Plastics - Determination of the molecular mass and molecular mass distribution of polymer species by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) (ISO 10927:2018)

This document specifies a general method for determining the average molecular mass and molecular mass distribution of polymers (see Reference [1]) from 2 000 g ⋅ mol−1 to 20 000 g ⋅ mol−1 by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS).
The average molecular masses and molecular mass distributions are calculated from a calibration curve constructed using synthetic-polymer and/or biopolymer standards. This method is therefore classified as a relative method.
The method is not applicable to polyolefins or to polymers with a polydispersity >1,2.

Kunststoffe - Bestimmung der Molmasse und Molmassenverteilung von polymeren Species durch matrixunterstütze Laser-Desorptions/Ionisations-Flugzeit-Massenspektrometrie (MALDI-TOF-MS) (ISO 10927:2018)

Dieses Dokument legt ein allgemeines Verfahren zum Bestimmen der mittleren Molmasse und der
Molmassenverteilung von Polymeren (siehe Literaturhinweis [1]) in einem Molmassenbereich von
2 000 g ⋅ mol−1 bis 20 000 g ⋅ mol−1 durch die matrixunterstützte Laser-Desorptions/Ionisations-Flugzeit-
Massenspektrometrie (MALDI-TOF-MS) fest.
Die mittleren Molmassen und Molmassenverteilungen werden über eine Kalibrierkurve berechnet, die mit
Hilfe von synthetischen und/oder Biopolymerstandards erstellt wird. Daher handelt es sich um eine relative
Methode.
Das Verfahren ist nicht für Polyolefine oder Polymere mit einer Polydispersität > 1,2 anwendbar.

Plastiques - Détermination de la masse moléculaire et de la distribution des masses moléculaires des polymères par spectrométrie de masse, à temps de vol, après désorption/ionisation laser assistée par matrice (SM-MALDI-TOF) (ISO 10927:2018)

Le présent document spécifie une méthode générale permettant de déterminer la masse moléculaire moyenne et la distribution des masses moléculaires moyennes de polymères (voir Référence [1]) comprises entre 2 000 g ⋅ mol−1 et 20 000 g ⋅ mol−1 par spectrométrie de masse, à temps de vol, après désorption/ionisation laser assistée par matrice (SM-MALDI-TOF).
Les masses moléculaires et les distributions des masses moléculaires moyennes sont calculées à partir d'une courbe d'étalonnage établie à l'aide d'étalons de polymères synthétiques et/ou de biopolymères. Par conséquent, la présente méthode est classée comme méthode relative.
La présente méthode n'est pas applicable aux polyoléfines et aux polymères ayant une polydispersité > 1,2.

Polimerni materiali - Ugotavljanje molekulske mase in porazdelitve molekulske mase polimerov z masno spektrometrijo po laserski desorpciji/ionizaciji v nosilcu (matriksu) (MALDI-TOF-MS) (ISO 10927:2018)

Ta dokument določa splošno metodo za ugotavljanje povprečne molekulske mase in porazdelitve molekulske mase polimerov (glej sklic [1]) od 2000 g ⋅ mol−1 do 20.000 g ⋅ mol−1 z masno spektrometrijo po laserski desorpciji/ionizaciji v nosilcu (matriksu) (MALDI-TOF-MS).
Povprečne molekulske mase in porazdelitve molekulskih mas se izračunajo na podlagi kalibracijske krivulje, izdelane z uporabo standardov za sintetični polimer in/ali biopolimer. Ta metoda je zato klasificirana kot relativna metoda.
Metoda se ne uporablja za poliolefine oziroma polimere s polidisperzijo > 1,2.

General Information

Status
Published
Publication Date
10-Jul-2018
Current Stage
6060 - Definitive text made available (DAV) - Publishing
Due Date
11-Jul-2018
Completion Date
11-Jul-2018

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SLOVENSKI STANDARD
SIST EN ISO 10927:2018
01-december-2018
1DGRPHãþD
SIST EN ISO 10927:2011
Polimerni materiali - Ugotavljanje molekulske mase in porazdelitve molekulske

mase polimerov z masno spektrometrijo po laserski desorpciji/ionizaciji v nosilcu

(matriksu) (MALDI-TOF-MS) (ISO 10927:2018)

Plastics - Determination of the molecular mass and molecular mass distribution of

polymer species by matrix-assisted laser desorption/ionization time-of-flight mass

spectrometry (MALDI-TOF-MS) (ISO 10927:2018)
Kunststoffe - Bestimmung der Molmasse und Molmassenverteilung von polymeren
Species durch matrixunterstütze Laser-Desorptions/Ionisations-Flugzeit-
Massenspektrometrie (MALDI-TOF-MS) (ISO 10927:2018)

Plastiques - Détermination de la masse moléculaire et de la distribution des masses

moléculaires des polymères par spectrométrie de masse, à temps de vol, après
désorption/ionisation laser assistée par matrice (SM-MALDI-TOF) (ISO 10927:2018)
Ta slovenski standard je istoveten z: EN ISO 10927:2018
ICS:
71.040.50 Fizikalnokemijske analitske Physicochemical methods of
metode analysis
83.080.01 Polimerni materiali na Plastics in general
splošno
SIST EN ISO 10927:2018 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 10927:2018
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SIST EN ISO 10927:2018
EN ISO 10927
EUROPEAN STANDARD
NORME EUROPÉENNE
July 2018
EUROPÄISCHE NORM
ICS 83.080.01 Supersedes EN ISO 10927:2011
English Version
Plastics - Determination of the molecular mass and
molecular mass distribution of polymer species by matrix-
assisted laser desorption/ionization time-of-flight mass
spectrometry (MALDI-TOF-MS) (ISO 10927:2018)

Plastiques - Détermination de la masse moléculaire et Kunststoffe - Bestimmung der Molmasse und

de la distribution des masses moléculaires des Molmassenverteilung von polymeren Species durch

polymères par spectrométrie de masse, à temps de vol, matrixunterstütze Laser-Desorptions/Ionisations-

après désorption/ionisation laser assistée par matrice Flugzeit-Massenspektrometrie (MALDI-TOF-MS) (ISO

(SM-MALDI-TOF) (ISO 10927:2018) 10927:2018)
This European Standard was approved by CEN on 28 June 2018.

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 CEN-CENELEC Management Centre 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 CEN-CENELEC Management

Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,

Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 10927:2018 E

worldwide for CEN national Members.
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SIST EN ISO 10927:2018
EN ISO 10927:2018 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

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SIST EN ISO 10927:2018
EN ISO 10927:2018 (E)
European foreword

This document (EN ISO 10927:2018) has been prepared by Technical Committee ISO/TC 61 "Plastics"

in collaboration with Technical Committee CEN/TC 139 “Paints and varnishes” the secretariat of 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 January 2019, and conflicting national standards shall

be withdrawn at the latest by January 2019.

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 EN ISO 10927:2011.

According to the CEN-CENELEC Internal Regulations, the national standards organizations of the

following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,

Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,

France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,

Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and the United Kingdom.
Endorsement notice

The text of ISO 10927:2018 has been approved by CEN as EN ISO 10927:2018 without any modification.

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SIST EN ISO 10927:2018
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SIST EN ISO 10927:2018
INTERNATIONAL ISO
STANDARD 10927
Second edition
2018-06
Plastics — Determination of the
molecular mass and molecular mass
distribution of polymer species by
matrix-assisted laser desorption/
ionization time-of-flight mass
spectrometry (MALDI-TOF-MS)
Plastiques — Détermination de la masse moléculaire et de la
distribution des masses moléculaires des polymères par spectrométrie
de masse, à temps de vol, après désorption/ionisation laser assistée
par matrice (SM-MALDI-TOF)
Reference number
ISO 10927:2018(E)
ISO 2018
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SIST EN ISO 10927:2018
ISO 10927:2018(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2018

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 the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2018 – All rights reserved
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SIST EN ISO 10927:2018
ISO 10927:2018(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 2

5 Reagents ........................................................................................................................................................................................................................ 2

5.1 Matrices ......................................................................................................................................................................................................... 2

5.2 Solvents ......................................................................................................................................................................................................... 2

5.3 Salts ................................................................................................................................................................................................................... 3

5.4 Molecular mass standards ............................................................................................................................................................ 3

6 Apparatus ..................................................................................................................................................................................................................... 3

6.1 General ........................................................................................................................................................................................................... 3

6.2 Sample introduction chamber/target ................................................................................................................................. 3

6.3 Laser source .............................................................................................................................................................................................. 4

6.4 Flight tube ................................................................................................................................................................................................... 4

6.5 Detector ......................................................................................................................................................................................................... 4

6.6 Data recording ......................................................................................................................................................................................... 4

6.7 Data handling ........................................................................................................................................................................................... 5

7 Procedure..................................................................................................................................................................................................................... 5

7.1 General ........................................................................................................................................................................................................... 5

7.2 Sample preparation ............................................................................................................................................................................ 5

7.2.1 General...................................................................................................................................................................................... 5

7.2.2 Preparation of polymer/matrix/salt solutions ..................................................................................... 5

7.2.3 Deposition of the sample on the sample plate (target) .................................................................. 5

7.2.4 Preparation and spotting of biopolymer/matrix solutions ........................................................ 6

7.3 Instrument settings ............................................................................................................................................................................. 6

7.4 Recording spectra ................................................................................................................................................................................. 7

8 Data acquisition and processing .......................................................................................................................................................... 7

8.1 General ........................................................................................................................................................................................................... 7

8.2 Calibration .................................................................................................................................................................................................. 8

8.2.1 General...................................................................................................................................................................................... 8

8.2.2 Calibration of mass axis using synthetic-polymer standards ................................................... 8

8.2.3 Calibration of mass axis using biopolymer standards ..................................................................... 8

8.2.4 Self-calibration method ............................................................................................................................................. 8

8.3 Generation of calibration curve ................................................................................................................................................ 8

8.4 Signal intensity axis calibration ............................................................................................................................................... 8

9 Expression of results ........................................................................................................................................................................................ 9

9.1 Calculation of molecular mass distribution ................................................................................................................... 9

9.2 Calculation of the average molecular masses ............................................................................................................... 9

10 Precision ....................................................................................................................................................................................................................... 9

11 Test report ................................................................................................................................................................................................................... 9

Annex A (normative) Calibrants .............................................................................................................................................................................11

Annex B (informative) Precision data ..............................................................................................................................................................12

Bibliography .............................................................................................................................................................................................................................13

© ISO 2018 – All rights reserved iii
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SIST EN ISO 10927:2018
ISO 10927:2018(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.

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 documents 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).

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. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation on 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 the following

URL: www .iso .org/iso/foreword .html.

This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 5, Physical-

chemical properties.

This second edition cancels and replaces the first edition (ISO 10927:2011), which has been technically

revised to update Figure 1 and 6.7 on data handling.
iv © ISO 2018 – All rights reserved
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SIST EN ISO 10927:2018
ISO 10927:2018(E)
Introduction

The molecular mass and molecular mass distribution of a synthetic polymer are fundamental

characteristics that result from the polymerization process. They may be used for a wide variety of

correlations for fundamental studies and for processing and product applications. Determination of

the molecular mass and molecular mass distribution is used for quality control of polymers and for

specification purposes in the commerce of polymers. The comparability of MALDI-TOF-MS results

obtained in different laboratories can be ensured by using standardized conditions of measurement,

identical samples and identical matrix preparation methods. The classification of MALDI-TOF-

MS as an equitable (standardized) method compared with other established methods of polymer

characterization could result in a significant increase in the use of MALDI-TOF-MS.

© ISO 2018 – All rights reserved v
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SIST EN ISO 10927:2018
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SIST EN ISO 10927:2018
INTERNATIONAL STANDARD ISO 10927:2018(E)
Plastics — Determination of the molecular mass and
molecular mass distribution of polymer species by matrix-
assisted laser desorption/ionization time-of-flight mass
spectrometry (MALDI-TOF-MS)
1 Scope

This document specifies a general method for determining the average molecular mass and molecular

−1 −1

mass distribution of polymers (see Reference [1]) from 2 000 g ⋅ mol to 20 000 g ⋅ mol by matrix-

assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS).

The average molecular masses and molecular mass distributions are calculated from a calibration

curve constructed using synthetic-polymer and/or biopolymer standards. This method is therefore

classified as a relative method.

The method is not applicable to polyolefins or to polymers with a polydispersity >1,2.

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 472, Plastics — Vocabulary
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 472 and the following apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— IEC Electropedia: available at http: //www .electropedia .org/
— ISO Online browsing platform: available at https: //www .iso .org/obp
3.1
matrix-assisted laser desorption/ionization time-of-flight-mass spectrometry
MALDI-TOF-MS

mass-spectrometric technique in which the separation is based on different flight times in a field free

flight tube depending on the mass of formed polymer ions after ionization by a laser, desorption and

acceleration by high voltage
3.2
number-average molecular mass
()NM×
∑ ii
i=1
M =
i=1
where N is the number of molecules of species i of molecular mass M
i i
© ISO 2018 – All rights reserved 1
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SIST EN ISO 10927:2018
ISO 10927:2018(E)
3.3
mass-average molecular mass
NM× mM×
∑ ii ii
i=1
i=1
M = =
∞ ∞
NM× m
ii i
∑ ∑
i=1 i=1
where
N is the number of molecules of species i of molecular mass M ;
i i
m is the mass of the i species (i.e. m = N M )
i i i i
3.4
z-average molecular mass
∞ ∞
3 2
NM× mM×
zM×
()ii ()ii
∑ ∑ ii
i=1 i=1
i=1
M = = =
∞ ∞ ∞
NM× mM× z
ii ii i
∑ ∑ ∑
i=1 i=1 i=1
where
N is the number of molecules of species i of molecular mass M ;
i i
m is the mass of the i species (i.e. m = N M );
i i i i
z = m M /Σm
i i i i
4 Principle

The MALDI process involves the desorption and the ionization of an analyte dispersed in an organic

small-molecule matrix. The matrix shall be able to absorb the laser energy. A metal salt may be added to

cationize the analyte. A polymer is co-crystallized or co-mixed with the matrix molecule and deposited

on the target. A short-duration UV laser pulse is used to desorb the matrix and the analyte. The laser

energy is transferred to the matrix molecules, causing them to vaporize. Analyte and matrix molecules

leave the target surface in a plume. Due to the very short desorption time, polymer molecules do not

degrade. The polymer in the desorption plume gains a cation and is accelerated by a high voltage, drifts

down the field-free flight tube and is detected at the end of the flight tube. The time of flight of the

species is a measure of its mass. From the distribution of arrival times and the calibration of the arrival

times with known mass standards, the mass distribution of the polymer is determined.

5 Reagents
5.1 Matrices

2,5-dihydroxybenzoic acid (gentisic acid, DHB), trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-

propenylidene]malononitrile (DCTB), and 1,8,9-trihydroxyanthracene (dithranol) are the recommended

matrices for this method. All of these materials shall be at least 97 % pure. They shall be stored in a

freezer and warmed to room temperature immediately before use.
5.2 Solvents

The recommended solvent is tetrahydrofuran (THF) with the purity more than 99 %. THF with

an antioxidant, such as 2,6-di-tert-butyl-4-methylphenol (dibutylated hydroxytoluene, BHT) at

a concentration of 0,025 % to 0,1 % (m/V), shall be stored in an amber container. If THF without an

2 © ISO 2018 – All rights reserved
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SIST EN ISO 10927:2018
ISO 10927:2018(E)

antioxidant is used, it shall be stored in an amber container under an inert gas. Otherwise, it will react

with oxygen to form peroxides which are hazardous on evaporative concentration.

Depending on the solubility of the polymer being investigated, toluene, methanol and acetone may also

be used.
High-purity solvents are recommended.
5.3 Salts

Lithium, sodium, potassium, cesium and silver trifluoroacetate are recommended since they are soluble

in THF and toluene. AgNO with ethanol as solvent may be used with the polymer and matrix in THF.

The salts shall be soluble in the solvent chosen for the polymer and the matrix. When silver nitrate is

used, relevant safety aspects should be borne in mind.
5.4 Molecular mass standards

The calibration of the mass spectrometer shall be carried out using biopolymers and/or synthetic

polymers with known repeating units and end groups. The molecular masses of the standards shall

lie within the range of the molecular mass of the polymer being investigated. The software of the mass

spectrometer shall be used for calibration. A list of recommended biopolymers and their molecular

masses is given in Annex A.
6 Apparatus
6.1 General

A schematic diagram of a MALDI-TOF mass spectrometer is shown in Figure 1. The main components are

a sample introduction chamber, a laser source, an ion source (target), a flight tube with an acceleration

region and an ion detector (linear detector). The instruments may have additionally an ion deflector

and a reflector detector.

Both commercially available TOF mass spectrometers and systems assembled in the laboratory may be

used for this method, provided they meet the required levels of performance.
6.2 Sample introduction chamber/target

A MALDI test sample consists of a film, containing the analyte, the matrix and a salt mixture, deposited

as so-called “spots” on a metal plate. The entire plate, with the sample spots, is often referred to as

the MALDI target. The MALDI target is introduced into the spectrometer vacuum chamber by either a

manual or an automatic operation. The target is moveable, so that all the sample spots on the target are

accessible to the laser beam.
© ISO 2018 – All rights reserved 3
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SIST EN ISO 10927:2018
ISO 10927:2018(E)
Key
1 vacuum pump system
2 laser source
3 optical system
4 test sample introduction chamber
5 target
6 ion acceleration optics
7 reflector detector
8 ion reflector
9 linear detector
10 control and processing unit
Figure 1 — Schematic diagram of a MALDI-TOF mass spectrometer
6.3 Laser source

The laser system comprises a pulsed laser, an attenuator which allows the adjustment of the laser

power, beam splitters to direct a fraction of the laser light to a photodiode to start the timing for the

TOF measurement, and a lens and mirror system to direct the laser beam onto the MALDI target.

The wavelength of the laser shall be in the absorption range of the matrix. Typically, UV-lasers are used.

6.4 Flight tube

The target is at a high voltage of several kilovolts and situated just behind the acceleration optics. The

analyte/matrix/salt mixture is deposited on this target and exposed to the pulsed laser beam. Thereby,

gaseous analyte ions are formed which are accelerated by the electric field, exit the source and pass

through into the flight tube. The flight tube is a field-free drift region.
6.5 Detector

Ion detection in a TOF mass analyser is based on the fast measurement of the electrode voltage after an

ion impact. This is done in a detector in which the signal is proportional to the number of ions hitting

the detector.
6.6 Data recording

A multichannel recorder based on the principle of “analogue-to-digital” conversion shall be used.

4 © ISO 2018 – All rights reserved
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SIST EN ISO 10927:2018
ISO 10927:2018(E)
6.7 Data handling

For data analysis, a computer which is able to read, store and analyse the data is needed. The software

shall be able to determine the baseline, convert the data from time to mass by means of a calibration

curve and calculate the average molecular masses. It is recommended that all isotopic peaks for each

species can be calculated automatically. If the software cannot integrate the peak area automatically, it

is acceptable to use the peak height of the most abundant isotopic peak instead of the peak area. If some

overlapping isotope patterns are observed, quit data analysis.
7 Procedure
7.1 General

The procedure includes setting up the MALDI-TOF mass spectrometer, preparation of the test sample

and calibration of the data acquisition and processing system.

Typically with a TOF-MS, the vacuum system, the high-voltage power supply and the computer and

other parts of the data collection system are left on at all times.
7.2 Sample preparation
7.2.1 General

Prepare targets as described in 7.2.2 and 7.2.3. If possible, prepare, from each polymer/matrix/salt

solution, three different sample spots and record one spectrum from each spot. If only one spot can be

made, record three spectra from different areas of the spot. Record a minimum of 100 shots for each

spectrum.

Each set of three sample spots shall be prepared from the same solution of polymer, matrix and salt. In

addition, the parameters of the mass spectrometer (laser, acceleration voltage, etc.) shall not be changed

during the acquisition of the three spectra. Additional spots on the sample target may, however, be made

to allow instrument adjustments to be made in order to obtain the optimum spectrometer settings. The

adjustment of the laser attenuation is describ
...

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