ISO/TS 15338:2009
(Main)Surface chemical analysis — Glow discharge mass spectrometry (GD-MS) — Introduction to use
Surface chemical analysis — Glow discharge mass spectrometry (GD-MS) — Introduction to use
ISO/TS 15338:2009 gives guidelines for the operation of glow discharge mass spectrometry (GD‑MS) instruments and recommendations for the use of GD‑MS. It is intended to be read in conjunction with the instrument manufacturers' manuals and recommendations.
Analyse chimique des surfaces — Spectrométrie de masse à décharge luminescente (GD-MS) — Introduction à l'utilisation
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TECHNICAL ISO/TS
SPECIFICATION 15338
First edition
2009-04-01
Surface chemical analysis — Glow
discharge mass spectrometry (GD-MS) —
Introduction to use
Analyse chimique des surfaces — Spectrométrie de masse à décharge
luminescente (GD-MS) — Introduction à l'utilisation
Reference number
ISO/TS 15338:2009(E)
©
ISO 2009
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ISO/TS 15338:2009(E)
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ISO/TS 15338:2009(E)
Contents Page
Foreword. iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 Safety . 2
4.1 Use of high-voltage power supply and connection of the instrument. 2
4.2 Use and storage of compressed-gas cylinders. 2
4.3 Handling of cryogenic materials . 2
5 Principle. 2
6 Materials . 2
7 Apparatus . 3
7.1 Ion source. 3
7.2 Mass analyser . 5
7.3 Detector system . 8
7.4 Vacuum system. 9
7.5 Data acquisition and control . 9
8 Samples and sample preparation . 9
8.1 General. 9
8.2 Sample type. 10
8.3 Sample geometry. 10
8.4 Sample preparation for bulk analysis. 10
8.5 Sample preparation for depth profiling . 11
9 Measurement procedures . 11
9.1 System precautions. 11
9.2 Selection of discharge parameters and isotopes. 12
9.3 Presputtering. 12
9.4 Optimizing the ion current . 12
9.5 Analytical set-up . 13
9.6 Data analysis . 13
9.7 Depth profile analysis. 14
9.8 Instrument performance . 14
9.9 Analysis . 14
10 Test report . 23
Bibliography . 26
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ISO/TS 15338:2009(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.
In other circumstances, particularly when there is an urgent market requirement for such documents, a
technical committee may decide to publish other types of document:
— an ISO Publicly Available Specification (ISO/PAS) represents an agreement between technical experts in
an ISO working group and is accepted for publication if it is approved by more than 50 % of the members
of the parent committee casting a vote;
— an ISO Technical Specification (ISO/TS) represents an agreement between the members of a technical
committee and is accepted for publication if it is approved by 2/3 of the members of the committee casting
a vote.
An ISO/PAS or ISO/TS is reviewed after three years in order to decide whether it will be confirmed for a
further three years, revised to become an International Standard, or withdrawn. If the ISO/PAS or ISO/TS is
confirmed, it is reviewed again after a further three years, at which time it must either be transformed into an
International Standard or be withdrawn.
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/TS 15338 was prepared by Technical Committee ISO/TC 201, Surface chemical analysis, Subcommittee
SC 8, Glow discharge spectrometry, based on Australian Standard AS 3685:1998.
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TECHNICAL SPECIFICATION ISO/TS 15338:2009(E)
Surface chemical analysis — Glow discharge mass
spectrometry (GD-MS) — Introduction to use
1 Scope
This Technical Specification gives guidelines for the operation of glow discharge mass spectrometry (GD-MS)
instruments and recommendations for the use of GD-MS. It is intended to be read in conjunction with the
instrument manufacturers’ manuals and recommendations.
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 referenced
document (including any amendments) applies.
ISO 18115, Surface chemical analysis — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 18115 and the following apply.
3.1
accuracy of measurement
closeness of the agreement between a result and the accepted reference value
3.2
elemental intensity
amount of ion current recorded for a particular element
3.3
pin cell
sample cell used for the analysis of wire and rod samples
3.4
precision of measurements
closeness of the agreement between independent test results obtained under stipulated conditions, normally
reported as a standard deviation
3.5
pin, rod and wire samples
samples with cylindrical or square cross-section of nominal length typically 20 mm and not normally exceeding
10 mm across
3.6
transmission
ratio of the number of ions reaching the detector relative to the number of ions entering the mass analyser
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ISO/TS 15338:2009(E)
4 Safety
4.1 Use of high-voltage power supply and connection of the instrument
Electrical connection should comply with the regulations in force. Particular care should be taken to ensure
that connection of the instrument to ground is correct, and the efficiency of the ground connection should be
checked.
4.2 Use and storage of compressed-gas cylinders
The compressed-gas cylinders should be regularly tested by the appropriate authorities. Cylinders should not
be stored or used inside the laboratory. Rather, they should be located outside the laboratory in a place that is
well ventilated, away from direct heat, and accessible to service and safety personnel. The cylinders should
be provided with suitable pressure-reducing valves. If more than one cylinder is to be used or stored in close
proximity, it is advisable to indicate in some way which cylinder or cylinders are currently in use.
4.3 Handling of cryogenic materials
Vessels containing cryogenic materials should be located so as to minimize the risk to personnel. Areas
where cryogenic liquids are stored and used should be ventilated to prevent the accumulation of gas or
vapour which could evaporate from the liquid. It is good practice to keep areas where cryogenic liquids are
used very clean. All transfer operations should be in accordance with statutory requirements. When a
cryogenic liquid is being transferred from one vessel to another, precautions should be taken to minimize any
spills and splashing. The requirements of the relevant regulatory authorities should also be met.
5 Principle
In a glow discharge source, electrical power is supplied between the sample (cathode) and the anode by a
power supply typically operated in direct current (dc) at 0,5 kV to 2 kV and 1 mA to 300 mA. Argon (or another
inert gas such as neon, krypton or helium) is introduced into the discharge cell. The pressure inside the
discharge cell is typically a few hundred pascals (Pa). A potential difference is applied between the cathode
and the anode and a glow discharge (plasma) is established. Sample material (single atoms and/or clusters)
which is sputtered by ions and neutrals diffuses into the plasma.
Ions formed in the glow discharge are extracted from the ion source and pass into a mass analyser. The mass
analyser is used to transmit ions of given mass-to-charge ratio to the detector(s). The ions reaching the
detector(s) are measured as ion current or counted by a counting system. This information is stored in a
computer system. Elemental mass fractions are typically calculated by the instrument software using the ion
currents of isotopes, by normalizing the signal to the signal of a matrix element and subsequently comparing
the normalized signals with those arising from the corresponding elements in calibration samples.
6 Materials
6.1 Deionized water, 18 MΩ⋅cm or better.
6.2 Argon gas, or other plasma support gases, of purity better than 99,999 9 % or in accordance with the
recommendations of the instrument manufacturer.
6.3 Liquid nitrogen, for cryogenic cooling of the discharge cell.
6.4 Compressed gas, to operate pneumatic valves.
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ISO/TS 15338:2009(E)
7 Apparatus
7.1 Ion source
7.1.1 General
A glow discharge ion source consists of a glow discharge cell and a power supply. In some designs, the ion
source will also contain a series of focusing plates, external to the cell, whose function is to extract ions from
the cell and focus these ions into the mass spectrometer.
Typically the body of the discharge cell is connected to the anode output of the power supply. The sample
serves in the glow discharge cell as a cathode and is connected to the cathode output of the power supply.
Discharge cells have been designed to accommodate samples in the geometries recommended in 8.3, and
examples of discharge cells are illustrated with the appropriate sample holders in Figures 1 and 2.
Key
1 sample holder
2 sample
3 insulator
4 ion exit slit
5 anode plate
6 cathode plate
Figure 1 — Example of a cell used for the analysis of pin samples
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ISO/TS 15338:2009(E)
Key
1 sample cathode
2 spring
3 insulator
4 cell body
5 ion exit slit
6 anode plate
Figure 2 — Example of a cell used for the analysis of flat samples
7.1.2 Source parameters
The source parameters are as follows:
a) Electrical
⎯ potential difference between anode and cathode;
⎯ current;
⎯ power.
b) Geometrical
⎯ dimension of sample exposed to plasma;
⎯ anode-to-sample distance;
⎯ cathode dimension;
⎯ mask dimension, where appropriate.
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ISO/TS 15338:2009(E)
c) Gas type and pressure.
d) Cell temperature.
e) Type of sample.
7.1.3 Operational modes
The direct-current source may be operated in different modes, including:
a) constant current with potential difference adjusted by adjusting the plasma gas pressure;
b) constant potential difference with current adjusted by adjusting the plasma gas pressure;
c) constant current with plasma gas pressure adjusted by adjusting the potential difference.
The discharge pressure may be regulated using a mass flow controller, needle valve or knife edge valve. For
some types of GD-MS instrument, the high accelerating voltages encountered require a capillary in the gas
line to prevent electrical breakdown through the gas line. Radio-frequency-powered GD sources are also
being developed for GD-MS.
7.2 Mass analyser
There are two types of mass analyser commonly used for glow discharge mass spectrometry: double-
focussing magnetic-sector instruments and quadrupole instruments. Other types, like time-of-flight instruments,
are also becoming more common.
a) Sector mass spectrometer: This type of instrument (see Figure 3) typically utilizes an electromagnet
and an electrostatic analyser (ESA). The magnet achieves mass separation and, as the magnetic field is
increased, ions with greater mass-to-charge ratio are transmitted. The ESA acts as an energy filter and
transmits only those ions with the appropriate energies.
This arrangement permits high-transmission and high-resolution operation, giving accurate mass
information advantageous with complex sample matrices where there is an increased possibility of
interferences. A resolving power of 4 000 is sufficient to overcome most common interferences.
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ISO/TS 15338:2009(E)
Key
1 ion beam
2 source slit
3 magnet
4 intermediate slit
5 ESA
6 detector slit
7 detector
Figure 3 — Schematic diagram of a magnetic-sector mass analyser
b) Quadrupole: This type of mass spectrometer consists of four parallel rods whose centres form the
corners of a square and whose diagonally opposite poles are connected (see Figure 4). The voltage
applied to the rods is a superposition of a static potential and a sinusoidal radio-frequency potential. The
motion of an ion in the x and y directions is described by the Mathieu equation, the solutions of which
show that ions in a particular m/z (mass-to-charge ratio) range can be transmitted along the quadrupole
axis.
Whilst a quadrupole instrument does not have the high resolution of a magnetic-sector instrument (the
resolving power at mass-to-charge ratio 100 is usually less than 200), it has a much faster scanning
speed, is compact and is able to achieve low detection limits if interferences are kept low.
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ISO/TS 15338:2009(E)
Key
1 from ion source
2 non-resonant ion
3 resonant ion
4 detector
5 d.c.
6 a.c.
Figure 4 — Schematic diagram of a quadrupole mass analyser
c) TOF (time-of-flight) mass spectrometer: In this type of mass spectrometer, an ensemble of ions is
accelerated by an electric field and then allowed to drift a certain distance before impinging on an ion
detector (see Figure 5). In the accelerating field, all ions receive the same kinetic energy, which can be
2
equated to ½mv . Therefore, ions with a lower m/z (mass-to-charge ratio) will have a higher velocity and
will arrive at the detector earlier than ions with a higher m/z. By measuring the arrival time of ions, the m/z
of those ions can be determined.
Whilst quadrupole instruments and sector instruments are m/z filters, TOF instruments do not have to
scan in order to record a mass spectrum and therefore have the potential for a higher-duty cycle. TOF
instruments intrinsically have a large mass range and good mass accuracy. They also have reasonably
good resolving power, allowing them to overcome some interferences.
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ISO/TS 15338:2009(E)
Key
1 ion source 5 high-voltage pulser (starts the ions)
2 high-mass particle 6 detector (generates stop signal)
3 low-mass particle 7 signal
4 extractor 8 data-acquisition system (records time of flight)
a
Drift.
b
One start signal.
c
Multiple stop signals.
Figure 5 — Schematic diagram of a time-of-flight mass analyser
NOTE Other types of mass spectrometer (e.g. ion trap mass spectrometers) are being adapted for use with glow
discharge ion sources.
7.3 Detector system
As a consequence of the wide mass fraction range measured using GD-MS, usually two detectors are
required and/or needed, as follows:
a) Ion signals from matrix and major trace elements present at mass fractions typically above 0,1 % are
measured using a coarse detector such as a Faraday plate or an electron multiplier, operating in the
analogue mode. These detectors simply measure the current generated by the ion beam striking the
detector.
b) Ion signals from trace elements present at mass fractions typically below 0,1 % are measured using ion-
1)
counting techniques. Examples of ion-counting detectors are the Daly detector and the Channeltron ,
multi-channel plate and venetian-blind electron multipliers.
NOTE Any differences in the response of the detectors are reflected in the instrument calibration.
®
1) Channeltron is the trade name of a product supplied by Burle. This information is given for the convenience of users
of this Technical Specification and does not constitute an endorsement by ISO of this product.
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ISO/TS 15338:2009(E)
7.4 Vacuum system
A glow discharge ion source operates at a pressure of approximately 100 Pa, but optimum mass spectrometer
performance, in terms of transmission, resolution and abundance sensitivity, requires a pressure in the mass
−4
analyser of less than 1 × 10 Pa. To achieve such a vacuum level, differential pumping is required. This
means that both the ion source housing and the mass analyser are pumped independently.
There are diverse designs:
a) Diode geometry type source
−2
The resulting pressure outside the cell in the ion source is typically 1 × 10 Pa under normal operating
conditions. In addition, the test sample is usually introduced via a sample interlock, which is evacuated to
typically 1 Pa using a rotary pump or other suitable primary vacuum pump. This maintains the integrity of the
vacuum inside the source housing and minimizes contamination by atmospheric gases.
Alternatively, the source can be isolated from the mass analyser via an interlock and/or another device to
protect the mass analyser while the test sample is being changed.
b) Grimm type source
The resulting pressure outside the cell is usually in the same range as that inside the cell, which is typically
around 100 Pa under normal operating conditions. The test sample is introduced at atmospheric pressure and,
after closing the cover around the sample holder, the entire region is pumped to typically 1 Pa using a scroll
pump or another suitable primary vacuum pump. During the sample exchange there is a continuous flow of
discharge gas through the cell and cover to prevent atmospheric gases from entering the source.
The source is isolated from the mass analyser via a slide valve to maintain the vacuum of the mass analyser
while the test sample is being changed.
7.5 Data acquisition and control
The data-acquisition system should be capable of the following:
a) selection of analytes to be determined and isotopes to be monitored;
b) monitoring of key instrument parameters (see 9.8);
c) data acquisition, analysis and storage;
d) data processing;
e) report generation;
f) archiving of data.
8 Samples and sample preparation
8.1 General
The following guidelines should be followed for general sample preparation:
a) use inert materials, e.g. polytetrafluorethylene (PTFE) or polypropylene beakers, when etching samples;
b) use non-contaminating materials for all equipment in contact with the sample;
c) use high-purity acids and solvents.
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ISO/TS 15338:2009(E)
8.2 Sample type
Glow discharge mass spectrometry is suitable for the trace and ultra-trace elemental analysis of metals, alloys,
semiconductors and non-conductors and for depth-profiling applications.
Samples should preferably be in the form of solid material, for example wires, rods, pins, sheets, coupons,
irregular pieces, chunks, flat wafers, targets or powders.
NOTE There are also potential applications for GD-MS in the analysis of liquid residues and organic samples.
8.3 Sample geometry
Various instrument manufacturers have developed sample holders for specific sample geometries,
e.g. pin/rod/wire samples typically 20 mm in length and up to 10 mm across. For flat samples, the sputtered
area is usually 4 mm to 10 mm in diameter. The maximum size of the sample is restricted by the size of the
sample holder. Smaller sample sizes are achievable, but not normally recommended because of the resulting
reduction in the signal. The thickness of flat samples is not critical and is restricted only by the sample holder
design.
8.4 Sample preparation for bulk analysis
8.4.1 General
The objective of sample preparation is to provide a clean representative test sample of the sample under
investigation.
All test samples should be of the same nominal size as the calibration or reference sample.
For flat samples, a gas-tight surface is required to seal against the sample holder to maintain the proper argon
pressure inside the discharge cell.
8.4.2 Metals, alloys and semiconductors
Samples may be formed into the required geometry by many methods, e.g. casting, rolling, drawing, cutting,
machining or etching.
Surface finishing may involve machining, polishing, etching, solvent cleaning or drying.
8.4.3 Powders
Powders may be either conducting or non-conducting and should be treated as follows:
a) Conducting powders should be compacted using a die compaction press into an appropriate geometry in
accordance with 8.3.
b) Non-conducting powders are commonly mixed with a conducting medium. This mixture should then be
treated as a conducting powder.
The conducting medium should provide a stable discharge whilst providing sufficient signal to perform a
meaningful analysis. In addition, a medium should be chosen that minimizes interferences with the analyte(s)
to be determined.
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ISO/TS 15338:2009(E)
8.4.4 Non-conducting samples
For analysis with a direct current source, a secondary cathode (a metal mask containing an aperture) is
placed on the surface of the non-conducting sample such that the mask is maintained at the cathode potential.
The secondary cathode should provide a stable discharge whilst providing a sufficient signal to perform a
meaningful analysis. In addition, the material of which the secondary cathode is made should be chosen to
minimize interferences with the analyte(s) to be determined.
8.5 Sample preparation for depth profiling
Surface preparation may not be necessary or desired. If preparation is carried out, care should be taken not to
contaminate the surface or remove surface material of interest.
9 Measurement procedures
9.1 System precautions
9.1.1 General
For general operation of the system, refer to the manufacturers’ manuals and recommendations.
The following general precautions should be observed while operating the system:
a) It is good practice to wear a pair of powder-free gloves when handling vacuum components, including all
parts of the discharge cell and extraction optics. Vacuum components should be kept in a dust- and
moisture-free environment, such as a desiccator cabinet.
b) No specific personal protection equipment is required during normal operation. However, the operator
should be aware of any potential hazards associated with specific samples. For example, there is a
possibility of toxic materials accumulating in traps, pumps and other reservoirs within the instrument.
9.1.2 Interferences
Interference may occur when two ions (possibly molecular fragments or species) have the same or a similar
mass-to-charge ratio. The significance of this interference will vary depending upon the type of mass
spectrometer. Where these interferences occur, they cannot be generally resolved using a quadrupole
instrument, but in most cases they can be resolved using a magnetic-sector instrument. The most appropriate
isotopes, free of interferences and with the highest abundances possible, should be chosen. This will vary
between matrices.
As a general guide, for a metal, M, in a discharge atmosphere of argon, Ar, ionization processes produce a
+ + +
stable spectrum consisting mainly of singly charged atomic ions, M and Ar , with some dimer ions, M and
2
+ 2+ 3+ 2+
Ar , present. Multiply charged argon ions, Ar and Ar , and the like are evident. M ions are more
2
significant for metals with a low second-ionization potential. Combinations of metal and argon species, such
+ +
as MAr and MAr , are seen but, in general, the more complex the species,
...
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