 50 μg ml⁻¹ with a detection limit of 0.08 μg ml⁻¹, R.S.D. of better than 1.0% and sampling frequency of 110 sample h⁻¹. The method is successfully applied to the determination of AsA in pharmaceuticals and foods.     

A near-infrared fluorescent chemodosimeter for silver(I) ion based on an expanded porphyrin

An expanded porphyrin [26]hexaphyrin(1.1.1.1.1.1) was exploited as a fluorescent chemodosimeter for Ag⁺ ions with high sensitivity and selectivity via near-infrared luminescence above 900 nm, a region that is free from optical interference in the visible wavelength range induced by the commonly used matrix and other organic compounds. The association constant for the Ag⁺-porphyrin complexation was evaluated by spectroscopic titration method to be 7.24 × 10¹⁰ M⁻¹.     

A borondipyrrolemethene-based turn-on fluorescent probe for silver ion with high sensitivity and selectivity and its application in water samples and living cells

A borondipyrrolemethene-based compound (1) is synthesized and used as a “turn-on” fluorescent probe for silver ions (Ag⁺). The probe displays highly sensitive fluorescence response toward Ag⁺ with a 40-fold fluorescence enhancement when 60 μM of Ag⁺ is added. The fluorescence intensity of the probe is linearly dependent on Ag⁺ concentration ranging from 0.05 to 60 μM. And the detection limit (LOD) can reach 0.02 μM, which complies with the standard of World Health Organization (WHO) for drinking water (0.9 μM). Moreover, the probe shows remarkable selectivity for Ag⁺ over other metal ions. Furthermore, the response behavior of 1 toward Ag⁺ is pH independent in the neutral range from 6.0 to 8.0. The response of 1 toward Ag⁺ is fast (response time is less than 2 min) and reversible chemically. What’s more, the sensing mechanism of probe 1 toward Ag⁺ is verified by mass spectra (MS) and density functional theory (DFT) calculations. In particular, the probe is applied for detection of Ag⁺ in water samples and living cells successfully.     

Flow injection on-line displacement/solid phase extraction system coupled with flame atomic absorption spectrometry for selective trace silver determination in water samples

A novel flow injection (FI) on-line displacement solid phase extraction preconcentration and/or separation method coupled with FAAS in order to minimize interference from other metals was developed for trace silver determination. The proposed method involved the on-line formation and subsequently pre-sorption of lead diethyldithiocarbamate (Pb-DDTC) into a column packed with PTFE-turnings. The preconcentration and/or separation of the Ag(I) took place through a displacement reaction between Ag(I) and Pb(II) of the pre-sorbed Pb-DDTC. Finally, the retained analyte was eluted with isobutyl methyl ketone (IBMK) and delivered directly to nebulizer for measuring. Interference from co-existing ions with lower DDTC complex stability in comparison with Pb-DDTC, was eliminated without need for any masking reagent. With 120 s of preconcentration time at a sample flow rate of 7.6 mL min−1, an enhancement factor of 110 and a detection limit (3 s) of 0.2 μg L−1 were obtained. The precision (RSD, n = 10) was 3.1% at the 10 μg L−1 level. The developed method was successfully applied to trace silver determination in a variety of environmental water samples and certified reference material.     

A novel planar miniaturized potentiometric sensor for flow injection analysis of nitrates in wastewaters, fertilizers and pharmaceuticals

A novel all-solid-state miniaturized nitrate sensor is developed, characterized and used for flow injection analysis (FIA) of nitrates in various samples. The sensor incorporates silver bis(bathophenanthroline) nitrate [Ag(bath)₂NO₃] as an electroactive material in a plasticized PVC membrane. The sensing membrane (3 mm × 5 mm) is immobilized on a wafer polyimide microchip (size 13.5 mm × 3.5 mm) to offer a planar miniaturized design easily used in a single channel wall-jet flow injection system. Under hydrodynamic mode of operation (FIA) the sensor displays fast response, high sensitivity, long term stability and good selectivity for NO₃⁻ in the presence of many common associated anions. The calibration slope is 55.1 ± 0.1 mV decade⁻¹ over the concentration range 1.0 × 10⁻¹ to 1.0 × 10⁻⁶ mol L⁻¹, the lower detection limit is 0.05 μg mL⁻¹, the working pH is 2-9,and the output is 70-90 samples h⁻¹. Validation of the assay method reveals good performance characteristics and suggests application for routine determination of NO₃⁻ in industrial wastewaters, fertilizers and pharmaceuticals. The results agree fairly well with data obtained by the standard spectrophotometric methods.     

Tubular potentiometric detector used to determine As(V) in sediment extracts by flow injection

The construction and evaluation of a tubular potentiometric detector sensitive to As(V) ions is described. This electrode, with no inner reference solution, is comprised of a FeOOH–SiO₂–graphite composite agglutinated with an epoxy resin. For As(V) ion concentrations in the range 1.0?×?10^?5 to 1.0?×?10^?1?mol?L^?1, the sensor is used as the selective electrode in an FIA system along with a commercial Ag/AgCl reference electrode. In optimal conditions, the practical limit of detection is 4?×?10^?6?mol?L^?1 and a sampling rate of 40?h^?1 can be achieved. The system was applied to estimate As(V) levels in sediments of a drinking water distributor in Zimapán (Mexico), an area known to be polluted with this element. The As(V) concentrations detected in the different extracts of sediments generated by the sequential modified BCR three-step extraction procedure (BCR-SEP) were comparable to those obtained by electrothermal atomic absorption spectroscopy (ET-AAS).     

Flow injection analysis system for monitoring of succinic acid in biotechnological processes

In this study, a flow injection analysis (FIA) system using a cartridge of immobilized isocitrate lyase (ICL) and isocitrate dehydrogenase (ICDH) was developed to monitor the concentrations of succinic acid in biotechnological processes. The ICL and ICDH immobilized on VA-Epoxy Biosynth E3-carrier had a good operational lifetime (up to 24 h) and storage stability (up to 30 days). The FIA system with the immobilized ICL/ICDH cartridge was characterized with respect to the factors affecting the activity of the immobilized enzymes, such as pH of carrier solution, temperature, sample matrix, etc. Optimal pH value of the immobilized enzymes was slightly shifted in the alkaline range, i.e. 9.0. Some components such as 10 g l⁻¹ lactose, 3 g l⁻¹ malate and 3 g l⁻¹ oxaloacetate in sample solution had significant activating effects (more than 10%) on the response of the FIA system. But the activity of the immobilized ICL and ICDH was not largely influenced by some components like imidazole (1 mM), sodium azide (10 mM) and semicarbazide (2 g l⁻¹) added to carrier buffer solution. The FIA system with an enzyme cartridge was applied to on-line monitor the concentrations of succinic acid in a continuously stirred reactor and a fermentation process of immobilized Escherichia coli, and showed good sensitivity and reliability of the FIA system developed in this work.     

Rapid determination of chromium(VI) in electroplating waste water by use of a spectrophotometric flow injection system

A new rapid and sensitive FI method is reported for spectrophotometric determination of trace chromium(VI) in electroplating waste water. The method is based on the reaction of Cr(VI) with sodium diphenylamine sulfonate (DPH) in acidic medium to form a purple complex (lambda(max) = 550 nm). Under the optimized conditions, the calibration curve is linear in the range 0.04-3.8 microg ml(-1) at a sampling rate of 30 h(-1). The detection limit of the method is 0.0217 microg ml(-1), and the relative standard deviation is 1.1% for eight determinations of 2 microg ml(-1) Cr(VI). The proposed method was applied to the determination of chromium in electroplating waste water with satisfactory results.     

New method for simultaneous determination of Fe(II) and Fe(III) in water using flow injection technique

The method exploits the possibilities of flow injection gradient titration in a system of reversed flow with spectrophotometric detection. In the developed approach a small amount of titrant (EDTA) is injected into a stream of sample containing a mixture of indicators (sulfosalicylic acid and 1,10-phenanthroline). In acid environment sulfosalicylic acid forms a complex with Fe(III), whereas 1,10-phenanthroline forms a complex with Fe(II). Measurements are performed at wavelength λ = 530 nm when radiation is absorbed by both complexes. After injection EDTA replaces sulfosalicylic acid and forms with Fe(III) more stable colourless complex. As a result, a characteristic “cut off” peak is registered with a width corresponding to the Fe(III) concentration and with a height corresponding to the Fe(II) concentration. Calibration was performed by titration of four two-component standard solutions of the Fe(II)/Fe(III) concentrations established in accordance with 2² factorial plan. The method was tested with the use of synthetic samples and then it was applied to the analysis of water samples taken from artesian wells. Under optimized experimental conditions Fe(II) and Fe(III) were determined with precision less than 0.8 and 2.5% (RSD) and accuracy less than 3.2 and 5.1% (relative error) within the concentration ranges of 0.1-3.0 and 0.9-3.5 mg L⁻¹ of both analytes, respectively.     

Automated stopped-in-dual-loop flow analysis system for catalytic determination of vanadium in drinking water

An automated stopped-in-dual-loop flow analysis (SIDL-FA) system is proposed for the determination of vanadium in drinking water. The chemistry is based on the vanadium-catalyzed oxidation reaction of p-anisidine by bromate in the presence of Tiron as an activator to produce a dye (λ_max = 510 nm). A SIDL-FA system basically consists of a selection valve, three pumps (one is for delivering of standard/sample, and others are for reagents), two six-way injection valves, a spectrophotometric detector and a data acquisition device. A 100-μL coiled loop around a heated device is fitted onto each six-way injection valve. A well-mixed solution containing reagents and standard/sample is loaded into the first loop on a six-way valve, and then the same solution is loaded into the second loop on another six-way valve. The solutions are isolated by switching these two six-way valves, so that the catalytic reaction can be promoted. The net waste can be zero in this stage, because all pumps are turned off. Then each resulting solution is dispensed to the detector with suitable time lag. A touchscreen controller is developed to automatically carry out the original SIDL-FA protocol. The proposed SIDL-FA method allows vanadium to be quantified in the range of 0.1-2 μg L⁻¹ and is applied to the determination of vanadium in drinking water samples.     

Optimization of a flow injection analysis system for tartaric acid determination in wines

The objective of this work is the development and optimization of a method for tartaric acid analysis in wines that does not require any sample pre-treatment and with adequate accuracy. A flow injection analysis manifold with three channels, using a dialysis unit to eliminate sample matrix interferences and to accomplish on-line dilution, is proposed for the spectrophotometrical determination of tartaric acid in wines making use of its reaction with vanadate. The proposed method is fast, accurate, simple, economic and does not require any sample pre-treatment. Preliminary studies using factorial designs were performed to determine which operational parameters should be included in the optimization stage. The optimization was performed using a modified simplex algorithm with a response function that included sensitivity, deviation from linearity at low concentrations and residence time, used as an inverse measure of sampling rate. The most relevant analytical parameters of the method are presented, including a comparison between the results provided by the proposed method and by an alternative procedure in the analysis of a set of wine samples from Portugal, with tartaric acid values in the range 0.5–4 g l⁻¹.     

A matrix-induced ion suppression method to normalize concentration in urinary metabolomics studies using flow injection analysis electrospray ionization mass spectrometry

Normalizing the total urine concentration is important for minimizing bias in urinary metabolomics analysis comparisons. In this study, we report a matrix-induced ion suppression (MIIS)-based method to normalize concentration using flow injection analysis coupled with electrospray ionization mass spectrometry (FIA-ESI-MS). An ion suppression indicator (ISI) was spiked into urine samples, and the intensity of the extracted ion chromatogram (EIC) for ISI in a urine matrix was subtracted by the EIC for a blank solution and used to calculate the extent to which the signal was reduced by the urine matrix. A series dilution of pooled urine samples was used to correlate the urine concentration and level of ion suppression for ISI. A regression equation was used to estimate the relative concentration of unknown urine samples. The MIIS method was validated for linearity, precision and accuracy. We obtained a good correlation using a quadratic regression model for 1- to 32-fold urine dilutions (R² = 0.998). The reproducibility (n = 4) and intermediate precision (n = 3) were below 5% RSD, and the accuracy ranged from 97.15% to 102.10%. The established method was used to estimate the relative concentrations of 16 urine samples, and the results were compared with commonly used normalization methods. Pearson’s correlation test was used to demonstrate that the MIIS method correlated highly with the creatinine and osmolarity methods; the correlation coefficients were 0.93 and 0.99, respectively. We successfully applied this method to a urinary metabolomics study on breast cancer. This study demonstrated the MIIS method is simple, accurate and can contribute to data integrity in urinary metabolomics studies.     

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.     

Comparison of soluble manganese(IV) and acidic potassium permanganate chemiluminescence detection using flow injection and sequential injection analysis for the determination of ascorbic acid in Vitamin C tablets

The limits of detection (3s) for ascorbic acid were 5×10⁻⁸ M with acidic potassium permanganate using both flow injection analysis (FIA) and sequential injection analysis (SIA) whereas the soluble manganese(IV) afforded 1×10⁻⁸ M and 5×10⁻⁹ M for FIA and SIA, respectively. Determinations of ascorbic acid in Vitamin C tablets were achieved with minimal sample pretreatment using a standard additions calibration and gave good agreement with those of iodimetric titration.     

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.