ISO 17322:2015

INTERNATIONAL ISO
STANDARD 17322
First edition
2015-06-01
Fertilizers and soil conditioners —
Analytical methods for Sulfur Coated
Urea (SCU)
Matières fertilisantes — Méthodes analytiques pour l’urée enrobée
de soufre (SCU)
Reference number
©
ISO 2015
© ISO 2015, Published in Switzerland
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ii © ISO 2015 – All rights reserved

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Sampling and sample preparation . 1
4 Determination of the appearance . 1
5 Determination of the mass fraction of total nitrogen . 1
6 Determination of 1DDR and 7DDR . 1
6.1 Titrimetric method after distillation . 1
6.1.1 Principle . 1
6.1.2 Reagents . 1
6.1.3 Apparatus . 2
6.1.4 Procedure . 2
6.1.5 Calculation . 2
6.2 Refractometer method . 3
6.2.1 Principle . 3
6.2.2 Reagents . 3
6.2.3 Apparatus . 3
6.2.4 Procedure . 4
6.2.5 Calculation . 5
7 Determination of the mass fraction of sulfur . 6
7.1 Principle . 6
7.2 Reagents. 6
7.3 Apparatus . 6
7.4 Procedure . 6
7.4.1 Determination of the sulfur content . 6
7.4.2 Blank test . 7
7.5 Calculation . 7
8 Determination of the mass fraction of biuret . 7
8.1 Principle . 7
8.2 Reagents. 8
8.3 Apparatus . 8
8.4 Procedure . 8
8.4.1 Preparation of the calibration curve. 8
8.4.2 Preparation of the solution to be analysed . 9
8.5 Calculation . 9
9 Determination of the water content .10
9.1 Principle .10
9.2 Reagents.10
9.3 Apparatus .10
9.4 Installation and test of the Karl Fischer titrator .10
9.5 Procedure .11
9.5.1 Standardization of the Karl Fischer reagent .11
9.5.2 Determination .11
9.6 Calculation .11
9.6.1 Water equivalent of the Karl Fischer reagent .11
9.6.2 Water content of the sample .12
10 Determination of particle size.12
11 Precision .12
11.1 Ring test .12
11.2 Repeatability .12
11.3 Reproducibility .13
12 Test report .13
Annex A (informative) Interlaboratory testing .14
Bibliography .48
iv © ISO 2015 – All rights reserved

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 meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT), see the following URL: Foreword — Supplementary information.
The committee responsible for this document is ISO/TC 134, Fertilizers and soil conditioners.
Introduction
Sulfur Coated Urea (SCU) is a coated, slow release fertilizer consisting of urea particles coated with sulfur,
which was first developed by the Tennessee Valley Authority’s National Fertilizer Development Center
(TVA/NFDC), Alabama in 1961, and produced commercially in 1967. SCU is made by coating urea with
sulfur and sealant. It contains 30 % to 40 % nitrogen and 10 % to 30 % sulfur. The main coating material of
SCU is sulfur. Sulfur is insoluble in water and its chemical properties are stable, thus, it is an impermeable
coating material. In addition, sulfur itself is a secondary nutrient and it does not pollute the soil.
This International Standard specifies analytical methods, including mass fraction of total nitrogen, one-
day dissolution rate (1DDR), seven-day dissolution rate (7DDR), mass fraction of sulfur, mass fraction of
biuret, mass fraction of water (H O), and SGN and UI of SCU. There are two methods for determining of
one-day dissolution rate (1DDR) and seven-day dissolution rate (7DDR): one is titrimetric method after
distillation, the other is refractometer method which is a fast analytical method.
NOTE Some countries or regions might have published other standards covering analytical methods for SCU.
vi © ISO 2015 – All rights reserved

INTERNATIONAL STANDARD ISO 17322:2015(E)
Fertilizers and soil conditioners — Analytical methods for
Sulfur Coated Urea (SCU)
1 Scope
This International Standard specifies analytical methods for the determination of mass fraction of total
nitrogen, one-day dissolution rate (1DDR), seven-day dissolution rate (7DDR), mass fraction of sulfur,
mass fraction of biuret, mass fraction of water (H O), and particle size of SCU.
These methods are applicable to SCU.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 760, Determination of water — Karl Fischer method (General method)
ISO 3310-1, Test sieves — Technical requirements and testing — Part 1: Test sieves of metal wire cloth
ISO 5315, Fertilizers — Determination of total nitrogen content — Titrimetric method after distillation
ISO 17323, Fertilizers and soil conditioners — Sulfur Coated Urea — General requirements
3 Sampling and sample preparation
Sampling and sample preparation shall be carried out in accordance with ISO 17323.
4 Determination of the appearance
It shall be determined by visual method.
5 Determination of the mass fraction of total nitrogen
It shall be determined in accordance with ISO 5315.
6 Determination of 1DDR and 7DDR
6.1 Titrimetric method after distillation
6.1.1 Principle
Digest the testing sample in static water at a constant temperature (38,0 ± 0,5) °C. Within a certain
period, the nitrogen component in the testing sample will dissolve into the water through the coatings,
and then the released nitrogen can be determined by titrimetric method after distillation. The percentage
of released nitrogen to the total nitrogen is defined as 1DDR or 7DDR.
6.1.2 Reagents
See ISO 5315.
6.1.3 Apparatus
6.1.3.1 Common laboratory apparatus.
6.1.3.2 The apparatus listed in ISO 5315.
6.1.3.3 Balance, capable of weighing to the nearest 0, 01 g.
6.1.3.4 Constant temperature incubator, capable of being controlled at (38,0 ± 0,5) °C.
6.1.4 Procedure
The replicate experiments shall be done for the determination.
6.1.4.1 Place 20 g uncrushed test sample (accurate to 0,01 g) into a small bag made of 100 meshes
nylon yarn nets. Then, seal the bag and place it into a 250 ml Erlenmeyer flask with a plug.
6.1.4.2 Add 200 ml of water into the flask precisely before the flask sealed with the plug.
6.1.4.3 Shake the glass flask gently to disperse the particle of test portion. Then, place the glass flask
into a constant temperature incubator with temperature set at (38,0 ± 0,5) °C and keep for 24 h and 7 d,
respectively.
6.1.4.4 After a set period, take out the flask from the incubator and reverse it gently three times to
ensure the uniformity of solution concentration throughout the flask.
6.1.4.5 Then, cool the flask down to room temperature, and the solution should be filtrated with dry
filter paper with a pore size of 30 µm to 50 µm.
6.1.4.6 Pipette 5 ml of the as-prepared solution; the total released nitrogen during a 24 h and 7 d period
should be determined in accordance with ISO 5315.
NOTE 1 Nylon yarn nets were used herein for the convenience of filtration (large undissolved particles of SCU
can be discarded together with the nylon yarn net).
NOTE 2 Replicate tests during the actual operation can refer to two, three, or more tests.
6.1.5 Calculation
6.1.5.1 Calculate the total released nitrogen during 24 h period, w , expressed in the mass fraction (%),
according to Formula (1):
w'
w = (1)
VV/
where
w’ is the total released nitrogen of the test solution pipetted during a 24 h period calculated
according to ISO 5315, in the unit of mass fraction (%);
V is the volume value of the test solution pipetted during the test, in the unit of millilitre (ml);
V is the total volume value of the test solution, in the unit of millilitre (ml).
Express the result to within two decimal places. The average value of the results of parallel tests shall
be defined as the final result of the determination.
2 © ISO 2015 – All rights reserved

6.1.5.2 Calculate the 1DDR, x , as the mass fraction (%), according Formula (2)
w
x =×100 (2)
w
where
w is the value of the total released nitrogen during 24 h period, expressed in the mass fraction
(%);
w is the value of the total nitrogen determined in accordance with the provision 5, expressed in
the mass fraction (%).
6.1.5.3 Calculate the total nitrogen release during 7 d, w , expressed in the mass fraction (%), with
Formula (1), prescribed in 6.1.5.1.
Express the results to within two decimal places. The average value of the results of two parallel tests
shall be defined as the result of the test.
6.1.5.4 Calculate the 7DDR, x , expressed in the mass fraction (%), according to Formula (3):
w
x =×100 (3)
w
where
w is the value of the total released nitrogen during 7 d, expressed in mass fraction (%).
6.2 Refractometer method
6.2.1 Principle
First, determine the solid contents in the sulfur coated urea product, and then calculate the mass of
urea in the sample. Based on the feature that the mass fraction of urea (%) in a solution at a certain
temperature is proportional to the refractive index of the solution, calculate the urea contents (g/l) in
the solution by determining the refractive index of the solution.
6.2.2 Reagents
6.2.2.1 Urea solution, 200 g/l.
Weigh 100 g urea, dissolve it in 250 ml water, and then dilute the solution to 500 ml and mix.
6.2.3 Apparatus
6.2.3.1 Ordinary laboratory apparatus.
6.2.3.2 Balance, capable of weighing to the nearest 0,000 1 g.
6.2.3.3 Magnetic stirring apparatus.
6.2.3.4 Temperature-controlled refractometer, readability, 0,000 01RI, Accuracy: ±0,000 05RI,
temperature accuracy: ±0,05 °C at 20 °C, thermometer resolution: 0,01 °C.
6.2.3.5 Constant temperature incubator, capable of being controlled at (38 ± 0,5) °C.
6.2.3.6 Drying oven, capable of being controlled at (100 ± 2) °C.
6.2.4 Procedure
6.2.4.1 Preparation of calibration curve
6.2.4.1.1 Preparation of the standard solution
As shown in Table 1, pipette into a series of eight 100 ml volumetric flasks, 0,00 ml (as compensation
solution), 2,50 ml, 5,00 ml, 10,00 ml, 20,00 ml, 30,00 ml, 40,00 ml, and 50,00 ml of the urea standard
solution. Make each flask up to the mark with water and mix thoroughly.
Table 1 — Amount of urea content per standard solution
Volumes of urea standard solution/ml The corresponding urea contents/g/l
0,00 0,00
2,50 5,00
5,00 10,0
10,00 20,0
20,00 40,0
30,00 60,0
40,00 80,0
50, 00 100,0
6.2.4.1.2 Preparation of the calibration curve
Prior to the test, set the optimum parameters for the refractometer, following the instruction of the guidebook.
Pipette 2 to 3 drops of the as-prepared urea standard solution and directly drop on the measuring disk
of the refractometer, then wait for 3 min to 4 min until the temperature is stable at (30 ± 0,1) °C. Then,
the refractive index of standard solutions with different concentrations can be measured and recorded.
With the refractive indexes of the urea standard solutions as the ordinate, and the urea contents (g/l) in
the corresponding standard solution as the abscissa, the calibration curve can be plotted, and determine
the equation of linear regression.
6.2.4.2 Determination of solid contents in samples
The replicate experiments shall be done for the determination.
Weigh 2 g (accurate to 0,000 2 g) of the as-prepared test sample (crushed) into a tall-type beaker, and
add 100 ml of water; the system should be mixed up on a magnetic stirrer at least 2 min to form a slurry
solution. Make sure that all the granules are completely crushed and the urea is dissolved completely.
Place a piece of weighted filter paper into a Buchner funnel, the paper should be soaked with water
and fitted to the shape of the Buchner funnel. Pour the sample containing slurry solution onto the filter
paper in the Buchner funnel; the residue on the stirrer should be washed onto the filter paper.
Place the insoluble substances into a drying oven at 103 °C to 105 °C and hold for 45 min, and then cool
down to room temperature in a dryer for 30 min. The mass of the insoluble substances together with the
filter paper should be weighed and recorded (m ).
4 © ISO 2015 – All rights reserved

The solid content, w, can be calculated, expressed in the mass fraction (%), according to Formula (4):
mm−
w= ×100 (4)
m
where
m is the mass of the insoluble substances and filter paper, in the unit of gram (g);
m is the mass of the filter paper, in the unit of gram (g);
m is the mass of the test portion, in the unit of gram (g).
The average value of the results of two parallel experiments shall be defined as the result of the test.
NOTE Replicate tests during the actual operation can refer to two, three, or more tests.
6.2.4.3 Determination of the urea contents in solution
Prepare the sample as set out in 6.1.4.1 to 6.1.4.5.
Pipette 2 or 3 drops of the filtered solution and directly drop on the measuring disk of the refractometer,
wait for 3 min to 4 min until the temperature of the solution stabilize at (30 ± 0,1) °C, and then the
refractive index should be measured by the refractometer and recorded.
6.2.5 Calculation
6.2.5.1 Calculate the mass of urea in the sample, m , in the unit of gram (g), according to Formula (5):
100−Mm×
()
m = (5)
where
m is the mass of the uncrushed test portion, in the unit of gram (g).
6.2.5.2 Calculate 1DDR or 7DDR, X, expressed in the mass fraction (%), according to Formula (6):
nn−×V
()
X = ×100 (6)
m ×1 000
where
N is the urea concentration of test solution prepared in a period of 24 h and 7 d, determined
directly from the calibration curve or calculated by the linear regression equation, corre-
sponding to the refractive indexes, in the unit of gram (g/l);
n is the urea concentration value corresponding to the blank refractive index, determined
directly from the calibration curve or calculated by the linear regression equation, in the unit
of gram(g/l);
V is the total volume value of the test solution, in the unit of millilitre (ml).
The average value of the results of two parallel experiments shall be defined as the result of the test.
7 Determination of the mass fraction of sulfur
7.1 Principle
Use water and sulfur-saturated acetone solution to extract water-soluble and acetone-soluble substances,
according to the sulfur’s behaviour of solubility. Then, extract all the sulfur by carbon disulfide. Calculate
the content of sulfur by the subtraction method.
7.2 Reagents
7.2.1 Acetone
7.2.2 Sulfur, solid.
7.2.3 Carbon disulfide.
7.2.4 Sulfur-saturated acetone solution.
Add a certain amount of sulfur into acetone, and stir continuously. Some more sulfur should be added
in the acetone as long as the former can be dissolved thoroughly, until sulfur precipitate from acetone.
7.3 Apparatus
7.3.1 Ordinary laboratory apparatus.
7.3.2 Balance, capable of weighing to the nearest 0,000 1 g.
7.3.3 Glass crucible filter, No. 4, volume of 30 ml.
7.3.4 Drying oven, capable of being controlled at (100 ± 2) °C.
7.4 Procedure
7.4.1 Determination of the sulfur content
Warning — This method of analysis involves the use of carbon disulfide (CS ). Special safety
measures shall therefore be taken, in particular with regard to the following:
;
— the storage of CS
— protective equipment for staff;
— occupational hygiene;
— prevention of fire and explosions;
— disposal of the reagent.
Warning — This method requires a highly skilled staff and a suitable equipped laboratory.
The replication experiments shall be done for the determination.
Weigh a certain amount of (with 200 mg to 300 mg sulfur contained) as-prepared test sample (crushed)
into a 125 ml Erlenmeyer flask with a plug. Add 50 ml of water into the flask precisely before the flask
sealed with the plug. Shake the flask vigorously to dissolve the urea content thoroughly. Remove all
6 © ISO 2015 – All rights reserved

contents from the triangular flask into a glass crucible filter (7.3.2) which has been dried to a constant
weight at (100 ± 2) °C, and then wash the flask five to six times with water.
Wash the glass crucible filter and its contents with 10 ml sulfur-saturated acetone solution (7.2.4), the
content should be dried up by a vacuum pump, repeat this operation four times. Then, dehydrate the
sample in the drying oven at (100 ± 2) °C for 1 h; after drying, remove the sample from the dryer and
cool it down to room temperature and weigh.
Pipette another 10 ml carbon disulfide to wash the test portion, then the content should be dried up by
a vacuum pump, repeat this operation 3 to 5 times, until all the sulfur content within the test portion
has been rinsed out.
Then, dehydrate the test portion in the drying oven at (100 ± 2) °C for 1 h; after drying, remove the
sample from the dryer and cool it down to room temperature and weigh.
The mass difference between the above two weights should be the mass of sulfur content.
7.4.2 Blank test
Replace the test portion with other inert material free of sulfur (ordinary urea, for example), and carry
out the blank test in parallel with the determination using the same procedure and the same quantities
of all reagents.
7.5 Calculation
Calculate the sulfur content (represented by the fraction of S element), w , expressed in the mass fraction
(%), according to Formula (7):
mm−−m
w = ×100 (7)
m
where
m is the mass of the test portion, in the unit of gram (g);
m is the mass of the test portion after washing by sulfur-saturated acetone, in the unit of gram
(g);
m is the mass of the test portion after washing by carbon disulfide, in the unit of gram (g);
m is the mass of sulfur in the blank test, in the unit of gram (g).
Express the result to within two decimal places. The average value of the results of parallel experiments
shall be defined as the result of the test.
8 Determination of the mass fraction of biuret
8.1 Principle
Under alkaline conditions in the presence of potassium sodium tartrate, biuret forms a purple complex
with copper salts. The absorbance of the solution is measured at a wavelength of 550 nm.
8.2 Reagents
8.2.1 Alkaline solution of potassium sodium tartrate.
In a 1 L volumetric flask, dissolve 40 g of sodium hydroxide in 500 ml water and leave it to cool. Add 50 g
of potassium sodium tartrate (NaKC H O 4H O). Make the flask up to the mark with water and leave
4 4 6 2
to stand for 24 h before use.
8.2.2 Copper sulfate solution.
In a 1 L volumetric flask, dissolve 15 g of copper sulfate pentahydrate (CuSO 5H O) in 500 ml water.
4 2
Make the flask up to the mark with water.
8.2.3 Freshly prepared biuret standard solution, corresponding to 0,002 g biuret per millilitre.
Biuret—to recrystallize, weigh 15 g reagent grade biuret (chemically pure), transfer to 1 L beaker, add
500 ml 95 % alcohol(analytical grade), and dissolve. Concentrate by gentle heating to 250 ml. Cool at
5 °C and filter through fritted glass funnel. Repeat crystallization and dry final product for 1 h at 105°in
oven. Remove from oven, place in desiccator, and cool to room temperature.
In a 250 ml volumetric flask, dissolve 0,500 0 g of recrystallized biuret in water, make the flask up to the
mark with water.
8.2.4 Hydrochloric acid solution, c = 1mol/l.
8.3 Apparatus
8.3.1 Common used laboratory apparatus.
8.3.2 Balance, capable of weighing to the nearest 0,000 1 g.
8.3.3 Spectrophotometer.
8.3.4 Water bath, capable of being controlled at (30 ± 5) °C.
8.4 Procedure
8.4.1 Preparation of the calibration curve.
As shown in Table 2, pipette into a series of six 100 ml volumetric flasks, 0,00 ml, 2,50 ml, 5,00 ml,
10,00 ml, 20,00 ml, and 30,00 ml of the biuret standard solution. Dilute them to 50 ml with water. Add
20,0 ml of the alkaline potassium sodium tartrate solution (8.2.1) and 20,0 ml of the copper sulfate
solution (8.2.2) into the volumetric flasks successively, make up to the mark with water, leave to stand
for 20 min in a water bath controlled at (30 ± 5)°C and shake again.
8 © ISO 2015 – All rights reserved

Table 2 — Amount of biuret content per standard solution
Volumes of biuret standard solution/ml The corresponding biuret contents/mg
0,00 0,00
2,50 5,00
5,00 10,0
10,00 20,0
20,00 40,0
30,00 60,0
Transfer the solutions to spectrophotometer cells and measure their absorbance at the wavelength
of 550 nm using the spectrophotometer, against the compensation solution containing 0 ml of biuret
standard solution, 200 ml of the alkaline tartrate solution (8.2.1) and 200 ml of the copper sulfate
solution (8.2.2).
Plot the calibration curve with the absorbance value on the ordinate and the corresponding quantities of
biuret (in milligrams) on the abscissa. Deduce the equation of regression from the data obtained.
8.4.2 Preparation of the solution to be analysed
Weigh 3 g (accurate to 0,000 2 g) of the as-prepared test sample (crushed) into a 50 ml beaker and add
20 ml of water; the system should be stirred by a glass rod until the urea dissolved. Then, the solution
should be filtered into a 100 ml volumetric flask. Add 0,3 ml of hydrochloric acid solution (8.2.4) into the
100 ml volumetric flask and vigorously shake the flask, for the solution might be a little turbid.
Pipette 20,0 ml of the alkaline potassium sodium tartrate solution (8.2.1) and 20,0 ml of the copper
sulfate solution (8.2.2) into the volumetric flasks successively. Then make up to the mark with water,
leave to stand for 20 min in a water bath controlled at (30 ± 5) °C and shake again.
Carry out a blank test in parallel with the determination using the same procedure and the same
quantities of all reagents but omitting the test portion.
Measure the absorbance of both the test portion and the blank, then, determine the mass of the biuret
from the corresponding calibration curve.
8.5 Calculation
Calculate the mass concentration, w (%), of the biuret within the sample according to Formula (8):
−3
mm− ×10
() mm−
11 12
11 12
w = ×=100 (8)
m m ×10
10 10
where
m is the mass of biuret, in the unit of milligrams;
m is the mass of biuret in blank test, in the unit of milligrams;
m is the mass of test portion, in the unit of grams.
Express the result to within two decimal places. The average value of the results of parallel experiments
shall be defined as the result of the test.
9 Determination of the water content
9.1 Principle
Extract the water from the SCU into dioxane and titrate it by the Karl Fischer reagent, previously
standardized by titration with an exactly known mass of water.
The equations are as follows:
HO + I + SO +3C HN→ 2C HN·HI + CH N·SO
22 25 5 55 55 3
CH N·SO + CH OH→CH NH·OSO OCH
55 33 65 23
9.2 Reagents
9.2.1 5A molecular sieve
Granules of 3 mm to 5 mm diameter is used as desiccant. Before using, the molecular sieve should be
heated at 500 °C for 2 h and then cooled down to room temperature in a desiccator filled with molecular
sieve. The molecular sieve once used can be regenerated by washing with water, drying, and calcinated.
9.2.2 Methanol
The water content (w/w %) should be not more than 0,05 %. If the water content (w/w%) is more than
0,05 %, about 50 g 5A molecular sieve (9.2.1)should be added to 500 ml methanol. Then, the bottle is
sealed and kept at room temperature (-25 °C) overnight. Extract the upper clear solution for use.
9.2.3 Dioxane
Dehydrating by the same way as described in 9.2.2.
NOTE Other commercially available solvent with equal effect can also be used
Caution — Dioxane is a hazardous chemical requiring specific safety precaution.
9.2.4 Karl Fischer reagent, prepared according to ISO 760
9.2.5 Sodium tartrate dihydrate, Na C H O ·2H O
2 4 4 6 2
9.3 Apparatus
9.3.1 Balance, capable of weighing to the nearest 0,000 1 g.
9.3.2 Karl Fischer titrator.
9.3.3 Centrifuge, (0 to 4 000) r/min.
9.3.4 Syringe, 5 ml and 50 ml.
9.4 Installation and test of the Karl Fischer titrator
Follow the instruction manual to install the Karl Fischer titrator.
10 © ISO 2015 – All rights reserved

9.5 Procedure
9.5.1 Standardization of the Karl Fischer reagent
Titrate the known quantity of water or sodium tartrate dihydrate (9.2.5) (accurate to 0,000 2 g)
introduced with the Karl Fisher reagent (9.2.4) to be standardized, until the galvanometer pointer
shows a sudden and constant deflection lasting for at least 1 min. Note the volume (V ) of reagent used
and calculate the water equivalent (T) of the Karl Fisher reagent.
9.5.2 Determination
Weigh 1,5 g to 2,5 g crushed test sample (accurate to 0,000 2 g) where the content of free water is no
more than 150 mg into a 125 ml conical flask with a rubber stopper. Seal it with rubber stopper and
inject 50 ml dioxane (9.2.3) with a syringe. Shake for a few minutes, leave to stand for 15 min and then
shake for a few minutes again. After the test portion subsides slightly, some portion of the solution
should be centrifuged in a centrifugal (speed: 2 000 r/min, time: 5 min) tube with a rubber plug.
Empty the titration vessel via its outlet. Add 50 ml of methanol into the titration vessel; the amount of
methanol should be capable of submerging the electrodes. Switch on the electromagnetic stirrer. Titrate
with the Karl Fischer reagent until the same deflection of the pointer of the Karl Fischer titrator is
reached as standardization of the Karl Fischer reagent and remains stable for at least 1 min.
Take 5,0 ml dioxane extraction from the centrifuge tube with a syringe, inject through the feed inlet into
the titration vessel, and titrate it to the equivalent point by Karl Fischer reagent. Record the volume (V )
of Karl Fischer reagent used.
As the dioxane is used as extraction reagent, the residue in the titration vessel should be emptied after
three measurements. Fill the vessel with methanol and titrate it to the equivalent point. Then start the
next test of sample.
Determine the volume (V ) of Karl Fischer reagent used by titrating 5 ml dioxane with the same method.
9.6 Calculation
9.6.1 Water equivalent of the Karl Fischer reagent
The water equivalent, T, of the Karl Fischer reagent, expressed in milligrams of water per millilitre of
reagent, is given by Formula (9):
m ×0,1566 m
14 15
T = or T = (9)
V V
3 3
where
m is the mass of the sodium tartrate introduced if this reagent is used for the standardization,
in the unit of milligrams (mg);
m is the mass of the water introduced if pure water is used for the standardization, in the unit
of milligrams (mg);
V is the volume of Karl Fischer reagent used for the standardization, in the unit of millilitre
(ml).
9.6.2 Water content of the sample
The water content of the sample, w , expressed as mass fraction (%), is given by Formula (10).
TV −V TV −V
() ()
45 45
w = ×= (10)
m
m ××1 000
where
T is the water equivalent of the Karl Fischer reagent, calculated in accordance with 9.6.1, in the
unit of milligram per millilitre (mg/ml);
V is the volume of Karl Fischer reagent used by 5 ml dioxane extraction solution, in the unit of
millilitre (ml);
V is the volume of Karl Fischer reagent used by 5 ml dioxane, in the unit of millilitre (ml);
m is the mass of the test portion, in the unit of grams (g).
Express the result withint two decimal places. The average value of the results of two parallel tests shall
be defined as the result of the test.
10 Determination of particle size
It shall be determined in accordance with ISO 3310-1, and the size of test sieving should been chosen
1,00 mm to 4,75 mm.
11 Precision
11.1 Ring test
Details of ring test on the precision of the method are summarized in Annex A.
11.2 Repeatability
Item Repeatability limit
r
%
mass fraction of total nitrogen 0,356
1DDR (Titrimetric method after distillation) 0,127x − 0,060 5
7DDR (Titrimetric method after distillation) 2,990
1DDR (Refractometer method) 3,102
7DDR (Refractometer method) 4,248
mass fraction of sulfur 0, 392
mass fraction of biuret 0,059
mass fraction of water (H
O) 0,067
12 © ISO 2015 – All rights reserved

11.3 Reproducibility
Item Repeatability limit
R
%
mass fraction of total nitrogen 1,151
1DDR (Titrimetric method after distillation) 0,0736x + 3,481 5
7DDR (Titrimetric method after distillation) 0,153x + 2,392 6
1DDR (Refractometer method) 0,101x + 3,957 0
7DDR (Refractometer method) 8,366
mass fraction of sulfur 1, 372
mass fraction of biuret 0,235
mass fraction of water (H O) 0,123
12 Test report
The test report shall contain at least the following information:
a) all the information necessary for the complete identification of the sample;
b) the test method used with reference to this International Standard (i.e. ISO 17322);
c) the test results obtained;
d) the date of sampling and sampling procedure (if known);
e) the date when the analysis was finished;
f) whether the requirement of the repeatability limit has been fulfilled;
g) all the operating details not specified in this International Standard, or regarded as optional,
together with details of any incidents occurred when performing the method, which might have
influenced the test results.
Annex A
(informative)
Interlaboratory testing
A.1 Overview
The interlaboratory testing of this International Standard was accomplished from September 2012 to
December 2012. Eleven laboratories participated in the two parallel tests on each four samples. These
eleven laboratories are Thornton Laboratories Testing and Inspection Services, Inc(USA), PT. Hanampi
Sejahtera Kahuripan (Indonesia), Soil and water research institute of Iran (Iran), Shanghai Research
Institute (China), Heilongjiang Research Institute (China), Shandong Research Institute 1 (China),
Jiangsu Research Institute 1 (China), Guangxi Research Institute (China), Jiangsu Research Institute 2
(China), Yunnan Research Institute (China), and Shandong Research Institute 2 (China) respectively.
This international ring test was conducted by Shanghai Research Institute of Chemical Industry, P. R.
China; the statistician analysis and final report was prepared by Shanghai Research Institute of Chemical
Industry, P. R. China.
The test methods described in Clauses 4 to 10 were adopted in this Annex for total nitrogen, one-
day dissolution rate (titrimetric method after distillation), seven-day dissolution rate (titrimetric
method after distillation), one-day dissolution rate (refractometer method), seven-day dissolution rate
(refractometer method), sulfur, mass fraction of biuret, and water in Sulfur Coated Urea.
Four different samples of SCU were used during the ring test, with the serial number of SCU-I, SCU-II,
SCU-III, and SCU-IV. Four different kinds of fertilizer samples were with several mean levels. All the SCU
samples encountered hereafter could be referred to the description in this subclause.
The precision of the test results is evaluated based on ISO 5725-2:1994.
A.2 Statistical analysis of the test results of the mass fraction of total nitrogen
A.2.1 Original test results
Ten laboratories have participated in the determination of the mass fraction of total nitrogen. The test
results are listed in Table A.1, expressed in the mass fraction (%).
Table A.1 — Original test results of the determination of the mass fraction of total nitrogen
Level j
Laboratory i
SCU-I SCU-II SCU-III SCU-IV
1 40,24 40,22 37,59 37,56 35,77 35,76 35,93 35,94
2 39,13 39,2 36,89 36,92 35,06 35,02 35,01 34,93
3 38,69 39,09 37,4 36,79 35,47 36,17 37,08 37,52
4 40,02 40,24 37,36 37,49 35,92 36,15 35,66 35,53
5 39,86 40,19 37,48 37,7 35,83 35,7 35,98 35,94
6 39,46 39,61 37,48 37,62 35,34 35,39 35,67 35,54
7 39,84 39,66 37,32 37,16 35,68 35,64 35,62 35,72
8 40,15 40,11 37,33 37,3 35,61 35,56 35,92 35,86
9 39,99 40,07 38,00 37,76 35,76 35,92 35,91 36,09
14 © ISO 2015 – All rights reserved

Table A.1 (continued)
Level j
Laboratory i
...