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 vanadinite [Pb5(VO4)3Cl], and patronite (possibly VS4), 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 V5. It is associated

with organic complexes and is insoluble in reducing environments. 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 evidence 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 gastrointestinal 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 inductively 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 electrothermal 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 reactants, 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 solutions treated identically.

b. Interference: The substances listed in Table 3500-V:I will interfere in the determination of vanadium if the specified concentrations are

exceeded. This is not a serious problem for Cr6, Co2, Mo6, Ni2,

Ag, and U6because the tolerable concentration is greater than that

commonly encountered in fresh water. However, in some samples the

tolerable concentration of Cu2, Fe2, and Fe3may 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 minimize their interference; however, mercuric ion itself interferes if

in excess. Adding 350 g mercuric nitrate, Hg(NO3)2, per sample permits determination of vanadium in the presence of up to

100 mg Cl/L, 250 g Br/L, and 250 g I/L. Dilute samples

containing high concentrations of these ions to concentrations

below the values given above and add Hg(NO3)2.

c. Minimum detectable concentration: 0.025 g V in approximately 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

Cr61.0

Co21.0

Cu20.05

Fe20.3

Fe30.5

Mo60.1

Ni23.0

Ag2.0

U63.0

Br 0.1

Cl 100.0

I

 0.001

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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 reagents, for dilutions, and as blanks.

a. Stock vanadium solution: Dissolve 229.6 mg ammonium

metavanadate, NH4VO3, in a volumetric flask containing approximately 800 mL water and 15 mL 1 1 nitric acid (HNO3).

Dilute to 1000 mL; 1.00 mL  100 g V.

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 intermediate vanadium solution with water to 100 mL; 1.00 mL 

0.010 g V.

d. Mercuric nitrate solution: Dissolve 350 mg

Hg(NO3)2  H2O in 1000 mL water.

e. Ammonium persulfate-phosphoric acid reagent: Dissolve

2.5 g (NH4)2S2O8 in 25 mL water. Bring just to a boil, remove

from heat, and add 25 mL conc H3PO4. Let stand approximately

24 h before use. Discard after 48 h.

f. Gallic acid solution: Dissolve2gH6C7O5 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(NO3)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 ammonium persulfate-phosphoric acid reagent (temperature equilibrated), 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 absorbance 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 standard deviation of 20% and no relative error.

7. Bibliography

FISHMAN, M.J. & M.V. SKOUGSTAD. 1964. Catalytic determination of

* Whatman No. 42 or equivalent. vanadium in water. Anal. Chem. 36:1643.

VANADIUM (3500-V)/Gallic Acid Method

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