Chapter 10: Atomic Emission Spectroscopy Using plasmas, Arcs or sparks

What are the three advantages of ICP-AES

'Inductively coupled Plasma Atomic Emission" 1. Increased atomization/excitation: 2. Wider range of elements 3. Wide Dynamic Range: larger linear range

What is a disadvantage of ICP-AES

-Spectra are highly complex (increase probability of interferences for qualitative work) -Need more expensive optical equipment (more difficult to maintain)

What is a Plasma?

-electrically conducting gaseous mixture -contains high concentration of cation and electrons (zero net charge) -very high temperature (10000k)

Plasma sources : advantages

1 more complete atomization in plasma 2. fewer chemical interferences 3. less oxide formation 4. plasma temperature is more uniform 5. larger linear range for calibrations curves 6. Plasma produces significant ionization - a plus for ICPMS

Sample Introduction: for solid samples can use laser ablation

1. A laser beam is focused and fired at the sample surface 2. As the laser drills into the sample, the material removed is picked up in a flow of gas 3. This is transported to an ICP touch where the material is atomized and ionized.

What are the steps that happen in the ICP (around the torch)?

1. Droplet 2. Desolvation (Solid) 3. Vaporization (Gas) 4. Atomization (Atom) 5. Ionization (Ion) In other words: from sample injector to mass spectrometer

What are the ICP-AES Performance characteristics

1. Elements determined - ~ 60 elements, Li, K, Rb Cs strongest lines in IR 2. Line selection - most element have several lines that can be selected 3. Linear ranger - better than AAS 4. Interferences -Chemical (lowered) -Spectral (still a problem ) 5. Detection limits -10ppb range most metals -comparable or better than other atomic spectral techniques

DCP vs ICP *GOOD

1. Multielement Analysis 2. Simple spectra and high sensitivity 3. Less argon and simple auxiliary power supply. 4. Better performance for organic/aqueous solutions with high solids content

Describe three ways of introducing a sample into an ICP torch

1. Nebulization 2. Electrothermal vaporization 3. Lase Ablation

What are the 3 types of ICP-Optical Emission Spec views?

1. Radial View 2. Axial View 3. Dual View

DCP vs ICP *bad

1. Short residence time- incomplete sample volatilization 2. Small optimum viewing region- careful alignment 3. High maintenance- graphite electrodes

What is the decision as to which viewing arrangement to use depends on?

1. The chemical behavior of the anlyte in the plasma 2. The spectral line chosen for the analysis 3. the quality of the data require 4. the detailed natured of the experiment

Solution Sample Introduction : Nebulizer

1. convert solution to fine spray or aerosol 2. use high pressure gas to entrain solution 3. only for introduction, NOT ATOMIZATION

What is Solution (liquid and solid) Sample Introduction: Electrothermal vaporizer

1. electric current rapidly heats sample 2. Sample carried to atomizer by gas (Ar) 3. Furnace is used only for intro 4. atomization occurs in the plasma

What are some of the advantages of plasma sources compared with flame sources for emission spectrometry ?

1. lower interferences 2. Emission spectra for many elements can be obtained with one set of excitation condition 3. spectra can be obtained for elements that tend to form refractory compounds 4. plasma sources usually have linearity range that covers several decades in concentration .

Sample Introduction: Hydride Generation

1. suck up (aspirate) liquid sample at a controlled rate 2. Mix liquid sample with sodium borohydride and HCl 3. Create a volatile hydride of the analyte metalloid from that reaction 4. Flow that gaseous hydride into the ICP Torch

Additional information on ICp

1.Brilliant white core: Ar continuum lines 2. Flame: like tail up to 2cm 3. transparent region : measurement made 4. hotter than flame (10,000K) more complete atomization/excitation 5. Atomized in "insert" atmosphere 6. Little ionization: too many electrons in plasma

What are the type of Plasma?

1.Inductively coupled plasma (ICP) 2. Direct Current Plasma (DCP) 3. Microwave induced plasma (MIP)

What are the Sample Introductions?

1: Solution Sample Introduction: Nebulizer 2. Solution (liquid and solid) Electrothermal Vaporizer 3. Solid samples can use ablation 4. Hydride generation

Elements determined

60 elements for UV radiation -all metallic elements can be determined B,P,N,S and C using a vacuum spectrometer at wavelengths below 180nm. Alkali metals are difficult since the prominent lines for Li, K, Rb, Cs are located in the near IR range

What is Radical View

Ability to measure both very high and reasonably low concentration of elements in samples (known as dynamic range). this design is also capable of handling samples with high levels of dissolved solids and is remarkably free of chemical interferences and easily ionized elements effects.

What is an internal standard and why is it used

An internal standard is a substance that responds to uncontrollable variables in a similar way as the analyte. It is introduced into or is present in both standards and samples in a fixed amount. The ratio of the analyte signal to the internal standard signal then serves as the analytical reading.

Internal Standard Calibration curves with an ICP source

An internal standard is a substance that responds to uncontrollable variables in a similar way as the analyted.

Direct Current Plasma (DCP)

DC current (10-15A) flows between C anodes and W cathodes Plasma core at 10000K viewing region at 5000k Simpler, less Ar than ICP- less expensive DRAW THE SCHEME

A pneumatic nebulizer in which the sample and nebulizing gas combine at right angles to form aerosol

DRAW THE SCHEME

A pneumatic nebulizer that uses the bernoulli effect for sample uptake

DRAW THE SCHEME

Why are atomic emission methods with an ICP source better suited for multi element analysis than are flame atomic absorption methods?

Flame atomic absorption required a separate lamp for each element, which is not convenient when multiple elements are to be determined.

How does ICP-AES wider range of elements

Good emission spectra fro most elements with same experimental setup (Can record all at the same time) - can determine low conc of refractory compounds (ex: oxides) -can determine nonmetal (ex Cl, BR I, S)

How does ICP-AES increased atomization/ excitation?

ICP are at least 2X as hot as flames or furnaces. (6000-10000K) Higher temperature to prevent the info of most interferences, break down oxides and eliminate most molecular spectral interference.

What is Axial View?

Improves on the sensitivity and detection limits of the radial view by a factor of 10 or more depending on the element. This is accomplished by looking down through the plasma rather than across (like radial). The dynamic range isn't changed but it shifted towards the lower concentration.

Why are ionization interferences less severe in ICP than in flame emission spectroscopy?

Ionization interferences are less serves in the ICP than in Flame emission because argon plasmas have a high concentration of electrons (from ionization of the argon) which represents ionization of the analyte

Plasma Source: Atomization of sample

Sample resides in the plasma for ~2 ms before being measured temperature ranges from 5500 to 8000k

Sample Introduction

Samples can be aerosol, vapor or solid

What is ICP and what is it's source?

Source is called a torch Consist of 3 concentric quartz tubes torch up to 2.5 cm diameter. 3 gas stream: cools outer tube defines plasma shape and delivery sample tesal coil: ionize Ar RF power: provide radio-frequency up to 2kW

Why is the internal-standard method often used in plasma emission?

The Internal Standard method is often used in preparing ICP calibration curves to compensate for random instrumental errors that arise from fluctuations in the output of the plasma source

what happens in a laser induced breakdown spectroscopy?

The plasma emission from the ablated sample is gathered using special optics. A spectrometer analyzes the white light emitted from the plasma, separation the light into it's colors (wavelengths)

What is Dual View?

This instrumental is able to view the plasma in both the axial and radial views. The system is an axial design that uses a mirror to observe the plasma from the side. This system combines the best features of the radial and axial, the dynamic range and freedom from interference of the radial and the improved sensitivity and detection of the axial.

Excitation and Atomization are based on and not on? Why

Traditionally based on Flame and electrothermal but plasma, Arc and spark because 1. higher temp 2. excitation conditions