Vapor Generation Techniques for Trace Element Analysis: Fundamental Aspects

Vapor Generation Techniques for Trace Element Analysis
Copyright
List of contributors
Contents
Preface
Reference
Abbreviations and symbols
1 Introduction to vapor generation techniques
1.1 Introduction
1.2 Limitations of current sample introduction and atomization techniques
1.3 Vapor generation techniques
1.4 Favorable features and shortcomings of VGTs
1.5 Overview of book structure and content
References
2 Chemical vapor generation by aqueous boranes
2.1 Introduction and historical background
2.1.1 Chemical vapor generation by aqueous boranes
2.1.2 Brief historical notes on boranes employed in chemical vapor generation
2.2 Borane reagents, reaction products, and apparatus
2.2.1 Stability of boranes in aqueous solution
2.2.2 Reaction products
2.2.2.1 Germanium, tin, and lead
2.2.2.2 Arsenic, antimony, and bismuth
2.2.2.3 Selenium and tellurium
2.2.2.4 Mercury and other elements
2.2.3 Chemical vapor generation by boranes other than [BH4]−
2.2.4 Chemical reactors
2.2.4.1 Batch reactors
2.2.4.2 Continuous-flow reactors
2.3 Processes and mechanisms of chemical vapor generation
2.3.1 Mechanism of hydrolysis of [BH4]−
2.3.1.1 Hydrolysis of [BH4]− is a stepwise reaction
2.3.1.2 General acid catalysis
2.3.1.3 Hydrolysis of [BH4]− under strongly acidic conditions
2.3.1.4 Hydrolysis of [BH4]− under strongly alkaline conditions
2.3.1.5 Hydrolysis of [BH4]− under intermediate pH conditions (≈3.8%3cpH%3c≈12)
2.3.2 Mechanism of acid-catalyzed hydrolysis of amine-boranes
2.3.3 Studies on the mechanism of generation of volatile hydrides
2.3.3.1 Deuterium-labeled experiments
2.3.3.2 Results of deuterium-labeled experiments
2.3.3.3 Mechanism of hydrogen transfer
2.3.4 Experimental evidence of intermediates using nonanalytical conditions
2.3.4.1 Hydrido–metal(loid) complex intermediates
2.3.4.2 Analyte–borane complex intermediates
2.3.4.2.1 Analyte–borane complexes in the generation of arsanes from arsenosugars
2.4 Factors controlling reactivity in chemical vapor generation
2.4.1 Accessibility of analyte atom to hydride
2.4.2 Role of additives
2.4.2.1 Studies on the role of additives
2.4.3 The role of pH
2.4.3.1 Activation of the analyte substrate
2.4.3.2 The role played by hydrolysis products of borane reagents
2.4.3.3 Ionization of the final products
2.5 Interferences
2.5.1 Categorization of interferences
2.5.1.1 Selectivity of borane complexes toward analyte and interfering species
2.5.2 Mutual interferences and self-interferences
2.5.3 A more general reaction model for chemical vapor generation
2.5.4 Mechanistic interference in arsane generation
2.5.4.1 Interaction of [BH4]− with metal ions and metal nanoparticles
2.6 Final remarks, open questions, and future trends
References
3 Chemical vapor generation of transition and noble metals
3.1 Introduction and background
3.2 Experimental implementations of chemical vapor generation
3.2.1 Experimental setup and detectors
3.2.2 Reaction conditions
3.2.3 Effect of additives as reaction modifiers
3.3 Efficiency of chemical vapor generation
3.4 Detailed discussion of mechanisms and fundamental processes in chemical vapor generation
3.4.1 Reaction model discussion
3.4.2 Transport properties of volatile species
3.4.3 Identity of volatile species
3.5 Shortcomings with theory, remaining problems, and limitations
3.6 Conclusions and future developments
Acknowledgements
References
4 Chemical vapor generation by aqueous phase alkylation
4.1 Introduction
4.2 CVG with tetraalkylborates
4.2.1 Historical background
4.2.2 Reaction products and applications
4.2.3 Properties and reactivity of tetraalkylborates
4.2.3.1 Interferences
4.2.3.2 Side reactions and transalkylation
4.3 CVG with trialkyloxonium salts
4.3.1 Historical background
4.3.2 Reaction products and applications
4.3.3 Properties and reactivity of trialkyloxonium
4.3.3.1 R3O+ acid hydrolysis and pH adjustment
4.3.3.2 Manipulating R3O+ salts
4.3.3.3 Reaction medium: aqueous or nonaqueous?
4.3.3.4 Interferences and other effects
4.4 Metal speciation with Grignard reagents
4.4.1 Historical background
4.4.2 Properties and reactivity of Grignard reagents
4.4.2.1 Interferences and transalkylation
4.5 Future trends and perspectives
References
5 Other chemical vapor generation techniques
5.1 Introduction
5.2 Chelate formation
5.2.1 Classical chelates
5.2.2 Online room temperature chelate vapor generation
5.2.2.1 Apparatus and optimization
5.2.2.2 Identity of volatile species and generation efficiency
5.3 Thermal chemical vapor generation
5.4 Generation of volatile oxides
5.4.1 Effect of oxide formation
5.4.2 Electrothermal vaporization of oxides
5.4.3 Volatilization of oxides from solution
5.5 Chemical vapor generation of volatile chlorides
5.5.1 Arsenic
5.5.2 Germanium
5.5.3 Tin
5.6 Chemical vapor generation of volatile fluorides
5.7 Chemical vapor generation of volatile bromides
5.8 Chemical vapor generation of volatile carbonyls
5.9 Chemical vapor generation of boron esters
5.10 Chemical vapor generation using SnCl2
5.11 Concluding remarks
References
6 Chemical vapor generation in nonaqueous media
6.1 Introduction and background
6.2 Early studies on chemical vapor generation in nonaqueous media
6.3 Experimental implementation of the technique
6.3.1 Instrumentation and apparatus
6.3.2 Typical procedure for NACVG
6.3.2.1 Liquid-phase microextraction procedure before NACVG
6.3.2.2 Summary of analytical performance
6.4 Fundamental processes; theory and mechanisms
6.4.1 Effect of types of reductant and reaction products
6.4.2 Parameters controlling nonaqueous phase derivatization
6.4.2.1 Chelating/complexing agents and acidity
6.4.2.2 Organic medium
6.4.3 Effect of surfactant as sensitizer
6.4.4 Interferences
6.5 Remaining problems, limitations, and shortcomings
6.6 Future developments
6.7 Conclusions
References
7 Photo-sono-thermo-chemical vapor generation techniques
7.1 General introduction
7.2 Photochemical vapor generation
7.2.1 Development and practical implementation of photochemical vapor generation
7.2.1.1 Photoreactor design considerations
7.2.1.2 Impact of irradiation wavelength
7.2.1.3 Sample processing
7.2.1.4 Analyte phase transfer
7.2.1.5 Practical implementation
7.2.1.6 Species identification and yield
7.2.2 Analytical performance, features, and shortcomings
7.2.3 Fundamental and mechanistic aspects
7.2.3.1 Alkyl halide generation
7.2.3.2 Se, Te, As, and Sb oxyanions
7.2.3.2.1 Se
7.2.3.2.2 Te
7.2.3.2.3 As
7.2.3.2.4 Sb
7.2.3.3 Photochemical vapor generation of transition metal carbonyls
7.2.3.3.1 Photochemical vapor generation of Fe, Ni, and Co
7.2.3.3.2 Photochemical vapor generation of Mo and W
7.2.3.4 Photochemical vapor generation of Pb, Sn, Cd, Cu, Tl, and Bi
7.2.3.5 Photochemical vapor generation of Hg
7.2.3.6 Photochemical vapor generation of Os
7.2.4 Role of catalysts: heterogeneous and homogeneous systems
7.2.5 Interferences
7.2.6 Future directions
7.3 Sonochemical vapor generation
7.3.1 Analytical performance, features, and shortcomings
7.3.2 Future directions
7.4 Thermochemical vapor generation
7.5 Concluding remarks
References
8 Catalysts in photochemical vapor generation
8.1 Introduction
8.2 Heterogeneous catalysis
8.2.1 TiO2
8.2.2 TiO2-based composites
8.2.3 Metal–organic frameworks
8.3 Homogeneous catalysis
8.3.1 Metal ion–assisted photochemical vapor generation
8.4 Conclusions
Acknowledgments
References
9 Plasma-mediated vapor generation techniques
9.1 General introduction
9.2 Sources for plasma-mediated vapor generation
9.2.1 Liquid electrode glow discharges
9.2.1.1 Solution cathode glow discharge
9.2.1.2 Alternating current–driven solution electrode glow discharge
9.2.1.3 Solution anode glow discharge
9.2.2 Dielectric barrier discharges
9.2.2.1 Coaxial dielectric barrier discharge
9.2.2.2 Thin-film dielectric barrier discharge
9.2.2.3 Liquid spray dielectric barrier discharge
9.3 Influence of coexisting ions on PMVG
9.4 Analytical performance and applications of PMVG
9.5 Possible mechanisms of PMVG
9.6 Concluding remarks and future trends
References
10 Electrochemical vapor generation
10.1 Introduction and background to electrochemical vapor generation
10.2 Fundamentals and experimental implementation of ECVG
10.2.1 Experimental aspects: cell designs and cathode material
10.2.1.1 Effects of cell geometry
10.2.1.2 Cathode material
10.2.2 Experimental variables affecting ECVG
10.2.2.1 Anolyte and catholyte solutions
10.2.2.2 Electrolytic current
10.2.2.3 Flow rate of the electrolyte
10.2.2.4 Carrier gas flow rate
10.3 Mechanisms of ECVG
10.4 Shortcomings and limitations: interferences in ECVG
10.4.1 Transition and noble metal ions
10.4.2 Strong oxidants
10.4.3 Hydride-forming elements
10.4.4 Interferences with cold vapor mercury generation and other volatile species
10.4.5 Limitations on applications of ECVG to real samples
10.5 Final remarks and future developments
References
11 Nonplasma devices for atomization and detection of volatile metal species by atomic absorption and fluorescence
11.1 Introduction
11.2 Processes taking place in online atomizers
11.3 Online atomization—preliminary considerations
11.4 Online atomizers
11.4.1 Conventional quartz tube atomizers
11.4.1.1 Conventional quartz tube atomizer without introduction of extra oxygen
11.4.1.2 Conventional quartz tube atomizer with introduction of extra oxygen
11.4.1.3 Influence of atomization parameters on sensitivity with the conventional quartz tube atomizer
11.4.1.4 Interferences in conventional quartz tube atomizer
11.4.1.5 Conventional quartz tube atomizer—assessment
11.4.2 Multiatomizer
11.4.3 Other designs of online atomizers for AAS
11.4.4 Miniature diffusion flame atomizer
11.4.5 Flame-in-gas-shield atomizer
11.4.6 Other miniature flame atomizers
11.5 In-atomizer collection—preliminary considerations
11.6 Experimental approaches to in-atomizer collection
11.6.1 In situ collection in graphite furnaces
11.6.2 Trapping on a quartz surface—atomization in a quartz tube atomizer
11.6.3 Trapping on a W coil
11.6.4 In situ collection in (quartz) integrated atom trap immersed in an air-acetylene flame
11.7 Conclusions and future perspectives
Acknowledgments
Dedication
References
12 Dielectric barrier discharge devices
12.1 Introduction
12.2 DBD concept and designs
12.3 Plasma chemistry: processes and species
12.4 Analytical applications
12.4.1 Selecting the best analytical parameters to evaluate performance
12.4.2 Experimental parameters affecting DBD atomizer performance
12.5 DBD atomizers for AAS
12.5.1 Analytes studied
12.5.2 Analytical figures of merit
12.5.3 Mechanistic studies
12.5.4 Fate of free atoms and atomization efficiency
12.6 DBD atomizers for AFS
12.7 DBD excitation for OES
12.7.1 Analytes studied
12.7.2 Parameters affecting DBD performance
12.7.3 Detection and data evaluation
12.8 Analyte preconcentration
12.8.1 Principle
12.8.2 Atomic absorption spectrometry
12.8.3 Atomic fluorescence spectrometry
12.8.4 Optical emission spectrometry
12.8.5 Preconcentration efficiency
12.8.6 Preconcentration mechanisms
12.9 Speciation analysis
12.10 Future perspectives
Acknowledgment
References
Index