CEN ISO/TS 19590:2024
(Main)Nanotechnologies - Characterization of nano-objects using single particle inductively coupled plasma mass spectrometry (ISO/TS 19590:2024)
Nanotechnologies - Characterization of nano-objects using single particle inductively coupled plasma mass spectrometry (ISO/TS 19590:2024)
This document specifies parameters, conditions and considerations for the reliable detection, characterization and quantification of nano-objects in aqueous suspension by spICP-MS.
Particle number concentration, particle mass, particle mass concentration, particle spherical equivalent diameter, and number-based size distribution are considered the main measurands, but the technique also allows for determination of the dissolved element mass fraction in the sample. This document provides general guidelines and procedures related to spICP-MS application, and specifies minimal reporting requirements.
Nanotechnologien - Charakterisierung von Nanoobjekten mit Hilfe der Massenspektrometrie mit induktiv gekoppeltem Einzelpartikelplasma (ISO/TS 19590:2024)
Dieses Dokument legt Parameter, Bedingungen und Überlegungen für den zuverlässigen Nachweis, die Charakterisierung und die Quantifizierung von Nanoobjekten in wässriger Suspension mit der spICP MS fest.
Partikel-Anzahlkonzentration, Partikelmasse, Partikel-Massenkonzentration, Kugeläquivalentdurchmesser der Partikel und anzahlbasierte Größenverteilung werden als Hauptmessgrößen betrachtet, allerdings ermöglicht die Technik auch die Bestimmung des Massenanteils gelöster Elemente in der Probe. Dieses Dokument enthält allgemeine Anleitungen und Verfahren für die Anwendung von spICP MS und legt Mindestanforderungen an den Prüfbericht fest.
Nanotechnologies - Caractérisation des nano-objets par spectrométrie de masse à plasma induit en mode particule unique (ISO/TS 19590:2024)
Le présent document décrit les paramètres, conditions et autres aspects à prendre en compte pour la détection, la caractérisation et la quantification fiables des nano-objets en suspension aqueuse par spICP-MS.
La concentration en nombre de particules, la masse des particules, la concentration massique des particules, le diamètre sphérique équivalent des particules et la distribution granulométrique en nombre sont considérés comme les principaux mesurandes, mais la technique permet également de déterminer la fraction massique d’un élément dissout dans l’échantillon. Le présent document fournit des lignes directrices générales et des modes opératoires liés à l’application de la spICP-MS, et spécifie les exigences minimales en matière de rapport.
Nanotehnologija - Karakterizacija nanoobjektov z uporabo masne spektrometrije z enim delcem v induktivno sklopljeni plazmi (ISO/TS 19590:2024)
Ta dokument določa parametre, pogoje in vidike za zanesljivo odkrivanje, karakterizacijo in kvantifikacijo nanopredmetov v vodni suspenziji z uporabo masne spektrometrije z enim delcem v induktivno sklopljeni plazmi.
Koncentracija števila delcev, masa delcev, masna koncentracija delcev, sferični ekvivalentni premer delcev in porazdelitev velikosti na osnovi števila so glavne merjene količine, vendar tehnika omogoča tudi določitev masnega deleža raztopljenega elementa v vzorcu. Ta dokument podaja splošne smernice in postopke v zvezi z uporabo masne spektrometrije z enim delcem v induktivno sklopljeni plazmi in določa minimalne zahteve za poročanje.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-november-2024
Nanotehnologija - Karakterizacija nanoobjektov z uporabo masne spektrometrije z
enim delcem v induktivno sklopljeni plazmi (ISO/TS 19590:2024)
Nanotechnologies - Characterization of nano-objects using single particle inductively
coupled plasma mass spectrometry (ISO/TS 19590:2024)
Nanotechnologien - Größenverteilung und Konzentration anorganischer Nanopartikel in
wässrigen Medien durch Massenspektrometrie an Einzelpartikeln mit induktiv
gekoppeltem Plasma (ISO/TS 19590:2024)
Nanotechnologies - Caractérisation des nano-objets par spectrométrie de masse à
plasma induit en mode particule unique (ISO/TS 19590:2024)
Ta slovenski standard je istoveten z: CEN ISO/TS 19590:2024
ICS:
07.120 Nanotehnologije Nanotechnologies
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
CEN ISO/TS 19590
TECHNICAL SPECIFICATION
SPÉCIFICATION TECHNIQUE
August 2024
TECHNISCHE SPEZIFIKATION
ICS 07.120 Supersedes CEN ISO/TS 19590:2019
English Version
Nanotechnologies - Characterization of nano-objects using
single particle inductively coupled plasma mass
spectrometry (ISO/TS 19590:2024)
Nanotechnologies - Caractérisation des nano-objets par Nanotechnologien - Charakterisierung von
spectrométrie de masse à plasma induit en mode Nanoobjekten mit Hilfe der Massenspektrometrie mit
particule unique (ISO/TS 19590:2024) induktiv gekoppeltem Einzelpartikelplasma (ISO/TS
19590:2024)
This Technical Specification (CEN/TS) was approved by CEN on 12 August 2024 for provisional application.
The period of validity of this CEN/TS is limited initially to three years. After two years the members of CEN will be requested to
submit their comments, particularly on the question whether the CEN/TS can be converted into a European Standard.
CEN members are required to announce the existence of this CEN/TS in the same way as for an EN and to make the CEN/TS
available promptly at national level in an appropriate form. It is permissible to keep conflicting national standards in force (in
parallel to the CEN/TS) until the final decision about the possible conversion of the CEN/TS into an EN is reached.
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United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
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CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2024 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN ISO/TS 19590:2024 E
worldwide for CEN national Members.
Contents Page
European foreword . 3
European foreword
This document (CEN ISO/TS 19590:2024) has been prepared by Technical Committee ISO/TC 229
"Nanotechnologies" in collaboration with Technical Committee CEN/TC 352 “Nanotechnologies” the
secretariat of which is held by AFNOR.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes CEN ISO/TS 19590:2019.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to announce this Technical Specification: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO/TS 19590:2024 has been approved by CEN as CEN ISO/TS 19590:2024 without any
modification.
Technical
Specification
ISO/TS 19590
Second edition
Nanotechnologies —
2024-08
Characterization of nano-objects
using single particle inductively
coupled plasma mass spectrometry
Nanotechnologies — Caractérisation des nano-objets par
spectrométrie de masse à plasma induit en mode particule unique
Reference number
ISO/TS 19590:2024(en) © ISO 2024
ISO/TS 19590:2024(en)
© ISO 2024
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
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Email: copyright@iso.org
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Published in Switzerland
ii
ISO/TS 19590:2024(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 3
5 Principles of operation . 4
5.1 Introduction to spICP-MS .4
5.2 Reference material dependent calibration methods .6
5.2.1 Particle frequency method .6
5.2.2 Particle size method .8
5.3 Reference material free calibration methods .9
5.3.1 Dynamic mass flow method .9
5.3.2 Microdroplet calibration method .11
5.4 Particle number concentration determination . 13
5.5 Particle mass and corresponding spherical equivalent diameter determination . .14
5.6 Dissolved element fraction .17
5.7 Multi-isotope and multi-elemental analysis .17
5.8 Data treatment .18
6 Method development . 19
6.1 Sample specification .19
6.2 Sample preparation .19
6.2.1 Aqueous suspensions and paste . 20
6.2.2 Non-aqueous suspensions and creams. 20
6.2.3 Powders .21
6.2.4 Larger pieces of solids .21
6.3 Selection of reference materials, quality control materials and representative test
materials .21
6.4 Optimization of ICP-MS operating conditions . 22
7 Qualification, performance criteria and measurement uncertainty .23
7.1 Applicability of spICP-MS . 23
7.2 System qualification and quality control . 23
7.3 Method performance criteria .24
7.3.1 Particle number concentration .24
7.3.2 Particle mass and equivalent spherical diameter .24
7.4 Method precision and measurement uncertainty . 25
8 General measurement procedure .25
9 Test report .26
9.1 Apparatus and measurement parameters . 26
9.2 Reporting test results . 26
Bibliography .27
iii
ISO/TS 19590:2024(en)
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.
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
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 229, Nanotechnologies, in collaboration with
the European Committee for Standardization (CEN) Technical Committee CEN/TC 352, Nanotechnologies, in
accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This second edition cancels and replaces the first edition (ISO/TS 19590:2017), which has been technically
revised.
The main changes are as follows:
— general restructuring;
— expansion of text on the test method;
— inclusion of considerations regarding method precision and measurement uncertainty;
— updates to normative and bibliographical references.
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
ISO/TS 19590:2024(en)
Introduction
Following the introduction of single particle inductively coupled plasma mass spectrometry (spICP-MS)
[1]
by Degueldre in 2003, the technique has increasingly been used for nano-object characterization due to
its high sensitivity, elemental specificity, the fact that often minimal sample preparation is needed and the
development of much improved instrumentation, along with user-friendly data analysis software.
In spICP-MS, a very diluted suspension containing nano-objects is introduced continuously into an ICP-MS
system with the intent that the ion cloud from one particle at a time arrives at the detector, set to acquire
data with a high time resolution (i.e. dwell time). Following the nebulization, a fraction of the nano-objects
enter the plasma where they are atomized, and the individual atoms ionized. Every atomized particle results
in a cloud of ions which is then sampled by the mass spectrometer. The mass spectrometer can be tuned to
measure any specific element. Typically, only one mass-to-charge value per single particle will be monitored
with a quadrupole-based MS instrumentation. However, the technique can also be used with time-of-flight
(TOF) mass spectrometers, allowing simultaneous multi-element and multi-isotope detection.
The number of events detected in each run (time scan) is directly proportional to the number of nano-objects
in the suspension introduced but necessitates calibration of the sample transport efficiency to calculate
the particle number concentration. Several available approaches to measure the transport efficiency are
described in detail in this document. The intensity of the measured signal is directly proportional to the
mass of the measured element in the nano-object, which can be derived following appropriate calibration
of the instrument’s response factor, also described in this document. For particles of known geometry,
composition and density, the mass can be related to particle size. Most of the currently available, commercial
data analysis software assumes spherical geometry; particle diameter is proportional to the cubic root of
the mass of element(s) in a spherical nano-object. In addition to nano-object characterization with spICP-MS,
mass concentrations of dissolved element present in the same sample can also be determined from the same
data, if a good separation between the dissolved and particulate fraction is achieved. This represents one of
the key advantages of the technique.
spICP-MS was once predominantly the domain of specialist laboratories, but with recent developments in
commercially available hardware and software, the technique is now more commonly used and increasingly
popular for high-throughput analysis as well as high accuracy reference measurements.
Further information on spICP-MS can be found in ISO/TS 24672, and References [1], [2], [3], [4] and [5].
v
Technical Specification ISO/TS 19590:2024(en)
Nanotechnologies — Characterization of nano-objects using
single particle inductively coupled plasma mass spectrometry
1 Scope
This document specifies parameters, conditions and considerations for the reliable detection,
characterization and quantification of nano-objects in aqueous suspension by spICP-MS.
Particle number concentration, particle mass, particle mass concentration, particle spherical equivalent
diameter, and number-based size distribution are considered the main measurands, but the technique also
allows for determination of the dissolved element mass fraction in the sample. This document provides
general guidelines and procedures related to spICP-MS application, and specifies minimal reporting
requirements.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements 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 18115-1, Surface chemical analysis — Vocabulary — Part 1: General terms and terms used in spectroscopy
ISO/TS 80004-6, Nanotechnologies — Vocabulary — Part 6: Nano-object characterization
ISO/TS 80004-8, Nanotechnologies — Vocabulary — Part 8: Nanomanufacturing processes
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/TS 80004-6, ISO/TS 80004-8,
ISO 18115-1 and the following apply.
ISO and IEC maintain terminological 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/
3.1
nano-object
discrete piece of material with one, two or three external dimensions in the nanoscale
[SOURCE: ISO 80004-1:2023, 3.1.5]
3.2
nanoscale
length range approximately from 1 nm to 100 nm
[SOURCE: ISO 80004-1:2023, 3.1.1]
3.3
particle
minute piece of matter with defined physical boundaries
Note 1 to entry: A physical boundary can also be described as an interface.
ISO/TS 19590:2024(en)
Note 2 to entry: This general particle definition also applies to nano-objects.
[SOURCE: ISO 80004-1:2023, 3.2.1]
3.4
nanoparticle
NP
nano-object with all external dimensions in the nanoscale
Note 1 to entry: If the dimensions differ significantly (typically by more than three times), terms such as "nanofibre"
or "nanoplate" are preferable to the term nanoparticle.
[SOURCE: ISO 80004-1:2023, 3.3.4]
3.5
agglomerate
collection of weakly or medium strongly bound particles where the resulting external surface area is similar
to the sum of the surface areas of the individual components
Note 1 to entry: The forces holding an agglomerate together are weak forces, for example, van der Waals forces or
simple physical entanglement.
Note 2 to entry: Agglomerates are also termed secondary particles and the original source particles are termed
primary particles.
[SOURCE: ISO 26824:2022, 3.1.2]
3.6
aggregate
particle comprising strongly bonded or fused particles where the resulting external surface area is
significantly smaller than the sum of surface areas of the individual components
Note 1 to entry: The forces holding an aggregate together are strong forces, for example, covalent or ionic bonds, or
those resulting from sintering or complex physical entanglement.
Note 2 to entry: Aggregates are also termed secondary particles and the original source particles are termed primary
particles.
[SOURCE: ISO 26824:2022, 3.1.3, modified — Note 1 to entry has been adapted.]
3.7
spICP-MS
single particle inductively coupled plasma mass spectrometry
method using inductively coupled plasma mass spectrometry whereby a dilute suspension of nano-objects
is analyzed, and the ICP-MS signals collected at high-time resolution, allowing particle-by-particle element
detection at specific mass peaks and number concentration, size and size distribution to be determined
3.8
dwell time
time during which the ICP-MS detector accumulates signal corresponding to an individual reading along the
time scan
Note 1 to entry: Following integration, the total ion count number per dwell time is registered as one data point,
expressed in counts or counts per second.
3.9
transport efficiency
ratio of detected particle events to particles introduced
Note 1 to entry: Depending on the solvent and analyte combination used, transport efficiency can be considered equal
to nebulization efficiency.
ISO/TS 19590:2024(en)
3.10
nebulization efficiency
ratio of the amount of nebulized sample reaching the plasma to the amount of the sample introduced
Note 1 to entry: It is often used interchangeable with "transport efficiency".
3.11
time scan
total acquisition time
duration of one replicate measurement
Note 1 to entry: This is typically set as 1 min, but can be extended to few minutes in order to increase the number of
registered particle events.
3.12
event
signal intensity registered by mass spectrometer caused by the ion cloud from a single particle, aggregate or
agglomerate
3.13
BED
background equivalent diameter
spherical equivalent diameter of the smallest particle that can be detected with spICP-MS
Note 1 to entry: Assuming spherical geometry, for particles of known chemical composition and density, the
corresponding background equivalent diameter can be calculated (see 5.3) from the mass of the smallest particle that
can be detected with spICP-MS, which in turn is determined by the instrument sensitivity along with the background
signal, for the given dwell time.
3.14
particle number concentration
number of particles in the specific mass of a suspension
-1 -1
Note 1 to entry: Particle number concentration is typically expressed as g or kg .
-1
Note 2 to entry: It can also be expressed per volume, e.g. L .
Note 3 to entry: To convert between units, the density of the suspension must be determined.
3.15
m/z
mass-to-charge ratio
positive absolute value of the quantity formed by dividing the mass of an ion by the unified atomic mass unit
and by its charge number
[SOURCE: ISO 18115-1:2023, 20.1]
4 Abbreviated terms
For the purposes of this document, the following symbols and abbreviations apply.
BIPM CCQM Bureau International des Poids et Mesures Consultative Committee for Amount of Substance:
Metrology in Chemistry and Biology
DI delegated institutes
DMF dynamic mass flow
EM electron-multiplier
ICP-MS inductively coupled plasma mass spectrometry
ISO/TS 19590:2024(en)
ILC interlaboratory comparison
IS internal standardization
LOD limit of detection
LOQ limit of quantification
NMI national measurement institute
PTA particle tracking analysis
PHD pulse-height distribution
QCM quality control materials
Q-MS quadrupole mass spectrometers
RM reference materials
RTM representative test material
SF-MS sector-field mass spectrometers
TE transport efficiency
TEM transmission electron microscopy
TOF time-of-flight
TRA time resolved analysis
ULOQ upper limit of quantification
ULOQsize upper size limit of quantification
VAMAS Versailles Project on Advanced Materials and Standards
5 Principles of operation
5.1 Introduction to spICP-MS
[1]
Since the introduction of spICP-MS by Degueldre in 2003, the technique has increasingly gained popularity
for nanoparticle analysis due to its high sensitivity, elemental specificity, often minimal sample preparation
and the development of much improved instrumentation with fast, continuous data acquisition and software
[2]
able to handle the large amount of data produced during spICP-MS experiments.
In spICP-MS, a very dilute particle suspension is introduced into the instrument to minimize the possibility
of more than one particle being detected in a single event (e.g. 2 or 3 particles). The inductively coupled
plasma atomizes and ionizes the constituent analyte, generating discrete pulses of ions above the continuous
background signal at a corresponding mass-to-charge ratio (m/z), lasting a few hundred microseconds. If
the MS detector is set to acquire data with dwell times in the range from microsecond to low millisecond,
individual or so called "single" particle events (signal intensity spikes) can be detected.
The number of events detected in each analysis window (time scan) is directly proportional to the number
of nano-objects in suspension introduced into the ICP-MS, whilst the intensity of the measured signal is
directly proportional to the mass of the measured element within the nano-object.
NOTE 1 Constituent particles as well as aggregates are counted as single objects, and in some cases, it can be
challenging to resolve the two.
ISO/TS 19590:2024(en)
In addition, the mass concentrations of dissolved element fraction present in the sample alongside nano-
objects can be determined from the same data, as illustrated in Figure 1.
Key
X time
Y event intensity, counts
A particle number-based concentration
B element mass per particle (~size)
C dissolved fraction
Figure 1 — Measurement principle of spICP-MS
The number of detected events in the time scan is related to the particle number concentration, whilst their
intensity is related to the mass of element in the particles, which in turn can be converted to particle size. A
dissolved element appears as constant background signal.
However, to obtain accurate particle number concentration and size values with spICP-MS, it is necessary
to establish what portion of the acquired nano-objects is actually detected as particle events. This is a key
parameter in spICP-MS analysis, called the transport efficiency (η ). The terms "transport efficiency"
transport
and "nebulization efficiency" are often used interchangeably and are related to sample introduction and
nebulization processes in atomic spectrometry.
NOTE 2 Reference [3] suggested transport efficiency is a combination of nebulization and transmission efficiencies.
In this regard, nebulization efficiency is the amount of introduced liquid actually converted into a spray and reaching
the plasma (i.e., 100 % in case of a total consumption nebulizer). While the transmission efficiency is the extent of
this spray effectively reaching the detector, i.e. after being desolvated, vaporized, atomized, ionized, passed into the
mass spectrometer, and then collected on the ion-detector after mass separation. However, the issue of the different
ionization, extraction, transmission and detection of particles versus dissolved elements can also be addressed
[4]
alternatively from a calibration approach, where the efficiency of these processes is included as a detection efficiency
(K ) in Formula (1):
ICP-MS
M M
YK==XK KK X (1)
RR introICP-MSM
where
ISO/TS 19590:2024(en)
M
K is the analytical sensitivity obtained from a conventional calibration of Y vs. X (signal
R R
intensity in cps vs. element mass concentration);
K (= ηQ ) is a factor related to the sample introduction;
intro sam
η is the analyte nebulization efficiency;
Q is the sample introduction flow rate;
sam
K is the detection efficiency, which represents the ratio of the number of ions detected
ICPM− S
versus the number of analyte atoms of the measured isotope introduced into the ICP;
K is a factor related to the element measured, including the atomic abundance of the
M
isotope considered, the Avogadro number, and the atomic mass of the element.
It is important to highlight that spICP-MS methods are not different from any other quantitative analytical
methods based on calibration and the use of standards. More importantly, both particle number
concentration and size can be derived by direct calibration using reference materials (RMs) characterized
for particle number concentration or size, respectively.
With classic sample introduction systems (i.e. pneumatic nebulizer and cyclonic or double pass spray
chamber), depending on the instrument manufacturer, the η is expected to be between 1 % to
transport
15 %. However, more efficient introduction systems are now available, such as total consumption sample
introduction systems, direct injection nebulizers, demountable direct injection high efficiency nebulizers
and single-cell introduction systems. These can be used to reach transport efficiencies of up to 100 %.
However, transport efficiency parameters should be determined for both standard and high consumption
sample introduction systems, in order to ensure reliable nano-object characterization.
Two of the most popular approaches used for calculation of the transport efficiency include the particle
frequency and the particle size methods. Both approaches rely on the use of nanoparticle RMs. Since the
number of RMs available commercially is limited (see Table 2), recent research efforts have focused on
the development of RM-free approaches to transport efficiency determination, such as dynamic mass flow
(DMF) and microdroplet methods. These methods can be used to characterize RM, representative test
materials (RTMs) or quality control materials (QCMs) in house for particle number concentration, amongst
other techniques, such as electron microscopy which can be used to characterize particle size.
5.2 Reference material dependent calibration methods
5.2.1 Particle frequency method
In the particle frequency method, one of the following is introduced into the ICP-MS:
a) a monodisperse nanoparticle RM with known particle characteristics, such as elemental composition
and density and with certified spherical equivalent diameter and elemental mass concentration (see
Formula 2);
b) a particle-number concentration (see Formula 3).
The number of particles is then measured over duration of time scan.
-1
In practical terms, for sample uptake rate in the range of (0,2 – 0,4) g min , and RM concentration in the
-1 -1
range of (50 000 – 200 000) g for (25 – 100) µs dwell time or (10 000 – 30 000) g for (3 – 10) ms dwell
-1
time, a typical particle flux into the plasma in the range of (1 000 – 3 000) min is observed for (25 – 100) µs
-1
dwell time and (150 - 1 000) min range for (3 – 10) ms dwell time.
ISO/TS 19590:2024(en)
Depending on the known characteristics of the RM, the transport efficiency (‘η ) is then calculated
transport’
[5]
from Formula (2):
3 −9
Nd··ρπ··10
NP ref NP
η = ·100% (2)
transport
6··CQ ·t
msam i
where
N is the number of events detected per time scan (a.u./no unit);
NP
t is time scan (min);
i
d is the mean spherical-volume-equivalent particle core diameter (nm);
ref
-3
ρ is the particle density (g cm );
NP
-1
C is the elemental mass concentration of particle suspension (pg g );
m
-1
Q is the average sample uptake rate (g min ).
sam
or Formula (3):
N
NP
η = ·100% (3)
transport
CQ··t
NP sami
where
N is the number of particles detected per time scan (a.u./no unit);
NP
t is time scan (min);
i
-1
C is the number concentration (g );
NP
-1
Q is the average sample uptake rate (g min ).
sam
It is important to note that the implementation of Formula (2) must include characterization of all input
particle characteristics, including the particle density (ρ ). This is because, particle density has been
NP
shown to be close to bulk density only for a limited number of materials, e.g., gold. For other materials, e.g.
-3
silicon dioxide, particles can have densities ranging from below 1,9 g cm (in the hydrated amorphous form
-3
of Stöber silica) to above 2,6 g cm for quartz. In case of silver particles in the size range from 30 nm to
[6]
100 nm, measured density was found to be 18 % to 24 lower than nominal density of metallic silver.
Because all parameters of Formula (2) and Formula (3) come with their associated uncertainty, the
combined uncertainty of η , estimated following the particle frequency method, is relatively high.
transport
It represents the main contributing factor to the overall uncertainty associated with the particle number-
based concentration measurements by spICP-MS in this case (assuming particle population is well-separated
from the background signal).
As an example, using 60 nm spherical gold particles (e.g. NIST RM 8013) and Formula (2), the uncertainty
associated with η is approximately 12 % relative expanded uncertainty (see Table 8 in Reference
transport
[7]). In case of Formula (3) and materials with a given number concentration value (e.g. LGCQC5050, 30 nm
colloidal gold nanoparticles), the uncertainty associated with the calculated transport efficiency will be
ISO/TS 19590:2024(en)
mostly impacted by the uncertainty associated with the C parameter given on the certificate of analysis.
NP
For example, 19 % relative expanded uncertainty for LGCQC5050.
NOTE NIST RM 8013 and LGCQC5050 are used as examples and are possibly not available commercially.
5.2.2 Particle size method
In the particle size method, an RM suspension of particles certified for particle spherical equivalent
diameter is used for the calculation of transport efficiency. Moreover, an elemental standard solution with
a known mass concentration of the same element is measured. Transport efficiency is then calculated from
Formula (4).
R
ionic
η = ·100% (4)
transport
R
NP
where
-1
R is the instrument’s response to ions (cps µg );
ionic
-1
R is the instrument’s response to the particle suspension (cps µg ).
NP
R and R can be calculated as follows from Formulas (5) and (6), respectively:
ionic NP
RF ··610
ion
R = (5)
ionic
Qt·
samd
where
RF is the instrument’s response factor to elemental standard, derived from regression analysis of the
ion
-1
calibration curve (cps µg kg);
t is the dwell time used (ms);
d
-1
Q is the sample uptake rate (g min ).
sam
II−
NP diss
R = (6)
NP
m
NP
where
I is the average particle intensity (cps);
NP
I is the average intensity of the dissolved background (cps);
diss
m is the mass of element in a single particle (µg).
NP
m can be calculated from Formula (7):
NP
d ··ρπ
ref NP
m = (7)
NP
−15
61· 0
where
ISO/TS 19590:2024(en)
d is the spherical equivalent diameter of particle core (nm);
ref
-3
ρ is the particle density (g cm ).
NP
For the purpose of transport efficiency determination with the particle size method, a suspension of
nanoparticle RM of known size is analyzed in combination with an ionic calibration standard of the same
element of interest. The ionic calibration standard is typically prepared from commercially available ICP-MS
elemental standard solution and measured using the same ICP-MS settings (e.g., dwell time, flow rate, etc.)
as the nanoparticle RM. The detector response should be linear in the range of intensities measured, since
larger particles can lead to detector saturation, resulting in an underestimation of the ICP-MS response and
[8]
therefore overestimation of the transport efficiency. As such, the following options are currently available:
a) to analyze nanoparticle RMs or RTMs of different sizes and to check the linearity of the regression line
for R ;
NP
b) to analyze several ionic calibration standards of different concentrations to encompass the intensities
(in cps) reached during the analysis of nanoparticle RMs or RTMs.
The particle size method is based on several assumptions, such as particle sphericity, and that dissolved
and NP analyte elements have equal ionization efficiencies in the plasma, as well as equal collection
efficiencies through the sampler cone into the MS. The equivalent spherical diameter of particle, chemical
composition and particle density are all required input parameters into the equations that come with their
associated uncertainty values, meaning that the uncertainty associated with η estimated following
transport
the particle size method is comparable with the particle frequency method. However, there are several
literature reports highlighting differences in the mean η values obtained with the two approaches.
transport
Some authors demonstrate that the frequency method systematically underestimates η compared
transport
[9]
to the size method by a factor as large as 25 % , while others report much smaller differences between
[10],[11]
the two methods. The reasons for this are still unknown, although an explanation can be found in
the differences in the transmission of atoms coming from dissolved material versus atoms coming from
[3]
nanoparticles, a phenomenon dependent on both the uptake rate and the mass spectrometer behaviour.
Other factors, such as the impact of inadequate sample storage can also be considered.
5.3 Reference material free calibration methods
5.3.1 Dynamic mass flow method
[12]
A methodology based on the DMF approach has been developed, which does not require an RM for
determination of the nebulization efficiency and transport efficiency. The DMF approach is performed by
continuously measuring the mass of sample uptake and the mass of sample reaching the plasma on-line over
time (sample mass flow), whilst the ICP-MS system is in equilibrium. The sample nebulization efficiency
value is then calculated as the ratio between the mass flow of sample reaching the plasma and the mass flow
of sample uptake using the Formula (8).
Mf
pl
η = (8)
transport
Mf
up
where
-1
Mf is the slope from the regression analysis representing mass flow reaching plasma (g min );
pl
-1
Mf is the slope from the regression analysis representing mass flow of sample uptake (g min ).
up
In this case, the η determination relies on weighing of the suspension over time, therefore its
transport
associated uncertainty has been demonstrated to be mostly based on mass measurements. These
measurements can be accomplished with high accuracy and precision and a relative expanded measurement
[12]
uncertainty of ~2,5 %, under the working conditions specified in the literature.
So far, the precision and accuracy of the method have been demonstrated for sample introduction systems
[12]
comprising double pass spray chamber cooled down to ~2 °C. Under these specific conditions, the
ISO/TS 19590:2024(en)
solvent and sample nebulization efficiency has been shown to be equal to the analyte nebulization and
transportation efficiency. Working with a cooled spray chamber helps to reduce the amount of water
vapor (produced from evaporation of water from aerosol in the spray chamber) entering the plasma, thus
minimizing the contribution of this source of error to the uncertainty of the mass-based η .
transport
a)
b)
Key
X time (min) 1 mass flow of sample reaching the plasma
Y mass (g) 2 mass flow of sample uptake
A sample uptake
B waste tube
S1 slope 1
S2 slope 2
T1 45 minutes
T2 15 minutes
Figure 2 — Schematic representation of transport efficiency determination using the DMF approach
This procedure is typically performed at the beginning and at the end of each analysis day. Due to possible
fluctuations in the mass flow of sample uptake caused by the pump during the analysis, and to improve
the accuracy of measurements, the mass flow of acquired sample should also be monitored throughout the
[12]
analysis.
Nebulization efficiency or transport efficiency determined by DMF, implemented correctly (e.g. using
double pass spray chamber
...
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