ANALYTICA
A
RAPID
(COMBINED)
METHOD
FOR
CHIMICA
THE
AND PHOSPHATE PHOSPHATE AND
5
DETERMINATION
OF
AMMONIA
IN THE SYSTEM OF DIAMMONIUM DIPOTASSIUM PHOSPHATE
13.PASCHICES Israel Mining
ACTA
Industries
(Received
33. BERNAS
AND
Labovatovies, Haifa (Israel)
June
10th.
1960)
INTRODUCTXON
A simple titration method was required to determine phosphate and ammonium ions in fhe system (NH4)zHP04 and &HP04 which would be suitable for rapid routine control analysis without instrumental techniques. When an excess of alkali is added to diammonium hydrogen phosphate, the ammonia can bc quantitatively eliminated by boiling. Back titration of the excess alkali with N/IO hydrochloric acid followed by titration from HP04-2 + HzP04yields titers which correspond to the ammonium and the phosphate. Methyl orange is the only indicator used. When dipotassium hydrogen phosphate is present, potassium can thus be calculated by difference. EXPERIMENTAL
Standard
sohtions
PANT
and reagents
Solutiott A. KzHP04 aclucous solution containing 26.43 mg PO4-3 per ml. Soldion H. (NH4)zHP04 aqueous solution containing 12.47 mg NH4+ per ml and 33.02 mg P04-3 per ml. AJelhyZ orange (M.O.) indicator, 0.050/~ nqucous. Phc~toZ~lttlzaZci~t (PA) indicator, o,5% in 50% ethanol. Mixed indicator (M.1.) phcnolph thalein + a-naphtholphthalein (z parts 0.5% phenolphthalein in 50% ethanol and I part 0.1 0/oa-naphtholphthalein in 50% ethanoll). Brilliant yellow indicatb’v @per obtained by soaking strips of filter paper with a 0.x0/~ brilliant yellow aqueous solution and drying. The first stage of the procedure where phosphate and ammonium ions arc dctermined by a single titration with phenolphthalein and methyl orange indicator, or mixed indicator and methyl orange indicator, is presented in Table I. Throughout cxperiments No. 1-3 a synthetic sample was obtained by mixing aliquots of solution A and solution B as given in TaWle I. The volume was brought to approximately TOO ml with carbon dioxide-free distilled water; standard carbon dioxide-free N/IO sodium ” hydroxide in the amounts stated in column 3 of Table I was added to the sample and the solution was boiled till free of ammonia. The solution was cooled and titrated first to phenolphthalein and subsequently to the methyl orange end-point. In cxperiment No. 2 the solution was half saturated with sodium chloride to repress hydrolysis2. In experiment No. 3 the mixed indicator was tested. If the total theoretical alkalinity to methyl orange is calculated (column 6, Table I) we see that the total titer to methyl orange found is correct and reproducible (column 5, Table I), the maximum deviation being j= 0.75% relative. Anal. Ghim. Acta, 24 (1961) s-10,
TABLE I TBE DETERXISATIOS
OF AXIJlOSIUX AE;D PHOSPHATE BY A SIMGLE TITRATIOS XETHYL
Expnimmt No.
POP m
I
KHt+ mg
?
(I =
x.034
ml 3
20.00
I
59-45
4
Ph Ph -*31.0.
Ph Ph -+X0.
12.47
20.00 59.45
IndhlW
“‘_4j
.iduaJJy f ifrnfcd N/IO HCJdf=x.w j) 5
3f.I. XI. 4 x.0.
ASD 3IETWL
USISG PilESOLPHTHALEIS
Thwficaffy rrquiwd Tctaf l&r
f# M.0. S/IO liG;J(f ==I.OO j) 6
ASD
ORdSGE
Found
Rrlalitv d&Jim
Pot-=
Mi4~
mg :
md 8
ror
0’ r* 9
Mi4+
0;
IO
KLiO
7.35 20.0jb
20.00
3
ISIXC~TOR
Tifrated
x2.47
2
59.45
OR&SGE OR flISED
Adaed X/IO XaOH
Tab.
CP
rg.god
70.31
I+2j
_t I&OS
-i_ 14 2s
r9.90
70.3x
r-l.79
+
IS.OS
+ IS.61
-l-13.44
+x123 + 5.45
12.40
T-35 19.jsb
12.90 - r3.30c 7.03 - 6.6jC r9.9jb
rQ.90
67~-636o
X32$-13.1 j
f
7-00
n LOOml of solution X plus LOOml of solution B were taken in each experiment. $’ bTota1 titerto X.0. 3 e The end-point was not clearly ~stinguished. ? rt d Calculation: zo,oo ml Ar/xo NaOH (column 3) corr. to 20.68 ml X/IO XaOH ff = 1.000). Alkali requirement for 12.1; mg XHaf (column 2) con= to rw.. 6.91 ml IV/IONaOH [f = I.OOO), 13.77 ml 3’110 NaOH (f = 1.000) corresponding to escess i\‘aOH in the solution = 13.65 ml X/IO HCl (f = 1.007). x 59.43 mg POa-3 ~column I) corresponds to 6.22 ml X/KONC1(f = 1.007) (HP0 a- -+ HIPO.X-~).rg.go is the theoretically required total back titer f FL A’lro HCl (f = 1.007). z:
DETERMINATION
OF AMMONIA
AND
PHOSPHATE
7
Representing the reaction schematically (Fig. I) we see that if UC(compare columns 5 and 6 in Table I) is exact, the interpretation of the point b is not correct at the endpoint of the phenolphthalein or mixed indicator (column 5, Table I). A displacement of b gives a displacement of d in the same direction. In our case it was displaced to the right giving too high results (by 5-18~h relative) for phosphate as well as for ammonium ion (see columns I, 2, 7. S, Table I). The second stage of the experimental part, therefore, involves the actual determination of point b by a direct titration of bc.
Fig. I. Addition of NaOH (bd) ; elimination of Nl-IJ CXCCYSNaOH to phenolphthaicin or mixed indicator from phcnolphthalein or mixed indicator end-point 3 displacement of b causes DETERMINATION
OF
I’EIOSPIIATII
AND
OICANGL:
by boiling (da) ; hck titriltion with HCl of end-point (ab) ; titration E-IPOJ-~ -c I-isPOdto methyl orange (bc). Total titer l-K1 (UC). displnccincnt of d.
AMMONIUM
AS TI-11: ONLY
BS
TWO
TITRATIONS
USING
hIl~TIIY1,
INDICATOR
When the simple is titrated directly with hydrochloric acid to methyl orange sntisfactory values are obtained for HJ?Oa-2 -+ H#Oa--: If this titer is deducted from the total titer to methyl orange obtained in the first experimental part (column 5, Tnblc I), the interference of the 1~ range of hydrolysis of the dibasic salt is avoided and stoichiomctrically correct results arc obtained.
In this experiment an aliquot of the synthetic sample of (NH4)&JP04 and &HP04 (same composition a5 in experiments No. r-3) was diluted to about 50 ml with distilled water and directly titrated with N/ro hydrochloric acid to methyl orange indicator. Amount of titrant used: $27 ml N/ro I-ICI (f = r.007) to methyl orange = 59.98 mg POP. This titer corresponds to bc, i.e. titration .‘of HPO4-2 -> HzP04-. The calculation of the NHq+ is therefore done in the following manner (see Fig. 2) : UC db -
bc a a6 (o.xccss NaOH in the solution) ab = (total NaOH - excess NaOH) = da (corresponds to NHa+).
For example: In experiment (column 5, Table I). IQ.95 ml (UC) -627 ml (bc) x3.68 ml N/IO
* calculated
to f =
1.000
No. 3 the total titer was x9.95 ml N/ro HCl (f =
I-ICI (/ =
Nef fiicr 20.68 ml N/IO NaOH added (db)* x.007) --+ -13.77 ml N/ro NaOH excess (ab)* 6.91 ml (for NH4+) (da) 6.~1-1.804 = 12.47 Tg NH&
x.oo7)
TABLE II v_fiUES
OBTAINED BP THE PROPOSED VOLUUETRIC
DETERSlISr\TIOS
Takn Containiq
Compositionojaliquats~ I and II
POr ’
m8 5
2.00 ml Solution _A. 0.50 ml Solution B
Total 5a
6
A-Ha+ mg
ml
-
8.00
13.22
ml Solution B Total
* In accordance with Fig. 2. b Calculated as in Experiment “%N.D . = Not determined.
No. 4.
r\SD PHOSPHATE
Found X/IO HCl (j= r.00;) Tifrafim of aliquofs I II m! ml
h’clatircdmbtion PO,-lb %
SH,‘b
PO*-’
A-H,+
mg
0’II
0, 10
7.32
23.91
70.01
6.096
$0.92
-2.23
not done
12.00
N.D.c
6.01
-
-3.6
s.32
Ig.jI
79.58
24.96
6.235 nil 6.235
As above
2.00
Biro XaOH(j= 1.00~) addedto aliquofII
20.00 I%zP 69.;7
0. j0 ml Solution X
OF A3131OSIC31
‘
nil
--66.01
w9-1
79.26
q-94
25.00
i-o.4
j-0.0s
DETERMINATION
OF AMMONIA
AND
PHOSPHATE
9
If the total titer of N/IO hydrochloric acid is taken from Expts. No. r and z (column 5, Table I) the results are respectively: 12.27 mg NH4+ and 12.82 mg NH4+ (relative deviation = --1.6~/~ ; +2.8o/o). These and the following results indicate that it is possible to determine the phosphate and ammonium content by two separate titrations in two alicluots of the sample using only methyl orange indicator. Schematically the two titrations can be represcntcd as follo\vs :
=
I-T&d
ut.r
“Cl
--.-I
Fig. 2. Aliquot I. Lhrcct titration with kiC1 to riictliyl orange cntl-point from l-1 PO,, -e to Hr1’04 titration with (DC). Aliquot II. Addition of NnOl-1 (bd) : elimination of Nl-13 by boiling (h) : IXIC~C I-ICI of cxcuss NnOl-I -+- I-1I’OJ-2 -. H~L’OJ- (UC).
From the above it follows that titers czc and bc were proved to bc correct; it follows thcrcforc that point b must be correct and consequently also u6 as well as cd are rcliablc. The reproducible values as obtainable by the method arc shown in Expts. No. 5 and G. CONDITIONS
OF DIZTERMINATIOS
Aliquot 1 (Fig. 2) : The alicluot taken was diluted to about 50 ml with distilled water and titrated to methyl orange indicator with N/ro hydrochloric acid. A Ziq,tcot II (Fig. 2) : Another aliquot of the same composition was diluted to about TOO ml; N/m sodium hydroxide was added and the solution boiled until free of ammonia; after cooling it was titrated to methyl orange indicator with N/TO hydrochloric acid. Details and results are summarized in Table II. When diammonium hydrogen phosphate is titrated directly with N/XC) hydrochloric acid to methyl orange (titer A ml) (first titration Fig. z) the ammonium ion will require the presence of 2 n ml titer of N/xc> sodium hydrosicle, assuming that all the phosphate is prcscnt as the diammonium salt; then 2 A + 5 ml will bc a sufficient excess to cover the total alkali requirement for the ammonia determination. If the amount of the ammonium ion is known to bc low the quantity of added alkali can bc decreased. This is shown in cxpcriment No. ~a (Table II). METHOD
Procedure I. Dilute
an aliquot
containing
about
60 mg of phosphate
with distilled
Anal. Chim. Ada,
water
24 (1961) 5-10
B. PASCHICES, B. BERNAS
IO
to about 50 ml and titrate with N/ICI hydrochloric acid to methyl orange (titer A). 2. Place another aliquot containing about 15 mg of ammonium ion in a z5o-ml Erlenmeycr flask, add N/IO sodium hydroxide* in an excess of at least 5 ml, dilute to about roi, ml and boil till ammonia-free (about 15 min) testing the vapours with moist brilliant yellow paper. When the paper remains yellow no more free r\r’Hais present in the solution. Cool and titrate with N/IO hydrochloric acid to methyl orange (titer 43).
titer --
2.
/I ./(N/lo
I-ICl)
- 0.00gg
*loo0
--
aliquot
=
ml
i>Od-3 in g/l
Ammonium ml N/ I o NnOl.1 _______._--_
corresponding alkliiot
to NH.,+ * o.oo180,~ * 1000 ml
titer 13 - titer A =1 ml I-ICI corrcsponcling Tota. N/IO NaOl-I adclctl**--cxcoss N/lo
to cxccss N,zOl-I**
NnOI-I =I N/IO
=
Na0l-I
Nll.lC in g/l
corresponding
to Nl-iaf.
NO/L’ The calculation
is made on the basis of iclcnticnl aliquots.
‘l’hanlts are clue to Dr. A. ALON, Chief Analyst, Mr. I>. ELROI ancl Mrs. V. VAHSANYI for their help and constructive criticism and the Management of Israel Mining Industries for the kind permission to puhlisli this work. SUMMARY arnmonitlm and In systcmw containinff (Nl&)~l-I PO J and I<~l-LiJO~, it is possiblu to clctcrminc phosphntc iOilS t)y titrating 2 ibliClU0tS Using methyl ornnjic as the only indicator. ~Jotassiunl Can for iI. single analysis. bc cnlci~krtcd by tliffcrcnco. About 20 niin arc‘ rcquirctl 12I%XlMI~ Unc tnbtliotlc volumbtriquc cst proposdc pour lc tlosagc tic l’ilmlnonium et clc l’anion phosphoriqtlc duns un nidlnn~i! tic p’hospliatc tli;lrnriioilirlilc ct de pl~oaphatc dipoti~ssi~~llc. La. tcncur cn potassium cst c;1.lcul6c par cliff~roncc. %IJSAMM1SNL~ASSIJNG Ucsclircibung cincr volunictriscllcn Mctllotlc zilr 13cstimniung von Ammonium unrl Phosphst in cincni Gcniiscll von I~intlininni~ilril)lioupl~nt und ~~il
MacMillan, rggz, p. 536. .__ ._.._.- __-._ ._-_ * If the order of magnituclc ** To bc calculatccl to factor
of Nl-Lb b is unknorvn, 1.000.
add
Y.
.A
ml
of N/IO
NaOI-I
+
5 ml cxccss,
Auat. Ciriw. Aclu, 24 (x961)
s-10