fertilizer analysis protocol

8/10/2019 Fertilizer Analysis Protocol

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FERTILIZER ANALYSIS PROTOCOL

Mineral and organic fertilizer analysisGenerally, the term fertilizer refers to mineral fertilizers, which are manufactured chemical

products of standard composition, while the term organic fertilizers refers to organic manures,

compost, agro-industrial wastes, etc. The compositions of organic fertilizers, unlike mineral

fertilizers, are quite variable and, thus, difficult to regulate precisely.The main objective in analysing fertilizers is to assess their quality. The analysis eamines both

their physical and chemical composition. The quality of fertilizers is stated by the manufacturers

and, in most countries, it is statutorily notified.!ence, analysis is carried out to determine whether the stated quality meets the statutorily

notified standards or not.

"ertilizer quality is notified in terms of physical and chemical characteristics.The physical parameters include moisture content and particle size. The chemical parameters

refer to the amount and form of nutrients, and to various impurities that may be toic to plants

above a critical limit, e.g. biuret in urea. The efficiency of a fertilizer depends on its form of

nutrient content. # phosphatic fertilizer may have water-soluble, citrate-soluble, water-insoluble

or citrate-insoluble forms of phosphate. # nitrogenous fertilizer may contain ammoniacal, nitrateand amide forms of $ in various proportions.

Therefore, in fertilizer analysis, in addition to estimating total nutrient content, it is necessary toestimate the forms of nutrients and other associated compounds in order to assess their quality

properly.

"or organic fertilizers, the % content and the total content of nutrients are considered relevant andnot their forms as they are low-analysis materials.

The analytical methods for fertilizers as described are applicable to most common fertilizers and

the forms of nutrient content in them. The procedures as applicable to a particular nutrient couldbe applicable to any fertilizer with the nutrient in that particular form.

Sa!le !re!aration for analysisThe sample received for analysis is recorded in the laboratory with adequate details, and a

laboratory code number is assigned in order to identify the sample and to keep its identityconfidential.

#bout half of the sample is ground, sieved through a & mm sieve, and stored in a sample bottle

for analysis. The remaining half is kept unground for particle size estimation. The samples are

stored in an airtight glass bottle or taken for analysis in a moisture-free room 'fitted with adehumidifier( as most fertilizers are hygroscopic in nature.

ANALYTICAL MET"O#S

There are a number of estimation methods available for each of the constituents.

P$ysical Paraeters

%& Moist're

Two important forms of water present in fertilizers are) 'i( absorbed*adsorbed water+ and 'ii( free

water. They are interchangeable depending on the degree of moisture saturation and temperature.ome fertilizers also contain water as an integral part of their composition, which is referred to

as water of crystallization, as in the case of n/.0!1 and %u/.2!1. #s fertilizers are


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generally hygroscopic in nature, they tend to absorb moisture from the atmosphere 'depending

on the relative humidity and their packing and storage conditions(.

3cessive moisture may damage the granular structure of fertilizers, affect their quality andinfluence their nutrient content by increasing the weight of fertilizers in a given container.

Therefore, moisture estimation is critical to determining the quality of a fertilizer. The method

used depends on the type of fertilizer and the nature of moisture held by it. ome commonmethods are)

i. gravimetric method+

ii. vacuum desiccator method+iii. 4arl "ischer titration method.

(ra)ietric et$od

5ith the gravimetric or oven-drying method, the loss of water on heating fertilizer samples at a

certain temperature is estimated. This method is suitable for fertilizers such as ammoniumsulphate, sodium nitrate, superphosphates, muriate of potash '67( and sulphate of potash

'7(. 8t is not suitable for fertilizers that yield volatile substances 'such as $! /( other than

moisture on drying at a specified temperature, e.g. calcium ammonium nitrate and di-ammoniumphosphate '9#7(.

6oisture is estimated by the gravimetric method where the loss in weight at a constant

temperature of &:: ;% < & ;% for 2 hours is measured, e.g. zinc sulphate, and copper sulphate. 8n

the case of sodium nitrate, superphosphates, ammonium sulphate, 7 and 67, the heating isat &=: ;% < & ;%. "or urea and urea-based fertilizers, the heating is at 0: ;%. !owever, heating at

0: ;% does not reflect full moisture content. Therefore, another method such as the 4arl "ischer

method is preferred.

The apparatus required consists of)

a glass weighing bottle+

an electronic balance+

a temperature-controlled oven.

T$e !roced're*

&. 5eigh 1.: g of fertilizer sample in a pre-weighed glass weighing bottle.

1. !eat in a temperature-controlled oven for about 2 hours at the specified temperature, as givenabove for different types of fertilizers.

=. %ool in a desiccator, and weigh.

The relevant calculation is)

where)

>A ? weight in grams of the empty sample bottle+

>B ? weight in grams of the bottle plus material before drying+


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> C ? weight in grams of the bottle plus material after drying.

+ac'' desiccator et$od

5ith the vacuum desiccator method, the free moisture present in the fertilizer is absorbed by thedesiccant 'sulphuric acid(, and the loss in weight is reported as moisture. This method is suitable

for fertilizers such as calcium ammonium nitrate, 9#7, and $74 complees.8n this method, the sample is kept in a vacuum desiccator over sulphuric acid. "ree moisture

present in fertilizers is absorbed by the acid, and the loss in weight of the sample is recorded asthe moisture content in the sample.


a vacuum desiccator+

a porcelain dish+

a balance.

T$e !roced're is*

&. 5eigh 'accurately( 2 g of sample in a porcelain dish, and keep it in a desiccator for 1/ hours.1. Take the weight again after 1/ hours. The loss in weight is equal to moisture content in the

sample.


where)

>A ? weight in grams of the porcelain dish+>B ? weight in grams of the porcelain dish plus the fertilizer sample+> C ? weight in grams of the porcelain dish plus the fertilizer sample after desiccation for 1/

hours.

,arl Fisc$er et$od

The 4arl "ischer titration method is suitable for fertilizers such as nitrophosphates, urea, andurea-based fertilizers, which do not withstand high temperatures.


a 4arl "ischer titrator+


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# 4arl "ischer Titrator.

a balance+

a beaker or flask+

a graduated cylinder.

T$e reagents re-'ired are*

4arl "ischer reagent 'pyridine-free(.

9isodium tartrate dihydrate '$a1%/@1!1( A #B-grade.

6ethanol A 4arl "ischer grade * spectroscopy grade containing less than :.:2 percentwater.

T$e !roced're is*

&. tandardization of 4arl "ischer reagent)

et up the instrument.

#dd about 12 ml of methanol to the titration vessel until the electrodes are dipped, and

titrate with 4arl "ischer reagent to a pre-set end point that persists for =: seconds.

#dd &:: mg of the disodium tartrate dihydrate to the titration vessel carefully, and titrate

with 4arl "ischer reagent to a pre-set end point 'the end point should persist for =:

seconds(. $ote the volume 'ml( of 4arl "ischer reagent used as C&.

1. 5eigh accurately about & g of the prepared sample, transfer it carefully to the titration vessel,and stir until dispersed.

=. Titrate with 4arl "ischer reagent to the same pre-set end point as above, and note the volume'ml( of 4arl "ischer reagent used as C1.



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where)

9isodium tartrate dihydrate contains :.&2@@ percent moisture.

.& Particle size

"ertilizers are manufactured with varying degrees of particle size. This property of fertilizer has abearing on its efficiency when used in various types of soil for crop production. The size and

strength of the particle determine its dissolution time when applied in soil. 6ost fertilizers arehighly water soluble+ hence, they dissolve quickly when they come into contact with soil

moisture."ertilizers can be crystalline or granular. 5ith a view to reducing losses caused by rapid

dissolution, fertilizers with large granules are also being manufactured, e.g. granular urea and

super granular urea.Granular fertilizers are considered superior for machine application, for preparing bulk blends

with greater homogeneity and uniformity, and they are also less vulnerable to adulteration.

Therefore, particle size estimation is an important aspect in determining the fertilizer quality.6ost granular fertilizers range between & and / mm, with a specific particle size for a specific

fertilizer.

The apparatus required for particle size estimation consists of sieves of various sizes.The procedure consists of sieving through a given sieve size. The material is passed through asieve with a mesh equal to the maimum particle size prescribed for a given fertilizer. The

material so sieved is retained on a sieve with a mesh equal to the minimum particle size

prescribed for that fertilizer."or eample, a fertilizer is sieved through a / mm sieve and is retained on a & mm sieve, kept

below the / mm sieve. The material retained on the / mm sieve is larger than / mm in size and

that passed through the & mm sieve is less than &.: mm in size. The material retained on the &mm sieve is that with a particle size of between & and / mm.

Generally, 12: g of the fertilizer is taken and sieved as per the requirement.

ieving can be done mechanically or manually.

/& C$eical Paraeters

i& Nitrogen

$itrogen in fertilizers may be present in various forms such as $!/-$, $=-$, urea-$ 'amide(and organic $. The estimations are carried out for total $ and its forms. "or urea fertilizer, the

total $ estimation method is followed. The principle of $ estimation is based on the 4jeldahl

method. "or including or ecluding a particular form of $ in total $ estimation, specific

chemicals*catalysts are used.


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"or eample, in nitrate-containing fertilizers, 1 g of salicylic acid and 2 g of sodium thiosulphate

are added in the digestion miture. This helps to bind the $ =-$ in the form of nitrosalicylic

acid, and it is converted eventually into $!/-$ in the presence of !1/and is estimated alongwith other forms of $ present in the sample. 9evardaDs alloy '1-= g per sample( can also be used

instead of salicylic acid and thiosulphate.

Total nitrogen 0y t$e ,1elda$l et$od

The method and procedure are the also used for estimation of total $ in soil. The fertilizer

sample size may vary between :.1 and :.2 g depending on the $ content of the sample. # smalleramount of sample may be taken for high-analysis fertilizers 'e.g. urea( and a larger amount for

low analysis fertilizer 'e.g. ammonium sulphate(.


a 4jeldahl distillation unit+

some flasks, beakers and pipettes+

a burette.

The reagents required are)

"reshly ignited carbonate-free 6g. tandard acid ':.&6 !%l(.

tandard alkali ':.&6 $a!(.

$a! '/: percent( for distillation.

6ethyl red indicator.

T$e !roced're is*

&. 7ut :.2 g of the sample in a @:: ml distillation flask with about 12: ml of water.

1. #dd 1 g of freshly ignited carbonate-free 6g or 2 ml of $a! solution '/: percent( by

tilting the flask and through the side of the flask so that the contents do not mi at once.

=. %onnect the flask to a condenser by a 4jeldahl connecting bulb and connecting tube./. tart heating, and distil about &:: ml of liquid into a measured quantity of standard acid

':.&6 !%l(.2. Titrate the distillate with standard $a! ':.&6( to determine the remaining amount of

unused acid, using methyl red indicator. The acid used to neutralize ammonia is equivalent to

the $ content in the sample.

@. %arry out a blank.


where)

A ? ml of standard acid ':.&6 !%l( taken to receive ammonia+

B ? ml of standard alkali ':.&6 $a!( used in titration+

W ? weight of the sample taken+

C ? ml of standard alkali used in the blank.

& ml :.&6 !%l ? :.::&/ g $


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Aoniacal nitrogen 0y t$e distillation et$od

Aoniacal !l's nitrate2nitrogen 0y t$e distillation et$od

9evardaDs alloy '2: percent %u, /2 percent #l, and 2 percent n( reduces $ = to $!/ in an

alkaline condition. The method is same as for $! /-$ estimation 'above(, ecept that 1A= g of

9evardaDs alloy is added before distillation in order to take into account the $ =by reducing it toammonia form.

Nitrate2nitrogen

8n fertilizers containing both $!/and $=-$, first ammoniacal nitrogen is estimated followed

by $!/ plus $= estimation. "rom the combined value of $!/ and $=, the value ofammoniacal $ is subtracted to obtain the nitrate-$ content.

3rea nitrogen

The urea form of $ can be estimated together with total $ by digestion with sulphuric acid. "or

eample, total $ is estimated for urea fertilizer. !owever, for some $74 complees, urea $ has

to be estimated separately. 8n such cases, it is done by the urease method.The apparatus required for the urease method consists of)

some beakers+

some flasks+

a Gooch crucible+

some filter paper.


$eutral urease solution) hake & g of jack bean meal with &:: ml of water for 2 minutes.

Transfer &: ml of the solution to a 12: ml 3rlenmeyer flask, dilute with 2: ml water, andadd / drops of methyl purple indicator. Titrate with :.&6 !%l to reddish purple, then

back titrate to green colour with :.&6 $a!. "rom the difference in volume used,


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calculate the amount of :.&6 !%l required to neutralize &: ml of solution. Eased on the

calculated acid required, add :.&6 !%l to the remaining F: ml of solution 'about 1.2 ml

of acid is required per &:: ml of solution(, and shake well.

!%l ':.&6() 9ilute &:: ml of concentrated !%l to & litre, and titrate with the standard

alkali to establish the eact strength of the acid.

$a! ':.&6() 9issolve / g of $a! in F:: ml of water in a &-litre volumetric flask,make the volume up, and standardize with the standard acid.

odium carbonate '&: percent(.

Earium hydroide 'saturated(.

T$e !roced're is*

&. 5eigh &: < :.:& g of the sample and transfer it to &2 cm $o. &1 fluted filter paper.

1. each with about =:: ml of water into a 2:: ml volumetric flask.

=. #dd 02A&:: ml of saturated barium hydroide solution to precipitate phosphates./. et it settle, and test for complete precipitation with a few drops of saturated barium hydroide

solution.

2. #dd 1: ml of &: percent sodium carbonate solution to precipitate ecess barium and anysoluble %a salts.@. et it settle, and test for complete precipitation 'when the addition of a few more drops of

sodium carbonate does not show further precipitation(.

0. 9ilute to volume, mi, and filter through &2 cm $o. &1 fluted paper.H. Transfer 2: ml of aliquot 'equivalent to & g of sample( to a 1:: or 12: ml 3rlenmeyer flask,

and add &A1 drops of methyl purple indicator.

F. #cidify solution with :.&6 !%l, and add 1A= drops in ecess 'after colour change is noticed(.&:. $eutralize 'titrate( solution with :.&6 $a! to the first change in colour of the indicator.

&&. #dd 1: ml of neutral urease solution, close flask with rubber stopper, and let it stand for &

hour at 1:A12 ;%.

&1. %ool the flask in ice water slurry, and titrate at once with :.&6 !%l to full purple colour, thenadd about 2 ml in ecess.

&=. Becord total volume added+ back titrate ecess !%l with :.&6 $a! to neutral end point.


4i'ret

Eiuret '%11$=!2( is a chemical compound formed by the combination of two molecules of ureawith a release of a molecule of ammonia when the temperature during the urea manufacturing

process eceeds the controlled level. "ertilizer grade urea contains biuret, which usually varies

between :.= and &.2 percent.

Eiuret is toic to plants particularly when applied through foliar spray.The apparatus required for estimating biuret consists of)

a water-bath shaker+

a spectrophotometer+


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some beakers and flasks+

a burette.


#lkaline tartrate solution) 9issolve /: g $a! in 2: ml of cold water and 2: g of

$a4%/!/@./!1, and dilute to & litre. et it stand for & day before use. %opper sulphate solution) 9issolve &2 g of %u/.2!1 in %1-free water, and dilute to

& litre.

Eiuret standard solution '& mg*ml() 9issolve &:: mg of reagent-grade biuret in %1-free

water, and dilute to &:: ml.

tandard !1/.

The procedure is)

&. 7reparation of the standard curve)

Transfer a series of aliquots, 1A2: ml of standard biuret solution, to a &:ml volumetric

flask. #djust the volume to about 2: ml with % 1-free water. #dd one drop of methyl red, and

neutralize with :.&6 !1/to a pink colour.

#dd, with swirling, 1: ml of alkaline tartrate solution and then 1: ml of %u/solution.

9ilute to volume. hake for &: seconds, and place in a water-bath for &2 minutes at =: ;%

< 2 ;%.

#lso prepare a reagent blank.

9etermine absorbance of each solution against the blank at 222 nm on the

spectrophotometer with a 1./ cm cell, and plot the standard curve.1. tir continuously 2 g of the sample in &:: ml of water for =: minutes.

=. "ilter and wash in 12: ml volumetric flask and dilute to volume.

/. Transfer 12 ml of aliquot to &:: ml volumetric flask and proceed as given under preparationof standard curve.


where)> C ? concentration in mg*ml of biuret as read from the standard curve+

> W ? weight of sample+

> df ? 1:: '2 g of fertilizer etracted to 12: ml, and 12 ml taken for further dilution to &:: ml(.

ii& P$os!$or's

7hosphate '712( in fertilizers may be present in different forms) 'i( water soluble+ 'ii( neutral

ammonium citrate soluble or insoluble+ 'iii( citric acid soluble or insoluble+ and 'iv( acid soluble.7hosphate is generally present as bound with %a as monocalcium phosphate, dicalcium

phosphate and tricalcium phosphate.


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6onocalcium phosphate is in water soluble form, is considered available, while dicalcium

phosphate becomes available in slightly acidic situations. Tricalcium phosphate is in an

unavailable form and can be available only in acidic situations. imilarly, the aluminium and ironphosphates are also in plant-unavailable forms.

$eutral ammonium citrate soluble form is also considered as available, which includes both

monocalcium phosphate and dicalcium phosphate.8n view of the variability in availability to plants, the estimation of different forms of phosphate

is critical.

"or the so-called IavailableJ forms of 7, appropriate etractants have been designed to etract 7from fertilizers under a set of well-defined sampling conditions) etractant ratio, temperature,

time of etraction, shaking period, etc.

The form of 7 as a fraction of the total 7 is etracted by a particular method.

3stimation of the etracted 7 utilizes various testing methods) 'i( gravimetric+ 'ii( volumetric+and 'iii( colorimetric.

The following methods are used for 7 estimation in fertilizers

gravimetric ammonium phosphomolybdate+

gravimetric quinolinium phosphomolybdate+

volumetric ammonium phosphomolybdate+

volumetric quinolinium phosphomolybdate+

spectrophotometric vanadium phosphomolybdate.

#ll the methods are used in various laboratories. "or total phosphate estimation, the gravimetricquinolinium phosphomolybdate method is generally preferred because of the minimal

interference of other ions and its accuracy and simplicity. #nother common method providing

acceptable accuracy and simplicity is volumetric ammonium phosphomolybdate.

(ra)ietric -'inolini' !$os!$ooly0date et$od

Carious forms of 7 present in fertilizers are first converted into orthophosphate through chemical

treatments. n reaction with quimociac reagent, the orthophosphate precipitates as quinoliniumphosphomolybdate K'%F!0$(=!=7/.&1 6o=L in a boiling medium. The precipitate is weighedgravimetrically, which gives the 7 content of the sample.

8n the gravimetric method, %a, "e, 6g, alkali metals and citrates do not affect the analysis. The

citrate in the reagent complees the ammonium ions, thus preventing interference fromprecipitation of ammonium phosphomolybdate by the ammonium salts usually present in mied

fertilizers. The citrates also reduce interference from soluble silica.


a volumetric flask+

some beakers+

a Gooch crucible+


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some filter paper+

an analytical balance.


%oncentrated nitric acid.

%oncentrated hydrochloric acid.

6agnesium nitrate solution 'F percent() 9issolve F: g of 7-free 6g'$ =(1in water, and

dilute to & litre.

#cetone.

%itric acid.

odium molybdate dihydrate.

Muinoline.

Muimociac reagent) 9issolve @: g of citric acid in a miture of H2 ml of !$ =and &2:

ml of water, and cool. 9issolve 0: g of sodium molybdate dihydrate in &2: ml of water.

Gradually add the sodium molybdate solution to the citric acid A nitric acid miture, with

stirring. 9issolve 2 ml of synthetic quinoline in a miture of =2 ml of !$ =and &:: ml

of water. Gradually add this solution to the molybdate citric-nitric acid solution, mi, letit stand for 1/ hours, and filter. #dd 1H: ml of acetone, dilute to & litre with water, and

mi well. tore in a polyethylene bottle.

#ccording to the nature of the fertilizer, the sample solution should be prepared using one of the

following methods)

"or materials and fertilizer mitures with a high 6 content) 7ut & g of the sample in an

evaporation dish. #dd 2 ml of 6g'$=-(1solution, and evaporate to dryness. 8gnite to

destroy the 6, and dissolve in &: ml of !%l.

"or materials with a low 6 content) 7ut & g of the sample in a 2: ml beaker. #dd =: ml

of !$=and 2 ml of !%l, and boil gently until the 6 is destroyed and red-brownfumes cease to appear.


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"or basic slag and fertilizers containing iron or aluminium phosphate) Treat & g of the

sample with =: ml of !%l and &: ml of !$ =, and boil gently until red-brown fumes

disappear.%ool the solution, prepared by any of the above three methods, dilute to 12: ml, mi, and filter

through a dry filter, if required 'may contain some insoluble material(.

The procedure is)&. 7ipette 2A12 ml of aliquot 'sample solution( depending on the 7 content 'containing not more

than 12 mg 712 in the aliquot( into a 12: ml beaker, and dilute to &:: ml with distilled

water.1. #dd 2: ml of quimociac reagent, cover with a watch glass, place on a hotplate, and boil for &

minute.

=. %ool the material to room temperature, swirl carefully =A/ times during cooling.

/. "ilter the precipitate with fiberglass filter paper 'or Gooch crucible G/( previously dried at12: ;% and weighed. 5ash /A2 times with 12 ml portions of water. 9ry the crucible*filter

paper and contents for =: minutes at 12: ;%. %ool in a desiccator to a constant weight.

2. Bun a reagent blank with each batch. ubtract the weight of the blank from the weight of the

sample precipitate.


where)

> S ? weight of sample precipitate in grams+>B ? weight of blank precipitate in grams+

> df ? dilution factor for aliquot taken)

uppose volume of the aliquot 'solution( taken for estimation ? 2 ml, and total volume offertilizer solution prepared ? 12: ml+

> W ? weight of sample taken in grams+

> "actor =.1:0 ? the quinolinium phosphomolybdate precipitate contains =.1:0 percent 712on

weight basis.8n cases where 6o=.$a16o/.1!1 'quinoline( is not of standard quality, the eact volume of

quimociac reagent to be added for precipitation should be calculated by running a series of

known standards and observing the phosphate recovery in them.


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+ol'etric aoni' !$os!$ooly0date et$od

7hosphorus is precipitated from the acidic solution as ammonium phosphomolybdate

K'$!/(=7/.&16o=L by adding ammonium molybdate solution. The precipitate is dissolved in ameasured ecess of the standard alkali after filtration and washing until free of the acid.


some volumetric flasks * beakers+

a burette+

a shaker+

a water-bath+

some $o. // filter paper.


6agnesium nitrate solution 'F percent() 9issolve F: g of 7-free 6g'$ =(1in water, and

dilute to & litre.

%oncentrated nitric acid.

%oncentrated hydrochloric acid. #mmonium molybdate solution '= percent() 9issolve =: g of ammonium molybdate in

hot distilled water, and make the volume up to & litre.

tandard $a! solution ':.&6() 9issolve / g of $a! in & litre of water, and

standardize against standard acid.

tandard !1/ solution ':.&6() Take 2.@ ml of concentrated !1/ and make the

volume up to & litre. tandardize against a primary standard alkali such as $a1%=.

odium nitrate '1 percent() 9issolve 1: g of #B-grade sodium nitrate in & litre of

distilled water.

7henolphthalein indicator '& percent() 9issolve & g of phenolphthalein in &:: ml of F2.2

percent ethanol.

#mmonium nitrate '#B-grade(.

odium carbonate '#B-grade(.

The sample solution should be prepared using one of the methods indicated for the

gravimetric quinolinium phosphomolybdate method 'above(.

T$e !roced're is*

&. 7ipette 2A12 ml of aliquot 'sample solution( depending on the 7 content 'containing notmore than 12 mg 712in the aliquot( in a 12: ml beaker, and dilute to &:: ml with

distilled water.

1. #dd about 2A&: ml of concentrated !$=and about &: g of ammonium nitrate.

=. !eat this miture on a water-bath at 22A@: ;% for &: minutes./. #dd = percent ammonium molybdate solution in the beaker drop by drop with the help of

a burette. %ontinue stirring with a glass rod until about 2: ml of molybdate solution isadded. tir for another few minutes until the yellow precipitate appears to become

granular.

2. %over the beaker with glass and allow it to settle for some time. 9ecant the clear solution

through $o. // filter paper, and wash the precipitate with 1 percent sodium nitratesolution, agitate thoroughly, and allow the precipitate to settle. Transfer the precipitate to


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the filter paper, and wash with $a$ =solution until free from acid 'by test with a litmus

paper(.

@. Transfer the precipitate and filter paper to a beaker, and add &: ml of :.&6 $a! at atime by pipette until the precipitate becomes soluble.

0. #dd &A1 drops of & percent phenolphthalein, and titrate the ecess of alkali against :.&6

sulphuric acid.H. Bun a reagent blank with each batch.


where)

F ? factor for 712corresponding to & ml of &6 alkali '$a!(.

The calculation is as follows) 1= g equivalent of $a! ? =& g 7 ? 0& g 712'7 N 1.1F ? 712(

> V& ? volume of :.&6 $a! required to dissolve the precipitate 'e.g. /: ml(+

> V1 ? volume of :.&6 !1/ used for titration to neutralize ecess alkali 'e.g. &: ml(+>M& ? molarity of the standard alkali '$a!(+

>M1 ? molarity of the standard acid '!1/(+

> df ? dilution factor for aliquot taken)

uppose, volume of the aliquot 'solution( taken for estimation ? 2 ml+ total volume of fertilizer

solution prepared ? 12: ml.

5ater2sol'0le !$os!$ate 6P.O78

The water-soluble phosphate is obtained from the sample by dissolving it in distilled water or bywashing the sample successively with distilled water. #s a procedure, put & g of the sample on a


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> Transfer the dry filter paper and contents to a crucible, ignite until all 6 is destroyed. 9igest

with &:A&2 ml of !%l until phosphates are dissolved.

> Transfer the filter paper and residue to a 12: ml 4jeldahl flask, boil for =:A/2 minutes with =:ml of !$=and &: ml of !%l. Eoil very gently until it is colourless and white dense fumes

appear in the flask.

0. 9ilute the solution to 12: ml, mi well, and filter through dry filter paper if required. 7ipetteout 12 ml of aliquot containing not more than 12 mg of 7 12into a 2:: ml 3rlenmeyer flask, and

proceed as described for estimation of total 712using quimociac reagent 'above(.


where)

> S ? weight of sample precipitate in grams+

>B ? weight of blank precipitate in grams+

> W ? weight of sample in grams+

7ercent available 'citrate-soluble( 712 ? O total 712 - O citrate-insoluble 712The procedure for total 712estimation is described above.

iii& Potassi'

8n all potassic fertilizers, 4 is generally present in water-soluble form. Therefore, it is estimateddirectly in fertilizer solution either gravimetrically, volumetrically or flame photometrically. 8n

manures and organic fertilizers, wet digestion with acid is required prior to determination of 4 in

order to bring the element into solution by digestion.The methods used for 4 determination in fertilizers and manures are)

> gravimetric perchloric acid method+

> gravimetric chloroplatinate method+> gravimetric and volumetric cobaltinitrite method+

> gravimetric and volumetric sodium tetraphenyl boron 'T7E( method.

The ##%-based T7E volumetric method is commonly used in laboratories because of itsaccuracy and simplicity.

STP4 et$od

7otassium from the fertilizer sample is first etracted with water or ammonium oalate. The 4 inetracted solution is precipitated with an ecess of T7E as potassium tetraphenyl boron. The

ecess of T7E is backtitrated with benzalkonium chloride 'E#%( or quaternary ammonium

chloride using %layton yellow as indicator)


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8nterference of $!/Ptakes place during 4 precipitation. 8t is avoided by compleing $! /

Pwith

formaldehyde under slightly alkaline conditions before precipitation of 4. The chlorides andsulphates do not interfere in the titration.

The apparatus required consists of)> some volumetric flasks and beakers+

> a burette * semi-microburette+> some filter paper.


> odium hydroide solution '1: percent() 9issolve 1: g of $a! in &:: ml of distilled water.> "ormaldehyde '!%!( solution '=0 percent(.

> T7E solution 'about &.1 percent() 9issolve &1 g of T7E in about H:: ml of water. #dd 1:A

12 g of #l'!(=, stir for 2 minutes, and filter through $o. /1 filter paper 'or equivalent( into a &litre volumetric flask. Binse the beaker sparingly with water and add to the filtrate. %ollect the

entire filtrate, add 1 ml of 1: percent $a! solution, dilute to volume '& litre( with water, and

mi.et it stand for /H hours, and then standardize 'as described below(. #djust 'by using 4 salt of

known composition for prior standardization by trial and error( so that & ml of T7E ? & percent

41. tore at room temperature.

> E#% or quaternary ammonium chloride solution 'about :.@12 percent() 9ilute 2: ml of &1.Hpercent E#% to & litre with water, mi and standardize 'as described below(. 8f a different

concentration is used, adjust the volume accordingly 'E#% of :.@12 percent strength is required

so the dilution can be done according to the concentration available(.> %layton yellow ':.:/ percent( indicator) 9issolve /: mg of %layton yellow powder in &:: ml

of water.

> #mmonium oalate solution K'$!/(1%1/L '/ percent() 9issolve /: g of ammonium oalate in

& litre of distilled water.The procedures for standardizing the solutions are)

> E#% solution) 7ut & ml of T7E solution in a 12: ml 3rlenmeyer flask+ add 1:A12 ml of

water, & ml of 1: percent $a!, 1.1 ml of !%!, &.2 ml of / percent ammonium oalate, and@AH drops of %layton yellow indicator. Titrate to pink end point with E#% solution, using a &:

ml semimicroburette.

#djust by increasing or decreasing the strength of the E#% solution so that 1 ml ? & ml of T7Esolution 'keeping & ml T7E ? & percent 41(.

> T7E solution) 9issolve 1.2 g of 4!17/in about &2: ml of water in a 12: ml volumetric

flask, add 2: ml of / percent ammonium oalate solution, dilute to volume with water, and mi.Transfer &2 ml of aliquot '2&.F1 mg of 41 or /=.&: mg of 4( to a &:: ml volumetric flask, add

1 ml of 1: percent $a!, 2 ml of !%! and /= ml of T7E solution. 9ilute to volume '&::ml( with water, and mi thoroughly. et it stand for 2A&: minutes, and then pass through dry $o.

/1 filter paper. Transfer 2: ml of aliquot of filtrate to a 12: ml 3rlenmeyer flask, add @AH dropsof %layton yellow indicator, and titrate ecess T7E with E#% solution to pink end point.

%alculate factor 'f( by) f ? percent 41*ml of T7E solution


18/24

where, =/.@& ? O 41 present in standard 4!17/.

T$e !roced're is*

&. 4 etraction*preparation of sample solution) 9issolve a known weight '1.2 g( of straight 4fertilizer '67, 7, potassium magnesium sulphate( in 1:: ml of distilled water, and make the

volume up to 12: ml for estimation. "or $74 comple fertilizers or $74 fertilizer mitures,

dissolve the sample in &12 ml of water, add 2: ml of / percent ammonium oalate solution, and

boil for =: minutes+ after cooling, filter through dry $o. &1 filter paper, and make the volume upto 12: ml for further estimation.

1. Transfer &2 ml of aliquot of sample solution to a &:: ml volumetric flask and add 1 ml of 1:

percent $a! and 2 ml of !%!.=. #dd & ml of standard T7E solution for each & percent of 41 epected in the sample plus an

additional H ml in ecess in order to ensure complete precipitation./. 9ilute to volume '&:: ml( with water, mi thoroughly, let it stand for 2A&: minutes, and passit through $o. &1 filter paper 'or equivalent(.

2. Transfer 2: ml of filtrate to a 12: ml 3rlenmeyer flask, add @AH drops of %layton yellow

indicator, and titrate ecess T7E with standard E#% solution to pink end point.The relevant calculation is)

where, f ? O 41*ml of T7E solution. This factor applies to all fertilizers where 1.2 g ofsample is diluted to 12: ml, and &2 ml of aliquot is taken for analysis. To epress the results as 4

rather than 41, substitute 1H.0= for =/.@& in calculating the value off.

Organic fertilizers

8n the case of organic fertilizers, the % content and the total content of nutrients are considered

relevant and not their forms as they are low-analysis materials.

The methods for estimation of total $, 7 and 4 in organic fertilizers are the same as describedabove for mineral fertilizers. 5ith organic fertilizers, the sample always needs to be prepared

using the wet-digestion method. The sample size should be &.: g 'to be weighed eactly(.

5et C$eistry Tec$ni-'es for t$e #eterination of Total Organic Car0on&

5et chemistry techniques can be divided into two phases, namely, sample etraction and sample

quantification. The etraction technique employed is essentially the same for all methods in the

literature with variations eisting only in the strength and combination of reagents used duringetraction. Muantification techniques associated with the wet chemistry determination of T%

either rely on titration 'volumietric( 'manual or automated(, calorimetric, or gravimetric

techniques.

+ol'etric et$od

Sa!le E9traction - The standard wet chemistry technique for the sample etraction involvesthe rapid dichromate oidation of organic matter. The 5alkley-Elack procedure is the best


19/24

known wet digestion method. 8n this procedure, potassium dichromate '41%r11( and

concentrated !1/ are added to & .: g of the organic fertilizer material. The solution is swirled

and allowed to cool 'note) the sample must be cooled as a result of the eothermic reaction whenthe potassium dichromate and sulfuric acids are mied( prior to adding water to halt the reaction.

rthophosphate !=7/is added to the digestive mi after the sample has cooled to eliminate

interferences from the ferric '"e=P

( iron that may be present in the sample.The chemistry of this etraction procedure is as follows)

1%r101-P= %: P &@!P ? /%r =P P =%1 P H!1:. '=(

The 5alkley-Elack procedure is widely used because it is simple, rapid, and has minimal

equipment needs. !owever, this procedure has been shown to lead to the incomplete oidation of

organic %. tudies have shown that the recovery of organic % using the 5alkley-Elack procedurerange from @: to H@O with a mean recovery being 00O. #s a result of the incomplete oidation

and in the absence of a site-specific correction factor, a correction factor of &.== is commonly

applied to the results to adjust the organic % recovery.To overcome the concern of incomplete digestion of the organic matter, the 5alkley-Elack

procedure was modified to include etensive heating of the sample during sample digestion. 8n

this variation of the method, the sample and etraction solutions are gently boiled at &2:;% for=: minutes, allowed to cool, and then water is added to halt the reaction. The addition of heat to

the system leads to a complete digestion of the organic % in the sample+ therefore: no correction

factor is needed. The temperature of this method must be strictly controlled because the acid

dichromate solution decomposes at temperatures above &2:;% '%harles and immons, &FH@(.

Sa!le ;'antification Qpon completion of the sample etraction phase, the quantity of

organic carbon present in the fertilizer material can be determined through a variety of different

techniques. These techniques include) manual titration, automated titration using potentiometricdetermination, calorimetry, gravimetric determination, or volumetric*manometric measurement.

Qpon eamination of the equation above, the three measurable products of the acid

dichromate digestion process are the ecess*unused dichromate '%r10(, chromate '%r=P( and

%1. Eoth the %r101-and %r=P will remain in solution and can be measured titrimetrically

'volumetrically( or calorimetrically while the evolved %1, in its gaseous state, can be measured

gravimetrically or manometrically.

To perform manual titrimetric quantification, an indicator solution is added to the digestate. The

most common indicators used are ortho-phenanthroline ferrous comple 'commercially availableas I"erroinJ(, barium diphenylamine sulfonate, and $-phenylanlhranilic acid. The ecess %r10

1-

is titrated with ferrous ammonium sulfate K"e'$!/(1'/(1R@!1L or ferrous sulfate '"e/(

until color change occurs in the sample. %olor changes associated with these indicators are) '&(

green to reddish brown for the orthophenanthroline ferrous comple, '1( purple*blue to green forthe barium diphenylamine sulfonate, and '=( dark violet-green to light green for the $-phenylan-

thranilic acid. The primary concern with the manual titration technique is the low visibility or

subtlety of color changes during titration. %olor changes may also be obscured by naturally-occurring high organic fertilizer materials.

The use of an automated titrator eliminates the need for indicators to be added to the digestate.

imilar to manual titrimetric quantification, ecess %r101- is titrated with ferrous ammonium

sulfate or ferrous sulfate. !owever, the endpoint is not a color change but is determined


20/24

potentiometrically. 8n this technique, a simple calomel electrode or platinum electrode is placed

in the digestate, and the titer is added until a fied electrical potential endpoint is reached. The

endpoint is dependent upon the type of electrode used. nce the endpoint is reached, the titrationis stopped and the T% content calculated. The automated titration technique has the distinct

advantage over manual titration since the endpoint is not dependent upon operator optical

determination of eactly when the color changed. The only disadvantage of the automatedtechnique is the necessity to purchase 'i.e., cost( an automated titrator and suitable electrodes.

The apparatus required for the volumetric method '5alkley and Elack, &F=/( consists of)

> a conical flask '2:: ml(+> some pipettes '1, &: and 1: ml(+

> a burette '2: ml(.


> 7hosphoric acid A H2 percent.> odium fluoride solution A 1 percent.

> ulphuric acid A F@ percent containing &.12 percent of #g1/.

> tandard :.&@@06 41%r10) 9issolve /F.:/ g of 41%r10in water and dilute to & litre.

> tandard :.26 "e/solution) 9issolve &/: g of ferrous sulphate or &F@.& g of "e/.'$!/(1.@!1 in H:: ml of water, add 1: ml of concentrated ! 1/and make the volume up to &

litre.> 9iphenylamine indicator) 9issolve :.2 g of reagent-grade diphenylamine in 1: ml of water and

&:: ml of concentrated !1/.

T$e !roced're is*

&. 5eigh &.: g of the prepared soil sample in a 2::-ml conical flask.

1. #dd &: ml of :.&@@06 41%r10solution and 1: ml of concentrated !1/ containing #g1/.

=. 6i thoroughly and allow the reaction to complete for =: minutes./. 9ilute the reaction miture with 1:: ml of water and &: ml of !=7/.

2. #dd &: ml of $a" solution and 1 ml of diphenylamine indicator.

@. Titrate the solution with standard :.26 "e/solution to a brilliant green colour.0. Bun a blank without sample simultaneously.

The percentage of organic % is given by)

#s & g of soil is used, this equation simplifies to)

where)

> S ? millilitres of "e/solution required for blank+> T ? millilitres of "e/ solution required for soil sample+


21/24

> :.::= ? weight of % '& ::: ml :.&@@06 41%r10? = g %. Thus, & ml :.&@@06 41%r10?

:.::= g %(.

rganic % recovery is estimated to be about 00 percent. Therefore, the actual amount of organic% will be)

r) percentage value of organic % N &.=.

Colorietric et$od

%olorimetric quantification of T% is performed through the measurement of the color change

that results from the presence of %r=P in solution. #fter sample digestion, the digestate iscentrifuged or filtered to remove any suspended particles and then placed in a calorimeter set to

measure the light absorbance at a wavelength of @@: n6. Muantification is performed by

comparison of the results against a standard curve. The calorimetric technique has the same

advantages 'i.e., a measurable fied endpoint with no human interpretation( and disadvantages'i.e., primarily initial cost( as the automated titration technique.

The apparatus required for the colorimetric method consists of)

> a spectrophotometer+> some conical flasks '&:: ml(+

> some pipettes '1, 2 and &: ml(.


> tandard potassium dichromate :.&@@06.

> %oncentrated sulphuric acid containing &.12 percent of #g1/.

> ucrose '#B-grade(.

The procedure is)

&. 7reparation of standard curve) ucrose is used as a primary standard % source. 7lace differentquantities of sucrose '&A1: mg( in &::-ml flasks. #dd &: ml of standard 41%r10and 1: ml

of concentrated !1/in each flask. wirl the flasks, and leave for =: minutes. 7repare a

blank in the same way without adding sucrose. # green colour develops, which is read onspectrophotometer at @@: nm, after adjusting the blank to zero. 7lot the reading so obtained

against milligrams of sucrose as % source '% ? weight of sucrose N :./1 A because the %

content of sucrose is /1 percent( or against milligrams of % directly.

Standard c'r)e for organic car0on on s!ectro!$otoeter


22/24

1. 7lace & g of soil in a &::-ml conical flask.

=. #dd &: ml of :.&@@06 41%r10and 1: ml of concentrated !1/containing &.12 percent of#g1/.

/. tir the reaction miture and allow it to stand for =: minutes.

2. The green colour of chromium sulphate so developed is read on a spectrophotometer at @@:nm after setting the blank, prepared in the similar manner, at zero.

The % content of the sample is found from the standard curve, which shows the % content

'milligrams of % vs spectrophotometer readings as absorbance() 7ercent % ? milligrams of %

observed N &:: * & ::: 'observed reading is for & g soil, epressed as milligrams(.

8n contrast to the three prior techniques, determination of T% content can also be determined by

measuring the evolved %1. The evolved %1 can either be absorbed on #scarite 'or similaradsorbent(. #bsorption of the evolved %1 by #scarite causes a weight change in a tared

weighing bulb. nce the digestion is completed, the weighing bulb is reweighed and the weight

difference is converted to T% content. This gravimetric technique has good accuracy, can beperformed with readily available equipment. !owever, this method requires careful analytical

techniques in which a %1free gas flow system is maintained throughout the digestion and %1collection process.

The use of a Can lyke-$eil apparatus involves the collection of the %1in its gaseous phase

and measuring the change in pressure with a gauge 'i.e., a manometric technique(. 5hile this

technique is relatively simple to conduct and doesnDt have the concern of maintaining a % 1 freeatmosphere as in the gravimetric technique, great skill is needed to operate the equipment and

the initial epense of purchasing the apparatus is somewhat high. #dditionally, the Can lyke-

$eil apparatus is easily damaged.


23/24

Total nitrogen

Total $ includes all forms of inorganic $, such as $!/, $=and $!1'urea(, and the organic $compounds such as proteins, amino acids and other derivatives.

9epending on the form of $ present in a particular sample, a specific method is to be adopted for

determining the total $ value. 5hile organic $ materials can be converted into simple inorganicammoniacal salt by digestion with sulphuric acid, for reducing nitrates into ammoniacal form,

the modified 4jeldahl method is adopted with the use of salicylic acid or 9evardaDs alloy. #t the

end of digestion, all organic and inorganic salts are converted into ammonium form, which isdistilled and estimated by using standard acid.

#s the precision of the method depends on complete conversion of organic $ into $! /-$, the

digestion temperature and time, the solidAacid ratio and the type of catalyst used have an

important bearing on the method. The ideal temperature for digestion is =1:A=0: ;%. #t a lowertemperature, the digestion may not be complete, while above /&: ;%, loss of $!=may occur. The

saltAacid 'weightAvolume( ratio should not be less than &)& at the end of digestion. %ommonly

used catalysts to accelerate the digestion process are %u/and mercury '!g(.

7otassium sulphate is added to raise the boiling point of the acid so that loss of acid byvolatilization is prevented.

The apparatus required for this method consists of)> a 4jeldahl digestion and distillation unit+

> some conical flasks+

> some burettes+> some pipettes.


> ulphuric acid 'F=AFH percent(.> %opper sulphate '%u/.!1( '#B-grade(.

> 7otassium sulphate or anhydrous sodium sulphate '#B-grade(.

> =2-percent sodium hydroide solution) 9issolve =2: g of solid $a! in water and dilute to &litre.

> :.&6 $a!) 7repare :.&6 $a! by dissolving /.: g of $a! in water and make the volume

up to & litre. tandardize against :.&$ potassium hydrogen phthalate or standard !1/.> :.&6 !%l or :.:26 !1/) 7repare approimately the standard acid solution and standardize

against :.&6 sodium carbonate.

> 6ethyl red indicator.

> alicylic acid for reducing $=to $!/, if present in the sample.> 9evardaDs alloy for reducing $=to $!/, if present in the sample.

The procedure is&. 5eigh & g of soil sample. 7lace in a 4jeldahl flask.

1. #dd :.0 g of copper sulphate, &.2 g of 41/and =: ml of !1/.

=. !eat gently until frothing ceases. 8f necessary, add a small amount of paraffin or glass beads toreduce frothing.

/. Eoil briskly until the solution is clear and then continue digestion for at least =: minutes.

2. Bemove the flask from the heater and cool, add 2: ml of water, and transfer to a distilling

flask.


24/24

@. 7lace accurately 1:A12 ml of standard acid ':.&6 !%l or :.:26 ! 1/( in the receiving

conical flask so that there will be an ecess of at least 2 ml of the acid. #dd 1A= drops of methyl

red indicator. #dd enough water to cover the end of the condenser outlet tubes.0. Bun tap-water through the condenser.

H. #dd =: ml of =2-percent $a! in the distilling flask in such a way that the contents do not

mi.F. !eat the contents to distil the ammonia for about =:A/: minutes.

&:. Bemove the receiving flask and rinse the outlet tube into the receiving flask with a small

amount of distilled water.&&. Titrate ecess acid in the distillate with :.&6 $a!.

&1. 9etermine blank on reagents using the same quantity of standard acid in a receiving conical

flask.

The calculation is)

where)

> V& A millilitres of standard acid put in receiving flask for samples+

> V1 A millilitres of standard $a! used in titration+> V= A millilitres of standard acid put in receiving flask for blank+

> V/ A millilitres of standard $a! used in titrating blank+

>M& A molarity of standard acid+

>M1 A molarity of standard $a!+> WA weight of sample taken '& g(+

> dfA dilution factor of sample 'if & g was taken for estimation, the dilution factor will be &::(.

$ote) & ::: ml of :.&6 !%l or :.:26 !1/corresponds to &./:& g of $.The following precautions should be observed)

>The material should not solidify after digestion.

> $o $!/ should be lost during distillation.>8f the indicator changes colour during distillation, determination must be repeated using either a

smaller sample weight or a larger volume of standard acid.

fertilizer analysis protocol

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