DETERMINATION OF THE PHOSPHATE
IN SOLID WASTE USING
THE VANADOMOLYBDOPHOSPHORIC
ACID METHOD
U.S. ENVIRONMENTAL PROTECTION AGENCY
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DETERMINATION OF THE PHOSPHATE IN SOLID WASTE
USING THE VANADOMOLYBDOPHOSPHORIC ACID METHOD
A Solid Waste Research
Open-File Report (RS-03-68-17)
written by
WILLIAM H. KAYLOR, Chemist
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Monitoring
Solid Waste Research
1971
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TABLE OF CONTENTS
Reagents
P roc edure -"
Page
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iii
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DETERMINATION OF THE PHOSPHATE IN SOLID WASTE
USING THE VANADOMOLYBDOPHOSPHORIC ACID METHOD
William H. Kaylor*
INTRODUCTION
The reclamation of useful products from solid waste is one method
of reducing the disposal problem of solid wastes. There are many re-
search projects concerned with recycling solid wastes into fertilizers
and food products. In the production of fertilizers and food products
from solid waste, the phosphorous concentration is of importance because
phosphorus is a nutrient. It is also important to know the phosphate
concentration in solid waste leachates, since these leachates may even-
tually drain into natural water supplies and cause pollution if standard
concentration limits are exceeded. This report describes and evaluates
one method for measuring phosphorus in the form of phosphates that are
present in solid wastes.
The vanadomolybdophosphoric acid method* was selected to be in-
vestigated as a method for solid waste analyses because of its high
range, simplicity, and freedom from interferences. The chemistry which
makes this method useful for determining phosphates is believed to in-
volve the substitution of oxyvanadium and oxymolybdenum radicals for the
0 of PO, to give a heteropoly compound that is chromogenic.
* Chemical and Radiological Activities Section, Engineering and Science
Branch, Office of Air and Water Programs, Environmental Protecti&n Agency,
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The intensity of yellow color produced is proportional to the con-
centration of phosphates present; thus the phosphates can be determined
colormetrically by measuring the intensity of the yellow color produced
when PO^ comes in contact with vanadate and molybdate in an acid solution.
EXPERIMENTAL
Vanadomolydophosphoric Acid Method for Phosphates
1. Equipment.
a. Erlenmeyer flasks - 125 ml
b. Kjeldahl flasks - 800 ml
c. Volumetric pipettes - 5, 10 and 20 ml
d. Filtering funnels
e. Filter paper - only specification is phosphate free
f Color comparison tubes or volumetric flasks - 50 ml
g. Spectrophotometer - wave length setting 400 mu
2. Reagents
a. Ammonium vanadate ~ molvbdate solution: Dissolve 2.35 g ammon
ium metavanadate in 300 ml of boiling distilled water; cool, then
add 400 ml concentrated HNO^ and cool. Dissolve 40 g ammonium
molybdate in 400 ml hot distilled water and cool. The molybdate
solution is then added to the vanadate solution and*diluted to
2 liters with distilled water.
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b. Sulfurlc acid solution; Add 310 ml concentrated H2SO^ cautiously
to 500 ml distilled water and dilute to 1.0 liter.
c. §9diupi hydroxide: Dissolve 450 g NaOH in distilled water; cool,
and dilute to 1.0 liter.
d. Phosphate standard: Dissolve 1.4330 NaH2PO^ (dried at 105 C) in
distilled water and dilute to 1.0 liter (1.0 ml = l.o mg PO^).
e. Working Standard: Pipet 50.0 ml of the phosphate standard into
a 1.0 liter volumetric flask and dilute volume with distilled
water (1.0 ml = 0.05 mg PO^).
f. Chemicals
(1) Concentrated acids - hydvobk&etic, nitric and sulfuric
(2) Potassium persulfate
(3) Sodium nitrate
3. Procedure
The solid sample may be prepared for analysis either by acid digestion
(a) or by dry ashing (b). Liquids are prepared by method (c). The com-
pletion of the analysts is substantially the same for all three procedures.
a. Acid digestion of soljfd. «fynples: Weigh accurately 1-2 g of homo-
geneously ground sample (predried at 105 C) and place in a kjeldahl
flask. Add 5 ml concentrated HMO- and 25 ml concentrated H^SO^ and
heat until the solution boils. Then add 1 g NaN03 to the solution
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and digest for two hours. After the sample is digested and cooled,
add 150 ml distilled water and boil the solution for five minutes.
Cool the sample and transfer to a 200 ml volumetric flask; fill to
volume with distilled water and filter.
Pipet 25 ml or an aliquot of the sample (1-25 ml depending on the
phosphate concentration in the sample) into a calibrated 50 ml con-
tainer. Add sodium hydroxide (450 g/1), 1 ml per 5 ml of sample,
to adjust the pH and dilute the sample to approximately 40 ml with
distilled water. Then mix the sample, add 5 ml of vanadate-molybdate
reagent, adjust the sample to the 50 ml mark with distilled water,
and mix again. Allow solution to stand 15 minutes for maximum
color development and read the absorbance on a spectrophotometer at
4OO mu.
Calculations: Plot a standard curve from 1-25 mg/1 PO, vs
absorbance. The sample results are read directly from the
standard curve taking into account the proper aliquot used
for each sample.
mg/1 P0/r=mg/l P04x 50 Percent P04= m8/l P04 x 10°
Aliquot used wt. of sample x 5
b. Ashing of solid ?flnpl?ff; Weigh accurately 1-2 of homogeneously
ground sample (predried at 105 C) and ash in a muffle furnace at
#
6OO C for 2 hours. Cool the ash, add 40 ml HC1 (1:3) and 3 drop
concentrated HNOq, and bring the solution to a boil. Cool the solu-
tion, transfer it to a 200 ml volumetric flask, dilute to volume
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with distilled water and filter.
Fipet 25.0 ml or an aliquot of sample (depending on phosphate concen-
tration in samples) into a calibrated 50 ml container and dilute to
about 40 ml with distilled water. Continue the procedure as described
in procedure (a), except the pH does not need adjusting in this pro-
cedure.
c. Digestion of liquid samples: Place 50 ml of the sample (or an
aliquot diluted to 50 ml) into an erlenmeyer flask. Add one ml of
H2SO^ (31Q ml/1) and 0.5 g potassium persulfate, and digest the sam-
ple for 30 minutes on a hot plate. Then dilute the sample to about
20-25 ml with distilled water, filter it into a calibrated 50 ml con-
tainer and dilute to approximately 40 ml with distilled, washing
thru the filter paper in the process. Add 0.5 ml of NaOH (450 g/1),
mix well, and continue the procedure as described in procedure (a)
with the addition of the vanadate reagent.
DISCUSSION
The vanadomolybdophosphoric acid method can be used to determine
phosphates in many types of solid waste. Results obtained from the
methods were compared to results from two other common-phosphate.
methods 2» 3» using standards and solid wastes samples (Table 1). The
analyses indicate that the vanadomolybdophosphoric acid method compared
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favorably to the other methods. This method is often more suited for
solid waste samples. The concentrations of phosphates in solid waste
are much higher than can be measured by the other methods without
large dilution factors. The vanadomolybdophophoric acid method has
a much higher range than the other methods; therefore little, if any,
dilution is needed.
This method was evaluated with standards and standard addition to
solid waste samples (Table 2). The results showed that at least 95
percent of the total phosphates present were recovered from all samples
and standards.
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TABLE 1 METHOD COMPARISON
Sample
Sodium Glycerophosphate
(Ashed) Mg/1 P04in
#1 151
#2 151
#3 151
Johnson City Compost
and sludge (Ashed)
#1
#2
Johnson City Compost (70
(Ashed)
#1
#2
#3
#4
#5
Johnson City Compost (70
(Digested)
n
#2
#3
Incin. Res. N.Y. #203
(Ashed)
#1
#2
#3
Incin. Res. N.Y. #203
(Digested)
#1
#2
#3
Food Wastes N.Y. #208
(Ashed)
#1
#2
#3
#4
#5
#6
V ^^^^^^WMHM^^B^^MVMMMVi
Molybdate Blue
Method
Dil. Factor
Std.
50
50
50
10
10
day)
25
25
25
25
25
day)
50
50
50
250
250
250
250
250
250
100
100
100
100
100
100
Me/1
148
146
146
13.8
21.9
43.0
38.0
35.3
39.4
43.8
52.5
48.0
47.5
228
226
226
122
121
120
136
156
130
135
143
134
Ascorbic
Method
Dil. Factor
50
50
50
25
25
25
25
25
50
50
50
250
250
250
250
250
250
100
100
100
100
100
100
Mp/1
160
150
155
48.8
43.3
40.3
43.3
49.8
46.0
43.5
44.0
217
230
225
117
111
115
144
173
151
161
153
160
Vanadate Yellow
Method
Dil. Fact or
10
10
10
5
5
5
5
5
5
5
5
5
5
10
10
10
5
5
5
10
10
10
10
10
10
Me/1
153
153
154
18.2
28.9
52.5
46.0
42.0
46.0
47.5
48.5
44.0
46.3
220
222
222
114
112
110
143
174
155
165
162
160
Quench Water
Wash., D.C.
2.40
2.44
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TABLE 2
PRECISION AND ACCURACY OF THE VANADOMOLYBDOPHOSPHORIC
ACID METHOD
P04
Sample mg/1
J. C. * compost
and sludge (Ashed)
#1 18.3
" 18.5
" 18.0
J. C. compost
and sludge (Ashed)
#2 29.0
" 28.8
" 28.8
J. C. compost (70-day)
(Ashed)
#1 52.5
#2 46.0
#3 42.0
#4 46.0
#5 47.5
J. C. compost (70-day)
(Digested)
#1 48.5
#2 44.0
#3 46.3
Quench Water
Wash. ,D.C. (1967) 2.43
» 2.44
" 2.44
7«P04
0.36
0.37
0.35
0.41
0.40
0.40
0.47
0.46
0.43
0.46
0.47
0.47
0.44
0.46
Standard Addition
P04 Std. Added P04
mg/l
5.0
10.0
15.0
5.0
10.0
15.0
«>_,_ 1 JIO Il<-rir1.,w; -
oampie V£. useo
5.0
5.0
5.0
10.0
10.0
10.0
Sample #2 Used-
10.0
10.0
10.0
20.0
20.0
20.0
10.0
10.0
10.0
Std . Recovered
mg/1
4.5
10.2
15.0
4.9
9.7
15.1
4.8
4.8
4.8
9.6
9.7
9.6
9.7
9.7
9.7
19.9
19.5
19.4
9.44
9.36
9.50
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PRECISION AND ACCURACY OF VANADOMOLYBDOPHOSPHORIC ACID
METHOD (Con'd)
Standard Addition
Sample
PO^
mg/1
P04 Std. Added PO^Std. Recovered
XPO^ mg/1 mg/1
N.Y. #203 Incinerator
(Ashed) Residue
N.Y.
#1
#2
#3
#203 (Digested)
222
222
222
2.22
2.21
2.21
Incinerator Ash
N.Y.
Food
#1
#2
#3
#208 (Ashed)
Refuse
#1
#2
#3
114
112
110
165
161
161
2.1
2.20
2.19
1.65
1.61
1.62
Sample #1 Only
10.0
10.0
10.0
20.0
20.0
20.0
N.Y. #203 (#3 Used)
10.0
10.0
10.0
20.0
20.0
20.0
N.Y. #208 (#1 Used)
10.0
10.0
10.0
20.0
20.0
20.0
9.4
9.4
9.7
19.6
19.6
19.2
208
9.6
9.9
9.7
19.3
19.3
19.5
203
9.9
9.8
9.7
19.2
19.7
19.7
*Johnson City
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REFERENCES
1. Jackson, M. L. Soil chemical analysis. Prentice-Hall, Inc., 1960.
p. 151-154.
2. Gales, M. E. Jr., Julian, E. C., Kroner, R. C., "A Method for the
Quantitative Determination of Total Phosphorus in Filtered and Un-
filtered Samples" JAWWA Vol. 58 #10 Oct., 1966.
3. "FWPCA Methods for Chemical Analysis of Water and Wastes" FWPCA
Division of Water Quality Research, Analytical Quality Control Labo-
ratory, Nov. 1969.
ACKNOWLEDGEMENT
The assistance of Donna L. Barnett is gratefully acknowledged.
?2-l-0035s
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