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Analyst CRITICAL REVIEW
Cite this: Analyst, 2014, 139, 3666
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Flow analysis in Brazil: contributions over the last four decades Alex D. Batista, Milton K. Sasaki, Fa´bio R. P. Rocha and Elias A. G. Zagatto* The main contributions of Brazilian researchers to the field of flow analysis are reviewed, with an emphasis on historical developments, conceptual aspects, system design, and analytical applications. Contributions after the advent of flow injection analysis are highlighted. Novel approaches (e.g. zone merging, zone sampling, zone trapping, multi-site detection, and multi-commutation), flow modalities (e.g. monosegmented flow analysis, flow-batch analysis, multi-pumping flow analysis), as well as the pioneering implementation of different detection techniques (e.g. potentiometry, turbidimetry, flame atomic absorption spectrometry, inductively coupled plasma-optical emission spectrometry, and gravimetry) and analytical steps (e.g. titrations, membrane-less gas diffusion, and electrolytic dissolution)
Received 10th February 2014 Accepted 1st May 2014
are highlighted. Strategies to improve analytical figures of merit and the use of the flow analyser as a tool for teaching purposes are also discussed. Contributions from Brazilian workers in the context of system miniaturization, “green” chemistry, analysis of complex samples, novel strategies and materials for in-line
DOI: 10.1039/c4an00295d
analyte separation/concentration, and proposals for expert systems are also highlighted. The large-scale
www.rsc.org/analyst
analysis of samples of agronomical, environmental, industrial, and clinical relevance is emphasized.
Introduction Flow analysis is a branch of analytical chemistry to which much has been contributed by Brazilian workers. The large-scale application of ow injection analysis (FIA)1 resulted from the high demand for the chemical analysis of natural waters and plant digests required by projects carried out at the Centre for
Nuclear Energy in Agriculture (CENA/USP/Brazil), sponsored by the International Atomic Energy Agency (IAEA). The seminal paper that coined the expression “ow injection analysis”2 was prepared at CENA in 1975 and began the classic ten-paper series2,3 discussing the theory, methodology, and applications of FIA. Most of these papers were prepared in Brazil or were coauthored by CENA researchers, or both. A focus on solving practical problems requiring large-scale routine assays culminated in several novel approaches to FIA.
Centro de Energia Nuclear na Agricultura, Universidade de S˜ ao Paulo, P.O. Box 96, 13400-970, Piracicaba, SP, Brazil. E-mail: [email protected]
From right: Elias A.G. Zagatto, 65, is agronomical engineer (University of S˜ ao Paulo), Ph.D. in Analytical Chemistry (State University of Campinas, UNICAMP) and Full Professor at Centre for Nuclear Energy in Agriculture, CENA/USP. In 1975, he experienced the pioneer implementation of ow injection to large-scale analyses. His research has been focused on the development of advanced owbased strategies for analysis of samples of agronomic, industrial, and environmental relevance. Alex D. Batista, 27, is chemist (State University of S. Paulo), M.Sc. in Analytical Chemistry (UNICAMP), and a Ph.D. student at CENA/USP, where he is member of Prof. Rocha's research group, developing ow-based analytical methods, mainly for the determination of organic emergent pollutants by sequential injection chromatography and ow injection analysis. Milton K. Sasaki, 28, is chemist (State University of Maring´ a), expert in environmental chemistry (UNICAMP), M.Sc. in Sciences (CENA/ USP), and a Ph.D. student at CENA/USP developing ow-based methods with spectrometric detection at the Prof. Zagatto's research group. F´ abio R.P. Rocha, 41, is chemist, Ph.D. in Chemistry (Federal University of S˜ ao Carlos) and Associate Professor at CENA/USP. His main research deals with instrumentation, automation, optical detectors linked to ow analysis, as well as green analytical chemistry.
3666 | Analyst, 2014, 139, 3666–3682
This journal is © The Royal Society of Chemistry 2014
View Article Online
Published on 01 May 2014. Downloaded by State University of New York at Stony Brook on 28/10/2014 07:08:08.
Critical Review
Many contributions to the early developments during the 1970s were jointly achieved by Brazilian and IAEA workers, including: (i) a system for the large-scale determination of phosphate in plant digests;4 (ii) the incorporation of potentiometric detection in the determination of total nitrogen in plant materials5 and in the rapid analysis of soil extracts and blood serum;6 (iii) the proposal of stream splitting for the determination of chloride over a wide range of concentrations in batches of samples with a high variability in analyte concentration;7 (iv) simultaneous determinations;8 and (v) the implementation of turbidimetry in ow analysis for the determination of sulphate.9 These contributions involved manual syringe-based sample injection and, with this approach, the carrier ow-rate increases suddenly during injection. This leads to an instantaneous instability in the ow system, especially when using conuent streams. A damper placed near the injection port minimizes this effect10 and the use of a sliding-bar injector circumvented this drawback, as demonstrated in the spectrophotometric determination of molybdenum in plants using liquid–liquid extraction.11 Flow stability was maintained and the separation of immiscible phases was accomplished efficiently. The double-proportional injector, a development of the sliding-bar injector, allowed the sample and a reagent solution to be inserted simultaneously into convergent carrier streams; this is the essence of the zone-merging approach.12 This device was also useful for achieving intermittent ows.13 The potential of the injector-commuter was expanded with the use of electronic operation, which allowed the implementation of zone sampling, zone trapping, and system reconguration by relocating devices. These approaches are discussed later in this paper. The need to modify reaction conditions to implement a given analytical method in a ow injection system became evident during the early development of FIA in Brazil. A noteworthy example is the determination of boron in plant materials using azomethine-H.14 The original procedure was carried out in a segmented ow analyser; the colour-forming reaction took place under slightly acidic conditions (pH 5.0) and about 2 h were needed to complete the reaction. In the FIA system, neutral conditions (pH 7.3) were used and the maximum absorbance was reached aer 2 min. Modication of the reaction conditions allowed the development of a rugged ow injection procedure; although the sensitivity was slightly reduced, a sampling rate of 60 samples per hour was attained. The main contributions of Brazilian workers to the development of ow analysis, including novel concepts, system modalities, real-time manifold modications, and applications are discussed in this paper. Fig. 1 shows a timeline of the main contributions.
Analyst
accountable for about 2.0% of the global production of scientic papers.15 A recent overview of the number of chemistry papers produced by Brazilian workers based on 45 international journals16 showed that analytical chemistry is one of the most prominent areas. Flow analysis is one of the most established elds in analytical chemistry and accounts for 15.7% of the papers published by Brazilian workers in these journals. These papers were produced by 30 different institutions17–50 and received more than 13 300 citations, which corresponds to 21.8% of the total number of citations of papers on analytical chemistry published by Brazilian workers. Moreover, of the 30 most cited Brazilian papers in analytical chemistry, 10 refer to ow analysis. The annual number of publications on ow analysis published by Brazilian researchers has been nearly constant since 1998 (about 60 publications per year; Fig. 2). Reference to these publications has been increasing and approached 1500 citations in 2012. Most of these papers have been published in journals with high impact factors (Table 1), such as Analytica Chimica Acta (20.96%) and Talanta (15.44%), which also concentrate papers on ow analysis from other countries. Brazilian papers in The Analyst correspond to 4.81%, including highly relevant work.9,29,51,52 In spite of being a relatively new journal, 0.71% of the Brazilian papers in this eld of research have been published in Analytical Methods. Selected contributions of different Brazilian research groups to ow analysis are presented in Table 2. In addition to collaborations with workers in Denmark and the USA,5–7 ow analysis has inspired the fruitful cooperation of Brazilian workers with colleagues from Argentina,53 Austria,54 Canada,55,56 Chile,57 Cuba,58 the UK,59,60 Germany,61 Greece,62 India,63 Italy,64 Japan,65 Mexico,66 Poland,67 Portugal,68–70 Slovenia,40 Spain,62,71–74 Sweden,75 The Netherlands,76 and Uruguay.77
Real-time manifold modifications A remarkable characteristic of ow analysers is that the manifolds can be simply recongured to implement different analytical tasks. Brazilian workers have made important contributions in this area of research, most of these taking advantage of the versatility of the sliding-bar injectorcommuter.11 Commutation can be fully exploited with this device, allowing the modication of sample processing,78 as shown in Fig. 3. In spite of the high versatility and low cost of this component, the sliding-bar commuter is not available commercially, which hinders its widespread use. This drawback has been circumvented by replacing it by commercially available valves, as demonstrated by Japanese workers.79 In fact, one section of a three-piece sliding-bar commuter can be replaced by three three-way solenoid valves.80
Scientometrics The publication of scientic papers by Brazilian researchers has increased signicantly in recent years and Brazil has consequently moved from the 16th (2004) to the 13th (2012) position in the worldwide scientic rankings. Brazil is currently
This journal is © The Royal Society of Chemistry 2014
Zone sampling Controlled dispersion is inherent to FIA, but sample dispersion cannot be increased indenitely, as the sample volume and the analytical path length cannot be freely modied. There is a
Analyst, 2014, 139, 3666–3682 | 3667
View Article Online
Published on 01 May 2014. Downloaded by State University of New York at Stony Brook on 28/10/2014 07:08:08.
Analyst
Fig. 1
Critical Review
Timeline showing the main contributions of Brazilian workers to flow analysis.
Table 1 Distribution of the publications of Brazilian workers on flow analysis in scientific journals
Journal
Impact factor (2013)
Articles (%)
Anal. Chim. Acta Talanta Quim. Nova J. Braz. Chem. Soc. Analyst Anal. Lett. Electroanalysis Microchem. J. Anal. Sci. J. Pharm. Biomed. Anal. Anal. Bioanal. Chem. J. Anal. At. Spectrom. J. Autom. Meth. Manag. Chem. Food Chem. J. Agric. Food Chem. Anal. Methods Others
4.344 3.498 0.737 1.283 3.969 0.965 2.817 2.879 1.569 2.853 3.659 3.155 0.565 3.334 2.906 1.855 —
20.96 15.44 8.58 7.26 4.81 4.50 3.48 3.37 2.97 1.94 1.84 1.84 1.53 0.92 0.92 0.71 18.93
minimum volume that can be reproducibly selected and the increase in wash time is critical when using long analytical path lengths. This limitation is overcome by zone sampling,81 which is a powerful tool for diluting samples, as demonstrated by the determination of potassium in plant digests by ame atomic absorption spectrometry.81 An aliquot of sample is introduced into the rst carrier stream and, aer a pre-set time interval (tZS), a portion of the dispersed zone is reproducibly selected and introduced into a second carrier stream, undergoing additional dispersion (Fig. 3a). The dispersion coefficient is then the product of those achieved in each step and the concentration of the re-sampled portion plays a relevant role. Values of the dispersion coefficient as high as 106 can be attained with this approach without hindering the analytical precision or sampling rate.82 Zone sampling is important in routine large-scale analyses in which high sample dilutions and
3668 | Analyst, 2014, 139, 3666–3682
high sample throughputs are needed. However, the performance of the ow system with zone sampling depends on reproducible timing and minimization of the pulsation of the propelling device. In addition to systems with a sliding-bar commuter, these characteristics can be achieved in ow systems exploiting multi-commutation83 or those designed with a sequential injection84 conguration. Simultaneous determinations involving different degrees of dispersion are feasible when using zone sampling, as demonstrated by the determination of aluminium and iron in plant digests.85 A small aliquot of the trailing portion of the dispersed sample zone was re-sampled and inserted into a second carrier stream for the spectrophotometric determination of aluminium, while most of the sample zone was directed to a ame atomic absorption spectrometer in which iron was determined under conditions of limited sample dispersion. In zone sampling, each tZS value corresponds to a different re-sampled aliquot, i.e. a different concentration. The entire sample zone can be examined with a tZS scan.86 By pre-setting specic values of tZS, analytical procedures relying on different, yet known, concentrations such as standard additions87 and ow titrations88 can be implemented efficiently. Calibration with a single standard solution is also feasible. Zone sampling is also used in monosegmented ow analysis. By mechanically removing the central portion of the owing sample before detection, the drawbacks inherent to the presence of the gas phase in the detector can be avoided.89 An ingenious procedure that exploits concentration gradients was proposed for the implementation of the standard additions method.90 The undispersed sample was merged with a highly reproducible dispersed zone of the analyte and measurements were carried out at denite time intervals at which the analyte concentrations had previously been determined. This approach successfully compensates for the matrix effects in atomic spectrometry, with a signicant increase in sample throughput.
This journal is © The Royal Society of Chemistry 2014
View Article Online
Critical Review
Published on 01 May 2014. Downloaded by State University of New York at Stony Brook on 28/10/2014 07:08:08.
Table 2
Analyst
Selected contributions of different Brazilian research groups to flow analysis
Application
Flow modality
Detection
Remarks
Ref.
In-line Cd concentration with multi-wall carbon nanotubes In-line Pb concentration with modied polyurethane foam Determination of total organic carbon
FIA
TS-FF-AAS
Sensitivity 640-fold better than FAAS
17
FIA
FAAS
Enrichment factor 26; sampling rate 48 h1
18
FIA
Turbidimetry
19
Binary search titration SPE with molecularly imprinted polymer Microuidic device manufactured by deep UV lithography Inexpensive gold electrodes from recordable CDs Pioneer application of internal standard method in ow analysis with amperometric detection
MCFA MCFA
UV-vis UV-vis
FIA
Fluorimetry
Microwave-assisted digestion; sampling rate 120 h1 True titration in
Analyst CRITICAL REVIEW
Cite this: Analyst, 2014, 139, 3666
View Article Online View Journal | View Issue
Flow analysis in Brazil: contributions over the last four decades Alex D. Batista, Milton K. Sasaki, Fa´bio R. P. Rocha and Elias A. G. Zagatto* The main contributions of Brazilian researchers to the field of flow analysis are reviewed, with an emphasis on historical developments, conceptual aspects, system design, and analytical applications. Contributions after the advent of flow injection analysis are highlighted. Novel approaches (e.g. zone merging, zone sampling, zone trapping, multi-site detection, and multi-commutation), flow modalities (e.g. monosegmented flow analysis, flow-batch analysis, multi-pumping flow analysis), as well as the pioneering implementation of different detection techniques (e.g. potentiometry, turbidimetry, flame atomic absorption spectrometry, inductively coupled plasma-optical emission spectrometry, and gravimetry) and analytical steps (e.g. titrations, membrane-less gas diffusion, and electrolytic dissolution)
Received 10th February 2014 Accepted 1st May 2014
are highlighted. Strategies to improve analytical figures of merit and the use of the flow analyser as a tool for teaching purposes are also discussed. Contributions from Brazilian workers in the context of system miniaturization, “green” chemistry, analysis of complex samples, novel strategies and materials for in-line
DOI: 10.1039/c4an00295d
analyte separation/concentration, and proposals for expert systems are also highlighted. The large-scale
www.rsc.org/analyst
analysis of samples of agronomical, environmental, industrial, and clinical relevance is emphasized.
Introduction Flow analysis is a branch of analytical chemistry to which much has been contributed by Brazilian workers. The large-scale application of ow injection analysis (FIA)1 resulted from the high demand for the chemical analysis of natural waters and plant digests required by projects carried out at the Centre for
Nuclear Energy in Agriculture (CENA/USP/Brazil), sponsored by the International Atomic Energy Agency (IAEA). The seminal paper that coined the expression “ow injection analysis”2 was prepared at CENA in 1975 and began the classic ten-paper series2,3 discussing the theory, methodology, and applications of FIA. Most of these papers were prepared in Brazil or were coauthored by CENA researchers, or both. A focus on solving practical problems requiring large-scale routine assays culminated in several novel approaches to FIA.
Centro de Energia Nuclear na Agricultura, Universidade de S˜ ao Paulo, P.O. Box 96, 13400-970, Piracicaba, SP, Brazil. E-mail: [email protected]
From right: Elias A.G. Zagatto, 65, is agronomical engineer (University of S˜ ao Paulo), Ph.D. in Analytical Chemistry (State University of Campinas, UNICAMP) and Full Professor at Centre for Nuclear Energy in Agriculture, CENA/USP. In 1975, he experienced the pioneer implementation of ow injection to large-scale analyses. His research has been focused on the development of advanced owbased strategies for analysis of samples of agronomic, industrial, and environmental relevance. Alex D. Batista, 27, is chemist (State University of S. Paulo), M.Sc. in Analytical Chemistry (UNICAMP), and a Ph.D. student at CENA/USP, where he is member of Prof. Rocha's research group, developing ow-based analytical methods, mainly for the determination of organic emergent pollutants by sequential injection chromatography and ow injection analysis. Milton K. Sasaki, 28, is chemist (State University of Maring´ a), expert in environmental chemistry (UNICAMP), M.Sc. in Sciences (CENA/ USP), and a Ph.D. student at CENA/USP developing ow-based methods with spectrometric detection at the Prof. Zagatto's research group. F´ abio R.P. Rocha, 41, is chemist, Ph.D. in Chemistry (Federal University of S˜ ao Carlos) and Associate Professor at CENA/USP. His main research deals with instrumentation, automation, optical detectors linked to ow analysis, as well as green analytical chemistry.
3666 | Analyst, 2014, 139, 3666–3682
This journal is © The Royal Society of Chemistry 2014
View Article Online
Published on 01 May 2014. Downloaded by State University of New York at Stony Brook on 28/10/2014 07:08:08.
Critical Review
Many contributions to the early developments during the 1970s were jointly achieved by Brazilian and IAEA workers, including: (i) a system for the large-scale determination of phosphate in plant digests;4 (ii) the incorporation of potentiometric detection in the determination of total nitrogen in plant materials5 and in the rapid analysis of soil extracts and blood serum;6 (iii) the proposal of stream splitting for the determination of chloride over a wide range of concentrations in batches of samples with a high variability in analyte concentration;7 (iv) simultaneous determinations;8 and (v) the implementation of turbidimetry in ow analysis for the determination of sulphate.9 These contributions involved manual syringe-based sample injection and, with this approach, the carrier ow-rate increases suddenly during injection. This leads to an instantaneous instability in the ow system, especially when using conuent streams. A damper placed near the injection port minimizes this effect10 and the use of a sliding-bar injector circumvented this drawback, as demonstrated in the spectrophotometric determination of molybdenum in plants using liquid–liquid extraction.11 Flow stability was maintained and the separation of immiscible phases was accomplished efficiently. The double-proportional injector, a development of the sliding-bar injector, allowed the sample and a reagent solution to be inserted simultaneously into convergent carrier streams; this is the essence of the zone-merging approach.12 This device was also useful for achieving intermittent ows.13 The potential of the injector-commuter was expanded with the use of electronic operation, which allowed the implementation of zone sampling, zone trapping, and system reconguration by relocating devices. These approaches are discussed later in this paper. The need to modify reaction conditions to implement a given analytical method in a ow injection system became evident during the early development of FIA in Brazil. A noteworthy example is the determination of boron in plant materials using azomethine-H.14 The original procedure was carried out in a segmented ow analyser; the colour-forming reaction took place under slightly acidic conditions (pH 5.0) and about 2 h were needed to complete the reaction. In the FIA system, neutral conditions (pH 7.3) were used and the maximum absorbance was reached aer 2 min. Modication of the reaction conditions allowed the development of a rugged ow injection procedure; although the sensitivity was slightly reduced, a sampling rate of 60 samples per hour was attained. The main contributions of Brazilian workers to the development of ow analysis, including novel concepts, system modalities, real-time manifold modications, and applications are discussed in this paper. Fig. 1 shows a timeline of the main contributions.
Analyst
accountable for about 2.0% of the global production of scientic papers.15 A recent overview of the number of chemistry papers produced by Brazilian workers based on 45 international journals16 showed that analytical chemistry is one of the most prominent areas. Flow analysis is one of the most established elds in analytical chemistry and accounts for 15.7% of the papers published by Brazilian workers in these journals. These papers were produced by 30 different institutions17–50 and received more than 13 300 citations, which corresponds to 21.8% of the total number of citations of papers on analytical chemistry published by Brazilian workers. Moreover, of the 30 most cited Brazilian papers in analytical chemistry, 10 refer to ow analysis. The annual number of publications on ow analysis published by Brazilian researchers has been nearly constant since 1998 (about 60 publications per year; Fig. 2). Reference to these publications has been increasing and approached 1500 citations in 2012. Most of these papers have been published in journals with high impact factors (Table 1), such as Analytica Chimica Acta (20.96%) and Talanta (15.44%), which also concentrate papers on ow analysis from other countries. Brazilian papers in The Analyst correspond to 4.81%, including highly relevant work.9,29,51,52 In spite of being a relatively new journal, 0.71% of the Brazilian papers in this eld of research have been published in Analytical Methods. Selected contributions of different Brazilian research groups to ow analysis are presented in Table 2. In addition to collaborations with workers in Denmark and the USA,5–7 ow analysis has inspired the fruitful cooperation of Brazilian workers with colleagues from Argentina,53 Austria,54 Canada,55,56 Chile,57 Cuba,58 the UK,59,60 Germany,61 Greece,62 India,63 Italy,64 Japan,65 Mexico,66 Poland,67 Portugal,68–70 Slovenia,40 Spain,62,71–74 Sweden,75 The Netherlands,76 and Uruguay.77
Real-time manifold modifications A remarkable characteristic of ow analysers is that the manifolds can be simply recongured to implement different analytical tasks. Brazilian workers have made important contributions in this area of research, most of these taking advantage of the versatility of the sliding-bar injectorcommuter.11 Commutation can be fully exploited with this device, allowing the modication of sample processing,78 as shown in Fig. 3. In spite of the high versatility and low cost of this component, the sliding-bar commuter is not available commercially, which hinders its widespread use. This drawback has been circumvented by replacing it by commercially available valves, as demonstrated by Japanese workers.79 In fact, one section of a three-piece sliding-bar commuter can be replaced by three three-way solenoid valves.80
Scientometrics The publication of scientic papers by Brazilian researchers has increased signicantly in recent years and Brazil has consequently moved from the 16th (2004) to the 13th (2012) position in the worldwide scientic rankings. Brazil is currently
This journal is © The Royal Society of Chemistry 2014
Zone sampling Controlled dispersion is inherent to FIA, but sample dispersion cannot be increased indenitely, as the sample volume and the analytical path length cannot be freely modied. There is a
Analyst, 2014, 139, 3666–3682 | 3667
View Article Online
Published on 01 May 2014. Downloaded by State University of New York at Stony Brook on 28/10/2014 07:08:08.
Analyst
Fig. 1
Critical Review
Timeline showing the main contributions of Brazilian workers to flow analysis.
Table 1 Distribution of the publications of Brazilian workers on flow analysis in scientific journals
Journal
Impact factor (2013)
Articles (%)
Anal. Chim. Acta Talanta Quim. Nova J. Braz. Chem. Soc. Analyst Anal. Lett. Electroanalysis Microchem. J. Anal. Sci. J. Pharm. Biomed. Anal. Anal. Bioanal. Chem. J. Anal. At. Spectrom. J. Autom. Meth. Manag. Chem. Food Chem. J. Agric. Food Chem. Anal. Methods Others
4.344 3.498 0.737 1.283 3.969 0.965 2.817 2.879 1.569 2.853 3.659 3.155 0.565 3.334 2.906 1.855 —
20.96 15.44 8.58 7.26 4.81 4.50 3.48 3.37 2.97 1.94 1.84 1.84 1.53 0.92 0.92 0.71 18.93
minimum volume that can be reproducibly selected and the increase in wash time is critical when using long analytical path lengths. This limitation is overcome by zone sampling,81 which is a powerful tool for diluting samples, as demonstrated by the determination of potassium in plant digests by ame atomic absorption spectrometry.81 An aliquot of sample is introduced into the rst carrier stream and, aer a pre-set time interval (tZS), a portion of the dispersed zone is reproducibly selected and introduced into a second carrier stream, undergoing additional dispersion (Fig. 3a). The dispersion coefficient is then the product of those achieved in each step and the concentration of the re-sampled portion plays a relevant role. Values of the dispersion coefficient as high as 106 can be attained with this approach without hindering the analytical precision or sampling rate.82 Zone sampling is important in routine large-scale analyses in which high sample dilutions and
3668 | Analyst, 2014, 139, 3666–3682
high sample throughputs are needed. However, the performance of the ow system with zone sampling depends on reproducible timing and minimization of the pulsation of the propelling device. In addition to systems with a sliding-bar commuter, these characteristics can be achieved in ow systems exploiting multi-commutation83 or those designed with a sequential injection84 conguration. Simultaneous determinations involving different degrees of dispersion are feasible when using zone sampling, as demonstrated by the determination of aluminium and iron in plant digests.85 A small aliquot of the trailing portion of the dispersed sample zone was re-sampled and inserted into a second carrier stream for the spectrophotometric determination of aluminium, while most of the sample zone was directed to a ame atomic absorption spectrometer in which iron was determined under conditions of limited sample dispersion. In zone sampling, each tZS value corresponds to a different re-sampled aliquot, i.e. a different concentration. The entire sample zone can be examined with a tZS scan.86 By pre-setting specic values of tZS, analytical procedures relying on different, yet known, concentrations such as standard additions87 and ow titrations88 can be implemented efficiently. Calibration with a single standard solution is also feasible. Zone sampling is also used in monosegmented ow analysis. By mechanically removing the central portion of the owing sample before detection, the drawbacks inherent to the presence of the gas phase in the detector can be avoided.89 An ingenious procedure that exploits concentration gradients was proposed for the implementation of the standard additions method.90 The undispersed sample was merged with a highly reproducible dispersed zone of the analyte and measurements were carried out at denite time intervals at which the analyte concentrations had previously been determined. This approach successfully compensates for the matrix effects in atomic spectrometry, with a signicant increase in sample throughput.
This journal is © The Royal Society of Chemistry 2014
View Article Online
Critical Review
Published on 01 May 2014. Downloaded by State University of New York at Stony Brook on 28/10/2014 07:08:08.
Table 2
Analyst
Selected contributions of different Brazilian research groups to flow analysis
Application
Flow modality
Detection
Remarks
Ref.
In-line Cd concentration with multi-wall carbon nanotubes In-line Pb concentration with modied polyurethane foam Determination of total organic carbon
FIA
TS-FF-AAS
Sensitivity 640-fold better than FAAS
17
FIA
FAAS
Enrichment factor 26; sampling rate 48 h1
18
FIA
Turbidimetry
19
Binary search titration SPE with molecularly imprinted polymer Microuidic device manufactured by deep UV lithography Inexpensive gold electrodes from recordable CDs Pioneer application of internal standard method in ow analysis with amperometric detection
MCFA MCFA
UV-vis UV-vis
FIA
Fluorimetry
Microwave-assisted digestion; sampling rate 120 h1 True titration in
