EN ISO 17294-1:2006

SLOVENSKI STANDARD
01-februar-2007
Kakovost vode - Uporaba induktivno sklopljene plazme z masno selektivnim
detektorjem (ICP-MS) - 1. del: Splošne smernice (ISO 17294-1:2004)
Water quality - Application of inductively coupled plasma mass spectrometry (ICP-MS) -
Part 1: General guidelines (ISO 17294-1:2004)
Wasserbeschaffenheit - Anwendung der induktiv gekoppelten Plasma
Massenspektrometrie (ICP-MS) - Teil 1: Allgemeine Anleitung (ISO 17294-1:2004)
Qualité de l'eau - Application de la spectrométrie de masse avec plasma a couplage
inductif (ICP-MS) - Partie 1: Lignes directrices générales (ISO 17294-1:2004)
Ta slovenski standard je istoveten z: EN ISO 17294-1:2006
ICS:
13.060.50
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 17294-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2006
ICS 13.060.50
English Version
Water quality - Application of inductively coupled plasma mass
spectrometry (ICP-MS) - Part 1: General guidelines (ISO 17294-
1:2004)
Qualité de l'eau - Application de la spectrométrie de masse Wasserbeschaffenheit - Anwendung der induktiv
avec plasma à couplage inductif (ICP-MS) - Partie 1: gekoppelten Plasma Massenspektrometrie (ICP-MS) - Teil
Lignes directrices générales (ISO 17294-1:2004) 1: Allgemeine Anleitung (ISO 17294-1:2004)
This European Standard was approved by CEN on 11 September 2006.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Central Secretariat or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania,
Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
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COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2006 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 17294-1:2006: E
worldwide for CEN national Members.

Foreword
The text of ISO 17294-1:2004 has been prepared by Technical Committee ISO/TC 147 "Water
quality” of the International Organization for Standardization (ISO) and has been taken over as
which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of
an identical text or by endorsement, at the latest by April 2007, and conflicting national
standards shall be withdrawn at the latest by April 2007.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of
the following countries are bound to implement this European Standard: Austria, Belgium,
Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary,
Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

Endorsement notice
The text of ISO 17294-1:2004 has been approved by CEN as EN ISO 17294-1:2006 without any
modifications.
INTERNATIONAL ISO
STANDARD 17294-1
First edition
2004-09-01
Corrected version
2005-03-01
Water quality — Application of
inductively coupled plasma mass
spectrometry (ICP-MS) —
Part 1:
General guidelines
Qualité de l'eau — Application de la spectrométrie de masse avec
plasma à couplage inductif (ICP-MS) —
Partie 1: Lignes directrices générales

Reference number
ISO 17294-1:2004(E)
©
ISO 2004
ISO 17294-1:2004(E)
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ii © ISO 2004 – All rights reserved

ISO 17294-1:2004(E)
Contents Page
Foreword. iv
1 Scope. 1
2 Normative references . 1
3 Terms and definitions. 1
4 Principle . 5
5 Apparatus. 5
6 Interferences by concomitant elements .13
7 Adjustment of the apparatus . 19
8 Preparatory steps. 21
9 Procedure. 26
Annex A (informative) Spectral interferences, choice of isotopes and method detection limits for
quadrupole ICP-MS instruments . 29
Bibliography . 33

ISO 17294-1:2004(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 17294-1 was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee SC 2, Physical,
chemical and biochemical methods.
ISO 17294 consists of the following parts, under the general title Water quality — Application of inductively
coupled plasma mass spectrometry (ICP-MS):
— Part 1: General guidelines
— Part 2: Determination of 62 elements
This corrected version of ISO 17294-1:2004 incorporates correction of symbols for instrument detection limit
and method detection limit, corrections to Equations (1) and (3), and various minor editorial corrections.

iv © ISO 2004 – All rights reserved

INTERNATIONAL STANDARD ISO 17294-1:2004(E)

Water quality — Application of inductively coupled plasma
mass spectrometry (ICP-MS) —
Part 1:
General guidelines
1 Scope
This part of ISO 17294 specifies the principles of inductively coupled plasma mass spectrometry (ICP-MS)
and provides general directions for the use of this technique for determining elements in water. Generally, the
measurement is carried out in water, but gases, vapours or fine particulate matter may be introduced too. This
International Standard applies to the use of ICP-MS for water analysis.
The ultimate determination of the elements is described in a separate International Standard for each series of
elements and matrix. The individual parts of this International Standards refer the reader to these guidelines
for the basic principles of the method and for configuration of the instrument.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the reference document
(including any amendments) applies.
ISO Guide 30, Terms and definitions used in connection with reference materials
ISO Guide 32, Calibration in analytical chemistry and use of certified reference materials
ISO Guide 33, Uses of certified reference materials
ISO 3534-1, Statistics — Vocabulary and symbols — Part 1: Probability and general statistical terms
ISO 3696:1987, Water for analytical laboratory use — Specification and test methods
ISO 5725-1, Accuracy (trueness and precision) of measurement methods and results — Part 1: General
principles and definitions
ISO 5725-2, Accuracy (trueness and precision) of measurement methods and results — Part 2: Basic method
for the determination of repeatability and reproducibility of a standard measurement method
ISO 6206, Chemical products for industrial use — Sampling — Vocabulary
ISO 6955, Analytical spectroscopic methods — Flame emission, atomic absorption and fluorescence —
Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 5725-1, ISO 6206, ISO 6955 and
ISO Guide 32 and the following apply.
ISO 17294-1:2004(E)
3.1
accuracy
closeness of agreement between test result and the accepted reference value
NOTE The term accuracy, when applied to a set of observed values, describes a combination of random error
components and common systematic error components. Accuracy includes precision and trueness.
3.2
analyte
element(s) to be determined
3.3
blank calibration solution
solution prepared in the same way as the calibration solution but leaving out the analyte
3.4
calibration solution
solution used to calibrate the instrument, prepared from (a) stock solution(s) or from a certified standard
3.5
check calibration solution
solution of known composition within the range of the calibration solutions, but prepared independently
3.6
determination
entire process from preparing the test sample solution up to and including measurement and calculation of the
final result
3.7
laboratory sample
sample sent to the laboratory for analysis
3.8
linearity
straight line relationship between the (mean) result of measurement (signal) and the quantity (concentration)
of the component to be determined
3.9
linearity verification solution
solution with a known concentration of the matrix components compared to the calibration solutions, but
having an analyte concentration half that of the (highest) calibration solution
3.10
instrument detection limit
L
DI
smallest concentration that can be detected with a defined statistical probability using a contaminant-free
instrument and a blank calibration solution
3.11
mean result
mean value of n results, calculated as intensity (ratio) or as mass concentration (ρ)
NOTE The mass concentration is expressed in units of milligrams per litre.
3.12
method detection limit
L
DM
smallest analyte concentration that can be detected with a specified analytical method with a defined
statistical probability
2 © ISO 2004 – All rights reserved

ISO 17294-1:2004(E)
3.13
net intensity
I
signal obtained after correction for (poly)atomic ion interferences using an elemental equation
3.14
net intensity ratio
I
R
net intensity divided by the signal of a reference element
3.15
optimization solution
solution serving for mass calibration and for the optimization of the apparatus conditions
EXAMPLE Adjustment of maximal sensitivity with respect to minimal oxide formation rate and minimal formation of
doubly charged ions.
3.16
precision
closeness of agreement between independent test results obtained under prescribed conditions
NOTE Precision depends only on the distribution of random errors and does not relate to true value or the specified
value.
3.17
“pure chemical”
chemical with the highest available purity and known stoichiometry and for which the content of analyte and
contaminants should be known with an established degree of certainty
3.18
raw intensity
I
raw
obtained uncorrected signal
3.19
reagent blank solution
solution prepared by adding to the solvent the same amounts of reagents as those added to the test sample
solution and with the same final volume
3.20
reproducibility
R
precision under reproducibility conditions
[ISO 3534-1]
3.21
reproducibility conditions
conditions where test results are obtained with the same method on identical test items in different
laboratories with different operators using different equipment
[ISO 3534-1]
3.22
reproducibility standard deviation
standard deviation of test results obtained under reproducibility conditions
[ISO 3534-1]
ISO 17294-1:2004(E)
3.23
reproducibility limit
value less than or equal to which the absolute difference between two single test results obtained under
reproducibility conditions may be expected to be, with a probability of, generally, 95 %
3.24
repeatability
r
precision under repeatability conditions
[ISO 3534-1]
3.25
repeatability conditions
conditions where independent test results are obtained with the same method on identical test items in the
same laboratory by the same operator using the same equipment within a short interval of time
[ISO 3534-1]
3.26
repeatability standard deviation
standard deviation of test results obtained under repeatability conditions
[ISO 3534-1]
3.27
repeatability limit
value less than or equal to which the absolute difference between two single test results obtained under
repeatability conditions may be expected to be, with a probability of, generally, 95 %
3.28
result
outcome of a measurement
NOTE The result is typically calculated as mass concentration (ρ), expressed in milligrams per litre.
3.29
sensitivity
S
ratio of the variation of the magnitude of the signal (dI) to the corresponding variation in the concentration of
the analyte (dC) expressed by the equation:
dI
S =
dC
3.30
stock solution
solution with accurately known analyte concentration(s), prepared from “pure chemicals”.
NOTE Stock solutions are reference materials within the meaning of ISO Guide 30.
3.31
test sample
sample prepared from the laboratory sample, for example by grinding or homogenizing
3.32
test sample solution
solution prepared with the fraction (test portion) of the test sample according to the appropriate specifications,
such that it can be used for the envisaged measurement
4 © ISO 2004 – All rights reserved

ISO 17294-1:2004(E)
3.33
trueness
bias
closeness of agreement between the average value obtained from a large series of test results and an
accepted reference value
NOTE The measure of trueness is usually expressed in terms of bias, which equals the sum of the systematic error
components.
3.34
uncertainty of measurement
parameter, associated with the result of a measurement, that characterises the dispersion of the values that
could reasonably be attributed to the analyte concentration
4 Principle
ICP-MS stands for Inductively Coupled Plasma Mass Spectrometry. In the present context, a plasma is a
small cloud of hot (6 000 K to 10 000 K) and partly ionized (approximately 1 %) argon gas. Cool plasmas have
temperatures of only about 2 500 K. The plasma is sustained by a radio-frequency field. The sample is
brought into the plasma as an aerosol. Liquid samples are converted into an aerosol using a nebulizer. In the
plasma, the solvent of the sample evaporates, and the compounds present decompose into the constituent
atoms (dissociation, atomization). The analyte atoms are in most cases almost completely ionized.
In the mass spectrometer, the ions are separated and the elements identified according to their mass-to-
charge ratio, m/z, while the concentration of the element is proportional to the number of ions.
ICP-MS is a relative technique. The proportionality factor between response and analyte concentration relates
to the fact that only a fraction of the analyte atoms that are aspirated reach the detector as an ion. The
proportionality factor is determined by measuring calibration solutions (calibration).
5 Apparatus
5.1 General
The principal components of the ICP-mass spectrometer are as shown in Figure 1 in the form of a schematic
block diagram.
Figure 1 — Schematic block diagram of an ICP-mass spectrometer
ISO 17294-1:2004(E)
5.2 Sample introduction
5.2.1 General
To introduce solutions to be measured into the plasma, a pump, a nebulizer and a spray chamber are
generally used. The pump supplies the solution to the nebulizer. In the nebulizer, the solution is converted into
an aerosol by an (argon) gas flow, except when an ultrasonic nebulizer is used; see 5.2.3. Large drops are
removed from the aerosol in the spray chamber by means of collisions with the walls or other parts of the
chamber and they are drained off as liquid. The resulting aerosol is then transferred into the plasma via the
injector tube of the torch (see 5.3) with the help of the nebulizer gas (sample-introduction gas).
The sample introduction system is designed in such a way that
a) the average mass per aerosol droplet is as low as possible;
b) the mass of the aerosol transported to the plasma in each period of time is as constant as possible;
c) the droplet size distribution and the added mass of the aerosol in each period of time is, as far as possible,
independent of the solution to be measured (matrix effect, see 6.3);
d) the time the aerosol takes to stabilize after introduction of a solution is as short as possible;
e) the parts of the system in contact with the sample or the aerosol are not corroded, degraded or
contaminated by the solution;
f) carry-over from one sample to subsequent samples is minimized.
The components of the sample introduction system shall be able to withstand corrosive substances that may
be in the solutions, such as strong acids. The material used for pump tubing should be resistant to dissolution
and chemical attack by the solution to be nebulized. Components that come into contact with the solution are
often made of special plastics. The use of glass and quartz shall be avoided if hydrofluoric acid is nebulized.
In those cases, the nebulizer, spray chamber and torch injector tube shall be made of suitable inert materials.
The various components of the sample introduction system are discussed hereafter in relation to the above
requirements and some “examples” are compared.
5.2.2 Sample pump
The use of a peristaltic pump to feed the solution to the nebulizer is not necessary with some nebulizers (see
5.2.3), but is desirable in almost all cases in order to render the supply of the solution less dependent on the
composition of the solution. A sampling pump is used on all modern instruments.
It is advisable to use a peristaltic pump having the largest possible number of rollers and a velocity as high as
possible to avoid major surges in the supply of the solution. The quantity of solution that is pumped is mostly
between 0,1 ml and 1,5 ml per minute.
5.2.3 Nebulizer
1)
The most common nebulizers are the concentric nebulizer [for example Meinhard ], the cross-flow nebulizer,
the V-groove nebulizer and the ultrasonic nebulizer (USN). The first one is self-aspirating, and the second one
can be, and these nebulizers can then be used without a pump (but seldom are). Nebulizers (except for the
USN) can be made of glass or of hard, inert plastic.

1) The Meinhard nebulizer is an example of a suitable product available commercially. This information is given for the
convenience of users of this part of ISO 17294 and does not constitute an endorsement by ISO of this product.
6 © ISO 2004 – All rights reserved

ISO 17294-1:2004(E)
The concentric nebulizer consists of two concentric tubes, the outer one being narrowed at the end. The
solution flows through the central tube and the nebulizer gas (see 5.4) through the tube around it, creating a
region of lower pressure around the tip of the central tube and disrupting the solution flow into small droplets
(the aerosol). This nebulizer performs best with solutions with a low content of dissolved matter, although
there are also models that are less sensitive to significant amounts of dissolved matter in the solution to be
nebulized.
The cross-flow nebulizer consists of two capillary tubes mounted at a right angle, one being used for the
supply of the solution and the other for the supply of the nebulizer gas. Depending on the distance between
the openings of the capillary tubes and their diameters, the nebulizer can be self-aspirating. With larger
diameters, the chance of blockages occurring is of course smaller, but a pump will have to be used to supply
the solution.
In the V-groove nebulizer, the solution flows through a vertical V-groove to the outflow opening of the
nebulizer gas. The solution is nebulized by the high linear speed of this gas at the very small diameter outflow
opening. The V-groove nebulizer was developed for solutions with a high concentration of dissolved matter
and/or with suspended particles, although it is also used successfully with diluted and/or homogenous
2)
solutions. Similar nebulizers are the Burgener nebulizer and the cone-spray nebulizer, with similar outer
shapes as the concentric nebulizer. With these nebulizers, the solution flows out into a cone-shaped area at
the tip of the nebulizer instead of a V-groove and flows over the outflow opening of the nebulizer gas.
In the ultrasonic nebulizer, the solution is pumped through a tube that ends near the transducer plate that
vibrates at an ultrasonic frequency. The amount of aerosol produced (the efficiency) is typically 10 % to 20 %
of the quantity of the pumped solution. This is so high that the aerosol has to be dried (desolvated) before
being introduced into the plasma, which would otherwise be extinguished. The aerosol is transported to the
plasma by the nebulizer gas. Disadvantages of the ultrasonic nebulizer include its greater susceptibility to
matrix effects, diminished tolerance to high dissolved solid contents and a longer rinsing time.
For the other nebulizers described above, the efficiency is typically only a few percent. The efficiency
increases when the solution introduction rate is decreased. Specially designed concentric micro-nebulizers
made of special types of hard plastic operate at solution flow rates of 10 µl/min to 100 µl/min and efficiencies
approaching 100 %. These concentric micro-nebulizers often show a very good precision (low relative
standard deviation of the signal) and can also be combined with a membrane desolvator [see 6.2.1 a)].
Several other types of nebulizer may be used for specific applications.
5.2.4 Spray chamber
In the spray chamber [for example Scott (double concentric tubes), cyclonic or impact bead], the larger drops
of the aerosol are drained off in liquid form. To create and keep over-pressure in the chamber, the liquid shall
be removed via a sealed drain tube utilizing hydrostatic pressure or by pumping. The liquid shall be removed
evenly in order to avoid pressure variations in the chamber, which can result in variations in the signal.
By cooling the spray chamber to 2 °C to 5 °C, the water vapour formed in the nebulization process condenses,
thereby reducing the water load of the plasma. This results in a reduction in the formation of interfering
polyatomic ions (oxides); see 6.2.2.
5.2.5 Other systems
There are other types of introduction systems for particular applications. They include laser or spark ablation
of a solid sample, evaporation of the solution by means of a graphite furnace or a metal filament, introduction
of a gas or a gas form of the analyte (as in the hydride generation technique), systems for the direct
introduction of solid matter into the plasma (for example in the form of a slurry of a finely dispersed powder in
a solvent) and the introduction with a graphite rod directly into the plasma.

2) The Burgener nebulizer is an example of a suitable product available commercially. This information is given for the
convenience of users of this part of ISO 17294 and does not constitute an endorsement by ISO of this product.
ISO 17294-1:2004(E)
With the Direct Injection Nebulizer (DIN), a pneumatic concentric micro-nebulizer, instead of the inner tube
(injector; see 5.3), is placed in the torch. It has a sample introduction efficiency of almost 100 % with a sample
uptake rate of typically 10 µl/min. A DIN can be used for techniques giving transient signals (for example
coupling to chromatographic or flow injection devices) and for minimizing the memory effects of, for instance,
boron, molybdenum and mercury.
These systems will not be discussed in this document.
5.3 Torch and plasma
The torch consists of three concentric tubes and can be designed as a single unit or a unit constructed of
independent parts. Quartz is the material generally used. Sometimes the innermost tube (the sample
introduction tube or injector tube) is made of inert material, for example aluminium oxide. It usually ends at
4 mm to 5 mm before the first winding of the coil. The aerosol produced in the sample introduction system
flows through the sample introduction tube, transported by an (argon) gas flow (the nebulizer gas) with a flow
rate of approximately (0,5 to 1,5) l/min.
The auxiliary gas flows between the sample introduction tube and the middle tube with a flow rate of 0 l/min to
3 l/min. Whether or not an auxiliary gas is used depends on the type of device concerned, the solvent used,
the salt concentration, etc. The function of the auxiliary gas is to increase the separation of the plasma and the
torch and thus reduce the temperature at the end of the injector (and intermediate) tube. This will avoid
deposits of dissolved material or the build-up of carbon (when organic solvents are nebulized) on the injector
tube.
The plasma gas flows between the middle and outermost tubes with a flow rate of 12 l/min to 20 l/min. The
function of the plasma gas is to maintain the plasma and to cool the outer tube of the torch.
Around the top of the torch there is a water- or argon-cooled coil with two to five windings. A high-frequency
current flows through the coil and excites the plasma (see 5.5).
The torch is generally placed in a separate metal compartment. This compartment shall be connected to an
exhaust system (extraction) because of the production of heat and harmful gases (including ozone). The metal
of the compartment protects the users and the instrument (electronics) against the high-frequency radiation,
which is released from the coil, and against the ultra-violet radiation emitted by the plasma. A special window,
covered with a darkened glass to protect the observer's eyes from the intense plasma emission radiation,
allows visual observation of the plasma.
A grounded metal shield (shield torch) can be placed between the coil and the torch to reduce the levels of
argon-based (poly)atomic ions (see 6.2) that interfere particularly with the determination of K, Ca and Fe. Cold
plasma conditions (relatively low plasma power and high nebulizer gas flow rate) can also be used to optimize
this reduction.
5.4 Gas and gas control
In virtually every instrument, argon is used as nebulizer gas (sample introduction gas), auxiliary gas and
plasma gas. Argon gas with a purity of greater than 99,995 % is preferred. Exact amounts of oxygen can be
added to the nebulizer gas to avoid carbon build-up on the sampling cone when analysing solutions made with
organic solvents. The additions of too much oxygen result in the burning away of the sampling cone (see also
5.6). Mixtures of argon and hydrogen or nitrogen may improve the sensitivity for certain elements and/or
reduce the formation of interfering polyatomic ions (see 6.2).
The various gas flow rates shall be stable. This applies particularly to the nebulizer gas. Best results are
obtained with mass-flow controllers that keep the mass flow rate of a gas constant and almost independent of
temperature and initial pressure.
8 © ISO 2004 – All rights reserved

ISO 17294-1:2004(E)
5.5 Generator
The generator delivers an alternating current with a frequency between 27 MHz and 56 MHz and a power
between 0,6 kW and 2 kW that sustains the plasma. In general, solid-state generators are used. Two types of
generator are available: crystal controlled and free oscillating.
Crystal-controlled generators are designed to control both power and frequency of the magnetic field. The
delivered power and the power not absorbed by the plasma (the reflected power) shall both be very constant
and vary as little as possible with the composition of the solution. The reflected power should be low
(preferably < 10 W).
Free-oscillating, also called free-running, generators are of a simpler construction and control basically the
power delivered to the torch (“forward” power). Small variations in frequency can occur in those types of
generators.
5.6 Transfer of the ions to the mass spectrometer
The ions are transferred from the plasma to the mass spectrometer (see 5.7) via the interface. The interface
consists of two water-cooled cones, a sampling and a skimmer cone, with a vacuum-pumped system, the
expansion chamber, in between. During the measurement the pressure in the expansion chamber is
2 3
maintained at 10 Pa to 10 Pa. At the centre of the cones is an orifice with a diameter of (0,3 to 1) mm, the
orifice of the skimmer cone usually being smaller than that of the sampling cone. The cones are usually made
of nickel. The centre of the cones can have different shapes.
The gas containing the ions is sampled from the central part or channel of the plasma through the orifice of
the sampling cone into the expansion chamber, where a supersonic jet is formed. The central part of this jet
−2
flows through the orifice of the skimmer cone into the vacuum (approximately 10 Pa) of the lens system.
Only about 1 % of the gas sampled from the plasma is transmitted to the lens system. Due to the short
residence time in the expansion chamber (a few microseconds), the composition of the gas hardly changes.
For the determination of nickel at low concentrations, sampling cones are available which are (partly) made of
platinum. The application of platinum cones is also preferred when oxygen is added to the nebulizer gas when
organic solvents are aspired. In this reactive atmosphere, platinum cones are more resistant than those made
of nickel (see also 5.4 and 8.3).
A deposit, consisting of constituents from the measurement solutions, is formed around the orifices of the
cones and may influence the analysis; see 6.2 and Clause 7.
5.7 Mass spectrometer
5.7.1 General
The mass spectrometer consists of an electronic lens system, an analyser and a detector. In the lens system,
the ions travel from the interface and are directed to and focused on the entrance of the analyser. In the
analyser, the ions are separated according to their mass-to-charge ratio, m/z.
5.7.2 Lens system
The lens system can consist of one ion lens, for instance, a metal cylinder or a metal plate with a hole, or of
several ion lenses strung together. Electrical potentials are exerted on the lenses, resulting in the formation of
a beam of ions directed towards the analyser; see also 7.2.5.6. The unwanted neutral particles are removed
by vacuum pumps.
Photons, emitted by the plasma in addition to the ions and neutral particles, also enter the lens system. To
minimize the number of photons hitting the detector, which causes an increase in the background signal and
noise, one or more metal plates (photon stops) are placed at the central axis. However, due to collision of the
ions with the photon stop(s), a part of the ions can be lost and the photon stop(s) can become contaminated.
ISO 17294-1:2004(E)
In some systems, a potential is exerted on the photon stop such that the ions are repelled and fewer are
stopped.
A number of mass spectrometers are constructed in such a way that no photon stop(s) is (are) required. In
these mass spectrometers, the trajectory of the ions deviates from the light path, for instance as a
consequence of a curvature of the ion trajectory in the lens system or in the analyser. The latter is the case for
double-focusing mass spectrometers (see 5.7.5).
5.7.3 Analyser
In most ICP-mass spectrometers, the separation of the ions is obtained using a quadrupole mass
−3
spectrometer located in a continuously evacuated (< 2 × 10 Pa) compartment.
A quadrupole mass analyser consists of four round or hyperbolic, parallel metal rods of about 20 cm length on
which DC (direct current) and RF potentials (radio-frequency) are exerted. The ions are introduced at the
central axis at the beginning of the rods. At a specific combination of DC potential and RF amplitude, the
entire trajectory between the rods is traversed only by ions with values of m/z within a specific band-width. Ions
with lower or higher m/z values are bent away, hit the rods and are neutralized. Thus, the quadrupole acts as a
mass filter.
A quadrupole mass spectrometer for ICP-MS resolves only at unit mass or somewhat better; the resolution is
usually characterized by the peak width at 5 % of the peak height. This is typically set at 0,7 amu (atomic
mass units); see also 7.2.4.
NOTE In ISO 17294-2, the resolution is defined as the peak width at 10 % of the peak height. Both definitions are
suitable.
An important quality characteristic of a quadrupole mass spectrometer is the abundance sensitivity.
Suppose a peak is present at m/z = M, and there is no peak at M−1 or M+1. The abundance sensitivity is then
defined as the ratio between the signal at M and the signal at M−1 or M+1. The abundance sensitivity,
therefore, indicates the ability to measure a small peak next to a major peak. Abundance sensitivity values of
6 8 4 6
10 for the lower masses and 10 for the higher masses may be obtained, although values of 10 and 10 ,
respectively, are more common in routine analysis. Sometimes the inverse value is presented.
5.7.4 Detector
The detection system usually consists of an electrode (the conversion dynode), an electron multiplier with
discrete dynodes and a pre-amplifier.
Under the influence of a high negative voltage, the ions exiting the analyser will hit the conversion dynode
resulting in the release of electrons. These electrons hit the first dynode of the electron multiplier, as a
consequence of which, double the amount of electrons is released.
Subsequently, these electrons hit the second dynode. Ultimately, one ion results in a pulse of approximately
10 electrons. The successive dynodes have progressively less negative voltages. The pulse is processed
using a fast pre-amplifier.
6 6
The maximum counting rate of this system is 2 × 10 to 4 × 10 cps (counts, or pulses, per second) and is
determined by two factors. First, the current flow that the detector can sustain is limited. The second limiting
factor is the response time, or “dead time”, of the detector and electronics, i.e., the time after the registration of
a signal during which the detector is not able to register a new pulse. If the time interval between the arrivals
at the detector of two ions is shorter than the dead time, the second ion is not detected. Both factors cause a
relative decrease in count rate at higher impact rates. For modern instrumentation, the response time is
usually about 10 ns to 20 ns. A mathematical correction has to be carried out to correct for the non-linearity
caused by the dead time. The ICP-MS software supplied will usually carry out this correction based on
Equation (1):
N′ = N / (1 − ND) (1)
10 © ISO 2004 – All rights reserved

ISO 17294-1:2004(E)
where
N′ is the true or estimated count rate;
N is the observed count rate;
D is the dead time.
The noise of this type of detector is very low, usually 1 cps or less, and is of minor importance for ICP-MS
measurements. However, the background that is observed in practice is 3 cps to 30 cps. This considerably
higher value is possibly caused by photons which, despite the measures taken (see 5.7.2), hit the detector.
Several methods are applied to increase the upper-limit of the dynamic range of the measurement, for
example by having fewer ions reaching the detector by, for example, defocusing the ion beam. Other methods
include lowering the multiplication factor by decreasing the potential on the detector or by collecting only a part
of the electrons generated. When one of the last two methods is applied, the current is measured in an analog
manner. This is called the analog mode, in contrast to the pulse-counting mode. Modern instrumentation
switches automatically to the analog mode when a signal that is too strong is detected to prevent damage to
the detector.
The lifetime of discrete dynode and similar detectors is limited to typically 1 year to 2 years. During this life-
span, the sensitivity of the detector slowly decreases and the high voltage has to be increased from time to
time to restore the original sensitivity.
3)
Other detectors that are sometimes applied are electron multipliers with a continuous dynode (Channeltron
3) 3)
detectors, Daly detectors and Coniphot detectors). For some applications, the signal is high enough that a
Faraday cup (a metal electrode without amplification) may be applied.
5.7.5 Alternative mass spectrometers/types of instruments
A disadvantage of a quadrupole mass spectrometer is the insufficient resolution to separate ions with the
same nominal value of m/z. Especially for m/z values lower than 80, this may be a problem due to the
presence of many interferences originating from polyatomic and doubly charged ions (see 6.2). Much of the
newer instrumentation has been developed to overcome these interferences.
A large number of the interferences can be avoided by applying a high-resolution mass spectrometer with a
magnetic and an electrostatic analyser (ESA). First, the ions are accelerated with an accelerating voltage of
5 kV to 8 kV and then separated by the magnetic and electric fields. Depending on the type of instrument, the
ESA can be located ahead of or behind the magnet (reversed Nier-Johnson geometry).The ions coming from
the interface are focused on a slit in front of the spectrometer by means of ion optics, and then on a slit in front
of the detector by the action of the magnet and the ESA. The ions are focused with respect both to direction of
movement and to the energy at the entrance slit (double focussing). The resolution can be changed by
changing the slit widths.
Depending on the type of instrument, this is performed with continuously adjustable slits or by using slits with
fixed widths. The maximum resolution that can be obtained is 10 000 to 20 000, depending on the type of
instrument.
Resolution is defined here as the average mass divided by the mass difference of two adjacent peaks of equal
height that are separated with a valley between them at 10 % of the peak heights, defined as m/∆m, where m
is the average mass and ∆m is the difference of the two masses. The parameter ∆m is equivalent to the width
of one peak at 5 % of the peak height. So, for the same effective separation of peaks, the resolution increases
with mass.
3) Channeltron, Daly, and Coniphot detectors are examples of suitable products available commercially. This information
is given for the convenience of users of this part of ISO 17294 and does not constitute an endorsement by ISO of this
product.
ISO 17294-1:2004(E)
The non-spectral background of this type of mass spectrometer is lower than 0,1 cps and the sensitivity at
low-resolution measurements in a standard configuration varies, depending on the isotopic mass, from > 10
cps per µg/l for Li to > 10 cps per µg/l for U. The higher sensitivity relative to the quadrupole instruments
results from the fact that an accelerating voltage is used and that the vacuum in the spectrometer is better.
Instrumental detection limits obtained are often below 0,1 µg/l for elements not subject to interference at low-
resolution measurements. For elements subject to interferences, the detection limits are on the order of 1 µg/l
or higher when measuring at a resolution of 10 000.
Mass scanning is slower with a magnet than with a quadrupole, while electrostatic scanning over a limited
mass range is fast.
A relatively
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