Sample Introduction Systems in ICPMS and ICPOES

Diane Beauchemin

• Publisher: Elsevier
• Year: 2020
• ISBN:
  9780444594839
• Topic: Physical Sciences
• Subtopic: Spectroscopy & Spectrum Analysis

Sample Introduction Systems in ICPMS and ICPOES provides an in-depth analysis of sample introduction strategies, including flow injection analysis and less common techniques, such as arc/spark ablation and direct sample insertion. The book critically evaluates what has been accomplished so far, along with what can be done to extend the capabilities of the technique for analyses of any type of sample, such as aqueous, gaseous or solid. The latest progress made in fields, such as FIA, ETV, LC-ICP-MS and CE-ICP-MS is included and critically discussed. The book addresses problems related to the optimization of the system, peak dispersion and calibration and automatization.

• Provides contributions from recognized experts that give credibility to each chapter as a reference source
• Presents a single source, providing the big picture for ICPMS and ICPOES
• Covers theory, methods, selected applications and discrete sampling techniques
• Includes access to core data for practical work, comparison of results and decision-making

Chapter 1

The inductively coupled plasma as a source for optical emission spectrometry and mass spectrometry

Yoseif Makonnen^a; Diane Beauchemin^{b a} SGS Canada Inc., Mississauga, ON, Canada
^b Department of Chemistry, Queen’s University, Kingston, ON, Canada

Abstract

The argon inductively coupled plasma (ICP) is a useful atom and ion emissions source for optical emission spectrometry (OES) and ion source for mass spectrometry (MS). This chapter will provide a general overview of ICP spectrometry: plasma generation, sampling/observation, analyte detection, common interferences (spectroscopic and non-spectroscopic) encountered during analysis and alternative mixed-gas plasmas. The mitigation of troublesome non-spectroscopic interferences (or matrix effects) is discussed with respect to instrumental conditions, a robust plasma approach and various calibration strategies (i.e., external calibration, internal standardization, standard addition and isotope dilution). Finally, a selection of representative examples from the literature is presented to demonstrate the applications of alternative mixed-gas plasmas in both ICPOES and ICPMS.

Keywords

Inductively coupled plasma optical emission spectrometry; Inductively coupled plasma mass spectrometry; Mixed-gas plasma; Matrix effects

Chapter outline

• 1.1 Introduction
• 1.2 The ICP torch
  • 1.2.1 Plasma generation
  • 1.2.2 Analyte excitation and ionization
• 1.3 Detection
  • 1.3.1 Plasma viewing mode in ICPOES
  • 1.3.2 Wavelength dispersion in ICPOES
  • 1.3.3 Detectors in ICPOES
  • 1.3.4 Plasma sampling interface in ICPMS
  • 1.3.5 Mass analyzer in ICPMS
  • 1.3.6 Detectors in ICPMS
• 1.4 Analytical figures of merit for an ICP spectrometer
• 1.5 Interferences
  • 1.5.1 Spectroscopic interferences in ICPOES
  • 1.5.2 Spectroscopic interferences in ICPMS
• 1.6 Matrix (non-spectroscopic) interferences
  • 1.6.1 Matrix interferences in ICPOES
  • 1.6.2 Matrix interferences in ICPMS
• 1.7 Mitigation of matrix effects
  • 1.7.1 Optimizing instrumental parameters
  • 1.7.2 Robust plasma approach
  • 1.7.3 Calibration strategies
  • 1.7.4 Sample pretreatment
• 1.8 Mixed-gas plasmas
  • 1.8.1 Mixed-gas plasmas in ICPOES
  • 1.8.2 Mixed-gas plasmas in ICPMS
• 1.9 Conclusions
• References

1.1 Introduction

Elemental analysis via optical emission spectrometry (OES), using an atmospheric pressure inductively coupled plasma (ICP) as an emission source, was first reported by Stanley Greenfield in 1964 [1]. Compared to earlier emission sources such as flames, AC (alternating current) sparks and DC (direct current) arcs, using a plasma source allowed for a high degree of stability, overcoming interference effects due to stable compound formation and exciting a greater number of elements than chemical flame methods [1]. Through the mid-1970s, studies by Velmer Fassel and co-workers lead to refinements to the ICP emission source (i.e., removal of noise sources and the optimization of torch designs, gas flows and plasma settings) that would make it practical for the OES analysis of nebulized solutions [2]. Since the introduction of the first commercially available ICPOES instrument in 1974, the argon (Ar) ICP has been a powerful source for OES, which features a wide linear dynamic range, freedom from chemical interferences (like those experienced in flame atomic absorption spectrometry (FAAS)), the advantage of working with solutions (i.e., better control of homogeneity and simplified calibration), similar precision and better sensitivity than FAAS, and multi-element capability [3,4]. Because all elements of the Periodic Table, with the exception of fluorine (F), helium (He) and neon (Ne) (which have a higher ionization potential than Ar), can be significantly ionized in the Ar ICP, it was coupled to mass spectrometry (MS) in an attempt to add several features: rapid acquisition of mass spectra, low detection limits and easy isotope analysis. Although ICPMS is not as robust (free of chemical interference) as ICPOES, it is nonetheless well established because of its multi-elemental, ultra-trace detection capability with a wider linear dynamic range than ICPOES [5].

In ICPOES/MS, solutions are introduced into the plasma using a nebulizer and spray chamber (see Chapter 2), where a majority of the sample (up to 95%) is lost to the drain [4,6]. Solid sampling techniques such as electrothermal vaporization (ETV; see Chapter 9) and laser ablation (LA; see Chapter 10) are also available when total sample introduction is required and/or the sample must be preserved, respectively. The major issues in ICPOES/MS are sample introduction efficiency and non-spectroscopic interferences (also called matrix effects). Only a handful of specialized systems are capable of 100% sample introduction efficiency for nebulized solutions. The simultaneous introduction of matrix components along with analytes into the plasma can produce both spectroscopic interferences, which bias results high, and matrix effects that can suppress (most of the time) or enhance (occasionally) analyte signals. Internal standardization and especially the method of standard addition can compensate for matrix effects, which nonetheless pose a significant problem for users through the degradation of sensitivity associated with analyte signal suppression. Additionally, the calibration methods used to compensate for matrix effects are susceptible to sample contamination or analyte loss. Instrumental parameters can be optimized within a specific matrix [7]; however, there are very few systems that allow the accurate determination of several elements (> 10) in complex sample matrices, without using internal standardization or matrix matching external calibration strategies.

1.2 The ICP torch

The current conventional ICP torch assembly is similar to the early design reported by Fassel and co-workers [8], which consists of three concentric quartz (fused-silica) tubes (Fig. 1.1). Two tangential gas flow inlets are used for the outer and intermediate channels of the torch, while the inner (or central) gas flow inlet is at the torch b...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributors
• Preface
• Chapter 1: The inductively coupled plasma as a source for optical emission spectrometry and mass spectrometry
• Chapter 2: Nebulization systems
• Chapter 3: Flow injection
• Chapter 4: Liquid chromatography
• Chapter 5: Gas chromatography
• Chapter 6: Capillary electrophoresis
• Chapter 7: Field-flow fractionation
• Chapter 8: Vapor generation
• Chapter 9: Electrothermal vaporization
• Chapter 10: Laser ablation
• Chapter 11: Electrochemical techniques
• Index