3500-V VANADIUM*
3500-V A. Introduction
1.
Occurrence and Significance
Vanadium (V) is the first element in Group VB in the periodic
table; it has an atomic number of 23, an atomic weight of 50.94,
and valences of 2, 3, 4, and 5. The average abundance of V in the
earth’s crust is 136 ppm; in soils it ranges from 15 to 110 ppm;
in streams it averages about 0.9
g/L, and in groundwaters it is
generally ⬍0.1 mg/L. Though relatively rare, vanadium is found
in a variety of minerals; most important among these are vana-
dinite [Pb
5
(VO
4
)
3
Cl], and patronite (possibly VS
4
), occurring
chiefly in Peru. Vanadium complexes have been noted in coal
and petroleum deposits. Vanadium is used in steel alloys and as
a catalyst in the production of sulfuric acid and synthetic rubber.
The dominant form in natural waters is V
5⫹
. It is associated
with organic complexes and is insoluble in reducing environ-
ments. It is considered nonessential for most higher plants and
animals, although it may be an essential trace element for some
algae and microorganisms. Laboratory and epidemiological ev-
idence suggests that vanadium may play a beneficial role in the
prevention of heart disease. In water supplies in New Mexico,
which has a low incidence of heart disease, vanadium has been
found in concentrations of 20 to 150
g/L. In a state where
incidence of heart disease is high, vanadium was not found in
water supplies. However, vanadium pentoxide dust causes gas-
trointestinal and respiratory disturbances. The United Nations
Food and Agriculture Organization recommended maximum
level for irrigation waters is 0.1 mg/L.
2.
Selection of Method
The atomic absorption spectrometric methods (3111D and E),
the electrothermal atomic absorption method (3113B), the in-
ductively coupled plasma methods (3120 and 3125), and gallic
acid method (3500-V.B) are suitable for potable water samples.
The atomic absorption spectrometric and inductively coupled
plasma methods are preferred for polluted samples. The electro-
thermal atomic absorption method also may be used successfully
with an appropriate matrix modifier.
3500-V B. Gallic Acid Method
1.
General Discussion
a. Principle: The concentration of trace amounts of vanadium
in water is determined by measuring the catalytic effect it exerts
on the rate of oxidation of gallic acid by persulfate in acid
solution. Under the given conditions of concentrations of reac-
tants, temperature, and reaction time, the extent of oxidation of
gallic acid is proportional to the concentration of vanadium.
Vanadium is determined by measuring the absorbance of the
sample at 415 nm and comparing it with that of standard solu-
tions treated identically.
b. Interference: The substances listed in Table 3500-V:I will inter-
fere in the determination of vanadium if the specified concentrations are
exceeded. This is not a serious problem for Cr
6⫹
,Co
2⫹
,Mo
6⫹
,Ni
2⫹
,
Ag
⫹
, and U
6⫹
because the tolerable concentration is greater than that
commonly encountered in fresh water. However, in some samples the
tolerable concentration of Cu
2⫹
,Fe
2⫹
, and Fe
3⫹
may be exceeded.
Because of the high sensitivity of the method, interfering substances in
concentrations only slightly above tolerance limits can be rendered
harmless by dilution.
Traces of Br
⫺
and I
⫺
interfere seriously and dilution alone
will not always reduce the concentration below tolerance limits.
Mercuric ion may be added to complex these halides and min-
imize their interference; however, mercuric ion itself interferes if
in excess. Adding 350
g mercuric nitrate, Hg(NO
3
)
2
, per sam-
ple permits determination of vanadium in the presence of up to
100 mg Cl
⫺
/L, 250
gBr
⫺
/L, and 250
gI
⫺
/L. Dilute samples
containing high concentrations of these ions to concentrations
below the values given above and add Hg(NO
3
)
2
.
c. Minimum detectable concentration: 0.025
g V in approx-
imately 13 mL final volume or approximately 2
g V/L.
d. Quality control (QC): The QC practices considered to be
an integral part of each method can be found in Section 3020.
2.
Apparatus
a. Water bath, capable of being operated at 25 ⫾0.5°C.
b. Colorimetric equipment: One of the following is required:
1) Spectrophotometer, for measurements at 415 nm, with a
light path of 1 to 5 cm.
* Approved by Standard Methods Committee, 1997. Editorial revisions, 2011.
Joint Task Group: 20th Edition—See 3500-Al.
TABLE 3500-V:I. CONCENTRATION AT WHICH VARIOUS IONS INTERFERE IN
THE DETERMINATION OF VANADIUM
Ion
Concentration
mg/L
Cr
6⫹
1.0
Co
2⫹
1.0
Cu
2⫹
0.05
Fe
2⫹
0.3
Fe
3⫹
0.5
Mo
6⫹
0.1
Ni
2⫹
3.0
Ag
⫹
2.0
U
6⫹
3.0
Br
⫺
0.1
Cl
⫺
100.0
I
⫺
0.001
1
2) Filter photometer, providing a light path of 1 to 5 cm and
equipped with a violet filter with maximum transmittance near 415 nm.
3.
Reagents
Use reagent water (see Section 1080) in preparation of re-
agents, for dilutions, and as blanks.
a. Stock vanadium solution: Dissolve 229.6 mg ammonium
metavanadate, NH
4
VO
3
, in a volumetric flask containing ap-
proximately 800 mL water and 15 mL 1 ⫹1 nitric acid (HNO
3
).
Dilute to 1000 mL; 1.00 mL ⫽100
gV.
b. Intermediate vanadium solution: Dilute 1.00 mL stock
vanadium solution with water to 100 mL; 1.00 mL ⫽1.00
g
V.
c. Standard vanadium solution: Dilute 1.00 mL intermedi-
ate vanadium solution with water to 100 mL; 1.00 mL ⫽
0.010
gV.
d. Mercuric nitrate solution: Dissolve 350 mg
Hg(NO
3
)
2
䡠H
2
O in 1000 mL water.
e. Ammonium persulfate-phosphoric acid reagent: Dissolve
2.5 g (NH
4
)
2
S
2
O
8
in 25 mL water. Bring just to a boil, remove
from heat, and add 25 mL conc H
3
PO
4
. Let stand approximately
24 h before use. Discard after 48 h.
f. Gallic acid solution: Dissolve2gH
6
C
7
O
5
in 100 mL warm water,
heat to a temperature just below boiling, and filter through filter paper.*
Prepare a fresh solution for each set of samples.
4.
Procedure
a. Preparation of standards and sample: Prepare both blank
and sufficient standards by diluting 0- to 8.0-mL portions (0 to
0.08
g V) of standard vanadium solution to 10 mL with water.
Pipet sample (10.00 mL maximum) containing less than 0.08
g
V into a suitable container and adjust volume to 10.0 mL with
water. Filter colored or turbid samples. Add 1.0 mL Hg(NO
3
)
2
solution to each blank, standard, and sample. Place containers in
a water bath regulated to 25 ⫾0.5°C and allow 30 to 45 min for
samples to come to the bath temperature.
b. Color development and measurement: Add 1.0 mL ammo-
nium persulfate-phosphoric acid reagent (temperature equili-
brated), swirl to mix thoroughly, and return to water bath. Add
1.0 mL gallic acid solution (temperature equilibrated), swirl to
mix thoroughly, and return to water bath. Add gallic acid to
successive samples at intervals of 30 s or longer to permit
accurate control of reaction time. Exactly 60 min after adding
gallic acid, remove sample from water bath and measure its absor-
bance at 415 nm, using water as a reference. Subtract absorbance of
blank from absorbance of each standard and sample. Construct a
calibration curve by plotting absorbance values of standards versus
micrograms vanadium. Determine amount of vanadium in a sample
by referring to the corresponding absorbance on the calibration
curve. Prepare a calibration curve with each set of samples.
5.
Calculation
mg V/L ⫽
g V (in 13 mL final volume)
original sample volume, mL
6.
Precision and Bias
In a synthetic sample containing 6
g V/L, 40
g As/L, 250
g Be/L, 240
g B/L, and 20
g Se/L in distilled water,
vanadium was measured in 22 laboratories with a relative stan-
dard deviation of 20% and no relative error.
7. Bibliography
FISHMAN, M.J. & M.V. SKOUGSTAD. 1964. Catalytic determination of
vanadium in water. Anal. Chem. 36:1643.
* Whatman No. 42 or equivalent.
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