3500-Mn MANGANESE*

3500-Mn A. Introduction

1. Occurrence and Significance

Manganese (Mn) is the first element in Group VIIB in the

periodic table; it has an atomic number of 25, an atomic weight

of 54.94, and common valences of 2, 4, and 7 (and more rarely,

valences of 1, 3, 5, and 6). The average abundance of Mn in the

earth’s crust is 1060 ppm; in soils it is 61 to 1010 ppm; in

streams it is 7 g/L, and in groundwaters it is 0.1 mg/L.

Manganese is associated with iron minerals, and occurs in nodules in ocean, fresh waters, and soils. The common ores are

pyrolusite (MnO2) and psilomelane. Manganese is used in steel

alloys, batteries, and food additives.

The common aqueous species are the reduced Mn2and the

oxidized Mn4. The aqueous chemistry of manganese is similar

to that of iron. Since groundwater is often anoxic, any soluble

manganese in groundwater is usually in the reduced state

(Mn2). Upon exposure to air or other oxidants, groundwater

containing manganese usually will precipitate black MnO2. Elevated manganese levels therefore can cause stains in plumbing/

laundry, and cooking utensils. It is considered an essential trace

element for plants and animals. The United Nations Food and

Agriculture Organization recommended maximum level for

manganese in irrigation waters is 0.2 mg/L. The U.S. EPA

secondary drinking water standard MCL is 50 g/L.

2. Selection of Method

The atomic absorption spectrometric methods (3111B and C),

the electrothermal atomic absorption method (3113B), and the

inductively coupled plasma methods (3120 and 3125) permit

direct determination with acceptable sensitivity and are the

methods of choice. Of the various colorimetric methods, the

persulfate method (B) is preferred because the use of mercuric

ion can control interference from a limited chloride ion concentration.

3. Sampling and Storage

Manganese may exist in a soluble form in a neutral water

when first collected, but it oxidizes to a higher oxidation state

and precipitates or becomes adsorbed on the container walls.

Determine manganese very soon after sample collection. When

delay is unavoidable, total manganese can be determined if the

sample is acidified at the time of collection with HNO3 to pH

2. See Section 3010B.

3500-Mn B. Persulfate Method

1. General Discussion

a. Principle: Persulfate oxidation of soluble manganous compounds to form permanganate is carried out in the presence of

silver nitrate. The resulting color is stable for at least 24 h if

excess persulfate is present and organic matter is absent.

b. Interference: As much as 0.1 g chloride (Cl) in a 50-mL

sample can be prevented from interfering by adding 1 g mercuric

sulfate (HgSO4) to form slightly dissociated complexes. Bromide and iodide still will interfere and only trace amounts may

be present. The persulfate procedure can be used for potable

water with trace to small amounts of organic matter if the period

of heating is increased after more persulfate has been added.

For wastewaters containing organic matter, use preliminary

digestion with nitric and sulfuric acids (HNO3 and H2SO4) (see

Section 3030G). If large amounts of Cl also are present, boiling

with HNO3 helps remove it. Interfering traces of Cl are eliminated by HgSO4 in the special reagent.

Colored solutions from other inorganic ions are compensated

for in the final colorimetric step.

Samples that have been exposed to air may give low results

due to precipitation of manganese dioxide (MnO2). Add 1 drop

30% hydrogen peroxide (H2O2) to the sample, after adding the

special reagent, to redissolve precipitated manganese.

c. Minimum detectable concentration: The molar absorptivity

of permanganate ion is about 2300 L g1 cm1

. This corresponds to a minimum detectable concentration (98% transmittance) of 210 g Mn/L when a 1-cm cell is used or 42 g Mn/L

when a 5-cm cell is used.

d. Quality control (QC): The QC practices considered to be

an integral part of each method can be found in Section 3020.

2. Apparatus

Colorimetric equipment: One of the following is required:

a. Spectrophotometer, for use at 525 nm, providing a light

path of 1 cm or longer.

b. Filter photometer, providing a light path of 1 cm or longer

and equipped with a green filter having maximum transmittance

near 525 nm.

c. Nessler tubes, matched, 100-mL, tall form.

* Approved by Standard Methods Committee, 1999. Editorial revisions, 2011.

Joint Task Group: 20th Edition—See 3500-Al.

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3. Reagents

a. Special reagent: Dissolve 75 g HgSO4 in 400 mL conc

HNO3 and 200 mL distilled water. Add 200 mL 85% phosphoric

acid (H3PO4), and 35 mg silver nitrate (AgNO3). Dilute the

cooled solution to 1 L.

b. Ammonium persulfate, (NH4)2S2O8, solid.

c. Standard manganese solution: Prepare a 0.1N potassium

permanganate (KMnO4) solution by dissolving 3.2 g KMnO4 in

distilled water and making up to 1 L. Age for several weeks in

sunlight or heat for several hours near the boiling point, then

filter through a fine fritted-glass filter crucible and standardize

against sodium oxalate as follows:

Weigh several 100- to 200-mg samples of Na2C2O4 to 0.1 mg

and transfer to 400-mL beakers. To each beaker, add 100 mL

distilled water and stir to dissolve. Add 10 mL 1 1 H2SO4 and

heat rapidly to 90 to 95°C. Titrate rapidly with the KMnO4

solution to be standardized, while stirring, to a slight pink

end-point color that persists for at least 1 min. Do not let

temperature fall below 85°C. If necessary, warm beaker contents

during titration; 100 mg Na2C2O4 will consume about 15 mL

permanganate solution. Run a blank on distilled water and

H2SO4.

Normality of KMnO4  g Na2C2O4

(A  B)  0.067 01

where:

A  mL titrant for sample and

B  mL titrant for blank.

Average results of several titrations. Calculate volume of this

solution necessary to prepare 1 L of solution so that 1.00 mL 

50.0 g Mn, as follows:

mL KMnO4  4.55

normality KMnO4

To this volume add 2 to 3 mL conc H2SO4 and NaHSO3

solution dropwise, with stirring, until the permanganate color

disappears. Boil to remove excess SO2, cool, and dilute to 1000

mL with distilled water. Dilute this solution further to measure

small amounts of manganese.

d. Standard manganese solution (alternate): Dissolve 1.000 g

manganese metal (99.8% min.) in 10 mL redistilled HNO3.

Dilute to 1000 mL with 1% (v/v) HCl; 1 mL  1.000 mg Mn.

Dilute 10 mL to 200 mL with distilled water; 1 mL  0.05 mg

Mn. Prepare dilute solution daily.

e. Hydrogen peroxide, H2O2, 30%.

f. Nitric acid, HNO3, conc.

g. Sulfuric acid, H2SO4, conc.

h. Sodium nitrite solution: Dissolve 5.0 g NaNO2 in 95 mL

distilled water.

i. Sodium oxalate, Na2C2O4, primary standard.

j. Sodium bisulfite: Dissolve 10 g NaHSO3 in 100 mL distilled

water.

4. Procedure

a. Treatment of sample: If a digested sample has been prepared

according to directions for reducing organic matter and/or excessive

chlorides in Section 3030G, pipet a portion containing 0.05 to 2.0 mg

Mn into a 250-mL conical flask. Add distilled water, if necessary, to 90

mL and proceed as in ¶ b.

b. To a suitable sample portion add 5 mL special reagent

and 1 drop H2O2. Concentrate to 90 mL by boiling or dilute to

90 mL. Add 1 g (NH4)2S2O8, bring to a boil, and boil for 1

min. Do not heat on a water bath. Remove from heat source,

let stand 1 min, then cool under the tap. (Boiling too long

results in decomposition of excess persulfate and subsequent

loss of permanganate color; cooling too slowly has the same

effect.) Dilute to 100 mL with distilled water free from

reducing substances and mix. Prepare standards containing 0,

5.00,... 1500 g Mn by treating various amounts of standard

Mn solution in the same way.

c. Nessler tube comparison: Use standards prepared as in ¶ 4b

and containing 5 to 100 g Mn/100 mL final volume. Compare

samples and standards visually.

d. Photometric determination: Use a series of standards from

0 to 1500 g Mn/100 mL final volume. Make photometric

measurements against a distilled water blank. The following

table shows light path length appropriate for various amounts of

manganese in 100 mL final volume:

Mn Range

g

Light Path

cm

5–200 15

20–400 5

50–1000 2

100–1500 1

Prepare a calibration curve of manganese concentration vs.

absorbance from the standards and determine Mn in the samples

from the curve. If turbidity or interfering color is present, make

corrections as in ¶ 4e.

e. Correction for turbidity or interfering color: Avoid filtration because of possible retention of some permanganate on the

filter paper. If visual comparison is used, the effect of turbidity

only can be estimated and no correction can be made for interfering colored ions. When photometric measurements are made,

use the following “bleaching” method, which also corrects for

interfering color: As soon as the photometer reading has been

made, add 0.05 mL H2O2 solution directly to the sample in the

optical cell. Mix and, as soon as the permanganate color has

faded completely and no bubbles remain, read again. Deduct

absorbance of bleached solution from initial absorbance to obtain absorbance due to Mn.

5. Calculation

a. When all of the original sample is taken for analysis:

mg Mn/L  g Mn/100 mL

mL sample



100

mL portion

b. When a portion of the digested sample (100 mL final

volume) is taken for analysis:

mg Mn/L  g Mn (in 100 mL final volume)

mL sample

MANGANESE (3500-Mn)/Persulfate Method

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6. Precision and Bias

A synthetic sample containing 120 g Mn/L, 500 g Al/L, 50

g Cd/L, 110 g Cr/L, 470 g Cu/L, 300 g Fe/L, 70 g Pb/L,

150 g Ag/L, and 650 g Zn/L in distilled water was analyzed

in 33 laboratories by the persulfate method, with a relative

standard deviation of 26.3% and a relative error of 0%.

A second synthetic sample, similar in all respects except for 50

g Mn/L and 1000 g Cu/L, was analyzed in 17 laboratories by

the persulfate method, with a relative standard deviation of

50.3% and a relative error of 7.2%.

7. Bibliography

RICHARDS, M.D. 1930. Colorimetric determination of manganese in

biological material. Analyst 55:554.

NYDAHL, F. 1949. Determination of manganese by the persulfate method.

Anal. Chem. Acta. 3:144.

MILLS, S.M. 1950. Elusive manganese. Water Sewage Works 97:92.

SANDELL, E.B. 1959. Colorimetric Determination of Traces of Metals,

3rd ed. Interscience Publishers, New York, N.Y., Chapter 26.

DELFINO, J.J. & G.F. LEE. 1969. Colorimetric determination of manganese in lake waters. Environ. Sci. Technol. 3:761.

MANGANESE (3500-Mn)/Persulfate Method

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