Liquid Sample Introduction in ICP Spectrometry

Inductively coupled plasma atomic or mass spectrometry is one of the most common techniques for elemental analysis. Samples to be analyzed are usually in the form of solutions and need to be introduced into the plasma by means of a sample introduction system, so as to obtain a mist of very fine droplets. Because the sample introduction system can be a limiting factor in the analytical performance, it is crucial to optimize its design and its use. It is the purpose of this book to provide fundamental knowledge along with practical instructions to obtain the best out of the technique.

• Fundamental as well as practical character
• Troubleshooting section
• Flow charts with optimum systems to be used for a given application

Practitioners, researchers, instrumentation company engineers

1. History-Introduction

2. Specifications of a sample introduction system to be used with an ICP 2.1 Introduction 2.2 Physical properties of a plasma 2.3 Energy delivered by the plasma 2.4 Carrier gas flow rate and droplet velocity 2.5 Desolvation and vaporization 2.6 Plasma loading 2.7 Organic solvents 2.8 Ideal aerosol 2.9 Chemical resistance 2.10 Other constraints in sample introduction systems

3. Nebulizers. Pneumatic designs. 3.1 Introduction 3.2 Mechanisms involved in pneumatic aerosol generation 3.2.1 Wave generation 3.2.2 Wave growing and break – up 3.2.3 Need for a supersonic gas velocity 3.2.4 Main pneumatic nebulizer designs used in ICP spectrometry 3.2.5 Sample delivery 3.3 Pneumatic concentric nebulizers 3.3.1 Principle 3.3.2 Different designs 3.3.3 Possibility of free liquid uptake rate 3.3.4 Critical dimensions 3.3.5 Renebulization 3.3.6 Nebulizer tip blocking 3.3.7 Aerosol drop characteristics 3.3.7.1 Influence of the gas and delivery rates on drop size distribution 3.3.7.2 Spatial distribution and velocity 3.4 Cross flow nebulizers 3.5 High solids nebulizers 3.6 Parallel path nebulizer 3.6.1 Principle 3.6.2 Critical dimensions 3.7 Comparison of the different conventional pneumatic nebulizers 3.8 Pneumatic micronebulizers 3.8.1 High Efficiency Nebulizer (HEN) 3.8.2 Microconcentric Nebulizer (MCN) 3.8.3 MicroMist nebulizer (MMN) 3.8.4 PFA micronebulizer (PFAN) 3.8.5 Demountable concentric micronebulizers 3.8.6 High efficiency cross-flow micronebulizer (HECFMN) 3.8.7 Parallel Path Micronebulizer (PPMN) 3.8.8 Sonic Spray Nebulizer (SSN) 3.8.9 Oscillating Capillary Nebulizer (OCN) 3.8.10 High Solids MicroNebulizer (HSMN) 3.8.11 Direct Injection Nebulizers 3.8.11.1 Direct Injection Nebulizer (DIN) 3.8.11.2 Direct Injection High Efficiency Nebulizer (DIHEN) 3.8.11.3 Vulkan Direct Injection Nebulizer 3.9 Comparison of micronebulizers

4. Spray chambers 4.1 Introduction 4.2 Aerosol transport phenomena 4.2.1 Droplet evaporation 4.2.2 Droplet coagulation 4.2.3 Droplet impacts 4.3 Different spray chambers designs 4.3.1 Double pass spray chamber 4.3.2 Cyclonic type spray chamber 4.3.3 Single pass spray chambers 4.4 Comparison of conventional spray chambers 4.5 Low inner volume spray chambers 4.5.1 Aerosol transport and signal production processes at low liquid flow rates 4.5.2 Low inner volume spray chamber designs 4.5.3 Tandem systems 4.6 Conclusions on spray chambers

5. Desolvation systems 5.1 Introduction 5.2 Overview of the effect of the solvent in ICP-AES and ICP-MS 5.3 Processes occurring inside a desolvation system 5.3.1 Solvent evaporation 5.3.2 Nucleation or recondensation 5.4 Aerosol heating 5.4.1 Indirect aerosol heating 5.4.2 Radiative aerosol heating 5.5 Solvent removal 5.5.1 Solvent condensation 5.5.1.1 Nucleation problem in the condenser 5.5.1.2 Design of desolvation systems 5.5.2 Solvent removal through membranes 5.6 Design of desolvation systems 5.6.1 Thermostated spray chambers. 5.6.2 Two steps desolvation systems. 5.6.3 Multiple steps desvolation systems. 5.6.4 Desolvation systems based on the use of membranes 5.6.5 Radiative desolvation systems 5.6.6 Desolvation systems for the analysis of microsamples 5.7 Comparison among different desolvation systems.

6. Matrix effects 6.1 Introduction 6.1.1 Effect of physical properties on the sample introduction system performance

   6.1.1.1 Effects on the aerosol generation 6.1.1.2 Effects on the aerosol transport

   6.2 Inorganic and organic acids

   6.2.1 Physical effects caused by inorganic acids 6.2.1.1. Influence on the sample uptake rate 6.2.1.2 Influence on the aerosol characteristics 6.2.1.3 Effect on the solution transport rate 6.2.2 Effects in the excitation/ionization cell 6.2.3 Effect of acids on analytical results. Key variables 6.2.3.1 Acid concentration and nature 6.2.3.2 Effect of the design of the sample introduction system 6.2.3.3 Effect of the plasma observation zone and observation mode 6.2.3.4 Effect of additional variables 6.2.3.5 Effect on the equilibration time 6.2.4 Methods for overcoming acid effects

   6.3 Easily and non easily ionized elements

   6.3.1 Physical effects caused by easily ionized elements 6.3.1.1 Influence on the aerosol characteristics 6.3.1.2 Effect on the solution transport rate 6.3.2 Effects in the excitation/ionization cell 6.3.3 Effect of elements on ICP-AES analytical results. Key variables 6.3.3.1 Effect of the interfering element concentration and nature 6.3.3.2 Effect of the analyte line properties 6.3.3.3 Effect of the nebulizer gas flow rate and RF power 6.3.3.4 Effect of the plasma observation zone 6.3.3.5 Effect of the plasma observation mode 6.3.3.6 Influence of the liquid flow rate 6.3.3.7 Effect of the liquid sample introduction system 6.3.4 Proposed mechanisms explaining the matrix effects in ICP-AES 6.3.5 Effect of elements on ICP-MS analytical results. Key variables

   6.3.5.1 Effect of the nebulizer gas flow rate 6.3.5.2 Effect of the plasma sampling position 6.3.5.3 Influence of the interferent and analyte properties and concomitant concentration

   6.3.5.4 Effect of the spectrometer configuration 6.3.5.5 Additional variables 6.3.6 Proposed mechanisms explaining the matrix effects in ICP-MS 6.3.7 Methods for overcoming elemental matrix effects 6.3.7.1 Internal standard and related methods 6.3.7.2 Methods based on empirical modeling 6.3.7.3 Methods based on the use of multivariate calibration techniques 6.3.7.4 Sample treatment and other methods

   6.4 Organic solvents

   6.4.1 Effects on the performance of sample introduction system 6.4.2 Plasma effects 6.4.3 Effect of the operating conditions 6.4.4 Effect of the solvent nature 6.4.5 Effect of the liquid sample introduction system and the related parameters 6.4.5.1 Conventional liquid sample introduction systems 6.4.5.2 Low sample consumption systems 6.4.5.3 Desolvation systems

   6.5. Conclusions

7. Selection and maintenance of sample introduction systems 7.1 Selecting a liquid sample introduction system. General aspects. 7.2 Conditions that must be fulfilled by a liquid sample introduction system 7.3 Sample introduction systems for particular kinds of samples or applications 7.4 Selecting a nebulizer 7.5 Selecting an aerosol transport device 7.6 Peristaltic pump 7.7 Diagnosis 7.7.1 Use of Mg as a test element 7.7.2 Measurement of the Mg II/Mg I ratio 7.7.3 Procedure 7.7.4 Non-exhaustive list of possible malfunctions 7.8 Operation and troubleshooting of concentric nebulizers 7.9 Operation, maintenance and troubleshooting of parallel pneumatic nebulizers 7.10 Operation, maintenance and troubleshooting of spray chambers

8. Applications 8.1 Introduction 8.2 Description of applications of low sample consumption systems 8.3 Selected applications