Fertilizers and soil conditioners -- Analytical methods for Sulfur Coated Urea (SCU)

ISO 17322:2015 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 (H2O), and particle size of SCU. These methods are applicable to SCU.

Matières fertilisantes -- Méthodes analytiques pour l'urée enrobée de soufre (SCU)

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Published
Publication Date
02-Jun-2015
Current Stage
9093 - International Standard confirmed
Start Date
06-Sep-2020
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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 17322:2015(E)
ISO 2015
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ISO 17322:2015(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2015, Published in Switzerland

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ii © ISO 2015 – All rights reserved
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ISO 17322:2015(E)
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

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ISO 17322:2015(E)

11.2 Repeatability ..........................................................................................................................................................................................12

11.3 Reproducibility ....................................................................................................................................................................................13

12 Test report ................................................................................................................................................................................................................13

Annex A (informative) Interlaboratory testing ......................................................................................................................................14

Bibliography .............................................................................................................................................................................................................................48

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ISO 17322:2015(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 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.

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ISO 17322:2015(E)
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.

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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.
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ISO 17322:2015(E)
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 = (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.
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ISO 17322:2015(E)
6.1.5.2 Calculate the 1DDR, x , as the mass fraction (%), according Formula (2)
x =×100 (2)
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):

x =×100 (3)
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.

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ISO 17322:2015(E)
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 ).
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ISO 17322:2015(E)

The solid content, w, can be calculated, expressed in the mass fraction (%), according to Formula (4):

mm−
w= ×100 (4)
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)
100
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.

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ISO 17322:2015(E)
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

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ISO 17322:2015(E)

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
789
w = ×100 (7)
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 dis
...

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