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