DEAS 90 7:2018  
 
© EAS 201 8                                                                                                               First Edition 201 8 
 
 
DRAFT EAST AFRICAN STANDARD  
Fertilizer  ― Potassium sulphate (sulphate of potash) ― Specification  
EAST AFRICAN COMMUNITY     
 
 
  
 Foreword  
Development of the East African Standards has been necessitated by the need for harmonizing requirements 
governing quality of  products and services in the East African Community. It is envisaged that through 
harmonized standardization, trade barriers that are encountered when goods and services are exchanged 
within the Community will be removed.  
In order to achieve this objecti ve, the Community established an East African Standards Committee mandated 
to develop and issue East African Standards.   
The Committee is composed of representatives of the National Standards Bodies in Partner States, together 
with the representatives from  the private sectors and consumer organizations. Draft East African Standards 
are circulated to stakeholders through the National Standards Bodies in the Partner States. The comments 
received are discussed and incorporated before finalization of standards,  in accordance with the procedures 
of the Community.  
East African Standards are subject to review, to keep pace with technological advances. Users of the East 
African Standards are therefore expected to ensure that they always have the latest versions of t he standards 
they are implementing .   
© EAC  2018 – All rights re served  Fertilizer ― Potassium sulphate (sulphate of potash) ― Specification  
1 Scope  
This Draft East African  Standard specifies  requirements and methods of sampling and test for potassium 
sulphate (sulphate of potash) fertiliz er. 
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 8157 , Fertilizers and Soil Conditioners ― Vocabulary  
DEAS 913 , Fertilizers ― Methods of sampling  
ISO 17318 , Fertilizers and soil conditioners ― Determination of arsenic, cadmium, chromium, lead and 
mercury contents  
ISO 8397 , Solid fertilizers and soil conditioners ― Test sieving  
ISO 10084 , Solid  fertilizers – Determination of mineral – acid- soluble sulphate content - Gravimetric method  
ISO 17319 , Fertilizers and soil conditioners ― Determination of water -soluble potassium content ― 
Potassium tetraphenylborate gravimetric method  
AOAC 928.02 , Chloi ne (Water -soluble) in fertilizers  
AOAC 983.04 , Sodium in fertilizers. Atomic absorption spect  
3 Terms and Definitions  
For the purpose of this standard, terms and definitions given in ISO 8157  shall apply . 
4 Requirements  
4.1 Physical  
The material shall be c rystalline , prills or powder , uniform  in colour  and free from any foreign matter.  
Not less than 90 % by weight of the material shall be of particles in the size range of 1 mm to 4 mm for prills or 
not less than 65  % particles in the size range of 0.25  mm t o 1.7  mm for powdered crystals. The fertilizer 
material shall be tested in accordance with  ISO 8397 . 
4.2 Chemical  
The potassium sulphate (sulphate of potash) fertilizer shall comply with the requirements given in Table 1.  
Table 1 ― Chemical requirements fo r potassium sulphate fertilizer  
Characteristic  Requirement  Method of Test  
Potash contents (as K 2O) % by mass, min . 50 ISO 17319  
Sulphur (as S) % by mass, min . 17.5 ISO 10084   
  Total chloride (as Cl), % by mass, max . 2.5 AOAC 928.02  
Sodium content (as Na Cl), % by mass, max . 2.0 AOAC 983.04  
Moisture %, by mass max . 1.5 Annex D  
 
5 Contaminants  
Heavy metal contaminants in the fertilizers shall conform to the limits given in Table 2 when tested with the 
method specified therein.   
Table 2 ― Requirements for heavy metal contaminants  
Heavy metal  Requirement  Method of test  
Arsenic , mg/kg, max . 20 
ISO 17318  Cadmium , mg/kg, max.  7 
Mercury , mg/kg, max . 0.1 
Lead , mg/kg, max.  30 
Chromium , mg/kg, max.  500 
 
6 Sampling   
Sampling of fertilize r shall be carried out as prescrib ed in DEAS 913.  
8 Packaging and labelling  
8.1 Packaging  
The fertilizer shall be packaged in materials that are clean and non -defective that protect the product from 
physical, chemical and moisture contamination and withsta nd multiple stages of handling (transportation and 
storage).  
8.2 Labelling  
Each package shall be indelibly labeled in English and/or any other language with the following information:  
a) name of the fertilizer i.e. "potassium sulphate (sulphate of potash” fer tilizer;  
b) nutrient content;  
c) name and address of the manufacturer and importer;  
d) net content by mass in kg;  
e) handling instructions – including the words “Use No hooks”;  
f) production date and expiry date;  
g) country of origin ; 
h) batch number ; and  
i) storage conditions .  
© EAC  2018 – All rights re served  Annex A  
(normative)  
Determination of potash content (flame photometric method)  
 
A.1   Reagents  
 
Potassium nitrate (KNO 3) or potassium chloride (KCI) . Recrystallise reagent grade salt twice from water 
and dry for 5 hours at 105 ºC.  
 
A.2   Preparation of sol ution  
 
Dissolve 1.5058 g of sample in water (H 20) and dilute to 500 ml.  
 
A.3   Preparation of standard curve  
 
Dissolve 1.2931 g of KNO3 (or 0.9535 g KCI) in water and dilute to 500 ml (1 000 ppm K). Prepare standard 
solutions by dilution to cover a range of 0 ppm –80 ppm K at intervals of 10 ppm, adding appropriate amounts 
of lithium nitrate (LiNO3) if internal standard is to be used. Prepare standard curve of emission against 
concentration, adjusting instrument so that 50 ppm K gives reading near mid-scale . Atomize portions of 
standard solutions until readings for the series are reproducible.  
 
A. 4   Procedure  
 
Transfer 10 ml aliquot of sample solution to 250 ml beaker. Dilute to 100 ml volume and mix (if internal 
standard instrument is used, add required L iNO 3 before diluting to volume). Atomize portions of sample 
several times to obtain reliable average reading for each solution.  
 
Determine ppm K from standard curve (temperature of standard and sample solutions must not differ by more 
than 2 ºC).  
 
Calculat e % K 2O as follows:  
 
0% – 30%, ppm K/2 = % K 2O  
 
> 30%. ppm K/1 = % K 2O 
  
  Annex B  
(normative)  
 
Determination of sodium content  
 
B.1    Reagents  
 
B.1.1  Concentrated hydrochloric acid , analytical grade.  
B.1.2  Barium chloride solution , 12 per cent.  
B.1.3  Ammonium carbonate solution , 1 M.  
B.1.4  Perchloric acid.  
B.1.5  Ethanol , 96 per cent.  
B.1 6  Washing alcohol , prepared by mixing ethanol with 0.2 per cent (v/v) of perchloric acid.  
B.1.7  Ammonium hydroxide , 2 M.  
B.1.8  Magnesium uranyl acetate solution  – Dissolve 90.0 g of crystallized uranyl acetate in 60 ml of glacial 
acetic acid and sufficient water by stirring and warming it to 70ºC. Dilute the solution to 1 litre. Dissolve 600 g 
of crystallized magnesium acetate in 60 ml of glacial acetic acid and su fficient water by stirring and warming to 
70ºC.Dilute the solution to 1 litre. Mix the two solutions. Allow to stand for several hours. Filter off any residue. 
The final solution should be kept at 20ºC in flasks made of glass with very low sodium content. The solution 
should also be used at 20ºC.  
 
B.2   Procedure  
 
Weigh accurately about 10 g of the prepared sample, add a few milliliters of concentrated hydrochloric acid 
and 100 ml of water and heat to boiling in a beaker. To the boiling solution, add slowl y in small quantities 
barium chloride solution. Heat for sometime and then cool. Transfer to a 250-ml volumetric flask and dilute to 
the mark with water, stir the solution and filter. Reject the first few milliliters of filtrate. Take exactly 10 ml of the 
filtrate and add a few milliliters of ammonium carbonate solution. Filter off the precipitated carbonates and 
wash the precipitate with water, the washings being added to the filtrate. Evaporate the filtrate and washings 
to dryness in a porcelain dish of 1 0 cm diameter and calcine gently. Add to the residue a small quantity of 
water and 6 ml of perchloric acid and evaporate almost to dryness in a water bath. Repeat the evaporation 
with perchloric acid twice again.  
 
Cool the residue, add a few milliliters of  ethanol and crush the moist mass to a fine state by using a glass 
pestle. Decant off the liquid. Repeat the crushing of the residue and decantation with further additions of 
washing alcohol, collecting all the decanted liquid. Transfer the precipitate to a small filter and wash 
thoroughly with ethanol adding these washings also to the decanted liquid. Neutralize the filtrate and washings 
with ammonium hydroxide and heat to dryness. Transfer the residue to a beaker with about 5 ml of water and 
add an excess  of magnesium uranyl acetate, maintaining the temperature at 20ºC. Stir the precipitation and 
allow it to stand for half an hour at 20ºC. Decant off the clear solution through a sintered glass crucible which 
has been previously washed with ethanol, dried a t 120°C ± 5ºC and weighed. Again, add a small quantity of 
ethanol and repeat the decantation twice. Finally wash the precipitate with ethanol on the filter. Dry the 
crucible with the precipitate for half an hour at 120°C ± 5ºC, cool in desiccator and weigh . 
 
B.3 Calculation   
 
Sodium (as NaCI), per cent by mass (on dry basis)  
              
 97.05 M1 
                   = 
                M 
where  
 
  M1 = mass in g of the precipitate and  
  M = mass in g of the prepared sample taken for the test.  
 
 
  
© EAC  2018 – All rights re served   
 
 
 
Annex    C 
(normative)  
Determination of chlorides other than ammonium chloride  
 
C.1    Reagents  
 
C.1.1 Standard silver nitrate solution – 0.1N  
C.1.2 Concentrat ed nitric aci d   
C.1.3 Ferric ammonium sulphate solution  - saturate d in water an d stabilize d by addit ion of 50ml nitric acid.  
 
C.2. Procedure  
 
C.2.1  Dissolve 0.2g of the prepare sample in 40ml.  
C.2.2  Add exactly 50ml of standard silver nitrate solution and 5ml of concentrat ed nitric aci d.    
C.2.3  Add 0.5ml of nitrobenzene and make up the volume of the m ixture to exactly 100ml with water.  
C.2.4  Take exactly 50ml of the solution and add 2ml of ferric ammonium sulphate solution.  
C.2.5  Titrate the excess of silver nitrate in this portion with standard ammonium thiocyanate solution.  
C.2.6  Carry out a blank t est following the procedure given as above but without using the material.  
 
C.3 Calculation   
 
Total chloride (as Cl), per cent by mass (on dry basis)  
 
              
 7.094 (V 1 – V2) N 
                   = 
                W 
where  
 
V1 = Volume in ml of sta ndard ammonium thiocyanate used in the blank determination  
V1 = Volume in ml of standard ammonium thiocyanate solution used in the test with the material.  
N = Normality of standard ammonium thiocyanate solution  
W = Weight in gram, of the prepared sample t aken for the test.  
  
  Annex D 
(normative)  
 
Determination of moisture content  
D.1 Oven dry method  
D.1.1 General  
The method does not apply to fertilizers that yield volatile substances other than water at drying temperature.  
D.1.2 Procedure  
D.1.2.1  Weigh accur ately 2 g of the prepared sample in a pre -weighed, clean and dry weighing bottle or 
petridish.  
D.1.2.2  Heat in an oven for about 5 hours at 1050C + 20C to constant weight. Cool in a desiccator and 
weigh. For urea, heat at 700C + 50C for  five hours to const ant weight.  
D.1.3 Calculation  
Moisture per cent by weight (%) =  
ABCB

100  
where,  
A is the weight in gram of the empty bottle;  
B is the weight of the bottle plus the material in gram, before drying;  
C is the weight of the bottle plus the materi al in gram, after drying.  
D.2 Vacuum desiccator method  
D.2.1 General  
The method is applicable to Ammonium Chloride, Calcium Ammonium Nitrate (CAN), Di -Ammonium 
Phosphate (DAP) and all types of complex and mixtures of NPK fertilizers.  
D.2.2 Procedure  
Weigh accurately in duplicate 5g of prepared sample in a weighed shallow porcelain dish. Put the sample in a 
desiccator over concentrated sulphuric acid, close and introduce vacuum for about 10 minutes, then stop the 
vacuum pump and leave the sample for 24 hours , then release vacuum, remove the sample from the 
desiccator and weigh.  
D.2.3 Calculation  
Moisture per cent by weight = 
) () (
100
1 23 2
W WW W

  
where,  
W1 is the Weight in gram of empty porcelain dish;   
© EAC  2018 – All rights re served  W2is the Weight in gram of porcelain dish with sample be fore putting the sample for 24 hours in the 
desiccator;  
W3 is the Weight in gram of porcelain dish with sample after putting the sample for 24 hours in the 
desiccator.  
D.3 Karl Fischer method  
D.3.1 General  
This method is applicable to fertilizers like CAN,  Urea and urea based complexes. This method is not suitable 
for phosphate rock based fertilizers and fertilizers containing monocalcium phosphate, calcium sulphate, alkali 
carbonates as well as aldehydes and ketone groups.  
D.3.2 Apparatus  
Karl F ischer titrator  
D.3.3 Reagents  
D.3.3.1  Karl Fischer reagent(KF) – Karl Fischer solution (pyridine free) (single solution).  
D.3.3.2  Di-sodium tartarate dihydrate (Na 2C4O62H2O) analytical grade  
D.3.3.3  Methanol -KF grade/spectroscopy grade containing less th an 0.05 % water.  
D.3.4 Procedure  
D.3.4.1  Standardization of KF reagent.  
D.3.4.1.1  Set up the instrument as per manufacturer’s manual.  
D.3.4.1.2  Add methanol to the titration vessel until the electrodes are dipped and titrate with Karl -Fischer 
reagent to a pre-set end point persists for 30 seconds.  
D.3.4.1.3  Add 100mg of the disodium tartarate dehydrate to the titration vessel carefully and titrate with Karl 
Fischer reagent to a pre -set end point (the pre -set end point should persist for 30 seconds). Note th e volume 
of KF reagent used as V 1 ml. 
D.3.4.2  Determination of moisture of sample  
D.3.4.2.1  Weigh accurately 1 g of the prepared sample and transfer to the titration vessel carefully and stir 
until dispersed.  
D.3.4.2.2  Titrate with KF reagent to the same p re-set end point as above and note the volume of KF 
reagent used as V 2 ml. 
D.3.5 Calculation  
Factor (F)(mgH 2O/1 ml of KF reagent ) = 
1added dihy drate tartarate sodiumofmg 0.1566
V  
Moisture per cent by weight = 
0001 (gram) sampleof Weight100 2
VF