Official methods
The association of official analytical chemists (AOAC) status to
method for total nitrogen using chromium powder and HCL to
reduce nitrates (2.049) .The method is applicable to all fertilizers
except those containing highly refractory organic matter. A single
precise , accurate method for total nitrogen in all fertilizers has not
yet been developed .flame photometric method for sodium using
anion exchange resins to remove interfering anions was given
official status (2.117).A spectro photometric method for cobalt
(2.012) and an atomic absorption method for the determination of
copper, iron, magnesium and zinc were also adopted (2.086). A
method for determining slow-release nitrogen which involves
adding boiling water to the sample, stirring for 30 minutes,
filtering and analyzing an aliquot an aliquot b AKjedahl method
was adopted.
An oven method (2.014) for the determination free water by
heating at 50 C for 2 hours under a partial vacuum was
collaboratively studies by the AOAC and given official status.
Sampling:
A bulk fertilizer sampling study was designed and initiated
direction by AOAC. Preparation Others cooperating in the
program were the Bulk Fertilizer Committee of the Association of
American Fertilizer Control Officials (AAFCO) the National Plant
Food Institute (NPFI) Chemical Control Committee Task Force on
Sampling Fertilizers, and industry. The report experiments were
designed to obtain information on the various sampling
instruments and sampling methods. Five different sampling tubes
ware studied The AOAC slotted single and double tubes, a
compartmented 524 grain probe, the modified Archer Trier, and a
Missouri interrupted-core compartmented double tube. It was
shown that an accurate fertilizer sample can be secured by passing
a stream sampling cup through the entire flow of material at equal
timed-spaced intervals during the loading of a truck; this “stream”
sample was found to be a more accurate indicator of the actual
plant nutrient content than any of the Trier samples. The stream
sample was used as the reference point.
It was conclusively found that the AOAC double or single tubes
were not suitable for sampling bulk loads of fertilizers, those tubes
were biased and tool 2/3 of the sample by the top 1/3 of the Trier.
The Missouri interrupted compartmented tube and the 524 grain
probe did a good sampling job on semi-granular and granular
fertilizers when used in accordance with the Baker-GRHTKR
sampling plan and if vertical cores were taken. The sampling plan
(26) using these compartmented Trier was adopted as official, first
action, at AOAC.
Smith, in a supporting study (80) concluded that most
representative Trier sample was obtained by inserting the probe in
a vertical position instead of at an angle.
Possible mechanisms of sampler bias on dry mixed fertilizers were
investigated in an effort to develop better official sampling
instruments and procedures. Three lots of dry mixed fertilizers
with known physical and chemical composition were prepared in
the laboratory. Twelve vertical and twelve horizontal cores,
arranged in a Latin square sampling pattern were secured from
each lot with four Trier: the AOAC double tube Trier, the double
tube Comartmented Trier (524 grain probe and Missouri tier), and
an experimental double half-tube trial, “Missouri D Tube) wherein
the core was encompassed in place rather than being required to
flow into a compartment as with conventional Trier. Individual
cores were analyzed physically and chemically. Only marginal
significant differences were found between cores on the basis of
tube opening size. The experimental double half-tube Trier was
less selective to particle shape or Size than ether the
compartmented or AOAC Trier. All Trier produced more
representative samples from vertical cores than from horizontal
cores. Also, cores drawn at an angle of 60 - 05 from horizontal
were not consistently different from vertical cores. Analytical data
confrmel the sieve analysis results quite closely. Horizontal cores
secured with the “Missouri D tube) confirmed that the bias
observed in horizontal cores was due to
a downward drifting of
small particles when the core area is disturbed by the insertion of
the sampler. Cores secured with the sampler-retaining face upward
contained an excess of fines, whereas cores secured with the
sampler-retaining face to the side or downward more nearly
resembled vertical cored in composition. The “Missouri D tube)
secured the most accurate sample and was the easiest sampler use.
Nitrogen
The AOAC continued studies in 1965 on methods for determining
nitrogen in fertilizers. A collaborative study was made comparing
the sulfuric-salicylic acid method, the reduced iron method, a
modified reduced iron method, a chromium powder method using
pacified chromium metal, and a Raney nickel catalyst powder
method. The report showed that no one method was applicable to
all types of fertilizers. The sulfuric salicylic acid method was the
easiest to perform but did not quantitatively recover nitrogen from
liquid samples and samples with high chloride: nitrate rations;
however, good results were obtained when organic nitrogen was
present in large amounts. The reduced iron method presented
problems with foaming and
bumping, was not precise, and did
not have general applicability to all samples. The modified reduced
iron, chromium powder, and Raney nice catalyst powder methods
gave essentially equal results. The chromium powder method was
favored for its ease of manipulation and saving of time. However,
the pacified chromium powder method did not quantitatively
reduce nitrates in the presence of organic matter in 1963 six
different methods for determining nitrogen in fertilizers were
subjected to YOUDE N’S ruggedness test (14,92) these were a
Chromous solution reduction method, the Raney catalyst powder
method, an improved reduced iron method, the chromium powder
method, the sulfuric-salicylic acid method, and the reduce iron
method. The reduced iron method failed the test; the other methods
proved “regged”
A comprehensive method for total nitrogen was developed in 1966
by GEHRKET al (29) which has the capability of reducing nitrates
either alone or in the presence organic matter. Quantitative
recovery of nitrogen was obtained from KNO3 containing various
organic substances and inorganic nitrogen sources including
inorganic fertilizers, as well as the highly refractory organic
compound nicotinic acid. The method was subjected to the
YOUDEN ruggedness test and was found to be rugged for all
samples analyzed except nicotinic acid the method is accurate and
precise and applicable to all types of solid, liquid and slurry
fertilizers. This method offers a significant saving in analysis time.
More studies were conducted on the Raney catalyst powder
method to shorten the time required to reduce nitrate (15). A
catalyst powder containing 10% Co, 40 % NI and 50%AL in 8N
H2so4 was found to reduce nitrate to NH3 within 10 minutes.
Neither chloride nor organic nitrogen interfered with the reduction.
The method passed YOUDENS
Ruggedness test and result of the analysis of fertilizers total
nitrogen were in good
Agreement with data from AOAC methods.
A method for the determination of total nitrogen using sulfuricsalicylic acid to prevent the loss of nitrogen as NOCI was reported
(55). In this method the fertilizer (80to 100mg N) was digested
with H2SO4contaning salicyLsalicylic acid in the presence of
Na2SO4.
because of its low volatility , the sulfonitric acid
(so2No2oH) formed prevents loss of nitrogen of So2No2OH on
salicylsalicylic forms a nitro compound which on digestion is
reduced to an amino compound and finally converted to NH3 .the
NH3 reacts with H2so4 to from (NH4)so4.with less than 10% urea
in the fertilizers , the absolute error was 0.4% at higher amounts of
urea , the absolute error did not exceed 2% .time of digestion was
2to 2.5 hours .an improvement of the sulfuric-salicylic acid method
of total nitrogen in fertilizers was reported by Tsai (86) . the
sample was combined with Zn –Fe powder and 10%H2so4 boiled
for 10 minutes , cooled , then saturated K2cr2o7 solution was
added and the Digestate boiled for an additional 5 minutes.
Subsequent distillation and titration gave the amount of nitrogen
results were obtained in 16% less time than with the salicylic acid
–Na2so4 method and in the range of 30to 44% less time than with
direct acid digestion. A method for determining nitrogen in
fertilizers containing ammonium, nitrate, and urea nitrogen was
reported (24) .urea was decomposed by adding 1%urease solution
and heating for 20minutes at 50 C ARDNDS alloy and a solution
of Mgcl2 were then added distillation of liberated NH3 beinto
0.1N H2so4 and back-titration with 0.1N NaOH gave the total
amount of nitrogen from these three sources .the procedure
required only 90 minutes and gave standard deviation of 0.15mg
nitrogen at level of less than 90mg of nitrogen .
Ion exchange resins have been used to determine nitrate-nitrogen
and ammonium-nitrogen in nitrogenous fertilizers salt (47). Nitrate
salts alone were analyzed by passing the sample solution through
acation exchang resin and titrated the effluent acid with 0.1 N
NaOH. ammonium salt were similarly analyzed with an Amberlite
resin, the effluent being titrated with 0.1N HCL. Results obtained
with samples containing NO3,NH4 or NO3 and NH4 combination
agreed
Well with those from established methods.
A revised method of analysis for water-insoluble and slow-release
nitrogen in fertilizers has been reported (37). instead of analyzing
the residue for the insoluble nitrogen ,the filtrate was analyzed for
the soluble nitrogen and another portion of the sample analyzed
for total nitrogen. Results obtained were much precise than those
from the AOAC official method (2.057). another method was
developed for water insoluble nitrogen in fertilizers based upon the
biodegradability method used to determine the biological oxygen
demand of wastes (24) by making the nitrogen content the limiting
factor in the growth medium the biodegradation of water-insoluble
nitrogen sources can be studied when the Warburg Respirometer is
used the relationship between oxygen utilization and nitrogen
content allows for a fairly accurate measurement of biodegradable
nitrogen. An analysis takes about 2 weeks .
A method for determining nitrogen in inorganic nitrates by the
Dumas method was reported by Ketchum (46) the sample was
mixed with anthracene at 1to 1.5 times its weight. The recovery of
nitrogen was quantitative. When more then 15 mg of anthracene
was used, it was necessary to chech the blank for the formation of
methane.
Conductometric titration has been used in the estimation of
ammonium, and nitrate-nitrogen in ammonium sulfate-nitrate
fertilizers
.total
ammonium
nitrogen
was
determined
by
conductometric titration with standard alkali .Ammonium nitrate
was quantitatively extracted with acetone-water and the nitrogen
remaining as(NH4)so4 was determined by conductometric titration
with standard alkali .the nitrogen present asNH4NO3 was
calculated by difference . several methods have been reported for
the determination of ammonium ions in fertilizers . the use of
timetemperature-gravimetric titration and its application to
ammonium fertilizers was reported . a constant drop rate was
maintained which enabled the titration of small volumes . also, The
determination of ammonium ions in the presence of phosphate was
acomplished by precipitating the phosphate as cepo4 then titrating
with 0.1N NaOH after the
addition of formaldehyde in another
approach the determination of ammonium salts alone in the
presence of acids or ammonia or in commercial fertilizers was
done by treating the sample with tetraethyl ammonium hydroxide
in acetone . the NH4OH produced in the reaction and the free
ammonia in the sample were determined by differential
potentiometric titration . alternatively the unchanged tetraethyl
ammonium hydroxide can be titrated with standard HCLO4
solution in methyl ethy ketone
. The relative error was
approximately 0.5% a rapid determination for ammonium nitrogen
in ammonium hydrogen carbonate fertilizer was reported reaction
of the NH4HCO3 with excess acid with standard base after
expelling the liberated CO2 was used. If other acids or bases were
present in the sample , the NH4HCO3 was first reacted with strong
acid, the solution boiled to expel co2 then adjusted with NaOH to a
methyl red end point . the sample was then reacted with HCHO
and excess standard NaOH added , then back-titration with
standard H2SO4 . the latter procedure was found to give a light
positive bias the use of Feso4 as a reductant for nitrate was
reported by Vajda the sample was reduced in aparnas-Wagner
apparatus with a solution of 20%Feso4.7H2O plus 10%
Cuso4.5H2so4 containing concentrated H2so4 30% NaOH was
introduced into the mixture and the liberated NH3 steam distilled
into 0.1N H2so4 the excess standard acid was back-titration with
0.1N NaOH. Deviations were less than 0.20% absolute
Amperometric and indicator titration methods for nitrates in
fertilizers have been reported (44). In the amperometric titration of
nitrate , the sample was dissolved with heating in 0.1N LiAc in
glacial acetic acid and titrated with 0.2Npb(OAc)2 in glacial acetic
acid at -1.0 volt in a polarographic cell. For indicater titration
method ,the nitrate was similarly precipitated with 0.1N pb(OAc)2
in glacial
acetic acid using diphenylamine as the indicator .
analysis time was 10 minutes and with a relative error of 1% the
reductimetric determination of nitrate by reaction with excess fe in
strongly acidic media was improved by alterations in the order of
reagent addition the same investigator gave details of various
potentimetric and automatic titrations of urea-containing fertilizers
using
k2cr2o7
or
ticl4
an
ultraviolet
spectrophotometric
determination of nitrate ion was developed based on fact that the
extinction wavelength curve falls steeply for nitrate between 312
and 320 m and is constant in region for the other components. The
amount of nitrate was calculated from a given equation the relative
error was less than 3% and the time for an analysis required only
15 to 20 minutes. Two methods were reported for determining
Ca(No3)2 in calcium ammonium nitrate (8,74). One method (74)
consist of extracting the Ca(NO3)2 into aqueous NH3-methanal
(3:97) solution and titrating the extract with EDTA using Zno2 as
an indicator ion . A polarograph with a dropping mercury electrode
and a standard calomed (8) was based on the relative insolubility
of Caco3 in aqueous NH3 methanol solution (3:97) and the
appreciable solubility of Ca(No3)2 in the same solvent system .the
methanol was removed by distillation , the residue dissolved in
H2O ,and the Ca equivalent to Ca(NO3)2 in the sample determined
by the KMNo4 method the standard deviation was 0.01%.
Biuret in 0.1 NaOH exhibits maximum absorption at 225 and 260
mµ but urea shows on absorption at this pH (77). In a buffer
solucontion at p 9.0, neither biuret nor sure show absorption at
these wavelengths. Measurements were thus made at 225 and 260
mµ in both solution to compensate for absorption by impurities,
and the biuret concentration was calculated from an equation.
Beer’s law was obeyed up to 5% biuret when measurements were
made in a 1-cm quartz cell. Also, estimations of biuret in urea
have been made spectrophoometrically by a cobalt-biuret complex
method (76). Biuret was reacted with Co(NO3)2 in the presence of
alkali and a few drops of 30% H2O2 were added to develop a
redcolored complex. The absorbance when measured at 500
mµobeyed Beer’s law.
The relative error was ±8%.
Christian and Jung (18) reported a coulometric determination of
total nitrogen. The samples were digested by official AOAC
methods; then an aliquot was adjusted to pH 8.6, and the ammonia
titrated with coulometrically-generated hypobromite. Results
agreed with standard methods and were generally more precise.
The method, while rapid for samall numbers of samples, woukd
require more man hours per sample for large numbers of samples
than the AOAC official methods. Bredstreet (12) published a
comprehensive survey of the Kjeldahl method for organic nitrogen
and its modifications as applied to natural products and organic
materials. The book includes a bibliography of published papers
covering the entire period from the in caption of the method.
Phosphorus
The use of a high concentration of
molybdate was found to
prevent citrate interference in the phosphomolybdvanadate
spectrophotometric determination of phosphours (52) for a solution
containing 14 to 20 mg of p2o5 in avolume of 250ml the reagent
used contained 0.4% citric acid , 4.5mmoles vanadium, and
0.11moles molybdenum in 1N HNO3 .the wavelength giving the
lowest reagent blank and the largest difference between the blank
and the colored complex is 420m .calcium did not interfere at
concentration less than 0.4gran per liter in the final solution . it was
found that temperature variation had no effect on the color
development it the standard and samples were prepared and read at
the same temperature .
Dahlgren (19) examined existing wet ashing methods for were
needed to give reproducible amount of mineral acid in the
remaining solution after destruction of the citrate. Different ways
of removing the acid, which interferes in the color development ,
were investigated . the preferred method employed partial
neutralization of theors acid after addition of the molybdovanadate
solution.
The
phosphomlybdovanadate
spectrometric
phosphorus has been automated by several investiga
method
for
Tors using the Technicon AutoAnalyzer Gehrke Baumgartner ,
and ussary (27) reported an automated method for direct available
p2o5 the method utilizes the autoanalyzed
to determine
phosphorus in the rang of 2.0to 4.5mg p2o5 per 100ml and at an
analysis rate of 40 samples per hour . citrate and organic coloring
matter were destroyed and non-orthophosphates were hydrolyzed
by digesting the sample aliquot with a 10:4:2 mixture of HNO3,
HCClO4 and H2SO4 and the effects of acidity and citrate
concentration on the color reaction were determined. Acid
concentration up to 1.4 N had no effect, and it was found that all
concentrations of citrate interfered with the color reaction. Heating
to 90̊ c for 30 minutes or passing the reaction mixture through time
delay coils of various lengths had no effect on the color
development. The automated method was found to give results
equally as accurate and precise as the AOAC official gravimetric
quinolinum phosphomolybdate method and with considerable
saving in time of analysis.
Foberts (73) descried a completely automatic on-stream system for
quality control of phosphate rock. The sample is split continuously
and reduced to a quantity suitable for analysis. This sample is
further dried to an established moisture level, weighed, and
analyzed all within 16 minutes I a fully automated system.
A dry ashing technique was proposed by Bannell (13) for the
destruction of citrate. Aliquots of the combined water and citrate
soluble ezxtracts were mixed with HNO3, sucrose and MgO, then
the mixture was evaporated on a hot plate to bydrolyze non-otho
phosphates and to react them with the MgO to form heat stable
compounds. The dry residue was then ashed at 550 C for 30
minutes.
It was reported that interference by Fe and sio2 on the
phosphomolybdovanadate color development was observed when
phosphate in compost was determined. The color was developed in
0.8N H2so4 and read at 420m to improve the accuracy and
precision
of
the
AOAC
official
volumetric
ammonium
molybdophosphate method (2.026th Ed) HNO3 was added to
eliminate sulfate interference prior to the formation of the yellow
precipitate and after the precipitate was dissolved in alkali, HCHO
was added to react with the ammonia. A mixed indicator (methyle
green-phenophthalein ) was used which changes color at the
equivalence point. This modification passed Youdens ruggedness
test and gave results in excellent agreement with those obtained by
the gravimetric quinolinium phosphomolybdatemethod .
Results from a collaborative study of methods for total phosphorus
procedures
with
the
AOAC
official
quinolinium
phosphomolybdate method, confirmed the accuracy and precision
of the quinolinium method . the volumetric procedures , presented
by the phosphorus Task force of the national plant institute
chemical control committee , gave accurate results but failed to
give acceptable precision . the volumetric procedure proposed by
Brabson gave a slight negative bias .
An alkalimetric quinolinium phosphomolybdate method for
phophorus was collaborated on by the AOAC, but it was
abandoned because of the difficulty of dissolving the precipitate
with standard alkali . in a later study Duncan and Brabson found
that by using lager amount of citric acid in the precipitating regent
larger crystals were formed which did not agglomerate during
filtration and were readily soluble in alkali . the method was found
to be rugged , and compared favorably in precision and accuracy
with the official gravimetric quinolinum phosphomolybdate
method.
A method for phosphate was reported in which the heteropholy
acid H3po4 (MoO3)12 is formed and them extracted with
chloroform and butanol (4:1) from excess molybdate reagent. The
molybdate combined with phosphate was then determined
spectrophotometrically at 710m as the green molybdenum (vi)
complex
with
2-ammino-4-chlorobenethiol
in
chloroform.
Amounts of phosphorus in the sample solution down to 0.008ppm
can be determined.
Phosphorus was determined indirectly with EDTA . the method
involves precipitating phosphorus as ZnNH4PO4, then adding
excess EDTA at ph7 to 10 to complex the Zn in the ZnNHPO4 ,
and titrating the excess EDTA . the method is slow but precise and
accurate .
A discussion of the EDTA titration of excess Bi(NO3)in 0.5N
HNO3 was given (43). Ions which interfere with this determination
, except Fe(III), are not normally found in fertilizers. Fe(III)can be
reduced with ascorbic acid .
Szekeres described a method for the sequential determination of
calcium and phosphorus in the presence of
Fe, Al SO4 and F . A measured excess of EDTA was added to
complex the Ca and the excess EDTA then titrated with 0.1M
MgCL2 to a thymolphthalien complexan end point. Crystalline
ammonium cohloride and ethanol are then added to precipitate
MgNH4PO4.6H2O thus causing the blue color to be discharged.
The titration of the the liberated EDTA with MgCL2 is then
continued unitl the blue end point is again reached . results agreed
well with those obtained gravimetrically . determinations for total
p2o5 , water soluble p2o5 , and citrate soluble p2o5 in
superphosphate of lime were made by precipitating the phosphate
as pb3(po4)2 filtering , and converting the precipitate to pbso4
with boiling standard H2so4 , then titrating with standard alkali .
The phosphate content of superphosphate was determined with two
titration using two mixed indicators methyl red and bromocresol
green , and cresol red and phenolphthalein . in the first step , free
acid was determined by titration with 0.1N NaOH to a light green
color . then ca was precipitated from a second sample with
potassium oxalate and the phosphate thus released were titrated
with 0.1N NaOH to the violet end point of second mixed indicator
.
Riedel eliminated silicate interference in the gravimetric
MgNH4PO4 determination by passing the sample solution through
an ion exchange column before the precipitation step .
Both total phosphorus and water soluble phosphorus were
determined with a are spectrograph the relative error was 4.0%for
fertilizers containing 30%p2o5 and 2.6%for those containing
5%p2o5 . the results agreed well with those obtained by
colorimetric procedures.
The Netherlands alkaline ammonium citrate extraction method for
the determination of available p2o5 was modified by Brabson
(11)for routine use. The results of this extraction method correlate
well with field tests on availability of p2o5 in the fertilizers.
Paper chromatography has been used for the separation of the
various compounds of phosphorus in fertilizer .this technique was
used to study the effects of the manufacturing process on the forms
of phosphorus present.
As a basis for the qualitative determination of the presence of the
different forms of phosphorus in fertilizer materials differential
thermal analysis curves were made of apatite (Ca5-(PO4)3F),
phosphorite meal (fluoro-and hydroxyl apatite with organic
constituents),
precipitated
phosphate(Ca-
HPO4.2H2O+Caso4.2H2O), plain superphosphate , and its
granulated
commercial
form,
Thomas
slag,
diamophos
(NH4)2HPO4 and a mixture of these compounds. Precipitated
phosphate and superphosphates were easily observed by their
characteristic endothermic effects.
Midlkiff described improved techniques for determining available
phosphorus
the
direct
available
gravimetric
quinoliniumphosphomolybdate method was modified so that the
analysis time was reduced by one half. This was accomplished by
using a multiple pipetter and other analytical glassware arranged in
multiple units.
Potassium
An automated flame photometric method for determination of
potassium salts was developed by ussary and Gehrke at the
Missouri experiment station chemical laboratories. This method
gives results equally as accurate and precise as the AOAC official
sodium tetraphenylborate method and at an analysis rate of 40
samples per hour . the automated method was applied to mixed
fertilizers and gave accurate and precise results without anion
exchange cleanup . these investigtors also applied the metod to the
analysis of potassium in the AOAC it was concluded that
extraction of potassium by neutral ammonium citrate was
quantitative and citrate did not interfere with the read-out . thus , a
single sample preparation and solution was used for the analysis of
both phosphate and potassium .
In other studies, obtained accurate flame photometric results for
potassium with a relative precision of 1%. Good agreement with
chemical methods was obtained . comparative studies were made
between the titrametric sodium tetraphenylborate method and the
flame photometric method for potassium by two different
Investigators found that concentration of interfering ions in
fertilizer sample solutions were too low to affect the flame
photometric determination of potassium when an air-butane flame
was used . the tetraphenylborate method gave slightly higher
results, but agreement was within 0.2% absolute with all samples
of varying phosphate content .
Compared the two methods for the analysis of hydroponic
solutions and found them to give equal accuracy .
However the tetraphenylborate method gave slightly better
precision .the anion exchange resin Dowex 2 was used to eliminate
sulfate and phosphate interference with the determination of
potassium . after anion exchange cleanup the choice of analytical
method was of secondary importance because of sampling error
Rapoport used formaldehyde and EDTA to eliminate interference
in the gravimetric sodium teteraphenlborate determination of
potassium .
Potassium in the row materials , the intermediates and the products
in potash fertilizer plants has been continuously and automatically
analyzed by registration of the beta ray emission from K(9).
Hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
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Determination of total nitrogen
Nitrogen was determined by KJEDAHL method (Buresh al,1982).
KJELDAHL nitrogen
APPARATUS
Block digester-distillation unit-Burette.
REAGENTS
A-digestion catalyst mixture , (KJELTABS) potassium sulphate
cupric
Sulphate (K2so4,Cuso4) .
B-sulfuri Acid , concentrated .
c-sodium hydroxide solution 10N
d-saturated boric acid .
E-hydrochloric acid 0.01N
F-Indicater (mixed indicater :0.5g green bromoceresol +0.1g
methyle red in 100 ml methanol)
Procedure
-0.01 g of sample was weighed and transferred quantitatively into
digestion tube .
-catalyst mixture was added (one tablet contain 1.5g K2so4, 0.15
Cuso4).
-10ml conc.H2so4 were added by using a dispenser and was stirred
until mixed well.
-tubes were placed in a block digester at 380c and digestion
continued for 2hur to get clear mixture.
-tubes were removed after complete digestion , cooled and brought
to volume (100ml)with DI water .
Reagents black was included.
Determination of N by distillation
-distillation apparatus was set and steamed out for at least
10minutes.
-the sample digest was mixed in the tube and 20ml was taken into
distillation flask.
-30ml 10 N NaOH were dispensed carefully and the flask was
connected immediately to distillation unit to begin distillation.
-Distillation started flowing into the collecting flask.
-the distillate was titrated using mixed indicator with standardized
0.01N HCL, titration volume of acid was recorded.
Calculation
Percentage N in sample:
%N= (V-B)*A*14.1*100/W*1000
Where:
V=sample titration volume.
B=digestion blank titration volume (ml).
W=weight of sample (g).
A=acid normality.
R=Ratio of total digest volume to distillation volume.
Determination of phosphorus
Phosphorus
was
determined
by
the
method
of
chlorostannusreduced molybdophosphoric blue , in hydrochloric
acid system (Jackson,1962)
For routine determination of phosphorus the following reagents
were prepared
1: chloromolybdic 1.5%
30g of ammonium molybdate (NH4)6Mo7o24-4H2o) were
dissolved in about 600ml hot distilled water. Filtered after cooling ,
and 700ml of 10N HCL were added slowly. The solution was
allowed to cool , then diluted to 2liter with distilled water and
stored in amber glass bottle ; this is 1 .5%olybdate in HCL
2: chlorostannass acid reductant (Sncl2-2H2O):
2 .50g of Sncl2-H2O were dissolved in 5ml concent-rated and
stored HCL with heating. The volume was diluted with recently
boiled distilled water to 50ml. the volume was ompleted to 100ml
with 1.2N HCL to give a 0.1M Sn solution (prepared fresh daily).
3: 10NHCL:
840ml concentrated HCL were diluted to a liter distilled water.
4: 1.2N HCl :
101ml concentrated HCL were diluted to a liter with distilled
water.
5: 4N NH4OH:
285ml concentrated ammonia solution (NH4OH) were diluted to a
liter with distilled water.
6: 2-4 dinitrophenol were dissolved in 50ml hot distilled water and
was heating to boiling, then the volume was completed to 100ml
Preparation of phosphorus standard
22.00 mg KH2po4 were dissolved in 100ml distilled water , each
ml contains 155g H2po4 aliquots containing 15.5, 31,62, 124 and
155ug H2po4 were taken in 50ml volumetric flask. The standard
curve was linear up to 155ug
Procedure:
From the wet ash solution (diluted 10 times) 2.5ml were pipetted in
50ml volumetric flask and about 25ml distilled water were added
followed by 1to 4 drops of 2-4 dinitrophenol indicator followed by
about 0.5 ml NH4OH which change the colour to yellow followed
by 10ml chloromolybdic acid reagent, and the volume was
completed
Introduction
On our plant , nitrogen interchanges from one chemical compound
to another and also transferred from one N pool to another the N
pools can be thought of in such global terms as atompheric