ASTM D511-93(1998)
(Test Method)Standard Test Methods for Calcium and Magnesium In Water
Standard Test Methods for Calcium and Magnesium In Water
SCOPE
1.1 These test methods cover the determination of calcium and magnesium in water by complexometric titration and atomic absorption spectrophotometric procedures. Two test methods are included, as follows: Sections Test Method A -- Complexometric Titration 7 to 14 Test Method B -- Atomic Absorption Spectrophotometric 15 to 23
1.2 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. >Specific hazard statements are given in Notes 2 and 7.
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Designation: D 511 – 93 (Reapproved 1998)
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Methods for
Calcium and Magnesium In Water
This standard is issued under the fixed designation D 511; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 5. Purity of Reagents
1.1 These test methods cover the determination of calcium 5.1 Reagent grade chemicals shall be used in all tests.
and magnesium in water by complexometric titration and Unless otherwise indicated, it is intended that all reagents shall
atomic absorption spectrophotometric procedures. Two test conform to the specifications of the Committee on Analytical
methods are included, as follows: Reagents of the American Chemical Society. Other grades
may be used, provided it is first ascertained that the reagent is
Sections
Test Method A—Complexometric Titration 7 to 14
of sufficiently high purity to permit its use without lessening
Test Method B—Atomic Absorption Spectrophotometric 15 to 23
the accuracy of the determination.
1.2 This standard does not purport to address all of the
5.2 Purity of Water—Unless otherwise indicated, references
safety concerns, if any, associated with its use. It is the to water shall be understood to mean reagent water conforming
responsibility of the user of this standard to establish appro-
to Specification D 1193, Type 1, II, or III water. Type I is
priate safety and health practices and determine the applica- preferred and more commonly used. Type II water was
bility of regulatory limitations prior to use. Specific hazard
specified at the time of round-robin testing of these test
statements are given in Note 2 and Note 7. methods.
NOTE 1—The user must ensure the type of reagent water is sufficiently
2. Referenced Documents
free of interferences. The water should be analyzed using this test method.
2.1 ASTM Standards:
D 1129 Terminology Relating to Water
6. Sampling
D 1193 Specification for Reagent Water
6.1 Collect the sample in accordance with Practices D 3370.
D 2777 Practice for Determination of Precision and Bias of
6.2 If total recoverable calcium and magnesium concentra-
Applicable Methods of Committee D-19 on Water
tions are being determined, acidify the water sample with
D 3370 Practices for Sampling Water from Closed Con-
HNO (sp gr 1.42) to a pH of 2 or less immediately at the time
duits
of collection; normally about 2 mL/L are required. The holding
D 4691 Practice for Measuring Elements in Water by Flame
time for the samples may be calculated in accordance with
Atomic Absorption Spectrophotometry
Practice D 4841.
D 4841 Practice for Estimation of Holding Times for Water
6.3 If dissolved calcium and magnesium concentrations are
Samples Containing Organic and Inorganic Constituents
being determined, filter the samples through a 0.45-μm mem-
brane filter and acidify with HNO (sp gr 1.42) to a pH of 2 or
3. Terminology
less immediately at time of collection; normally about 2 mL/L
3.1 Definitions—For definitions of terms used in these test
are required.
methods, refer to Terminology D 1129.
6.4 A number of sources of calcium contamination have
been encountered in laboratories. Among the most common are
4. Significance and Use
plastic ware, paper towels, and dust. Rinsing plastic ware with
4.1 Calcium and magnesium salts in water are the primary
sample prior to use, avoiding contact of apparatus with paper
components of water hardness which can cause pipe or tube
towels, and keeping exposure to the air to a minimum will limit
scaling.
the possibility of contamination.
Reagent Chemicals, American Chemical Society Specifications, American
These test methods are under the jurisdiction of ASTM Committee D-19 on
Water and are the direct responsibility of Subcommittee D19.05 on Inorganic Chemical Society, Washington, DC. For suggestions on the testing of reagents not
Constituents in Water. listed by the American Chemical Society, see Analar Standards for Laboratory
Current edition approved April 15, 1993. Published June 1993. Originally Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
published as D 511 – 37. Last previous edition D 511 – 92. and National Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville,
Annual Book of ASTM Standards, Vol 11.01. MD.
NOTICE:¬This¬standard¬has¬either¬been¬superceded¬and¬replaced¬by¬a¬new¬version¬or¬discontinued.¬
Contact¬ASTM¬International¬(www.astm.org)¬for¬the¬latest¬information.¬
D511
TEST METHOD A—COMPLEXOMETRIC Orthophosphate will precipitate calcium at the pH of the test.
TITRATION 9.4 A possible interference from the commonly used poly-
phosphates, organic phosphonates, and EDTA/NTA com-
7. Scope
pounds in water treatment should be recognized.
7.1 This test method is applicable to most waters in a range
10. Apparatus
from 1 to 1000 mg/L of calcium plus magnesium expressed as
calcium, but may fail in the analysis of highly colored waters,
10.1 Titration Assembly—Some analysts prefer to use con-
brines, or waters that contain excessive amounts of metals. The
ventional lighting and hand stirring. Others report better results
upper and lower limits may be extended by either dilution or
by using a visual-titration assembly consisting of a motor-
use of micro apparatus.
driven stirrer, 25-mL buret, white-porcelain-base buret holder,
7.2 Data are not available to determine which matrices were
and shaded incandescent lamp. The sample beaker is placed
used to obtain the precision and bias data, and it is the
near the front of the porcelain base and the reaction is viewed
responsibility of the analyst to determine the acceptability of
diagonally downward through the side of the beaker and
this test method for the matrix being analyzed.
against the white background. Illumination is from behind the
beaker. The capacity of the buret, type lighting, and back-
8. Summary of Test Method
ground color may be varied depending on the ionic concentra-
8.1 EDTA (ethylenediamine tetraacetic acid or its salts) is
tions normally encountered and the indicator chosen.
added to a sample containing calcium and magnesium ions
11. Reagents
after the pH of the solution is adjusted to 10 for the determi-
nation of calcium and magnesium or from pH 12 to 13 for the
11.1 Buffer Solution, Ammonium Chloride-Ammonium
determination of calcium alone. The EDTA initially complexes
Hydroxide—Dissolve 67.6 g of ammonium chloride (NH Cl)
the calcium and then the magnesium. The end point is observed
in 200 mL of water. Add 570 mL of concentrated ammonium
by the use of a suitable indicator. At a pH of 12 to 13
hydroxide (NH OH, sp gr 0.900). Add 5.00 g of magnesium
magnesium is precipitated. Magnesium is determined by the
salt of EDTA and dilute to 1000 mL. Store in a tightly
difference between an aliquot titrated at pH 10 and one titrated
stoppered plastic bottle to prevent the loss of ammonia.
at pH 12 to 13.
Discard the solution when 1 mL added to a neutralized sample
fails to produce a pH of 10.0 6 0.1 at the titration end point.
9. Interferences
To attain highest accuracy, adjust the magnesium level to exact
9.1 EDTA reacts with iron, manganese, copper, zinc, lead,
equivalence through the appropriate addition of a small amount
cobalt, nickel, barium, strontium, calcium, magnesium, and
of either disodium EDTA or magnesium sulfate (MgSO ).
several other metals. The interference of heavy metals is
11.2 Calcium Indicator Solution:
minimized by the addition of hydroxylamine and cyanide,
11.2.1 Ammonium Purpurate—Mix thoroughly 1.0 g of
which reduce or complex the metals, or both. Metal concen-
ammonium purpurate with 200 g of sucrose. Place in a bottle
trations as high as 5 mg/L of iron, 10 mg/L of manganese, 10
provided with a dispensing spoon of 0.2-g capacity.
mg/L of copper, 10 mg/L of zinc, and 10 mg/L of lead can be
11.2.2 Fluorescein Methylene Iminodiacetic Acid —Grind
tolerated when hydroxylamine and cyanide are added.
0.2 g of fluorescein methylene iminodiacetic acid and 0.12 g of
9.2 In the titration of calcium plus magnesium, the higher
thymolphthalein with 20 g of potassium chloride to 40 to 50
+2
oxidation states of manganese above Mn react rapidly with
mesh size. Place in a bottle provided with a dispensing spoon
the indicator to form discolored oxidation products. Hydroxy-
of 0.2-g capacity.
lamine hydrochloride reagent is used to reduce manganese to
11.3 Calcium Solution, Standard (1.00 mL 5 0.400 mg
the divalent state. The divalent manganese interference can be
calcium)—Suspend 1.000 g of calcium carbonate (CaCO ),
eliminated by addition of one or two small crystals of potas-
dried at 180°C for 1.0 h before weighing, in approximately 600
sium ferrocyanide.
mL of water and dissolve cautiously with a minimum of dilute
9.2.1 Orthophosphate and sulfate ions interfere at concen-
HCl. Dilute to 1000 mL with water in a volumetric flask.
trations in excess of 500 and 10 000 mg/L, respectively.
11.4 Chrome Black T Solution (4.0 g/L)—Dissolve 0.4 g of
9.2.2 In the presence of aluminum concentrations in excess
Chrome Black T in 100 mL of water. This solution has a shelf
of 10 mg/L, the blue color that indicates that the end point has
life of approximately 1 week. Alternatively, a dry powder
been reached will appear and then, on short standing, will
mixture composed of 0.5 g of dye and 100 g of powdered
revert to red. The reversion should not be confused with the
sodium chloride may be used. Store this in a dark-colored
gradual change that normally takes place in the titrated sample
bottle provided with a dispensing spoon of approximately 0.2-g
several minutes after the titration has been completed.
capacity. The shelf life is at least 1 year.
9.3 In the titration of calcium, ammonium purpurate reacts
11.5 EDTA Solution, Standard (0.01 M,1mL 5 0.401 mg
with strontium but not with magnesium or barium. However,
calcium or 0.243 mg manganese)—Dissolve 3.72 g of
the end point in the presence of strontium is sluggish, and the
Na EDTA dihydrate, which has been dried overnight over
titration is not strictly stoichiometric. Barium does not titrate as
H SO in a desiccator, in water and dilute to 1000 mL in a
2 4
calcium, but affects the indicator in some unknown way so that
no end point, or at best a poor end point, is obtained. Barium
can be removed by prior precipitation with sulfuric acid, but
Calcein, W., Fluoroscein Complexon, and Fluorexon, supplied by various
care must be exercised to prevent precipitation of calcium. commercial firms, have been found satisfactory for this purpose.
NOTICE:¬This¬standard¬has¬either¬been¬superceded¬and¬replaced¬by¬a¬new¬version¬or¬discontinued.¬
Contact¬ASTM¬International¬(www.astm.org)¬for¬the¬latest¬information.¬
D511
volumetric flask. The reagent is stable for several weeks. 12.1.12 Titrate with standard EDTA solution until blue or
Check the titer of the reagent by titrating 25.00 mL of CaCO purple swirls begin to show. The end point is reached when all
standard solution as described in the procedure for sample traces of red and purple have disappeared and the solution is
analysis. clear blue in color. The titration should be completed within 5
11.6 Hydroxylamine Hydrochloride Solution (30 g/L)— min of the buffer addition. If more than 15 mL of titrant is
Dissolve 30 g of hydroxylamine hydrochloride (NH OH·HCl) required, take a smaller sample aliquot and repeat the test.
in water and dilute to 1000 mL.
12.1.13 Record the volume of EDTA solution required to
11.7 Potassium Ferrocyanide—(K Fe(CN) ·3H O). titrate calcium plus magnesium.
4 6 2
11.8 Sodium Cyanide Solution (25 g/L)—Dissolve 25 g of
12.1.14 Determine a reagent blank correction by similarly
sodium cyanide (NaCN) in water and dilute to 1000 mL.
titrating 50 mL of water including all added reagents.
12.2 Calcium:
NOTE 2—Warning: Sodium cyanide is a deadly poison. Do not add
12.2.1 Refill the buret with EDTA standard solution.
NaCN to any acid solution or acidify any solution containing it. Use this
reagent in a fume hood.
12.2.2 Pipet another aliquot of the same sample (50.00 mL
maximum) into a 150-mL beaker and adjust the volume to
11.9 Sodium Hydroxide Solution (80 g/L)—Dissolve 80 g of
approximately 50 mL (see Note 5).
sodium hydroxide (NaOH) in 800 mL of water. Cool and dilute
12.2.3 Insert the beaker in the titration assembly and start
to 1000 mL.
the stirrer.
12. Procedure
12.2.4 Add 1 mL of NH OH·HCl.
12.1 Calcium Plus Magnesium:
12.2.5 Add 1 mL of NaOH solution. The pH should range
12.1.1 Measure 100.0 mL of a well-mixed acidified sample
from 12 to 13.
into a 125-mL beaker or flask.
12.2.6 Add 1 mL of NaCN (Warning, see Note 2).
12.2.7 Add 0.2 g of calcium indicator solution and proceed
NOTE 3—If only dissolved calcium plus magnesium is to be deter-
immediately with the titration.
mined, omit 12.1.1 and proceed to 12.1.5.
12.2.8 Titrate with standard EDTA solution to the appropri-
12.1.2 Add 5 mL of hydrochloric acid (HCl, sp gr 1.19) to
ate end point. If ammonium purpurate is used, the end point
each sample.
will be indicated by color change from salmon pink to orchid
12.1.3 Heat the samples on a steambath or hot plate until the
purple. If fluorescein methylene iminodiacetic acid is used, the
volume has been reduced to 15 to 20 mL, making certain that
end point will be indicated by a color change from deep green
the samples do not boil.
to purple. The titration should be completed within 5 min of the
NOTE 4—For samples with high levels of dissolved or suspended
addition of NaOH solution. If more than 15 mL of titrant is
matter, the amount of reduction in volume is left to the discretion of the
required, take a smaller sample aliquot and repeat the test.
analyst.
12.2.9 Record the volume of EDTA solution required to
12.1.4 Cool and filter the samples through a suitable filter
titrate the calcium.
(such as fine-textured, acid-washed, ashless paper) into
12.2.10 Determine a reagent blank correction by similarly
100-mL volumetric flasks. Wash the paper 2 or 3 times with
titrating 50 mL of water including all added reagents.
water and bring to the volume.
12.1.5 Pipet the filtered sample (50.00-mL maximum) into a
13. Calculation
150-mL beaker and adjust the volume to approximately 50 mL.
13.1 Calculate the concentration of calcium and magn
...
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