ISO/TS 15338:2025

Technical
Specification
ISO/TS 15338
Third edition
Surface chemical analysis — Glow
2025-03
discharge mass spectrometry —
Operating procedures
Analyse chimique des surfaces — Spectrométrie de masse à
décharge luminescente (GD-MS) — Introduction à l'utilisation
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
5 Apparatus . 1
5.1 Ion source .1
5.2 Mass analyser .5
5.3 Detector system.5
6 Routine operations . 6
6.1 Cleaning the system .6
6.2 Support gas handling .6
7 Calibration . 7
7.1 Mass calibration .7
7.2 Detector calibration .7
7.3 Routine checks .8
8 Data acquisition . 9
8.1 Sample preparation .9
8.2 Procedure setup .9
8.3 Data acquiring .10
9 Quantification .10
9.1 Element integral calculation .10
9.2 Ion beam ratios.11
9.3 Fully quantitative analysis .11
9.4 Semi quantitative analysis . 12
9.5 Combination of semi quantitative and quantitative analysis . 12
Bibliography .13

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
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This document was prepared by Technical Committee ISO/TC 201, Surface chemical analysis, Subcommittee
SC 8, Glow discharge spectroscopy.
This third edition cancels and replaces the second edition (ISO/TS 15338:2020), which has been technically
revised.
The main changes are as follows:
— additional technical information have been added to the principle, apparatus and routine operations
— minor editorial changes.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Technical Specification ISO/TS 15338:2025(en)
Surface chemical analysis — Glow discharge mass
spectrometry — Operating procedures
1 Scope
This document specifies procedures for the operation and use of glow discharge mass spectrometry (GD-
MS). There are several GD-MS systems from different manufacturers in use and this document describes the
differences in their operating procedures when appropriate.
NOTE This document is intended to be read in conjunction with the instrument manufacturers’ manuals and
recommendations.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Principle
In a glow discharge source, a potential difference is applied between the cathode (the sample to be analysed)
and the anode, and a plasma is supported by the introduction of an inert gas, normally argon, but other inert
gases can be used. This potential difference can be either direct current (DC) or radio frequency (RF), the
advantage of RF being that electrically insulating materials can be analysed directly. The impacts of inert
gas ions and fast neutrals formed within the plasma on the surface of the sample result in the production of
neutrals by sputtering from surface.
These neutrals diffuse into the plasma where they are subsequently ionised within the equipotential area of
the plasma and can then be extracted to a mass spectrometer for analysis. Both magnetic sector and time of
flight spectrometers are available.
5 Apparatus
5.1 Ion source
There are two fundamental types of ion source used for the GD-MS, a low flow or “static” source, and a
fast flow source. Both types can accept pin samples or samples with a flat surface. A typical pin would be
20 mm long with a diameter of 3 mm, and a typical flat sample would be 20 mm to 40 mm diameter. It must
be big enough to cover the hole in the chosen anode plate and provide a good gas seal. More details of these
dimensions can be found later.
In the low flow source, the plasma cell is effectively a sealed unit held within a high vacuum chamber, with
a small exit slit or hole to allow the ions to exit the cell and enter the mass spectrometer. The cell body is
at anode potential, the acceleration potential of the mass spectrometer, and the sample is held at cathode

potential, typically 1 kV below anode potential. In this type of source, the argon flow is typically one sccm
(standard atmosphere cubic centimetres per minute) or less, and the gas used, normally argon, should be of
very high purity, six nines five or better. The power of the plasma is relatively low, typically 2 W or 3 W; the
potential difference is typically 1 kV and the current 2 mA or 3 mA.
Key
1 insulator
2 sample (cathode)
3 anode (GD cell)
a
Gas inlet (0,3 sccm to 0,6 sccm).
b
To mass spectrometer.
Figure 1 — Low flow source pin geometry
A schematic diagram of the low flow source in pin geometry is shown in Figure 1. The gas is introduced
into the cell through a metal pipe which forms a metal to metal seal with the cell body. On some systems an
alternative of a PEEK tube with a ferrule seal to the cell body is used. If a metal pipe is used, then an insulating
material must be included in the gas line as the cell is at anode potential. This is normally a piece of quartz
with a very small diameter hole through which the gas passes. The pin sample is held in a chuck which sits at
cathode potential and the cell body is at anode potential, so the two are separated by an insulating disc. The
chuck is actually located against a metal (tantalum) plate which also sits at cathode potential (not shown
in the schematic diagram). The whole assembly forms a good gas seal while maintaining good electrical
insulation. The only escape for the gas and any ions formed in the plasma is through a small slit or hole at the
back of the cell, and this creates a pressure differential between the cell and the surrounding source vacuum
chamber. It is normal to measure the pressure outside the cell in a low flow source rather than in the cell
itself, the presence of a plasma making the measurement difficult. In this geometry, the potential difference
between the anode and cathode “drops” in a small sheath approximately 1 mm around the sample, thus
leaving the main gas volume in the cell at the same potential. So any ions formed in the “plasma cloud” will
not be electrically attracted back to the cathode.
It is standard practice in the low flow source to cool the plasma to near liquid nitrogen temperatures. This
has been shown to reduce significantly the formation of molecular species associated with the matrix and
plasma support gas combined as dimers or trimers, or with gas backgrounds such as hydrogen, nitrogen and
oxygen. Cooling the sample in this way also allows for the measurement of low melting point materials such
as gallium and indium, materials that would melt under normal plasma conditions.
Heat transfer between the components of the plasma cell needs to be considered. The whole cell assembly is
floated up to the accelerating potential, so the anode will typically be around 6 kV to 8 kV while the sample
(cathode) is at approximately 1 kV lower during operation. The design of the heat exchanger, or cooling

assembly, means that it will be sitting at ground potential, and so it is connected to the cell insulating
disc which is of a larger diameter than the cell body (not shown in Figure 1). Thus, it is necessary for the
insulating disc to have a good coefficient of heat transfer at the same time as being electrically insulating;
the material boron nitride is ideal for this and is used in most systems. It is important to consider heat
transfer through all junctions, particularly from the cell body and cathode plate through the insulator to the
heat exchanger. In order to make the sample cold, it is important to use a sample holder, or chuck, that is of a
similar diameter to the sample itself. It is possible to maximise the heat transfer if attention is paid to detail,
for example, a piece of Indium foil can be cut and shaped to fit between the heat exchanger and the insulator,
providing that care is taken to ensure that there can be no electrical leakage. If a pin sample of square cross
section is analysed, then the contact with the round hole in the holder gives very poor heat transfer, limiting
the cooling of the sample. This can be improved by warming the chuck and filling with pure Gallium before
inserting the sample.
Key
1 insulator
2 sample (cathode)
3 anode (GD cell)
a
Gas inlet (0,2 sccm to 0,4 sccm).
b
To mass spectrometer.
Figure 2 — Low flow source flat geometry
Figure 2 shows a schematic of the low flow source in flat geometry. The sample, which forms the cathode in
the plasma, is pressed against an insulator which in turn is pressed against the cell body which is at anode
potential. Again, a good gas seal is formed and the only escape route for the gas and the sputtered particles
is through the ion exit slit or hole. The area of the sample exposed to the plasma can be varied by the choice
of the insulator used. If a larger area of sample is exposed then a larger ion beam will be produced, but it is
possible to use smaller insulators to allow smaller samples to make a gas seal, or to reduce the area exposed
to analysis. Commercial systems will generally have insulators available to allow areas from 2 mm to 20 mm
diameter to be exposed, but 10 mm to 15 mm is the normal. The most important need is that the sample
surface shall be flat in order to make a good gas seal with the insulating disc.
The gap between the sample (cathode) and the anode has to be small (less than a critical distance, typically
1 mm) to avoid creation of a discharge in the gap. It is often a problem that sputtered material can be
deposited on the inner diameter of the insulator, creating a short circuit between anode and cathode. This
can be avoided by the use of two insulators with different diameter holes.

Figure 3 shows the fast flow source. In this geometry the sample (shown here as a flat sample) is pushed
against the back of the source and is raised to cathode potential. The discharge gas (normally argon) is
injected between a tube at anode potential and a concentric flow tube and is directed towards the sample
surface. The flow rate of the argon is in the region of 300 ml/min to 500 ml/min. The same high purity
support gas as used in the low flow source is not required, a typical purity would be five nines.
Key
1 insulator
2 sample (cathode)
3 anode
4 flow tube
5 cone
Figure 3 — Fast flow source flat geometry
The potential difference between anode and cathode is typically 800 V and the current typically 30 mA or
40 mA. Sample atoms that are sputtered from the surface and ionised enter the mass spectrometer through
an orifice in the sampling cone as shown in the diagram.
In a fast flow source, the signals are largely independent of the sample temperature and Peltier cooling is
used to reduce sample overheating. The use of liquid nitrogen cooling is not necessary as the high power
of the plasma inhibits the formation of molecular ions. A significant reduction from room temperature is
required only for certain high melting point samples.
In all cases described above, the ions are accelerated into the mass analyser by a high potential difference,
typically 6 kV to 8 kV. In most cases the source is held at high potential and the analyser at ground, but it is
possible to achieve the same potential difference by grounding the source and taking the analyser section to
a negative high voltage.
The extracted ions are focussed and steered onto a source defining slit by a series of steering plates and
lenses at different potentials. This source defining slit or sampling cone is typically at ground potential and
forms the object that the analyser will focus onto the detector. Different sizes of source defining slit are
available, in some instruments there is a finite number of alternatives, in others the source defining slit
is infinitely adjustable. For high resolution, where interference peaks need to be separated from the peak
of interest, a small source defining slit shall be used. But for the analysis of impurities where there is no
interference peak, it can be possible to have a large source defining slit to allow more ionised particles to
pass through, hence making it possible to detect lower levels of the impurity.

The potential between anode and cathode can either be a steady DC voltage, a radio frequency (RF) voltage,
or can be a modulated pulsed voltage. In this last case, the cathode potential is switched rapidly, typically
at a frequency of 2 000 Hz with a pulse duration of 50 μs, a duty cycle of 10 %. It has been shown that in
the case of the fast flow source, this mode of operation can be beneficial for bulk analysis by improving
long term stability and precision. It also makes possible depth profiling of layered samples and secondary
cathode analysis of insulators.
In the case of the recently developed time of flight (TOF) mass spectrometer, the source is similar to the fast
flow source and the accelerating potential is always pulsed so that very short bursts of ions are introduced
to the analyser section.
5.2 Mass analyser
The purpose of the mass analyser is to separate ions of different species by mass. More precisely the
separation is by mass charge ratio; an Ar ion with a single charge would be seen at 40 u (atomic mass units),
but the same ion with two electrons removed would appear at 20 u. As well as multiple charged species,
40 +
some molecular species are seen in the spectrum, an example being Ar which would appear at 80 u.
Some GD-MS instruments work at high resolution and are capable of resolving most interferences from the
peak of interest. These systems can also be operated at low resolution if there are no interferences to be
resolved, thereby giving a larger signal and more precise measurement or better detection limits.
All mass spectrometers operate under vacuum to ensure that the mean free path without collision is as
great as possible, resulting in a cleaner signal at the collector. The analyser section of the instrument should
be left under vacuum whenever possible, and for this reason all systems incorporate a valve to isolate the
analyser from the source which needs to be exposed to atmosphere frequently.
In those systems which consist of a magnet and ESA (electrostatic analyser) the ions are separated in mass
by the magnetic field, and any small spread in energy is removed by the ESA. Some systems use a forward
style Nier Johnston geometry (ESA then magnet), others use a reverse style (magnet then ESA). A continuous
stream of ions will enter the analyser and the masses of interest are measured sequentially. In the case of
the TOF, a complete spectrum is acquired for each individual pulse.
5.3 Detector system
The magnetic sector GD-MS instruments are designed to measure as large a spread of signal intensities as
possible, and there may be more than one type of detector on an instrument.
−9 10
Very large signals (around 10 A) can be produced by GD-MS instruments, an ion current equivalent to 10
ions per second. These signals cannot be measured by any ion counting system and so are collected by a
Faraday cup and converted to a voltage by a current amplifier. A typical amplifier will produce a signal of 1 V
−9 −14
for an ion current of 10 A. Currents down to 10 A can be registered by the same amplifier using a digital
voltmeter with good resolution.
−13 6
Below 3 × 10 A, equivalent to 2 × 10 counts per second, ion counting systems are used. On some
instruments this is a Daly system, which consists of a conversion electrode, a scintillator and a
photomultiplier tube outside the vacuum. On others it is an electron multiplier mounted inside the vacuum
system of the mass analyser. For both of these alternatives, the associated electronics will be able to switch
the signal between the alternative detectors and will protect the more sensitive multiplier for the incidence
of large signals which could cause damage.
On systems which use more than one detector, there will be software to cross calibrate the detectors.
Signals of suitable strength are measured both detectors to show the effective efficiency of the multipliers.
This can change for many reasons, supply voltage changes or aging being two reasons, and so it is important
to monitor it on a regular basis. More details of this calibration and the monitoring are given later.
In time of flight systems, micro channel plates (MCPs) are used to measure the signal as a very fast response
is needed. When a pulse of ions is introduced into the analyser, all ions have the same kinetic energy and so
different masses travel at different velocities and reach the detector at different times. Data for the whole

mass spectrum is acquired and stored for each individual pulse, a full spectrum being acquired in a few tens
of microseconds.
6 Routine operations
6.1 Cleaning the system
As with all vacuum systems, cleanliness is extremely important. Any components that fit within the vacuum
system should only be handled when wearing gloves. Powder free gloves are preferred otherwise a residue
of chemical such as silicon can be left behind.
Some systems have the internal source parts made from tantalum as this is effectively mono-isotopic with
an odd number mass that produces less background interferences and can be thoroughly cleaned with
acids. The source parts need to be cleaned regularly to remove sputter deposited coating that can produce
instability, and if different matrices are analysed these depositions can cause memory effects. In the case of
tantalum parts, they should be cleaned mechanically by scrubbing with an abrasive sponge-like material,
then soaked in an acid suitable to dissolve the matrix material. For particularly difficult matrices, a strong
acid such as aqua regia (1:3, HNO :HCl) with a small percentage (~2 %) HF can be used. The acid wash should
then be followed with several washes with deionised water and finally with methanol.
Stainless steel components should be treated more carefully than the tantalum items, but as they are not
usually in direct contact with the ion beam a mechanical wash followed by soaking briefly in 50 % HNO and
a rinse in deionised water then methanol is normally sufficient.
Any ceramic components should not be cleaned with liquids as they tend to be absorbent, a simple mechanical
scrub should suffice.
In order to reduce down time as a result of cleaning sourc
...