1
Chem415
Quantitative Bio-Element
Imaging Center (QBIC): Part II
APRIL 13, 2015
DIRECTOR: PROFESSOR THOMAS V. O’HALLORAN
MANAGING DIRECTOR: KEITH MACRENARIS, PH.D
2
Analytical Advantages of ICP over AA?
3
ICP is The Choice for Multi-Element Analysis
4
Component Breakdown of ICP
Front End Integration
• For Liquid Samples: autosamplers coupled to peristaltic pumps
• For Separations/Speciation Analysis: Systems can be designed with GC, HPLC, IC or CE prior to
integration into the ICP
• For Imaging: Laser ablation units can be integrate for quantitative elemental imaging/mapping
Sample Introduction
• Nebuliser – Need to produce a fine mist for efficient sample introduction – Usually made of
quartz or PFA – concentric, self-aspirating, and cross-flow
• Spray Chambers – Need to discern between large and small droplets from the nebulizer prior to
introduction into the plasma torch – bead impact, cyclonic
Plasma Torch
• More efficient and reproducible vaporization, atomization, excitation, and ionization due to
high temperatures of the plasma 6000 K - 10000 K versus 3300 K for flames and furnaces
• Uses mainly argon as carrier gas an torch source so low noise or contamination due to
electrode materials required in Flame AA or GFAAS
Detection
• Optical Emission Spectrometer – Usually a echelle polychromator and CCD, CID, or CMOS
detector chips
• Mass Spectrometer – Quadropole, Magnetic Sector Field, or Orbitrap with pulse counting and
analog detectors
5
Autosampler/Peristaltic Pump

Autosamplers: Usually come in a variety
of configurations with multiple rack types

Peristaltic Pumps are typically used due
to low cost and consistency

2 issues with peristaltic pumps: 1) with
ICP-MS you have to average out the
peristalsis. 2) sample contamination of
tubing is difficult to remove (also known
as memory artifacts)

Newer valve/syringe assemblies allow for
auto-dilution and decrease uptake and
washout times while increasing
accuracy and precision

Even using new valve and syringe-driven
autosampling peristaltic pumps are still
required for waste and washout
6
Nebulizers

Nebulizers use 2 priniciple to create a
fine mist for sampling:

1) Venturi effect whereby a fluid’s
velocity must increase as it passes
through a constriction

2) Pneumatic Induction whereby a
gas is used as the driving force to
convert a liquid into a fine spray

The main types of nebulizers used are
concentric and burgener or
enhanced parallel path nebulizers
(usually for Highly corrosive samples
such as HF)
7
Spray Chambers

Purpose of a Spray Chamber is to
remove droplets produced by the
nebulizer that are > 8 µm in diameter,
smooth out pulses produced by the
peristaltic pump, and if cooled keep
the sample thermally stable

Two main types are double-pass and
cyclonic spray chambers

Use correct material and choose
proper design for particular sample
types
8
Plasma Torch

Want to increase energy for more efficient
atomization and ionization

ICP torches form the plasma by a tangential
stream of argon gas flowing between 2 quartz
tubes followed by pulsing AC of RF power
through the coil producing an oscillating
magnetic field (27.12 MHz usually)

An electric spark is applied to introduce free
electrons into the gas stream which are then
accelerated by the rapidly changing magnetic
field

Accelerated electrons collide with argon atoms
forcing the loss of an electron which in turn
accelerate in the oscillating magnetic field

Results in multiple temperature zones within the
produced plasma
9
ICP-OES Optics

After sample passes through the
plasma the atom is allowed to drop
from a high energy state back to the
ground state through emission of a
photon

These photons are analyzed through a
monchromator and echelle grating
before hitting the detector

Allows readouts in 2 dimensions
providing better resolution and faster
analysis than old PMT methods

Can get full spectrum analysis for
every sample (called full frame
capture)
10
ICP-OES: Axial versus Radial Viewing

Radial View: Off-axis plasma viewing
provides highest upper linear ranges (~
100 pm or greater depending upon
intensity of spectral line)

Axial View: Views the light looking down
the center of the torch providing better
detection limits than radial view by up to
10-fold

Dual View: Allows viewing in both axes

Radial viewing is accomplished through a
hole in the plasma torch allowing for
faster transitions between axial and radial
views (shorter run times)
11
Advantages and Disadvantages for ICP-OES
Advantages


Due to high temperature of ICP
plasma most species are broken into
atoms or ions for excitation and
subsequent emission
Of all analytical atomic spectrometry
techniques has the fewest
interferences

Can tolerate up to 20%-30% TDS

Multi-element capability due to
CCD/CID chips
Disadvantages

Prone to spectral interferences

Easily-ionize-element (EIE) effect –
happens with elements with low
ionization potentials such as alkaline
elements which can suppress or
enhance emission signals

Does not provide ultra-trace or realtime analysis

Does not provide information about
the different naturally occurring
isotopes of a particular element
12
ICP-MS

ICP-OES was commercialized in 1974,
whereas ICP-MS wasn’t commercialize
until 1983

Use Mass Spectrometer to analyze
samples due to atomization and more
importantly ionization of elements in
the plasma

Singly charged ions are being
detected according to there mass-tocharge ratio

Have to get the system into a low
vacuum state between 10-5 to 10-7 Torr
which is accomplished using a sample
and skimmer cone interface
13
ICP-MS Detection: Cones

Cones are generally made out of Ni:
Robust, minimal interferences, tolerate
high matrix, relatively long-lasting and
realtively low cost

Can be made out of platinum: More
resistant to corrosion, longer lasting, no
Ni interference, cost 5-10 times more
than Ni cones

Helps restrict the amount of sample
going into the ion lenses and
quadrupole and helps decrease the
pressure incrementally
Sample Cone
Skimmer Cone
14
ICP-MS Detection: Lens Stack

Positioned between the skimmer cone
and mass separation device

Consisting of multiple electrostatically
controlled lens components

Steer the ions from the hostile
environment of the plasma at
atmospheric pressure and steer them
into the mass analyzer at high vacuum

Ions with high kinetic energy will be
transmitted in preference to ions with
medium or low kinetic energy

Recent advancements have led to the
design of a 90° lens prior to entry into the
KED/CCT reaction cell or quadrupole
15
Quadrupole Mass Analyzer

Using a quadrupole mass analyzer
consisting of 4 rods that are 15-20 cm in
length

Place a direct current on one pair of
rods and a radio frequency field on the
opposite pair ions of a selected mass are
allowed to pass through to the detector
while the others are ejected from the
quadrupole

In the example 63Cu is repeatedely
scanned as electrical pulses are stroed
and counted by a multichannel analyzer

Scan rates are typically 2500 amu per
second and can cove the entire mass
range of 0-300 amu in about 0.1 s
16
Mass Interferences

Common interferences are argides,
oxides, and chloride

Collision cell and reaction cell
technology were developed to
handle major mass interferences

Another solution is for high resolution
magnetic sector field ICP-MS which is
cost prohibitive
17
Advantages and Disadvantages for ICP-MS
Advantages

Due to high temperature of ICP
plasma most species are broken into
atoms or ions for excitation and
subsequent emission

Low level detection down to ppt

Isotope abundance determination

Large linear range due to multiple
detectors PC and analog
Disadvantages

Prone to mass interferences

Low tolerance for TDS usually < 0.5%

Difficult to analyze complicated
matrices

More maintenance and associated
cost
18
Laser Ablation ICP-MS
Information

For Microscopy and LA-ICP-MS email: Keith
MacRenaris at
keithmacrenaris2009@u.northwestern.edu

For STEM/EDS analysis email: Reiner Bleher at
bleherreiner@gmail.com

QBIC website:
http://qbic.facilities.northwestern.edu/

NUANCE website:
http://www.nuance.northwestern.edu/