FERTILIZER ANALYSIS ANALYSIS PROTOCOL Mineral and organic fertilizer analysis Generally Generally,, the term fertilizer fertilizer refers refers to mineral mineral fertiliz fertilizers, ers, which are manufacture manufactured d chemical 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, c ountries, 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, nitrate and amide forms of $ in various proportions. Therefore, in fertilizer analysis, in addition to estimating total nutrient content, it is necessary to estimate the forms of nutrients and other associated compounds in order to assess their quality properly. properly. "or organic fertilizers, the % content and the total content of nutrients are considered relevant and not 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 could be applicable to any fertilizer with the nutrient in that particular form. form. Sa!le !re!aration for analysis The 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 identity confidential. #bout half of the sample is ground, sieved through a & mm sieve, and stored in a sample bottle for analysis. analysis. The remaining remaining half is kept unground for particle particle size estimatio estimation. n. The samples are stored in an airtight glass bottle or taken for analysis in a moisture-free room 'fitted with a dehumidifier( as most fertilizers are hygroscopic in nature. ANALYTICAL MET"O#S There are a number of estimation methods available a vailable for each of the constituents. P$ysical Paraeters %& Moist're Two important forms of water present in fertilizers are) 'i( absorbed*adsorbed water+ and 'ii( free water. They are interchangeable depending on the degree of moisture saturation and temperature. ome fertilizers also contain water as an integral part of their composition, which is referred to as water of crystallization, as in the case of n/.0!1 and %u/.2!1. #s fertilizers are
generally generally hygroscopic hygroscopic in nature, nature, they tend to absorb moisture moisture from the atmosphere atmosphere 'depending 'depending on the relative humidity and their packing and storage conditions(. 3cessive moisture may damage the granular structure of fertilizers, affect their quality and influence their nutrient content by increasing the weight of fertilizers in a given container. Therefore, moisture estimation is critical to determining the quality of a fertilizer. The method used depends on the type of fertilizer and the nature of moisture held by it. ome common methods are) i. gravimetric me method+ ii. vacu vacuum um des desiccat ccator or met method+ hod+ iii. iii. 4arl 4arl "isc "ische herr titr titrat atio ion n met metho hod. d. (ra)ietric et$od 5ith the gravimetric or oven-drying method, the loss of water on heating fertilizer samples at a certai certain n tempera temperatur turee is estim estimate ated. d. This This method method is suitab suitable le for fertil fertilize izers rs such such as ammoni ammonium um sulphate, sodium nitrate, superphosphates, muriate of potash '67( and sulphate of potash '7(. 8t is not suitable for fertilizers that yield volatile substances 'such as $! /( other than moisture on drying at a specified temperature, e.g. calcium ammonium nitrate and di-ammonium phosphate '9#7(. 6ois 6oistu ture re is esti estima mate ted d by the the grav gravim imet etri ricc meth method od where where the the loss loss in weigh weightt at a const constan antt temperature of &:: ;% < & ;% for 2 hours is measured, e.g. zinc sulphate, and copper sulphate. 8n the case of sodium nitrate, superphosphates, ammonium sulphate, 7 and 67, the heating is at &=: ;% < & ;%. "or urea and urea-based fertilizers, the heating is at 0: ;%. !owever, heating at 0: ;% does not reflect full moisture content. Therefore, another method such as the 4arl "ischer method is preferred.
The apparatus required consists of) a glass weighing bottle+ • an electronic balance+ • a temperature-controlled oven. • T$e !roced're* &. 5e 5eigh igh 1.: g of fertil fertilizer izer sample sample in a pre-weighe pre-weighed d glass weighi weighing ng bottle. bottle. 1. !eat in a temperature-controlled oven for about 2 hours at the specified temperature, as given above for different types of fertilizers. =. %ool in a desic desiccat cator, or, and weigh. weigh.
The relevant calculation is)
where) > A > A ? weight in grams of the empty sample bottle+ > B > B ? weight in grams of the bottle plus material before drying+
> 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 the desiccant '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 $74 complees. 8n this method, the sample is kept in a vacuum desiccator over sulphuric acid. "ree moisture present in fertilizers is absorbed by the acid, and the loss in weight of the sample is recorded as the moisture content in the sample.
The apparatus required consists of) a vacuum desiccator+ • a porcelain dish+ • a balance. • T$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. The relevant calculation is)
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, and urea-based fertilizers, which do not withstand high temperatures.
The apparatus required consists of) a 4arl "ischer titrator+ •
# 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 percent • water. 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.
The relevant calculation is)
where)
9isodium tartrate dihydrate contains :.&2@@ percent moisture. .& Particle size "ertilizers are manufactured with varying degrees of particle size. This property of fertilizer has a bearing 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 are highly 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 a sieve 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.
"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 along with 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. # smaller amount of sample may be taken for high-analysis fertilizers 'e.g. urea( and a larger amount for low analysis fertilizer 'e.g. ammonium sulphate(. The apparatus required consists of) 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.
The relevant calculation is)
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 $
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 to ammonia form. Nitrate2nitrogen 8n fertilizers containing both $!/ and $=-$, first ammoniacal nitrogen is estimated followed by $!/ plus $= estimation. "rom the combined value of $!/ and $=, the value of ammoniacal $ 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. •
The reagents required are) $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, and add / 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,
•
•
• •
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 any soluble %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, then add about 2 ml in ecess. &=. Becord total volume added+ back titrate ecess !%l with :.&6 $a! to neutral end point.
The relevant calculation is)
4i'ret Eiuret '%11 $=!2( is a chemical compound formed by the combination of two molecules of urea with 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+ •
• •
some beakers and flasks+ a burette.
The reagents required are) #lkaline tartrate solution) 9issolve /: g $a! in 2: ml of cold water and 2: g of • $a4%/!/@./!1, and dilute to & litre. et it stand for & day before use. %opper sulphate solution) 9issolve &2 g of %u/.2!1 in %1-free water, and dilute to • & litre. Eiuret standard solution '& mg*ml() 9issolve &:: mg of reagent-grade biuret in %1-free • water, and dilute to &:: ml. tandard !1/. • The procedure is) &. 7reparation of the standard curve) Transfer a series of aliquots, 1A2: ml of standard biuret solution, to a &:ml volumetric • flask. #djust the volume to about 2: ml with % 1-free water. #dd one drop of methyl red, and • neutralize with :.&6 !1/ to a pink colour. #dd, with swirling, 1: ml of alkaline tartrate solution and then 1: ml of %u/ solution. • 9ilute to volume. hake for &: seconds, and place in a water-bath for &2 minutes at =: ;% • < 2 ;%. #lso prepare a reagent blank. • 9etermine absorbance of each solution against the blank at 222 nm on the • spectrophotometer with a 1./ cm cell, and plot the standard curve. 1. tir continuously 2 g of the sample in &:: ml of water for =: minutes. =. "ilter and wash in 12: ml volumetric flask and dilute to volume. /. Transfer 12 ml of aliquot to &:: ml volumetric flask and proceed as given under preparation of standard curve. The relevant calculation is)
where) > C ? concentration in mg*ml of biuret as read from the standard curve+ > W ? weight of sample+ > df ? 1:: '2 g of fertilizer etracted to 12: ml, and 12 ml taken for further dilution to &:: ml(. ii& P$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.
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 iron phosphates are also in plant-unavailable forms. $eutral ammonium citrate soluble form is also considered as available, which includes both monocalcium phosphate and dicalcium phosphate. 8n view of the variability in availability to plants, the estimation of different forms of phosphate is critical. "or the so-called IavailableJ forms of 7, appropriate etractants have been designed to etract 7 from fertilizers under a set of well-defined sampling conditions) etractant ratio, temperature, time of etraction, shaking period, etc. The form of 7 as a fraction of the total 7 is etracted by a particular method. 3stimation of the etracted 7 utilizes various testing methods) 'i( gravimetric+ 'ii( volumetric+ and 'iii( colorimetric. The following methods are used for 7 estimation in fertilizers gravimetric ammonium phosphomolybdate+ • gravimetric quinolinium phosphomolybdate+ • volumetric ammonium phosphomolybdate+ • volumetric quinolinium phosphomolybdate+ • spectrophotometric vanadium phosphomolybdate. • #ll the methods are used in various laboratories. "or total phosphate estimation, the gravimetric quinolinium phosphomolybdate method is generally preferred because of the minimal interference of other ions and its accuracy and simplicity. #nother common method providing acceptable accuracy and simplicity is volumetric ammonium phosphomolybdate. (ra)ietric -'inolini' !$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 quinolinium phosphomolybdate K'%F!0 $(=!=7/.&1 6o=L in a boiling medium. The precipitate is weighed gravimetrically, which gives the 7 content of the sample. 8n the gravimetric method, %a, "e, 6g, alkali metals and citrates do not affect the analysis. The citrate in the reagent complees the ammonium ions, thus preventing interference from precipitation of ammonium phosphomolybdate by the ammonium salts usually present in mied fertilizers. The citrates also reduce interference from soluble silica. The apparatus required consists of) a volumetric flask+ • some beakers+ • a Gooch crucible+ •
• •
some filter paper+ an analytical balance.
The reagents required are) %oncentrated nitric acid. • %oncentrated hydrochloric acid. • 6agnesium nitrate solution 'F percent() 9issolve F: g of 7-free 6g'$ =(1 in 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, let it 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'$=-(1 solution, and evaporate to dryness. 8gnite to destroy the 6, and dissolve in &: ml of !%l. "or materials with a low 6 content) 7ut & g of the sample in a 2: ml beaker. #dd =: ml • of !$= and 2 ml of !%l, and boil gently until the 6 is destroyed and red-brown fumes cease to appear.
"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 at 12: ;% 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. •
The relevant calculation is)
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 of fertilizer solution prepared ? 12: ml+
> W ? weight of sample taken in grams+ > "actor =.1:0 ? the quinolinium phosphomolybdate precipitate contains =.1:0 percent 712 on weight basis. 8n cases where 6o=.$a16o/.1!1 'quinoline( is not of standard quality, the eact volume of quimociac reagent to be added for precipitation should be calculated by running a series of known standards and observing the phosphate recovery in them.
+ol'etric aoni' !$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 a measured ecess of the standard alkali after filtration and washing u ntil free of the acid. The apparatus required consists of) some volumetric flasks * beakers+ • a burette+ • a shaker+ • a water-bath+ • some $o. // filter paper. •
The reagents required are) 6agnesium nitrate solution 'F percent() 9issolve F: g of 7-free 6g'$ =(1 in 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 not more than 12 mg 712 in 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 is added. 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 nitrate solution, agitate thoroughly, and allow the precipitate to settle. Transfer the precipitate to
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 $a! at a time by pipette until the precipitate becomes soluble. 0. #dd &A1 drops of & percent phenolphthalein, and titrate the ecess of alkali against :.&6 sulphuric acid. H. Bun a reagent blank with each batch. The relevant calculation is)
• •
where) F ? factor for 712 corresponding to & ml of &6 alkali '$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 $a! required to dissolve the precipitate 'e.g. /: ml(+ > V 1 ? volume of :.&6 !1/ used for titration to neutralize ecess alkali 'e.g. &: ml(+ > M & ? molarity of the standard alkali '$a!(+ > M 1 ? 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 by washing the sample successively with distilled water. #s a procedure, put & g of the sample on a
filter paper fitted on a &1 cm funnel. 5ash with small portions of water at a time to collect about 12: ml of filtrate and make up the eact volume. 7our water into the funnel only when the earlier portion has drained fully. therwise, filtration and complete washing may be prolonged 'which should be completed in & hour(. The filtrate so obtained is used for estimation of phosphate by the gravimetric quinolinium phosphomolybdate method or volumetric ammonium phosphomolybdate method as described above. The residue remaining on the filter paper contains the water-insoluble portion of 7 in the sample. A)aila0le !$os!$ate 6ne'tral aoni' citrate2sol'0le P .O78 "or estimating available phosphate, an indirect method is followed whereby total, water-soluble and ammonium citrate-insoluble fractions are estimated. Ey subtracting citrate-insoluble 7 from total 7, estimates are made for the available 7. The apparatus required for estimation of citrate-insoluble 7 consists of) > a volumetric flask * beaker+ > a burette+ > a water-bath-cum-shaker+ > a Euchner funnel. The reagents required are) > %oncentrated !$=. > %oncentrated !%l. > %oncentrated !1/. > #mmonium hydroide. > #mmonium nitrate '2 percent(. > Muimociac reagent 'same as described in total 712 estimation(. > "ilter paper. > $eutral ammonium citrate solution) 9issolve =0: g of pure citric acid in & 2:: ml of distilled water. #dd about =/2 ml of 1HA1F percent ammonium hydroide so that the acid is neutralized. #fter neutralization, the solution must attain a p! of 0.:+ if it does not, adjust the p! by adding $!/! or citric acid solution. T$e !roced're is* &. "ollow the procedure as described above for the preparation of a sample solution for estimation of water-soluble phosphate. 5ithin & hour, transfer the filter paper and residue to a 12: ml conical flask containing &:: ml of ammonium citrate solution previously heated to @2 ;%. 1. %lose the flask tightly with a smooth rubber stopper, shake vigorously until the filter paper is transformed to pulp, and release pressure by removing stopper occasionally. =. #gitate continuously the contents of the stoppered flask in a controlled temperature '@2 ;% <:.2 ;%( water-bath-cum-shaker for & hour. /. 3actly & hour after adding the filter paper and residue, remove the flask from the shaker, and filter immediately by suction as rapidly as possible through $o. 2 filter paper or equivalent, using a Euchner or ordinary funnel. 2. 5ash with distilled water at @2 ;% until the volume of filtrate is about =2: ml, allowing time for thorough draining before adding more water. 8f the material is such that it will yield a cloudy filtrate, wash with 2 percent $!/ $= solution. @. 9etermine the 712 in the citrate-insoluble residue 'remainder on filter paper( after digestion by one of the following methods)
> Transfer the dry filter paper and contents to a crucible, ignite until all 6 is destroyed. 9igest with &:A&2 ml of !%l until phosphates are dissolved. > Transfer the filter paper and residue to a 12: ml 4jeldahl flask, boil for =:A/2 minutes with =: ml of !$= 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. 7ipette out 12 ml of aliquot containing not more than 12 mg of 7 12 into a 2:: ml 3rlenmeyer flask, and proceed as described for estimation of total 712 using quimociac reagent 'above(. The relevant calculation is)
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 712 The procedure for total 712 estimation is described above. iii&
Potassi' 8n all potassic fertilizers, 4 is generally present in water-soluble form. Therefore, it is estimated directly 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 its accuracy and simplicity. STP4 et$od 7otassium from the fertilizer sample is first etracted with water or ammonium oalate. The 4 in etracted 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)
8nterference of $!/ P takes place during 4 precipitation. 8t is avoided by compleing $! /P with formaldehyde under slightly alkaline conditions before precipitation of 4. The chlorides and sulphates do not interfere in the titration. The apparatus required consists of) > some volumetric flasks and beakers+ > a burette * semi-microburette+ > some filter paper. The reagents required are) > 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 $a! solution, dilute to volume '& litre( with water, and mi. et it stand for /H hours, and then standardize 'as described below(. #djust 'by using 4 salt of known composition for prior standardization by trial and error( so that & ml of T7E ? & percent 4 1. tore at room temperature. > E#% or quaternary ammonium chloride solution 'about :.@12 percent() 9ilute 2: ml of &1.H percent E#% to & litre with water, mi and standardize 'as described below(. 8f a different concentration is used, adjust the volume accordingly 'E#% of :.@12 percent strength is required so the dilution can be done according to the concentration available(. > %layton yellow ':.:/ percent( indicator) 9issolve /: mg of %layton yellow powder in &:: ml of water. > #mmonium oalate solution K'$!/(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 T7E solution 'keeping & ml T7E ? & percent 4 1(. > 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 4 1 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 $o. /1 filter paper. Transfer 2: ml of aliquot of filtrate to a 12: ml 3rlenmeyer flask, add @AH drops of %layton yellow indicator, and titrate ecess T7E with E#% solution to pink end point. %alculate factor 'f( by) f ? percent 4 1*ml of T7E solution
where, =/.@& ? O 4 1 present in standard 4!17/. T$e !roced're is* &. 4 etraction*preparation of sample solution) 9issolve a known weight '1.2 g( of straight 4 fertilizer '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 up to 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 4 1 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 pass it 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 4 1*ml of T7E solution. This factor applies to all fertilizers where 1.2 g of sample is diluted to 12: ml, and &2 ml of aliquot is taken for analysis. To epress the results as 4 rather than 4 1, substitute 1H.0= for =/.@& in calculating the value of f . 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 $, 7 and 4 in organic fertilizers are the same as described above for mineral fertilizers. 5ith organic fertilizers, the sample always needs to be prepared using the wet-digestion method. The sample size should be &.: g 'to be weighed eactly(. 5et C$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 during etraction. 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 involves the rapid dichromate oidation of organic matter. The 5alkley-Elack procedure is the best
known wet digestion method. 8n this procedure, potassium dichromate '4 1%r 11( 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 when the 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%r 10 1-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 procedure range 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 potentiometric determination, 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 '%r 10(, chromate '%r =P( and %1. Eoth the %r 101-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 available as I"erroinJ(, barium diphenylamine sulfonate, and $-phenylanlhranilic acid. The ecess %r 101is titrated with ferrous ammonium sulfate K"e'$! /(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 for the barium diphenylamine sulfonate, and '=( dark violet-green to light green for the $-phenylanthranilic acid. The primary concern with the manual titration technique is the low visibility or subtlety of color changes during titration. %olor changes may also be obscured by naturallyoccurring high organic fertilizer materials. The use of an automated titrator eliminates the need for indicators to be added to the digestate. imilar to manual titrimetric quantification, ecess %r 101- is titrated with ferrous ammonium sulfate or ferrous sulfate. !owever, the endpoint is not a color change but is determined
potentiometrically. 8n this technique, a simple calomel electrode or platinum electrode is placed in the digestate, and the titer is added until a fied electrical potential endpoint is reached. The endpoint is dependent upon the type of electrode used. nce the endpoint is reached, the titration is stopped and the T% content calculated. The automated titration technique has the distinct advantage over manual titration since the endpoint is not dependent upon operator optical determination of eactly when the color changed. The only disadvantage of the automated technique is the necessity to purchase 'i.e., co st( an automated titrator and suitable electrodes. The apparatus required for the volumetric method '5alkley and Elack, &F=/( consists of) > a conical flask '2:: ml(+ > some pipettes '1, &: and 1: ml(+ > a burette '2: ml(. The reagents required are) > 7hosphoric acid A H2 percent. > odium fluoride solution A 1 percent. > ulphuric acid A F@ percent containing &.12 percent of #g1/. > tandard :.&@@06 4 1%r 10) 9issolve /F.:/ g of 4 1%r 10 in water and dilute to & litre. > tandard :.26 "e/ solution) 9issolve &/: g of ferrous sulphate or &F@.& g of "e/. '$!/(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 4 1%r 10 solution 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 $a" solution and 1 ml of diphenylamine indicator. @. Titrate the solution with standard :.26 "e/ solution to a brilliant green colour. 0. Bun a blank without sample simultaneously.
The percentage of organic % is given by)
#s & g of soil is used, this equation simplifies to)
where) > S ? millilitres of "e / solution required for blank+ > T ? millilitres of "e / solution required for soil sample+
> :.::= ? weight of % '& ::: ml :.&@@06 4 1%r 10 ? = g %. Thus, & ml :.&@@06 4 1%r 10 ? :.::= g %(. rganic % recovery is estimated to be about 00 percent. Therefore, the actual amount of organic % will be)
r) percentage value of organic % N &.=. Colorietric et$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 is centrifuged 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(.
The reagents required are) > 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 different quantities of sucrose '&A1: mg( in &::-ml flasks. #dd &: ml of standard 4 1%r 10 and 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 on spectrophotometer 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!$otoeter
1. 7lace & g of soil in a &::-ml conical flask. =. #dd &: ml of :.&@@06 4 1%r 10 and 1: ml of concentrated !1/ containing &.12 percent of #g1/. /. tir the reaction miture and allow it to stand for =: minutes. 2. The green colour of chromium sulphate so developed is read on a spectrophotometer at @@: nm after setting the blank, prepared in the similar manner, at zero. The % content of the sample is found from the standard curve, which shows the % content 'milligrams of % vs spectrophotometer readings as absorbance() 7ercent % ? milligrams of % observed N &:: * & ::: 'observed reading is for & g soil, epressed as milligrams(. 8n contrast to the three prior techniques, determination of T% content can also be determined by measuring the evolved %1. The evolved %1 can either be absorbed on #scarite 'or similar adsorbent(. #bsorption of the evolved %1 by #scarite causes a weight change in a tared weighing bulb. nce the digestion is completed, the weighing bulb is reweighed and the weight difference is converted to T% content. This gravimetric technique has good accuracy, can be performed with readily available equipment. !owever, this method requires careful analytical techniques in which a %1 free gas flow system is maintained throughout the digestion and %1 collection process. The use of a Can lyke-$eil apparatus involves the collection of the %1 in 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 free atmosphere 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.
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 inorganic ammoniacal 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 is distilled 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 lower temperature, 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 by volatilization is prevented. The apparatus required for this method consists of) > a 4jeldahl digestion and distillation unit+ > some conical flasks+ > some burettes+ > some pipettes.
The reagents required are) > 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 4 1/ and =: ml of !1/. =. !eat gently until frothing ceases. 8f necessary, add a small amount of paraffin or glass beads to reduce 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.
@. 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+ > V 1 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+ > M 1 A molarity of standard $a!+ > W A weight of sample taken '& g(+ > df A 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.
