UGANDA STANDARD  
     US ISO 7485
First Edition
   2009 -09-04
 
Reference numbe r 
  US ISO 7485:2000
 © UNBS 200 9 
  
Animal feeding stuffs — Determination of potassium and 
sodium contents — Methods using flame-emission 
spectrometry 
 US ISO 7485:2000  
 
© UNBS  2009 – All rights reserved Compliance with this standard does not, of itself confer immunity from legal obligations 
A Uganda Standard does not purport to include all necessary provisions of a contract. Users are 
responsible for its correct application  
© UNBS 2009 
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilised in any 
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Uganda National Bureau of Standards 
P.O. Box 6329 
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Tel: 256 41 505 995 
Fax: 256 41 286 123 
E-mail: unbs@infocom.co.ug
     US ISO 7485:2001  
© UNBS  2009 - All rights reserved National foreword 
Uganda National Bureau of Standards (UNBS) is a parastatal under the Ministry  of Tourism, Trade and 
Industry established by the Act of Parliament of 198 3, of the Laws of Uganda.  UNBS is mandated to co-
ordinate the elaboration of standards and is  
(a) a member of International Organisation for Standardisation (ISO) and  
(b) a contact point for the WHO/FAO Codex A limentarius Commission on Food Standards, and  
(c) the National Enquiry Point on TBT/SPS Agr eements of the World Trade Organisation (WTO). 
The work of preparing Uganda Standards is carried out through Technical Committees. A Technical 
Committee is established to deliberate on standards in a gi ven field or area and consists of representatives of 
consumers, traders, academician s, manufacturers, governme nt and other stakeholders. 
Draft Uganda Standards adopted by the Technical Committ ee are widely circulated to stakeholders and the 
general public for comments. The committee reviews the comments before recommending the draft standards 
for approval and declaration as Uganda Standards by the National Standards Council. 
This Uganda Standard, US ISO 7485:2000,  Animal feeding stuffs — Determination of potassium and sodium
contents — Methods using flame-emission spectrometry, is identical with and has been reproduced from
an International Standard ISO 7485:2000,  Animal feeding stuffs — Determination of potassium and
sodium contents — Methods using flame-emission spectrometry, and has been adopted as a Uganda
Standard. 
Wherever the words, "International Standard" a ppear, they should be replaced by "Uganda Standard." Reference number
ISO7485:2000(E)
©ISO2000INTERNATIONAL
STANDARDISO
7485
Firstedition
2000-08-15
Animal feedingstuffs— Determinationof
potassiumandsodiumcontents—
Methods usingflame-emission
spectrometr y
Aliments des animaux — Déterminationdes teneurs enpotassium et
sodium— Méthodes par spectrométried'émission deflammeISO 7485:2000(E)
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ii © ISO2000 –All rights reservedISO 7485:2000(E)
© ISO2000 –All rights reserved iiiForeword
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 hasthe right to be represented on that committee. International organizations, governmental and non-governmental, inliaison with ISO, also take part in the work. ISO collaborates closely with the International ElectrotechnicalCommission(IEC) onall matters of electrotechnicalstandardization.
InternationalStandards are drafted in accordance with the rules givenintheISO/IEC Directives, Part3.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publicationas anInternationalStandardrequires approval byat least 75% of themember bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of
patent rights. ISO shall not beheldresponsiblefor identifyinganyor allsuch patent rights.
International Standard ISO7485 was prepared by Technical Committee ISO/TC34, Agricultural food products ,
SubcommitteeSC 10, Animalfeedingstuffs .
Annex A of this International Standardis for informationonly.INTERNATIONAL STANDARD ISO 7485:2000(E)
© ISO2000 –All rights reserved 1Animalfeedingstuffs —Determinationofpotassium andsodium
contents —Methods usingflame-emissionspectrometry
1 Scope
This International Standard specifies a calibration method and a standard addition method for the determination of
potassium andsodium contents of animalfeedingstuffs byflame-emissionspectrometry.
The standard addition method applies if it is not known whether the emissions measured for potassium or sodium
aresubject tomatrix effects.Thelimit of determinationfor potassium andsodium is 0,04 g/kg.
Thecalibrationmethodapplies if suchmatrix effects havebeenshown tobeabsent.
2 Normative reference
The following normative document contains provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent edition of the normative document indicated below. Forundated references, the latest edition of the normative document referred to applies. Members of ISO and IECmaintain registers of currentlyvalid InternationalStandards.
ISO6498:1998, Animalfeedingstuffs —Preparationof test samples.
3P r i n c i p l e
Thetest portion is incinerated todestroyanyorganic matter. The potassium and sodium are dissolved bytreatment
with hydrochloric acid. The potassium and sodium contents are determined by flame-emission spectrometry at
wavelengths of 766nm and 589nm respectively, by means of a calibration curve (calibration method) or astandard addition graph(standardadditionmethod).
4 Reagents
Useonlyreagents of recognized analyticalquality.
4.1 Water , double distilled, or double deionized.
4.2 Potassium chloride (KCl), dried for 2hat (110 /Gb12)°C.
4.3 Sodiumchloride (NaCl), dried for 2 h at (110 /Gb12)°C.
4.4 Concentrated hydrochloric acid ,c(HCl)=12mol/l( /G7220(HCl) =1,19 g/ml).
4.5 Hydrochloric acid ,c(HCl)=6 mol/l.
4.6 Dilutehydrochloric acid ,c(HCl)=0,1mol/l.ISO 7485:2000(E)
2 © ISO2000 –All rights reserved4.7 Ionizationandreleasebuffersolution.
Dissolve 50g of caesium chloride and 250g of aluminium nitrate nonahydrate [Al(NO 3)3/Gd7/Gd7/Gd7/Gd79H2O] in water. Dilute to
1litre with water andmix.Store in aplastic bottle, e.g.polyetheneor polypropylene.
4.8 Potassium standard solutions.
4.8.1 Potassium stock solution ,/G72(K)=1mg/ml.
Weigh 1,906g of potassium chloride (4.2) and transfer to a 1000ml volumetric flask with approximately 250ml of
dilute hydrochloric acid(4.6). Dissolve anddilutetothemark with the hydrochloric acid(4.6).
Store in a plastic bottle, e.g. polyethene or polypropylene. At room temperature the solution is stable for up to
6months.
4.8.2 Potassium intermediate solution ,/G72(K)=100 /G6dg/ml.
Transfer 10ml of the potassium stock solution (4.8.1) to a 100ml volumetric flask. Dilute to the mark with dilute
hydrochloric acid(4.6) andmix.
Store in aplastic bottle, e.g. polyethene or polypropylene. At room temperaturethesolutionis stablefor 1month.
4.8.3 Potassium calibration solution ,/G72(K)=10 /G6dg/ml.
Transfer 10ml of the potassium intermediate solution (4.8.2) to a 100ml volumetric flask. Add 10ml of the
ionization andreleasebuffer solution (4.7). Dilute tothemark withdilute hydrochloric acid(4.6) and mix.
Prepare freshonthedayof use.
4.9 Sodiumstandardsolutions.
4.9.1 Sodiumstock solution ,/G72(Na)=1mg/ml.
Weigh 2,542g of sodium chloride (4.3) and transfer to a 1000ml volumetric flask with approximately 250ml of
dilute hydrochloric acid(4.6). Dissolve anddilutetothemark with the hydrochloric acid(4.6). Mix well.
Store in aplastics bottle. At room temperaturethe solutionis stablefor upto6months.
4.9.2 Sodium intermediate solution ,/G72(Na)=100 /G6dg/ml.
Transfer 10ml of the sodium stock solution (4.9.1) to a 100ml volumetric flask. Dilute to the mark with dilute
hydrochloric acid(4.6) andmix.
Store in aplastics bottle. At room temperaturethe solutionis stablefor 1month.
4.9.3 Sodiumcalibration solution ,/G72(Na)=10 /G6dg/ml.
Transfer 10 ml of the sodium intermediate solution (4.9.2) to a 100ml volumetric flask. Add 10ml of the ionization
andreleasebuffer solution(4.7). Dilutetothemark with the hydrochloric acid(4.6) andmix.
Prepare freshonthedayof use.
4.10 Biological Certified ReferenceMaterials.
For example: V8-Ryeflour or V10-Hay (powdered), from the International Atomic Energy Agency (IAEA), Austria;
SRM157-Wheatflour, SRM1568a-Riceflour or SRM1548-Total diet, from the National Institute of Standards and
Technology(NIST), USA.ISO 7485:2000(E)
© ISO2000 –All rights reserved 35 Apparatus
Usual laboratoryequipmentand,inparticular,thefollowing.
5.1 Analyticalbalance , capable of weighing tothenearest 1mg.
5.2 Mufflefurnace , electricallyheated, capable of beingmaintainedat (550 /Gb120)°C.
5.3 Ashing dishes , of platinum or silica.
5.4 Flame photometer with an air-butane, air-propane or air-acetylene flame in a ratio allowing complete
combustion; or an atomic absorption spectrometer operating in emission mode and equipped to determine
potassium andsodium with an air-acetyleneflame.
5.5 Sand bath orhot plate , capableof being maintained at approximately150 °C.
5.6 TD (to deliver) precision pipettes ormicroburette of 5mlcapacity.
5.7 TC(tocontain) precisionpipettes, of various capacities.
5.8 Beakers, of 250mlcapacity.
5.9 Volumetricflasks, of various capacities.
6 Sampling
Sampling is not part of the method specified in this International Standard. A recommended sampling method is
given in ISO 6497 [1].
It is important that the laboratory receive a sample which is truly representative and has not been damaged or
changedduringtransport or storage.
7 Preparationoftestsample
Prepare the test sampleinaccordance withISO6498.
8 Procedure
8.1 Test portion
8.1.1 Samplescontainingorganic matter
Depending on the expected content, weigh 1g to 5g of the prepared test sample (clause 7) to the nearest 1mg
into an ashingdish(5.3). Proceed in accordance with8.2.1.
8.1.2 Samplesnot containingorganicmatter
Depending on the expected content of potassium and sodium, weigh 1g to 5g of the prepared test sample to the
nearest 1mgintoa beaker (5.8). Proceed inaccordance with8.2.2.ISO 7485:2000(E)
4 © ISO2000 –All rights reserved8.2 Preparation oftestsolution
8.2.1 Incineration and rendering silicainsoluble
Place the incineration dish containing the test portion (8.1.1) in the cold muffle furnace (5.2). Close the furnace and
graduallyincrease the temperatureto550 °C and ashfor 3h at this temperature.
If manycarbon particles are present, allow tocool down, moistenthecontents of thedish with 2mlof water and dry
thedishonthesandbathor hot plate(5.5). Ashfor another 2h at 550 °C inthemufflefurnace.
Allow to cool down, moisten the ash with a few drops of water and transfer it to a 250ml beaker (5.8). Rinse the
incineration dish with a total of approximately 5ml of concentrated hydrochloric acid (4.4) and then with a fewmillilitres of water, collecting the rinsings in the beaker.
CAUTION —Take careduring the addition of hydrochloric acid, as an effervescent reaction mayoccur with
somesamples.
Put a watch glass on the beaker to reduce spattering and slowly evaporate the contents of the beaker to near
dryness onthesandbathor hot plate(5.5). Allowtocoolto room temperature.
Proceed in accordance with 8.2.3.
8.2.2 Dissolution of potassium and sodium
Add to the beaker containing the test portion (8.1.2), slowly and carefully, a sufficient quantity (15ml to 30ml) of
concentrated hydrochloric acid (4.4). Put a watch glass on the beaker to reduce spattering and slowly evaporate
thecontents of thebeaker todryness onthesand bath or hotplate(5.5). Allow tocool toroom temperature.
8.2.3 Re-dissolutionof potassiumand sodium
Treat the residue (8.2.1 or 8.2.2) with 5ml of hydrochloric acid (4.5) and 45ml of water. Bring to the boil and allow
tocooltoroom temperature. Transfer quantitativelyinto a100ml volumetric flask. Dilute to the mark with water andmix. Allow particles tosettlefor at least 4h. Filter if thesolution is not clear.
CAUTION —Performtheaboveoperations in an effectivefume-removaldevice.
8.3 Blank test solution
Prepare a solution in the same way as for the test solution, carrying out all the operations specified in 8.2 but
omittingthetest portion.
8.4 Selectionofmethod
If it is not known whether the emissions measured for potassium or sodium are subject to matrix effects, proceed in
accordance with 8.6.
If suchmatrix effects havebeenshownto be absent,proceed in accordance with 8.5.
8.5 Calibrationmethod
8.5.1 Test solutions
Transfer to a 100ml volumetric flask an aliquot portion of the test solution (8.2.3) containing a maximum of 1 mg of
potassium or sodium. Add 10mlof the ionization and release buffer solution (4.7), dilute to the mark with water and
mix.
Prepare the samedilutionof the blank test solution(8.3) inthesameway.ISO 7485:2000(E)
© ISO2000 –All rights reserved 58.5.2 Calibration solutions
Transfer to six 100ml volumetric flasks 0 ml, 2,0 ml, 4,0 ml, 6,0 ml, 8,0ml and 10,0ml of the potassium
intermediate solution (4.8.2) or sodium intermediate solution (4.9.2). Add 10ml of the ionization and release buffersolution (4.7) to each flask. Dilute to the mark with hydrochloric acid (4.6) and mix. The potassium or sodium
contents of thesesolutions are 0 /G6dg/ml,2,0 /G6dg/ml,4,0 /G6dg/ml, 6,0 /G6dg/ml, 8,0 /G6dg/ml and10,0 /G6dg/ml respectively.
Prepare freshonthedayof use.
8.5.3 Spectrometric measurements
8.5.3.1 Adjustment of theinstrument
Adjust theinstrument inaccordance with themanufacturer's instructions.
Light the flame and allow some minutes for flame stabilization. Adjust the burner position, the gas flows and the
wavelengths (theoretically 766nm for potassium and 589nm for sodium) or select the filters so that maximum
reading is obtained whenthe calibrationsolution of potassium (4.8.3) or sodium (4.9.3) is atomized intheflame.
8.5.3.2 Test solution measurements
Measure the emissions of thecalibrationsolutions (8.5.2) andthen the emissionof thetest solution(8.5.1).
Correct the emission of the test solution for the emission of the diluted blank test solution (8.5.1), if the latter differs
from theemissionof the zeroconcentrationcalibrationsolution.
8.5.4 Calibration graph
Draw the calibration graph by plotting the emissions of the calibration solutions against their respective potassium
or sodium contents inmicrograms per millilitre.
8.6 Standard additionmethod
8.6.1 Test solutions
Carryout thedilutions accordingtotheexpected potassium or sodium content.
Transfer to each of three volumetric flasks of suitable capacity (flasks A, B and C) the same aliquot portion of the
test solution (8.2.3). Add to flasks B and C aliquot portions of the potassium intermediate solution (4.8.2) or sodium
intermediatesolution(4.9.2) corresponding to acontent of 2,5 /G6dg/mlfor flask B and 5 /G6dg/ml for flask C. Add to each
flask an aliquot portion of the ionization and release buffer solution (4.7) corresponding to 10ml per 100ml of the
finalsolution.
Dilutethecontents of thethreeflasks (A, BandC) tothe mark with water and mix.
Thepotassium or sodium content of thesolution inflask Ashallbesmaller than5 /G6dg/ml.
Prepare the samedilutionof the blank test solution(8.3) inthesamewayas for thesolution inflask A.
8.6.2 Spectrometric measurements
8.6.2.1 Adjustment of theinstrument
Adjust theinstrument inaccordance with 8.5.3.1.ISO 7485:2000(E)
6 © ISO2000 –All rights reserved8.6.2.2 Test solution measurements
Set the instrument to zerowiththediluted blank test solution(8.6.1).
Reset the maximum reading with the calibration solution (4.8.3 for potassium and 4.9.3 for sodium). Atomize the
solutions from flasks A, BandC (8.6.1) andmeasurethe correspondingemissions ( E1,E2andE3respectively).
8.6.3 Graphicpresentation
Draw a graph by plotting the measured emissions against the respective added potassium or sodium contents in
micrograms per millilitre. The graph shall be a straight line intersecting the ordinate axis at E2. The intersection of
the extension of this line with the concentration line at /G72xrepresents the unknown content of the test solution (in
flask A).
9 Expression of results
Calculate the numerical value of thepotassium content or sodium content of thetest sample bythe equation:
xfwm/G72/Gd7/G3d
where
wis the potassium or sodium content, ingrams per kilogram, of thetest sample;
/G72xis the potassium or sodium content, inmicrograms per millilitre, of the test solution determined from the
calibrationcurve(8.5.4) or from thegraph(8.6.3);
fis the reciprocaldilution factor;
mis themass, ingrams, of thetest portion (8.1).
Report theresult rounded in accordance with Table1.
Table1—Roundingof thecalculatedcontent
Values ingramsperkilogram
Content Roundto
from to
— 1,0 0,01
1,0 10,0 0,1
10,0 — 1,0
10 Control test
Analyse a Biological Certified Reference Material (4.10) with known contents of potassium and sodium in order to
check thereagents and apparatus.ISO 7485:2000(E)
© ISO2000 –All rights reserved 711 Precision
11.1 Interlaboratorytest
Details of an interlaboratory test on the precision of the method are summarized in annexA. The values derived
from this interlaboratorytest maynot be applicableto concentrationranges andmatrices other thanthosegiven.
11.2 Repeatability
The absolute difference between two independent single test results, obtained using the same method on identicaltest material in the same laboratory by the same operator using the same equipment within a short interval of time,
willinnot morethan 5% of cases exceedtherepeatabilitylimit ( r) derivedfrom Table2.
Table2—Repeatabilitylimit (r)and reproducibilitylimit (R)
Element r
g/kgR
g/kg
Potassium 0,168g/kg+0,073 w 0,555g/kg+0,161 w
Sodium 0,0054g/kg+0,105 w 0,03g/kg+0,164 w
wis the meanof thetwo single test results, ingrams per kilogram.
11.3 Reproducibility
The absolute difference between two single test results, obtained using the same method on identical test material
in different laboratories with different operators using different equipment, will in not more than 5% of cases
exceed the reproducibilitylimit ( R) derived from Table2.
12 Testreport
Thetest report shallspecify:
/Gbeall information necessaryfor the complete identification of the sample;
/Gbethesamplingmethodused, if known;
/Gbethetest methodused, withreferencetothis International Standard;
/Gbeall operating details not specified in this International Standard, or regarded as optional, together with details of
anyincidents whichmayhave influenced the test result(s);
/Gbethetest result obtained, or thetwo test results obtained if therepeatabilityhas beenchecked.ISO 7485:2000(E)
8 © ISO2000 –All rights reservedAnnex A
(informative)
Results oftheinterlaboratorytests
The precision of the method was established by interlaboratory tests carried out in accordance with ISO57251).I n
this test 13laboratories from 5countries participated, each performing determinations in duplicate on 5different
samples (maize, soybean meal, alfalfa meal, finished mixed feed and mixed feed concentrate). The statistical
results are summarized in TablesA.1 andA.2.
TableA.1 —Statistical resultsforthe determination of potassium content
Parameter Samplea
12345
Number of laboratories retained after eliminating
outliers13 13 13 13 13
Number of outliers (laboratories) -----
Number of acceptedresults 26 26 26 26 26
Mean potassium content,g/kg 3,30 23,00 28,30 9,34 12,05
Repeatabilitystandard deviation( sr),g/kg 0,148 0,70 0,78 0,28 0,40
Repeatabilitycoefficient of variation,% 4,5 3,0 2,8 3,0 3,3
Repeatabilitylimit ( r)[r=2 , 8 /Gb4sr],g/kg 0,414 1,96 2,18 0,78 1,12
Reproducibilitystandard deviation ( sR),g/kg 0,40 1,43 2,13 0,69 0,92
Reproducibilitycoefficient of variation,% 12,2 6,2 7,5 7,4 7,6
Reproducibilitylimit ( R)[R=2,8 /Gb4sR],g/kg 1,12 4,00 5,96 1,93 2,58
aSample 1: Maize;
Sample 2: Soybean meal;
Sample 3: Alfalfa meal;
Sample4: Finishedmixedfeed;
Sample5: Mixedfeedconcentrate.
1)ISO5725:1986 (nowwithdrawn)was used toobtain the precision data.ISO 7485:2000(E)
© ISO2000 –All rights reserved 9TableA.2 —Statistical resultsforthedetermination of sodium content
Parameter Samplea
12345
Number of laboratories retained after eliminating
outliers8 8 13 13 13
Number of outliers (laboratories) 5 5 - - -
Number of acceptedresults 16 16 26 26 26
Mean sodium content,g/kg 0,284 0,391 0,853 1,62 0,293
Repeatabilitystandard deviation( sr),g/kg 0,014 0,015 0,036 0,064 0,013
Repeatabilitycoefficient of variation,% 4,93 3,84 4,22 3,95 4,44
Repeatabilitylimit ( r)[r=2 , 8 /Gb4sr],g/kg 0,039 0,042 0,100 0,179 0,036
Reproducibilitystandard deviation ( sR),g/kg 0,030 0,032 0,055 0,118 0,027
Reproducibilitycoefficient of variation,% 10,6 8,08 6,45 7,3 9,2
Reproducibilitylimit ( R)[R=2,8 /Gb4sR],g/kg 0,084 0,090 0,154 0,33 0,076
aSample 1: Maize;
Sample 2: Soybean meal;
Sample 3: Alfalfa meal;
Sample4: Finishedmixedfeed;
Sample5: Mixedfeedconcentrate.ISO 7485:2000(E)
10 © ISO2000 –All rights reservedBibliography
[1] ISO 6497, Animalfeedingstuffs —Sampling.
[2] ISO 5725:1986, Precision of test methods —Determination of repeatability and reproducibility for a
standard testmethodby inter-laboratory tests.
[3] ISO 5725-1:1994, Accuracy (trueness and precision) of measurement methods and results —Part 1:
General principles and definitions.
[4] ISO 5725-2:1994, Accuracy (trueness and precision) of measurement methods and results —Part 2: Basic
methodfor the determination of repeatability andreproducibility of a standardmeasurement method.ISO 7485:2000(E)
ICS 65.120
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© ISO2000 –All rights reserved