ISO 21437:2020

INTERNATIONAL ISO
STANDARD 21437
First edition
2020-12
Pulps — Determination of
carbohydrate composition
Pâtes — Détermination de la composition des hydrates de carbone
Reference number
ISO 21437:2020(E)
©
ISO 2020

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ISO 21437:2020(E)

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ISO 21437:2020(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Apparatus . 1
6 Reagents . 2
7 Sampling . 3
8 Test Specimens . 4
9 Procedure. 4
9.1 Determination of dry matter content . 4
9.2 Test specimen preparation for acid hydrolysis . 4
9.3 Hydrolysis . 4
9.4 Determination of monosaccharides . 4
9.4.1 Determination using an IC instrument . 5
9.4.2 Determination using a GC instrument. 5
10 Calculation . 7
11 Precision . 8
12 Test Report . 8
Annex A (informative) Precision . 9
Bibliography .15
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ISO 21437:2020(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
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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
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www .iso .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 6, Paper, board and pulps.
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.
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ISO 21437:2020(E)

Introduction
The carbohydrate composition - the contents of the five principal, neutral monosaccharides; arabinose,
galactose, glucose, xylose and mannose - provides chemical information about the main polysaccharides
in wood pulps. The most commonly-used methods are based on acid hydrolysis of the polysaccharides
using sulfuric acid, followed by subsequent chromatographic determination of the monosaccharides.
This document describes a method for the determination of the contents of the five principal, neutral
monosaccharides; arabinose, galactose, glucose, xylose and mannose, as they appear in wood pulps. The
procedure is based on the sulfuric acid hydrolysis of the samples. The monosaccharides are determined
either by using high performance anion exchange chromatography with a pulsed amperometric detector
(HPAEC-PAD) – subsequently referred to as ion chromatography (IC), or by using gas chromatography
with a flame ionization detector (GC-FID) – subsequently referred to as gas chromatography (GC).
The determination of carbohydrate composition can also be carried out by HPLC (High Performance
Liquid Chromatography), as described, for example, in Reference [3], provided that the results have
been validated against those obtained with this document.
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INTERNATIONAL STANDARD ISO 21437:2020(E)
Pulps — Determination of carbohydrate composition
1 Scope
This method describes the determination of the carbohydrate composition in wood pulp samples. This
method makes it possible to determine concentrations of individual anhydrous monosaccharides down
to 1 mg/g oven-dry pulp.
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 638, Paper, board and pulps — Determination of dry matter content — Oven-drying method
ISO 7213, Pulps — Sampling for testing
ISO 14453, Pulps — Determination of acetone-soluble matter
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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 http:// www .electropedia .org/
3.1
carbohydrate composition
amounts of the five principal, neutral monosaccharides; arabinose, galactose, glucose, mannose and
xylose, in a sample, in milligrams per gram
4 Principle
The pulp samples are hydrolysed with sulfuric acid using a two-step technique. The amounts of the
different monosaccharides are determined using either ion chromatography (IC) or gas chromatography
(GC) in the presence of an internal standard to validate the results. If GC is used, the hydrolysed sample
is reduced and acetylated, and the resulting alditol acetates of the monosaccharides are then separated
and determined by GC.
5 Apparatus
5.1 Grinder with a 40 mesh screen or equivalent equipment.
5.2 Filtration equipment: filtering flask; filtering crucible, fritted glass, medium or fine porosity,
30 ml; adapter for the filtering crucible, siphon tube (optional).
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ISO 21437:2020(E)

NOTE The choice of fritted glass porosity depends on the rate of filtration of the particular type of sample.
For slow filtering samples, the use of medium (M) porosity is preferable. In low-yield sulfite pulps especially,
lignin forms a fine dispersion and clogs the pores of the filter. Filtration can be facilitated by using a medium
porosity crucible with a disc of fine porosity glass-fibre filter paper fitted over the sintered glass in the crucible.
Other types of filtering crucibles, such as alundum or porous porcelain crucibles lined with a mat of
glass fibres can also be used.
5.3 Constant temperature water bath, capable of maintaining a temperature of 30 ± 1 °C.
5.4 Autoclave, capable of maintaining a temperature of 120 ± 3 °C.
5.5 Drying oven, 105 ± 2 °C for determining dry matter content in accordance with ISO 638.
The apparatus in 5.6 is used for IC determination only:
5.6 Ion chromatograph (IC) with an anion-exchange column for monosaccharide determination and
pulsed amperometric detector (PAD).
Apparatuses in 5.7 and 5.8 are used for GC-determinations only:
5.7 Water bath, maintained at a temperature of 40 ± 0,5 °C.
5.8 Gas chromatograph (GC) with a suitable column for monosaccharide determination and flame
ionization detector (FID).
6 Reagents
All chemicals shall be of reagent grade or better, unless otherwise indicated.
6.1 Water of high purity, distilled or deionized
6.2 Monosaccharide standards
Monosaccharide standards, for calibration: arabinose, galactose, glucose, mannose and xylose.
Prepare standard solutions of appropriate concentrations, each standard solution containing all five
monosaccharides.
6.3 Sulfuric acid, 72 % w/w (specific gravity 1,633 8 at 20 °C). 72 % sulfuric acid can be prepared
from concentrated sulfuric acid as follows:
Slowly add 650 ml of concentrated sulfuric acid (H SO sp gr 1,84) to 400 ml of water, while cooling
2 4
under a cold-water tap. When the temperature has reached equilibrium with the ambient temperature,
adjust the specific gravity of the acid solution to 1,633 8 with the use of a hydrometer, by careful
addition of concentrated sulfuric acid or water.
NOTE 72 % H SO is also available commercially.
2 4
6.4 Eluent solution (for IC determination)
The composition of this solution depends on the type of IC column to be used. Therefore, follow the
recommendations given by the IC column supplier.
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ISO 21437:2020(E)

Reagents 6.5 to 6.12 are required only for GC determinations.
NOTE Alternative reagents (to those in 6.5 to 6.12) and procedures (to those in 9.4.2.1, 9.4.2.2, and 9.4.2.3)
[2]
for the neutralization, reduction and derivatization steps, such as those described in TAPPI T249 , can also be
used provided this is indicated in the report.
6.5 Ammonia, NH conc. 25 %
3
6.5.1 Ammonia 13 M
Mix 9 parts ammonia (25 %) with 1 part of water.
6.6 Potassium hydroxide, KOH
6.6.1 Potassium hydroxide 7,5 M
Weigh 105 g KOH pellets into a 250 ml beaker. Add approx. 150 ml water while stirring. Transfer the
solution into a 250 ml volumetric flask, using an additional 20-30 ml of water to rinse the beaker in
order to complete the transfer.
The reaction is exothermic; heat is evolved. Allow the solution to cool to ambient temperature and
dilute to the mark with water.
6.7 Potassium borohydride, KBH
4
6.7.1 Potassium borohydride solution
Dissolve 150 mg KBH in 250 µl 13 M NH and 750 µl distilled water in a septum vial (4 ml).
4 3
This solution shall be freshly prepared every day before use.
6.8 Acetic acid, CH COOH, conc.
3
6.9 Acetic acid anhydride, conc.
6.10 1-methylimidazole
6.11 Ethanol, 95 - 99 %
6.12 Sodium sulfate, Na SO , water-free
2 4
6.13 2-Deoxy-galactose
6.13.1 Internal standard solution, 2-deoxy-galactose 20 mg/ml
Weigh 1,00 g 2-deoxy-galactose to the nearest 0,1 mg, transfer it quantitatively to a 50 ml volumetric
flask, and dilute to the mark with distilled water.
Other internal standards than 2-deoxy-galactose, such as fucose or myo-inositol, can also be used.
However, this shall be specified in the report.
7 Sampling
If the analysis is being made to evaluate a lot of a consignment of pulp, the sample shall be taken in
accordance with ISO 7213. If the analysis is made on another type of sample, report the origin of the
sample, and if possible, the sampling procedure. Pulp samples shall be ground before analysis using an
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ISO 21437:2020(E)

appropriate grinder (5.1). Groundwood and high yield pulps containing a significant amount of resins
shall be extracted with acetone according to ISO 14453 before testing.
NOTE Resins, if not extracted from the pulp prior to analysis, would remain insoluble in acid and can
interfere with the determination of carbohydrate composition.
NOTE Acetone is considered an effective solvent for extracting resin from pulp. Dichloromethane and
ethanol/benzene (1:2), as specified in other methods, are not recommended due to health hazards. In particular,
benzene is a confirmed carcinogen.
8 Test Specimens
Make sure that the test portions taken are representative of the sample received.
9 Procedure
Carry out the preparation and testing in duplicate.
9.1 Determination of dry matter content
Determine the dry matter content of the pulp according to ISO 638 by drying a 2-3 g specimen in an
oven (5.5) at 105 °C ± 2 °C to constant weight. If the pulp needs to be pre-extracted, the dry matter
content shall be determined on the extracted pulp.
9.2 Test specimen preparation for acid hydrolysis
Weigh a portion, of the sample from Clause 7, of 300 ± 10 mg to the nearest 0,1 mg into a glass beaker
with a volume of at least 150 ml.
Calculate and record the oven-dry mass M of the test specimen, in grams.
9.3 Hydrolysis
To the test specimen in the beaker, add exactly 3 ml of 72 % sulfuric acid (6.3) with a pipette. Stir the
contents of the beaker with a glass rod until the test material begins to dissolve. Leave the glass rod in
the beaker.
NOTE Some pulps do not absorb the acid and therefore do not disperse readily. In such cases, after addition
of acid, place the beaker under vacuum in a vacuum desiccator for at least 15 min to facilitate wetting and
absorption.
Place the beaker in a 30 ± 1 °C water bath (5.3) for 1 h. Stir occasionally with the glass rod. Add 84 ml of
water (6.1), using some of this water to rinse the glass rod, making sure all the washing is captured in
the beaker.
Cover the beaker with aluminium foil and place it in autoclave (5.4) at 120 ± 3 °C for 1 h. Allow the
beaker and its contents to cool to approximately 80 °C.
9.4 Determination of monosaccharides
Carry out the determination according to either 9.4.1 or 9.4.2.
NOTE The determination of carbohydrate composition can also be carried out by HPLC (High Performance
Liquid Chromatography), as described in Reference [3] for example, provided that the results have been validated
against those obtained with this document.
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