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Analytica Chimica Acta (v.600, #1-2)

Contents (pp. vii-ix).

Editorial Board (pp. co1).

Publisher¿s note volume 600 (pp. 1-2).

Foreword by Purnendu Dasgupta; José L.F.C. Lima; Lúcia Saraiva; Marcela Segundo (pp. 3-3).

30 years of flow injection analysis—And passing the torch by E.H. Hansen (pp. 4-5).

Versatile flow injection manifold for analytical calibration by Paweł Kościelniak; Marcin Wieczorek; Joanna Kozak; Małgorzata Herman (pp. 6-13).

A flow injection calibration system, originally designed and tested in our laboratory, is presented here as a versatile analytical tool serving for calibration purposes. It is characterized by a simple construction, easy operation and the possibility of offering rich measurement information with the use of a single standard solution. It is shown that depending on instrumental conditions and the composition of the calibration solutions the manifold is able to realize various calibration procedures according to interpolative, extrapolative and integration modes. As an experimental example, the determination of calcium in the cabbage sample by flame atomic absorption spectrometry has been calibrated by means of dilution method (DM) in the integration mode.

Keywords: Calibration; Flow injection analysis; Dilution method

Piezoelectric pumping in flow analysis: Application to the spectrophotometric determination of gabapentin by Marta F.T. Ribeiro; João L.M. Santos; José L.F.C. Lima (pp. 14-20).

Solutions propelling devices are fundamental components of a flow-based analytical manifold. In this work different manifold configurations were implemented to evaluate the performance of multiple piezoelectric micro-pumps used as solutions insertion and propulsion devices. The micro-pumps are piezo-actuated micro-diaphragm pumps with passive check valves characterised by a small compact size and low power demands, and are able to produce reproducible flow rates of up to 4mLmin⁻¹. The flow rate is controlled by the frequency of the piezoelectric actuator (up to 20Hz). As an additional feature, piezoelectric micro-pumps actuation generates a pulsed flowing stream that ensures a faster sample/reagent mixing contributing to improved reaction development.The developed flow approach was assessed in the spectrophotometric determination of gabapentin in pharmaceutical preparations upon reaction with 1,2-naphthoquinone-4-sulfonate in alkaline medium. Distinct flow manifold configurations were designed for achievement of different solutions management. Linear calibrations plots for gabapentin concentrations of up to 150mgL⁻¹, with relative standard deviations of less than 1.50% ( n=10) and a sample throughput of about 28 determinations per hour, were obtained.

Keywords: Piezoelectric micro-pump; Flow analysis; Pulsed flow; Gabapentin; 1,2-Naphthoquinone-4-sulfonate; Multi-pumping

Multi-pumping flow systems: The potential of simplicity by João L.M. Santos; Marta F.T. Ribeiro; Ana C.B. Dias; José L.F.C. Lima; Elias E.A. Zagatto (pp. 21-28).

Nowadays, the trend towards more compact, smarter and simpler devices is generally recognized as one of the most challenging aspects in the development of analytical instrumentation. Modern flow-based procedures do not escape this tendency. The level of integration and automation and the operational functionality of Multi-pumping flow systems (MPFS) would, in most of the situations, meet this requirement. The essential elements of MPFS are multiple solenoid actuated micro-pumps strategically positioned in the flow manifold, which are accountable for solutions insertion, propelling and commutation, conditioning the establishment and subsequent detection of the reaction zone. Being the only active components of the flow manifold they provide a great operational simplicity and assure a straightforward run-time control of important analytical variables. Moreover, the reduction of active components minimizes the probability of occurrence of equipment failures, malfunctions or errors. The low size and low cost of solenoid micro-pumps make them ideal tools to build up compact environmentally friendly analytical systems, which are characterized by low solutions consumptions and the minimisation of hazardous waste generation. Furthermore, the reproducible pulsed flowing stream produced by micro-pumps actuation has proven to be a valuable feature regarding sample/reagent mixing and reaction zone homogenisation.

Keywords: Multi-pumping flow system; Solenoid micro-pumps; Pulsed flow; Flow analysis

A multi-commuted flow injection system with a multi-channel propulsion unit placed before detection: Spectrophotometric determination of ammonium by Sara M. Oliveira; Teresa I.M.S. Lopes; Ildikó V. Tóth; António O.S.S. Rangel (pp. 29-34).

A flow system with a multi-channel peristaltic pump placed before the solenoid valves is proposed to overcome some limitations attributed to multi-commuted flow injection systems: the negative pressure can lead to the formation of unwanted air bubbles and limits the use of devices for separation processes (gas diffusion, dialysis or ion-exchange). The proposed approach was applied to the colorimetric determination of ammonium nitrogen. In alkaline medium, ammonium is converted into ammonia, which diffuses over the membrane, causing a pH change and subsequently a colour change in the acceptor stream (bromothymol blue solution). The system allowed the re-circulation of the acceptor solution and was applied to ammonium determination in surface and tap water, providing relative standard deviations lower than 1.5%. A stopped flow approach in the acceptor stream was adopted to attain a low quantification limit (42μgL⁻¹) and a linear dynamic range of 50–1000μgL⁻¹ with a determination rate of 20h⁻¹.

Keywords: Multi-commuted flow system; Gas diffusion; Waters; Trace levels of ammonium; Spectrophotometry

Potential of multisyringe flow-based multicommutated systems by V. Cerdà; R. Forteza; J.M. Estela (pp. 35-45).

This work is aimed at emphasizing the potential of the multicommutated systems based on the multisyringe flow injection analysis (MSFIA) modality. First, the characteristics, advantages and withdraws offered by flow analysis systems based on the different non-segmented modalities are briefly described. In these systems, multicommutation and computer control of the analytical process occupy a predominant place, as in the case of sequential injection analysis (SIA), multicommutated flow injection analysis (MCFIA), MSFIA and multipumping flow systems (MPFS). Next, several examples are given and different aspects of the implementation of analysers based on MSFIA designs for the construction of different analysis systems, including intelligent (smart) systems, use of sample pre-treatment automatic systems, for chromatographic and non-chromatographic determinations as well as use of monolithic or capillary electrophoresis columns are considered.

Keywords: Flow techniques; Flow system; Flow analyser

Miniaturization of environmental chemical assays in flowing systems: The lab-on-a-valve approach vis-à-vis lab-on-a-chip microfluidic devices by Manuel Miró; Elo Harald Hansen (pp. 46-57).

The analytical capabilities of the microminiaturized lab-on-a-valve (LOV) module integrated into a microsequential injection (μSI) fluidic system in terms of analytical chemical performance, microfluidic handling and on-line sample processing are compared to those of the micro total analysis systems (μTAS), also termed lab-on-a-chip (LOC). This paper illustrates, via selected representative examples, the potentials of the LOV scheme vis-à-vis LOC microdevices for environmental assays. By means of user-friendly programmable flow and the exploitation of the interplay between the thermodynamics and the kinetics of the chemical reactions at will, LOV allows accommodation of reactions which, at least at the present stage, are not feasible by application of microfluidic LOC systems. Thus, in LOV one may take full advantage of kinetic discriminations schemes, where even subtle differences in reactions are utilized for analytical purposes. Furthermore, it is also feasible to handle multi-step sequential reactions of divergent kinetics; to conduct multi-parametric determinations without manifold reconfiguration by utilization of the inherent open-architecture of the micromachined unit for implementation of peripheral modules and automated handling of a variety of reagents; and most importantly, it offers itself as a versatile front end to a plethora of detection schemes. Not the least, LOV is regarded as an emerging downscaled tool to overcome the dilemma of LOC microsystems to admit real-life samples. This is nurtured via its intrinsic flexibility for accommodation of sample pre-treatment schemes aimed at the on-line manipulation of complex samples. Thus, LOV is playing a prominent role in the environmental field, whenever the monitoring of trace level concentration of pollutants is pursued, because both matrix isolation and preconcentration of target analytes is most often imperative, or in fact necessary, prior to sample presentation to the detector.

Keywords: Lab-on-a-valve; Lab-on-a-chip; Microfluidics; Environmental assays

A multicommuted stop-flow system employing LEDs-based photometer for the sequential determination of anionic and cationic surfactants in water by André F. Lavorante; Ángel Morales-Rubio; Miguel de la Guardia; Boaventura F. Reis (pp. 58-65).

It has been developed an automatic stop-flow procedure for sequential photometric determination of anionic and cationic surfactants in a same sample of water. The flow system was based on multicommutation process that was designed employing two solenoid micro-pumps and six solenoid pinch valves, which under microcomputer control carry out fluid propelling and reagent solutions handling. A homemade photometer using a photodiode as detector and two light emitting diodes (LEDs) with emission at 470nm (blue) and 650nm (red) as radiation sources, which was tailored to allow the determination of anionic and cationic surfactants in waters. The procedure for anionic surfactant determination was based on the substitution reaction of methyl orange (MO) by the anionic surfactant sodium dodecylbenzene sulfonate (DBS) to form an ion-pair with the cetyl pyridine chloride (CPC). Features such as a linear response ranging from 0.35 to 10.5mgL⁻¹ DBS ( R=0.999), a detection limit of 0.06mgL⁻¹ DBS and a relative standard deviation of 0.6% ( n=11) were achieved. For cationic surfactant determination, the procedure was based on the ternary complex formation between cationic surfactant, Fe(III) and chromazurol S (CAS) using CPC as reference standard solution. A linear response range between 0.34 and 10.2mgL⁻¹ CPC ( R=0.999), a detection limit of 0.05mgL⁻¹ CPC and a relative standard deviation of 0.5% ( n=11) were obtained. In both cases, the sampling throughput was 60 determinations per hour. Reagents consumption of 7.8μg MO, 8.2μg CPC, 37.2μg CAS and 21.6μg Fe(III) per determination were achieved. Analyzing river water samples and applying t-test between the results found and those obtained using reference procedures for both surfactant types provide no significant differences at 95% confidence level.

Keywords: Flow injection analysis; Multicommutation; Sequential determination; Surfactants; Solenoid micro-pump; Solenoid pinch valve; Light emitting diode-based photometer

An automatic falling drop system based on multicommutation process for photometric chlorine determination in bleach by Sivanildo da Silva Borges; Boaventura F. Reis (pp. 66-71).

In this work an automatic photometric procedure for the determination of chlorine in bleach samples employing N, N′-diethyl- p-phenylenediamine (DPD) as chromogenic reagent is described. The procedure was based on a falling drop system where the analyte (Cl₂) was collected by a DPD solution drop (50μL) after its delivery from the sample bulk that was previously acidified. The flow system was designed based on the multicommutation process assembling a set of three-way solenoid valves, which under microcomputer control afforded facilities to handle sample and reagent solution in order to control analyte delivering and solution drop generation. The analyte volatilization was improved by coupling online a little heating device. The detection system comprised a green LED (515nm) and a phototransistor. Aiming to prove the usefulness of the proposed procedure a set of bleach samples was analyzed. Comparing the results with those obtained with reference method no significant difference at 95% confidence level was observed. Other profitable features such as a linear response ranging from 15 up to 100mgL⁻¹ Cl₂ ( R=0.999); a detection limit of 4.5mgL⁻¹ Cl₂ estimated based on the 3 σ criterion; a relative standard deviation of 2.5% ( n=10) using a typical bleach sample containing 25.0mgL⁻¹ Cl₂; a consumption of 55μg of DPD per determination; and a analytical frequency of 20 determinations per hour were also achieved.

Keywords: Multicommutation; Flow analysis; Spectrophotometry; Chlorine; Falling drop system; Breach

Rapid microstill determination of free and total sulfite in wine with conductimetric detection by Stan McLeod; David E. Davey (pp. 72-77).

The development and optimization of on-line microdistillation for free and total sulfite (S(IV)) in grape juice and wine is reported. The microstill used both heat and an air stream to separate sulfur dioxide from the wine samples; the distillation product was captured in a peroxide solution, and converted to sulfuric acid, mirroring accepted industry practice. Measured from 1 to 300mgL⁻¹ as SO₂ by conductance, sample throughputs of 60h⁻¹ for free and 20h⁻¹ for total sulfite were achieved. Data for bound S(IV) emphasises the slow kinetics of release reactions in some wines. The microstill method is more efficient for total sulfite than the accepted manual technique. Good correlation was found between the microstill and manual methods under specified control conditions.

Keywords: Microdistillation; Continuous flow; Conductance detection; Sulfite; Wines

Novel approaches to analysis by flow injection gradient titration by Marzena Wójtowicz; Joanna Kozak; Paweł Kościelniak (pp. 78-83).

Two novel procedures for flow injection gradient titration with the use of a single stock standard solution are proposed. In the multi-point single-line (MP-SL) method the calibration graph is constructed on the basis of a set of standard solutions, which are generated in a standard reservoir and subsequently injected into the titrant. According to the single-point multi-line (SP-ML) procedure the standard solution and a sample are injected into the titrant stream from four loops of different capacities, hence four calibration graphs are able to be constructed and the analytical result is calculated on the basis of a generalized slope of these graphs. Both approaches have been tested on the example of spectrophotometric acid–base titration of hydrochloric and acetic acids with using bromothymol blue and phenolphthalein as indicators, respectively, and sodium hydroxide as a titrant. Under optimized experimental conditions the analytical results of precision less than 1.8 and 2.5% (RSD) and of accuracy less than 3.0 and 5.4% (relative error (RE)) were obtained for MP-SL and SP-ML procedures, respectively, in ranges of 0.0031–0.0631molL⁻¹ for samples of hydrochloric acid and of 0.1680–1.7600molL⁻¹ for samples of acetic acid. The feasibility of both methods was illustrated by applying them to the total acidity determination in vinegar samples with precision lower than 0.5 and 2.9% (RSD) for MP-SL and SP-ML procedures, respectively.

Keywords: Flow injection titration; Calibration; Fully rotary valve; Acid–base titration

Robust flow–batch coulometric/biamperometric titration system: Determination of bromine index and bromine number of petrochemicals by Celio Pasquini; Emerson Vidal de Aquino; Marcio das Virgens Reboucas; Fabiano Barbieri Gonzaga (pp. 84-89).

A flow–batch system was constructed and evaluated to perform coulometric titrations with biamperometric end point detection. The flow section of the system is employed for sampling by injecting a sample volume (50–300μL) in a flow injection-like system. About 1.5mL of a suitable carrier solution is delivered by a peristaltic pump in order to quantitatively transfer the sample to the system titration cell (2.0mL total inner volume). The carrier contains the coulometric precursor for the titrant species. The cell contains two pairs of platinum electrodes used for coulometric generation of reagent and biamperometric detection and is actively stirred. The titrant species is generated and the titration is performed by the usual batch procedure with the excess of titrant being detected by biamperometry following the analysis of the titration curve. System operation is computer controlled and all operations are automated, including titration curve analysis and cell cleaning after the titration is ended. The system is characterized by its robustness because its operation does not depend on flow rates, and the work using coulometric methods which generate gases at the counter-electrode is not troublesome. The flow–batch system has been evaluated for determination of bromine index and bromine number (relative to the total reactive olefin content) in petrochemicals according to an ASTM procedure. Typical precision (R.S.D.) is between 0.5 and 6% for different petrochemicals whose bromine number/index vary from 1000 to 10mg of bromine per 100g of sample, respectively. Recoveries for standard additions are between 92 and 123% for 10mg of Br₂ per 100g increments and 98 to 101% for 100mg per 100g increments. Accuracy of the proposed system was evaluated against results obtained by the standard ASTM with no significant difference detected at 95% confidence level.

Keywords: Flow analysis; Flow–batch titration; Coulometry; Biamperometry; Bromine index; Bromine number; Petrochemicals

Electronic tongues in flow analysis by A. Gutés; F. Céspedes; M. del Valle (pp. 90-96).

This review presents the evolution of recent flow-based analytical systems, characterized by the use of arrays of sensors as a detection scheme. For the proper processing of the complex responses generated, the systems require the use of advanced chemometric treatment, in which received the term “electronic tongue”. Applications employing the flow injection analysis (FIA) and sequential injection analysis (SIA) are described. Chronologically, the progresses made by different research groups are shown, emphasizing their final applications in real problem solving.

Keywords: Electronic tongue; Flow injection analysis; Sequential injection analysis; Classification tool; Multivariate determination

Use of sequential injection analysis to construct an electronic-tongue by Daniel Calvo; Alejandro Durán; Manel del Valle (pp. 97-104).

An electronic tongue based on the transient response of an array of non-specific-response potentiometric sensors was developed. A sequential injection analysis (SIA) system was used in order to automate its training and operation. The use of the transient recording entails the dynamic nature of the sensor's response, which can be of high information content, of primary ions and also of interfering ions; these may better discriminated if the kinetic resolution is added. This work presents the extraction of significant information contained in the transient response of a sensor array formed by five all-solid-state potentiometric sensors. The tool employed was the Fourier transform, from which a number of coefficients were fed into an artificial neural network (ANN) model, used to perform a quantitative multidetermination. The studied case was the analysis of mixtures of calcium, sodium and potassium. Obtained performance is compared with the more traditional automated electronic tongue using final steady-state potentials.

Keywords: Potentiometric sensor array; Electronic tongue; Sequential injection analysis; Fourier transform; Artificial neural network

Sequential injection chemiluminescence immunoassay for nonionic surfactants by using magnetic microbeads by RuiQi Zhang; Hizuru Nakajima; Nobuaki Soh; Koji Nakano; Takashi Masadome; Kazumi Nagata; Kazuhira Sakamoto; Toshihiko Imato (pp. 105-113).

A rapid and sensitive immunoassay based on a sequential injection analysis (SIA) using magnetic microbeads for the determination of alkylphenol polyethoxylates (APnEOs) is described. An SIA system was constructed from a syringe pump, a switching valve, a flow-through type immunoreaction cell equipped with a photon counting unit and a neodymium magnet. Magnetic beads, to which an anti-APnEOs monoclonal antibody was immobilized, were used as a solid support in an immunoassay. The introduction, trapping and release of the magnetic beads in and from the immunoreaction cell were controlled by means of a neodymium magnet and adjusting the flow of a carrier solution. The immunoassay was based on an indirect competitive immunoreaction of an anti-APnEOs monoclonal antibody immobilized on the magnetic beads with a sample APnEOs and a horseradish peroxidase (HRP)-labeled APnEOs in the same sample solution, and was based on the subsequent chemiluminscence reaction of HRP on the magnetic microbeads with a luminol solution containing hydrogen peroxide and p-iodophenol. The anti-APnEOs antibody was immobilized on the magnetic microbeads by coupling the antibody with the magnetic beads after activation of a carboxylate moiety on the surface of the magnetic beads that had been coated with a polylactic acid film. The antibody immobilized magnetic beads were introduced in the immunoreaction cell and trapped in it by the neodymium magnet, which was equipped beneath the immunoreaction cell. An APnEOs sample solution containing the HRP-labeled APnEOs at a constant concentration, and a luminol solution containing hydrogen peroxide and p-iodophenol were sequentially introduced into the immunoreaction cell, according to an SIA programmed sequence. Chemiluminescence emission was monitored by means of a photon counting unit located at the upper side of the immunoreaction cell by collecting the emitted light with a lens. A typical sigmoidal calibration curve was obtained, when the logarithm of the concentration of APnEOs was plotted against the chemiluminescence intensity as the number of photons in 100ms using standard APnEOs sample solutions at various concentrations (0–1000ppb) under optimum conditions. The lower detection limit defined as IC₈₀ is ca 10ppb. The time required for analysis is less than 15min per a sample. The present method was successfully applied to the determination of APnEOs in river water.

Keywords: Sequential injection analysis; Nonionic surfactants; Chemiluminescence; Magnetic microbeads; Immunoassay

Sequential injection analysis (SIA)-chemiluminescence determination of indomethacin using tris[(2,2′-bipyridyl)]ruthenium(III) as reagent and its application to semisolid pharmaceutical dosage forms by Kateřina Mervartová; Miroslav Polášek; José Martínez Calatayud (pp. 114-121).

Automated sequential injection (SIA) method for chemiluminescence (CL) determination of nonsteroidal anti-inflammatory drug indomethacin (I) was devised. The CL radiation was emitted in the reaction ofI (dissolved in aqueous 50% v/v ethanol) with intermediate reagent tris(2,2′-bipyridyl)ruthenium(III) (Ru(bipy)₃³⁺) in the presence of acetate. The Ru(bipy)₃³⁺ was generated on-line in the SIA system by the oxidation of 0.5mM tris(2,2′-bipyridyl)ruthenium(II) (Ru(bipy)₃²⁺) with Ce(IV) ammonium sulphate in diluted sulphuric acid. The optimum sequence, concentrations, and aspirated volumes of reactant zones were: 15mM Ce(IV) in 50mM sulphuric acid 41μL, 0.5mM Ru(bipy)₃²⁺ 30μL, 0.4M Na acetate 16μL andI sample 15μL; the flow rates were 60μLs⁻¹ for the aspiration into the holding coil and 100μLs⁻¹ for detection. Calibration curve relating the intensity of CL (peak height of the transient CL signal) to concentration ofI was curvilinear (second order polynomial) for 0.1–50μMI ( r=0.9997; n=9) with rectilinear section in the range 0.1–10μMI ( r=0.9995; n=5). The limit of detection (3 σ) was 0.05μMI. Repeatability of peak heights (R.S.D., n=10) ranged between 2.4% (0.5μMI) and 2.0% (7μMI). Sample throughput was 180h⁻¹. The method was applied to determination of 1 to 5% ofI in semisolid dosage forms (gels and ointments). The results compared well with those of UV spectrophotometric method.

Keywords: Indomethacin; Sequential injection analysis; Chemiluminescence; Tris(bipyridyl)ruthenium complex; Pharmaceuticals; Semisolid dosage forms

On-line coupling of sequential injection extraction with restricted-access materials and post-column derivatization for sample clean-up and determination of propranolol in human plasma by Dalibor Šatínský; Hugo S. Serralheiro; Petr Solich; Alberto N. Araújo; Maria C.B.S.M. Montenegro (pp. 122-128).

The presented paper deals with a new methodology for direct determination of propranolol in human plasma. The methodology described is based on sequential injection analysis technique (SIA) coupled with solid phase extraction (SPE) column based on restricted access materials (RAM). Special RAM column containing 30μm polymeric material— N-vinylacetamide copolymer was integrated into the sequential injection manifold. SIA–RAM system was used for selective retention of propranolol, while the plasma matrix components were eluted with two weak organic solutions to waste.Due to the acid–basic and polarity properties of propranolol molecule and principles of reversed-phase chromatography, it was possible to retain propranolol on the N-vinylacetamide copolymer sorbent (Shodex MSpak PK-2A 30μm (2mm×10mm)). Centrifuged plasma samples were aspirated into the system and loaded onto the column using acetonitrile–water (5:95, v/v), pH 11.00, adjusted by triethylamine. The analyte was retained on the column while proteins contained in the sample were removed to waste. Interfering endogenous substances complicating detection were washed out by acetonitrile–water (15:85), pH 11.00 in the next step. The extracted analyte was eluted by means of tetrahydrofuran–water (25:75), pH 11.00 to the fluorescence detector (emission filter 385nm). The whole procedure comprising sample pre-treatment, analyte detection and column reconditioning took about 15min. The recoveries of propranolol from undiluted plasma were in the range 96.2–97.8% for three concentration levels of analyte. The proposed SIA–RAM method has been applied for direct determination of propranolol in human plasma.

Keywords: Sequential injection analysis; Solid phase extraction; Restricted access materials; Propranolol; Human plasma; Sample preparation

An overview of sequential injection chromatography by Petr Chocholouš; Petr Solich; Dalibor Šatínský (pp. 129-135).

New generation of sequential injection analysis (SIA) called sequential injection chromatography (SIC) has already been consolidated as a good alternative of high performance liquid chromatography (HPLC) for fast analysis of simple samples. Benefits of flow methods are automation, miniaturization and low sample and mobile phase consumption. Implementation of short monolithic chromatographic column into SIA opens new area—on-line chromatographic separation of multi-compound sample in low-pressure flow system, with the advantage of flow programming and possibility of sample manipulation. In the presented review the potential of SIC and its comparison with HPLC for determination of pharmaceutical mixtures is discussed and outlines past and recent trends focused on separation with SIC.

Keywords: Sequential injection chromatography; Monolithic column; Pharmaceutical analysis

A hybrid FIA/HPLC system incorporating monolithic column chromatography by Jacqui L. Adcock; Paul S. Francis; Kent M. Agg; Graham D. Marshall; Neil W. Barnett (pp. 136-141).

We have combined the generation of solvent gradients using milliGAT pumps, chromatographic separations with monolithic columns and chemiluminescence detection in an instrument manifold that approaches the automation and separation efficiency of HPLC, whilst maintaining the positive attributes of flow injection analysis (FIA), such as manifold versatility, speed of analysis and portability. As preliminary demonstrations of this hybrid FIA/HPLC system, we have determined six opiate alkaloids (morphine, pseudomorphine, codeine, oripavine, ethylmorphine and thebaine) and four biogenic amines (vanilmandelic acid, serotonin, 5-hydroxyindole-3-acetic acid and homovanillic acid) in human urine, using tris(2,2′-bipyridyl)ruthenium(III) and acidic potassium permanganate chemiluminescence detection.

Keywords: Flow injection analysis; Gradient elution; Monolithic column chromatography; Chemiluminescence detection; Neurotransmitter metabolites

Determination of cilnidipine, a new calcium antagonist, in human plasma using high performance liquid chromatography with tandem mass spectrometric detection by Xianhua Zhang; Suodi Zhai; Rongsheng Zhao; Jin Ouyang; Xiaoguang Li; Willy R.G. Baeyens (pp. 142-146).

A rapid, sensitive and reliable high performance liquid chromatographic method coupled with tandem mass spectrometry (HPLC–MS/MS) has been developed and validated for the determination of cilnidipine, a relatively new calcium antagonist, in human plasma. The reversed-phase chromatographic system was interfaced with a TurboIonSpray (TIS) source. Nimodipine was employed as the internal standard (IS). Sample extracts following protein precipitation were injected into the HPLC–MS/MS system. The analyte and IS were eluted isocratically on a C18 column, with a mobile phase consisting of CH₃OH and NH₄Ac (96:4, v/v). The ions were detected by a triple quadrupole mass spectrometric detector in the negative mode. Quantification was performed using multiple reaction monitoring (MRM) of the transitions m/ z 491.2→122.1 and m/ z 417.1→122.1 for cilnidipine and for the IS, respectively. The analysis time for each run was 3.0min. The calibration curve fitted well over the concentration range of 0.1–10ngmL⁻¹, with the regression equation Y=(0.103±0.002) X+(0.014±0.003) ( n=5), r=0.9994. The intra-day and inter-day R.S.D.% were less than 12.51% at all concentration levels within the calibration range. The recoveries were between 92.71% and 97.64%. The long-term stability and freeze-thaw stability were satisfying at each level. The present method provides a modern, rapid and robust tool for pharmacokinetic studies of cilnidipine.

Keywords: Cilnidipine; Nimodipine; High performance liquid chromatographic method coupled with tandem mass spectrometry (HPLC–MS/MS); Human plasma

Flow-injection determination of total organic fluorine with off-line defluorination reaction on a solid sorbent bed by Jacek Musijowski; Marek Trojanowicz; Bogdan Szostek; José Luis Fontes da Costa Lima; Rui Lapa; Hiroki Yamashita; Toshio Takayanagi; Shoji Motomizu (pp. 147-154).

Considering recent reports on widespread occurrence and concerns about perfluoroalkyl substances (PFAS) in environmental and biological systems, analysis of these compounds have gained much attention in recent years. Majority of analyte-specific methods are based on a LC/MS/MS or a GC/MS detection, however many environmental or biological studies would benefit from a total organic fluorine (TOF) determination. Presented work was aimed at developing a method for TOF determination. TOF is determined as an amount of inorganic fluoride obtained after defluorination reaction conducted off-line using sodium biphenyl reagent directly on the sorbent without elution of retained analytes. Recovered fluoride was analyzed using flow-injection system with either fluorimetric or potentiometric detection. The TOF method was tested using perfluorocarboxylic acids (PFCA), including perfluorooctanoic acid (PFOA), as model compounds. Considering low concentrations of PFAS in natural samples, solid-phase extraction as a preconcentration procedure was evaluated. Several carbon-based sorbents were tested, namely multi-wall carbon nanotubes, carbon nanofibres and activated carbon. Good sorption of all analytes was achieved and defluorination reaction was possible to carry out directly on a sorbent bed. Recoveries obtained for PFCAs, adsorbed on an activated carbon sorbent, and measured as TOF, were 99.5±1.7, 110±9.4, 95±26, 120±32, 110±12 for C4, C6, C8, C10 and C12-PFCA, respectively. Two flow systems that would enable the defluorination reaction and fluoride determination in a single system were designed and tested.

Keywords: Perfluorocarboxylic acids; Solid-phase extraction; Flow-injection analysis; Total organic fluorine; Sodium biphenyl

Flow-through solid-phase reflectometric method for simultaneous multiresidue determination of nitrophenol derivatives by Matías Manera; Manuel Miró; José Manuel Estela; Víctor Cerdà; Marcela A. Segundo; José L.F.C. Lima (pp. 155-163).

In this paper, a flow-through optosensor based on diffuse reflectance spectroscopy and multivariate regression modelling is proposed for simultaneous multiresidue determination of trace level concentrations of nitro-substituted phenols. The optrode integrates on-line anion-exchange sorptive preconcentration and matrix removal with direct detection of sorbed species onto the sensing layer and chemometric deconvolution of overlapped spectra. After recording of the reflectometric spectrum, fast chemosensor regeneration is accomplished with an acidic methanolic eluent followed by a metered volume of alkaline solution. The full automation of the analytical procedure is ensured by flow-programming as executed via a software-controlled multisyringe pump and a set of multiposition and solenoid valves.Under the optimized chemical and physical variables, the 3 σ_blank detection limits for 2-, and 4-nitrophenol and 2,4-dinitrophenol were 0.69, 0.42 and 0.37μgL⁻¹, respectively, for a sample loading volume of 4.0mL with enrichment factors of 73, 74 and 81, respectively, and repeatability better than 3.0%. The analytical applicability of the optosensing system was asserted by the satisfactory results attained in its application to monitoring of nitrophenol derivatives in spiked environmental waters including highly saline matrices via the standard additions method.

Keywords: Optical sensor; Sorptive preconcentration; Extraction membrane; Nitrophenol derivatives; Environmental waters

Flow-through optosensor combined with photochemically induced fluorescence for simultaneous determination of binary mixtures of sulfonamides in pharmaceuticals, milk and urine by Javier López Flores; María L. Fernández de Córdova; Antonio Molina Díaz (pp. 164-171).

A sensitive and selective flow-through optosensor implemented with photochemically induced fluorescence (PIF) is proposed for the simultaneous determination of mixtures sulfamethoxazole/sulfanilamide and sulfathiazole/sulfanilamide. The resolution was accomplished by placing in the flow system a minicolumn filled with an appropriate solid support. Whereas one of the sulfonamides is not retained in the minicolumn and is determined by measuring its native fluorescence on the solid surface of the sensing microbeads in the detection area, the other one is retained and, after its elution, it is photochemically converted into a strongly fluorescent photoproduct which is transitorily retained on the sensing support in the flow cell and monitored. Linear calibration graphs were obtained over a concentration range of 2–3 orders of magnitude. The detection limits for the determination of sulfamethoxazole, sulfanilamide and sulfathiazole are 8.1, 2.9 and 5.7ngmL⁻¹, respectively. The method was applied to pharmaceuticals, milk and human urine. The recovery of sulfamethoxazole from pharmaceuticals was 102.5% indicating no interference from trimethoprim which is not photochemically active. The recoveries for urine and milk samples fortified with sulfonamides at levels between 0.1 and 0.7μgmL⁻¹ agreed within 95.0–107.5% of spiked levels.

Keywords: Multi-optosensor; Sulfamethoxazole; Sulfathiazole; Sulfanilamide; Photochemically induced fluorescence; Milk; Urine; Pharmaceuticals

Flow-injection determination of acetone with diazotized anthranilic acid through a fluorescent reaction intermediate by C. García de María; K.B. Hueso Domínguez; N. Martín Garrido (pp. 172-176).

Acetone and diazotized anthranilic acid react in alkaline solution, giving a fluorescent intermediate that can be measured at excitation and emission wavelengths of 305 and 395nm, respectively. Based on this, a fluorimetric flow-injection method is proposed for the determination of acetone in aqueous solution. Under the proposed conditions, acetone can be detected at concentrations higher than 8×10⁻⁷M, with a linear application range from 1×10⁻⁶ to 2×10⁻⁴M and an R.S.D. of 2.7% (1.0×10⁻⁵M, n=10). A sampling frequency of 24h⁻¹ is achieved. Some potentially interfering species are investigated.

Keywords: Acetone; Flow injection; Fluorimetry; Anthranilic acid

Spectrophotometric simultaneous determination of nitrite, nitrate and ammonium in soils by flow injection analysis by C.E. López Pasquali; P. Fernández Hernando; J.S. Durand Alegría (pp. 177-182).

A new rapid flow injection procedure for the simultaneous determination of nitrate, nitrite and ammonium in single flow injection analysis system is proposed. The procedure combines on-line reduction of nitrate to nitrite and oxidation of ammonium to nitrite with spectrophotometric detection of nitrite by using the Griess-llosvay reaction. The formed azo dye was measured at 543nm. The influence of reagent concentration and manifold parameters were studied. Nitrite, nitrate and ammonium can be determined within the range of 0.02–1.60μgmL⁻¹, 0.02–1.60μgmL⁻¹ and 0.05–1.40μgmL⁻¹, respectively. R.S.D. values ( n=10) were 2.66; 1.41 and 3.58 for nitrate, nitrite and ammonium, respectively. This procedure allows the determination and speciation of inorganic nitrogen species in soils with a single injection in a simple way, and high sampling rate (18h⁻¹). Detection limits of 0.013, 0.046 and 0.047μgmL⁻¹were achieved for nitrate, nitrite and ammonium, respectively. In comparison with others methods, the proposed one is more simple, it uses as single chromogenic reagent less injection volume (250mL in stead of 350mL) and it has a higher sampling rate.

Keywords: Nitrite; Nitrate; Ammonium; Simultaneous; Spectrophotometry; Flow injection analysis

Exploiting kinetic spectrophotometric determination of captopril, an angiotensin-converting enzyme inhibitor, in a multi-pumping flow system by João A.V. Prior; João L.M. Santos; José L.F.C. Lima (pp. 183-187).

The implementation of a differential kinetic spectrophotometric method for the determination of angiotensin-converting-enzyme inhibitors in pharmaceutical formulations is described. The determination method was based on the monitoring (350nm) of the reaction between captopril and iodate, in the presence of iodide, versus time and was fully automated by exploiting the multi-pumping flow concept. The developed multi-pumping flow system included four discretely actuated solenoid micro-pumps as unique flow manifold active components. The automatic control of the solenoid micro-pumps, under time-based and pulse-counting routines, allowed the implementation of a reliable and versatile analytical determination, with the additional advantage of permitting a runtime access to important analytical parameters, such as flow rate, sample insertion and reagent addition synchronisation, facilitating this way the establishment of an approach for kinetic measurements, directly due to the efficient solution handling and accurate timing control.A linear range of determination was verified for captopril concentrations between 10.0 and 60.0μgmL⁻¹ with a sample throughput of about 100 determinations per hour. The results were in agreement with those obtained by the reference procedure with relative deviations between 1.81 and 4.48%.

Keywords: Multi-pumping; Flow analysis; Kinetic; Pulsed flow; Captopril; Spectrophotometry

Online assay of bone specific alkaline phosphatase with a flow injection-bead injection system by Supaporn Kradtap Hartwell; Duangporn Somprayoon; Prachya Kongtawelert; Siriwan Ongchai; Olarn Arppornchayanon; Lucksagoon Ganranoo; Somchai Lapanantnoppakhun; Kate Grudpan (pp. 188-193).

Alkaline phosphatase (ALP) has been used as one of the biomarkers for bone resorption and liver diseases. Normally, total alkaline phosphatase is quantified along with other symptoms to determine the releasing source of the alkaline phosphatase. A semi-automated flow injection-bead injection system was proposed to conveniently and selectively assay bone alkaline phosphatase (BALP) based on its specific binding to wheat germ coated beads. Amount of BALP in serum was determined from the intensity of the yellow product produced from bound BALP on the retained beads and its substrate pNPP. The used beads were discarded and the fresh ones were introduced for the next analysis. The reaction cell was designed to be opened and closed using a computer controlled solenoid valve for a precise incubation time. The performance of the proposed system was evaluated by using it to assay BALP in human serum. The results were compared to those obtained by using a commercial ELISA kit. The system is proposed to be an easy and cost effective system for quantification of BALP as an alternative to batch wise wheat germ specific binding technique.

Keywords: Bone alkaline phosphatase; Wheat germ; Flow injection; Bead injection

Potentiometric flow-injection system for determination of alkaline phosphatase in human serum by Dominika Ogończyk; Robert Koncki (pp. 194-198).

A flow-injection system for detection of alkaline phosphatase (ALP) activity in human serum samples has been developed. As a specific and inexpensive ALP substrate for this kinetic assay monofluorophosphate (MFP) was applied. For detection of fluoride ions, generated in the course of the biocatalytic hydrolysis of MFP, conventional fluoride ion-selective electrode based on LaF₃-crystalline membrane was applied. After optimization the system allows analysis of human serum with high selectivity and relatively short time of analysis (5–6samplesh⁻¹). Volume of serum required for analysis is 0.05mL. The system is useful for determination of the enzyme activity in human serum samples at physiological and pathological levels as well as for detection of isoenzymatic forms of ALP.

Keywords: Alkaline phosphatase; Human serum; Flow-injection analysis; Potentiometry

Flow injection visible diffuse reflectance quantitative analysis of nickel by Matthieu Tubino; Carlos A.R. Queiroz (pp. 199-204).

Flow injection (FI) methodology, using diffuse reflectance in the visible region of the spectrum, for the analysis of nickel, precipitated in the form of dimethylglyoximate, is presented. A reflectance cell, constructed in polytetrafluoroethylene, using a LED (light emitting diode) as light source and a LDR (light dependent resistor) as detector, is described. The analytical signal ( S) correlates with nickel concentration ( C) between 1.6×10⁻⁴ and 6.6×10⁻⁴molL⁻¹. This correlation is described by the equation S=−1.108+3.314×10⁴ C−2.081×10⁷ C² ( r=0.9996). The experimentally observed limit of detection is about 1.3×10⁻⁴molL⁻¹, as in lower concentrations the formation of precipitate is not observed. The experimental quantitation limit is about 1.6×10⁻⁴molL⁻¹. The mean R.S.D. (relative standard deviation) is about 2.7%. Samples containing nickel were analyzed and the results obtained in this method were compared with those of other methods using the statistical Student's t-test.

Keywords: Flow injection; Nickel; Determination; Diffuse reflectance; Visible; Dimethylglyoxime

Dithiocarbamate functionalized or surface sorbed Merrifield resin beads as column materials for on line flow injection–flame atomic absorption spectrometry determination of lead by R.S. Praveen; G.R.K. Naidu; T. Prasada Rao (pp. 205-213).

This article describes the preparation of dithiocarbamate immobilized/functionalized and diethylammonium dithiocarbamate (DDTC) sorbed Merrifield Chloromethylated Resin (MCR) beads and comparison of these materials for on-line flow injection (FI)–flame atomic absorption spectrometry (FAAS) determination of lead. The above two materials enrich lead quantitatively over an identical optimal pH range (8.0–9.0), a preconcentration/loading time (up to 4min) and elution with acidified methanol (a minimum of 0.01molL⁻¹ HNO₃ in methanol). However, the detection limit for lead using dithiocarbamate functionalized MCR beads is 1.3μgL⁻¹ compared to 3μgL⁻¹ for DDTC sorbed MCR beads. Again, the sensitivity enhancement over direct FAAS signal is 48- and 27-fold, respectively. In addition, dithiocarbamate functionalized MCR beads offers better precision compared to DDTC sorbed MCR beads as the corresponding relative standard deviation (R.S.D.) values for five successive determinations of 0.20μgmL⁻¹ are 1.44 and 4.36%, respectively. The accuracy of the developed on-line FI–FAAS procedure employing dithiocarbamate functionalized MCR beads as column material was tested by analyzing Certified Reference Material (CRM) of soil (IAEA soil-7) and marine sediment reference material (MESS-3) supplied by International Atomic Energy Agency (IAEA), Vienna and National Research Council (NRC), Canada, respectively. Furthermore, the developed procedure has been successfully tested for the analysis of surface, pond, ground and effluent water and soil samples collected from the vicinity of lead acid battery industry in India.

Keywords: Chemical immobilization; Surface sorption; Dithiocarbamate; Lead; Flow injection-flame atomic absorption spectrometry; Waters and soils

Flow injection on-line dilution for zinc determination in human saliva with electrothermal atomic absorption spectrometry detection by Margarita Burguera-Pascu; Alberto Rodríguez-Archilla; José Luis Burguera; Marcela Burguera; Carlos Rondón; Pablo Carrero (pp. 214-220).

An automated method is described for the determination of zinc in human saliva by electrothermal atomic absorption spectrometry (ET AAS) after on-line dilution of samples with a significant reduction of sample consumption per analysis (<0.4mL including the dead volume of the system). In order to fulfill this aim without changing the sample transport conduits during the experiments, a flow injection (FI) dilution system was constructed. Its principal parts are: one propulsion device (peristaltic pump, PP) for either samples, standards or washing solution all located in an autosampler tray and for the surfactant solution (Triton X-100) used as diluent, and a two-position time based solenoid injector (TBSI₁) which allowed the introduction of 10μL of either solution in the diluent stream. To avoid unnecessary waste of samples, the TBSI₁ also permitted the recirculation of the solutions to their respective autosampler cups. The downstream diluted solution fills a home made sampling arm assembly. The sequential deposition of 20μL aliquots of samples or standards on the graphite tube platform was carried out by air displacement with a similar time based solenoid injector (TBSI₂). The dilution procedure and the injection of solutions into the atomizer are computer controlled and synchronized with the operation of the temperature program. Samples or standards solutions were submitted to two drying steps (at 90 and 130°C), followed by pyrolysis and atomization at 700 and 1700°C, respectively. The aqueous calibration was linear up to 120.0μgL⁻¹ for diluted standard solutions/samples and its slope was similar ( p>0.05) to the standard addition curve, indicating lack of matrix effect. The precision tested by repeated analysis of real saliva samples was less than 3% and the detection limit (3 σ) was of 0.35μgL⁻¹. To test the accuracy of the proposed procedure, recovery tests were performed, obtaining mean recovery of added zinc of 97.8±1.3%. Furthermore, Zn values estimated by the procedure developed in this work were compared with those obtained by a standard addition flame-AAS method applied to 20 randomly selected saliva samples. No significant differences ( p>0.05) were obtained between the two methods. Zinc levels in saliva samples from 44 healthy volunteers, 15 male and 29 female, with ages between 20 and 51 years (mean 30.50±9.14 years) were in the range 22–98μgL⁻¹ (mean of 55±17μgL⁻¹), similar to some and different from others reported in the literature. It was found that zinc values for male were statistically higher ( p=0.006) than for female.

Keywords: On-line dilution; Flow injection-electrothermal atomic absorption spectrometry (FI-ET AAS); Saliva samples; Baseline zinc levels; Contamination-free determination

Flow injection determination of lead and cadmium in hair samples from workers exposed to welding fumes by R.M. Cespón-Romero; M.C. Yebra-Biurrun (pp. 221-225).

A flow injection procedure involving continuous acid leaching for lead and cadmium determination in hair samples of persons in permanent contact with a polluted workplace environment by flame atomic absorption spectrometry is proposed. Variables such as sonication time, nature and concentration of the acid solution used as leaching solution, leaching temperature, flow-rate of the continuous manifold, leaching solution volume and hair particle size were simultaneously studied by applying a Plackett–Burman design approach. Results showed that nitric acid concentration (leaching solution), leaching temperature and sonication time were statistically significant variables (confidence interval of 95%). These last two variables were finally optimised by using a central composite design. The proposed procedure allowed the determination of cadmium and lead with limits of detection 0.1 and 1.0μgg⁻¹, respectively. The accuracy of the developed procedure was evaluated by the analysis of a certified reference material (CRM 397, human hair, from the BCR). The proposed method was applied with satisfactory results to the determination of Cd and Pb in human hair samples of workers exposed to welding fumes.

Keywords: Continuous ultrasonic extraction; Hair of occupationally exposed workers; Lead; Cadmium; Flame atomic absorption spectrometry

Determination of Rh, Pd and Pt in urine samples using a pre-concentration sequential injection analysis system coupled to a quadrupole-inductively coupled plasma-mass spectrometer by Cristina M.P.V. Lopes; Agostinho A. Almeida; M. Lúcia M.F.S. Saraiva; José L.F.C. Lima (pp. 226-232).

The proposed flow system was developed in order to minimize the drawbacks related to the PGEs determination by quadrupole-inductively coupled plasma-mass spectrometry (Q-ICP-MS). It was intended not only to lower the limits of detection (LODs) but also to eliminate the interferences originating from some atomic and molecular ions produced in the argon plasma. This was accomplished by means of an on-line sample clean-up/pre-concentration step, using a chelating resin (Metalfix™ Chelamine™) in which Rh, Pd and Pt were preferably retained when compared with the interfering species.The results obtained by using the developed flow system in the analysis of urine samples are presented. With a sampling rate of 9 samples h⁻¹ (i.e., 27 determinations) and a sample consumption of ca. 10mL, the developed flow system allowed linear calibration plots up to 100ngL⁻¹ with detection limits of 1.2ngL⁻¹ (Rh), 0.4ngL⁻¹ (Pd) and 0.9ngL⁻¹ (Pt). Repeatability studies showed good precision (R.S.D.%, n=5): 3.7% (Rh); 2.6% (Pd) and 2.4% (Pt), for 10ngL⁻¹; 2.4% (Rh); 1.4% (Pd) and 1.9% (Pt), for 50ngL⁻¹; and 1.3% (Rh); 0.58% (Pd) and 0.62% (Pt), for 100ngL⁻¹. By spiking human urine samples, recovery tests were performed, and the values obtained ranged between 89% and 105% (Rh); 90% and 104% (Pd); and 93% and 105% (Pt).

Keywords: Sequential injection analysis flow system; Platinum group elements; Urine; Quadrupole-inductively coupled plasma-mass spectrometry

Matrix effect in second-order data by V. Gómez; R. Cuadros; I. Ruisánchez; M.P. Callao (pp. 233-239).

The aim of this paper is to determine the concentration of three dyes throughout the tanning process of leather using vegetable tanning agents with a sequential injection analyser with second-order data treatment. As the vegetable tanning agents used are highly absorbent species, we focus on three aspects: (i) difficulties with the resolution (ii) the reduction in the working concentration range; and (iii) matrix effects. Ideally, second-order instruments provide “second-order advantage”; i.e. calibration is possible in the presence of uncalibrated interfering species. However, if the interfering species change the instrumental response of the analyte (in scale or shape), standard additions must be used to ensure the accuracy of the estimated analyte concentration. Here we study the presence of matrix effects for three dyes in several samples in order to significantly improve the accuracy of predictions in the presence of such effects. We found that there were matrix effects in at least 80% of the samples with an alpha risk of 5%. We used this method to study the exhaustion of dyes in the dyeing process.

Keywords: Dye determination; Vegetable tanning agent; Tanning of leather; Matrix effect; Sequential injection analysis; Multivariate curve resolution

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Analytica Chimica Acta (v.600, #1-2)

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Analytica Chimica Acta (v.600, #1-2)