Provisional Method for Carbonate, Dissolved; Bicarbonate, Dissolved; and Carbonate Alkalinity, Dissolved; Electrometric Tritration,
Incremental, Field

In Reply Refer To:                       December 11, 1981
EGS-Mail Stop 412


Subject: WATER QUALITY--Provisional Method for Carbonate, 
         Dissolved; Bicarbonate, Dissolved; and Carbonate 
         Alkalinity, Dissolved; Electrometric Tritration, 
         Incremental, Field

Attached is a description of the incremental field tritration 
for carbonate, bicarbonate, and carbonate alkalinity, which 
is similar to the method described by Barnes in U.S. 
Geological Survey Water-Supply Paper 1535-H (1964). The 
method of Barnes was referred to in Quality of Water Branch 
Technical Memorandums 80.27 and 81.04 as the only acceptable 
method for determination of the carbonate species.

This method is provisional and will remain so until the 
precisions of the determinations in the field have been 
established. We would urge the users of this method to assist 
in the determination of the field precision in the following 
manner. At an appropriate sampling site when the streamflow 
is stable, collect six replicate samples and determine the 
carbonate, bicarbonate, and carbonate alkalinity in each by 
this method. Report the original data plus any statistical 
analyses you may choose to make to this office. We would also 
appreciate any comments, discussions of difficulties, or 
suggestions for any improvements that might be made to the 
method description.

After further review and incorportation of any comments, the 
method will be published in the forthcoming Field Methods 

                   R. J. Pickering
                   Chief, Quality of Water Branch


This memorandum supplements Quality of Water Branch Technical 
Memorandums 80.27 and 81.04

Key words: water quality, analytical methods, carbonate, 
           bicarbonate, carbonate alkalinity

WRD Distribution: A, B, S, FO, PO

                    PROVISIONAL METHOD

Carbonate, Dissolved; Bicarbonate Dissolved;
Carbonate Alkalinity, Dissolved; Electrometric Titration,
Incremental, Field

Parameters and Codes: Carbonate, dissolved (mg/L as C03): 
                      Bicarbonate, dissolved (mg/L as HC03):
                      Carbonate Alkalinity, dissolved 
                        (mg/L as CaC03): 99430

1. Application

1.1  This procedure is applicable to surface and ground 
waters, either filtered or unfiltered, although an unfiltered 
sample is preferred (see Sections 3.4 and 3.5).

1.2  Accurate values for pH, and carbonate and bicarbonate 
ion concentrations in an aqueous solution are essential in 
studies involving carbonate chemistry and equilibrium 
calculations. These parameters are especially subject to 
rapid changes in water samples owing to loss of dissolved 
gases. Determinations by this procedure are to be made in the 
field to minimize exchange of carbon dioxide gas between the 
sample and its surroundings.

2. Summary of Method

Although method I-1030-78 (Skougstad and others, 1979), a 
fixed-pH endpoint (pH 4.5) titration, is commonly used to 
determine alkalinity, accurate determination of alkalinity 
due to carbonate species, as well as determination of the 
concentrations of those species, can be made by constructing 
a titration curve from measurements of pH versus volume of 
strong acid titrant added to the sample in small increments. 
The endpoints for titration of successive proton absorbing 
species are taken as the inflection points of the titration 
curve, or as the maximum rates of change of pH per volume of 
titrant added (see fig. 1).

A detailed description of the theory of potentiometric 
titration of carbonate and bicarbonate, sampling procedures, 
and the occurrence of alkalinity, are given in Barnes (1964), 
Wood (1976), and Hem (1970).

3. Interferences

3.1  Any ionized substance that reacts with a strong acid can 
contribute to alkalinity if the reaction occurs at a pH above 
that of the specified endpoint; examples are salts of weak 
organic and inorganic acids. The weak inorganic bases 
SiO(OH)3, H2B04, NH3 and Al(OH)2(H20)4+ will accept a 
hydrogen ion in the titration to the first endpoint near pH 
8.3. The weak inorganic bases H2P04 and Al(OH)(H20)5 as well 
as most of the weak organic bases found in natural waters 
will accept a hydrogen ion in the titration between the first 
endpoint and the second endpoint near pH 4.5. Corrections for 
these interferences may be required.

3.2  The hydroxide ion (OH-) will contribute significant 
alkalinity when the initial sample pH exceeds 11.0 units. In 
this case, a correction for the OH- ion should be applied to 
the calculation of carbonate.

3.3  All surface waters carry particulate matter ranging in 
concentrations from several lO's of milligrams per liter to 
several lOO's of grams per liter. Compostion varies from 
mainly organic to mainly inorganic rock fragments and is 
largely controlled by the geologic terrain traversed by the 
stream. Particulates can take up some strong acid by 
dissolution, adsorption, or ion exchange and, thereby, cause 
anomalously high measurements. For this reason, filtration 
through a 0.45 micron pressure-type stainless steel barrel 
filter using an inert gas such as nitrogen or argon for 
pressure may be needed for some samples. Experience indicates 
that small amounts of particulate matter do not interfere 
appreciably. The effect of particulate matter should be 
determined by comparing shapes of and analytical values 
obtained from titration curves determined on filtered versus 
unfiltered samples.

3.4  Ground water obtained from wells usually has much less 
particulate matter than surface water but may contain 
sufficient particulate matter to justify filtration. For 
discussion of ground-water sample filtration see Wood (1976). 
An in-line filter that permits exclusion of the atmosphere 
during filtration is recommended.

3.5  Wind-borne dust can be a source of contamination of the 
sample and direct sunlight can warm the sample appreciably, 
causing loss of carbon dioxide. Every precaution should be 
taken to minimize these effects. The field procedure is best 
performed in an enclosed van-type vehicle containing all the 
reagents and equipment required for on-site determination of 
unstable constituents.

4. Apparatus

4.1  Beakers, 150 mL capacity, glass or disposable plastic.

4.2  Bottle, 500 mL capacity, plastic squeeze, for rinsing 
with distilled or deionized water.

4.3  Buret, 25-mL capacity with 0.1 mL graduations. A lO-mL 
semi-micro buret with .02 graduations may be used for samples 
containing less than 200 mg/L of carbonate and bicarbonate.

4.4  Buret stand and holder.

4.5  pH electrode, combination; Orion 91-62 or equivalent and 
filling solution.

4.6  pH meter, battery operated, with expanded scale or scale 
length of at least 15 cm for detailed work of +0.02 pH units.

4.7  Pipets, class A volumetric, 50 mL, or other appropriate 

4.8  Stirrer, portable magnetic with small teflon coated 
stirring bar. If this is not available, hand stirring with 
glass stirring rod or with hand-held battery-powered cocktail 
stirrer with glass stirring rod will suffice.

4.9  Thermometer, 0! to 50!C, graduated in 0.1!C.

5. Reagents

5.1  pH buffer solutions, pH 4, 7 and 10 accurate to +.02 
units and changes with temperature specified.

5.2  Sodium carbonate standard solution, 0.01639N: 1.00 mL = 
1.00 mg HC03: Dry 1.0 g primary standard Na2C03 at 150!C to 
160!C for 2 h. Cool in a desiccator. Dissolve 0.8685 g in 
carbon dioxide-free water prepared by boiling for 15 minutes 
and cooling without agitation; dilute to 1,000 mL in a 
volumetric flask.

5.3  Sulfuric acid standard solution, 0.01639N: 1.00 mL = 
1.00 mg HC03: Cautiously add 0.5 mL concentrated H2S04 (sp gr 
1.84) to 950 mL water. After the solution has been thoroughly 
mixed, standardize by titrating 25.00 mL Na2C03 standard 
solution to pH 4.5. Adjust the concentration of the sulfuric 
acid standard solution to exactly 0.01639N by dilution with 
water or by addition of dilute acid as indicated by the first 
titration. Confirm the exact normality by restandardization. 
Keep the solution in a sealed glass bottle or volumetric 
flask until used. Although the sulfuric acid standard 
solution is reasonably stable if protected from ammonia 
fumes, the normality should be verified at least monthly 
(NOTE 1).

NOTE 1. It may be found more convenient to prepare standard 
sulfuric acid that is not exactly 0.01639N but the exact 
normality of which is known. Such standards may be used if 
the appropriate factor is applied in the calculations.

6. Procedure

6.1  Standardize the pH meter as described in method 
I-1586-78 (Skougstad and others, 1979).

6.2  Rinse electrode thoroughly (at least 3 times) with 
sample water, and adjust temperature of titrant to +2!C of 
the sample temperature.

6.3  Measure and record pH value of a freshly-collected 
representative sample.

6.4  Pipet an appropriate volume of sample (usually not more 
than 50 mL) into a clean dry 150 mL beaker and insert pH 
probe and teflon stirring bar. (See section 3.4 and 3.5 for 
guidelines on need for prior filtration).

6.5  If pH is greater than 8.3, add sulfuric acid standard 
solution dropwise and carefully record the volume delivered 
in 0.02 mL increments (0.05 increments with a 25-mL burette) 
and record the pH after each addition until pH is below 8.0. 
Stir gently with magnetic stirrer or other appropriate 
stirring device while adding titrant and making readings. 
Allow 15-20 seconds for equilibration after each acid 

6.6  If initial pH is less than 8.3, skip step 6.5 and go 
directly to step 6.7

6.7  Titrate rapidly to pH 5.0 and record the volume of 
titrant at pH 5.0 to the nearest 0.02 mL (0.05 mL on 25-mL 
buret). Allow 15-20 seconds for equilibration.

6.8  From pH 5.0 to 4.0, add acid dropwise in 0.02 mL 
increments and record the pH after each addition, allowing 
15-20 seconds for pH equilibration after each. The most 
sensitive part of the titration curve is usually between 
pH 4.8 and 4.3.

7. Calculations

7.1  The true endpoints are determined by either 7.lA or 

7.lA  Construct a titration curve plotting the volume of the 
titrant (sulfuric acid standard solution) added against pH. 
The endpoints are the inflection points of the curve, the 
points at which the pH changes are greatest for a given 
amount of titrant (see fig. 1).

7.lB  Plot the rate of change of pH with change in titrant 

           _ pH
      _ mL of titrant

against the total volume of titrant. The endpoints are the 
volumes of titrant delivered at which there occur maximum 
rates of change of pH per volume of titrant added (see 
fig. 1).

7.2  Calculate carbonate

C03 (mg/L) = 1000    x [mLa at ep near pH 8.3] x .9835
(See NOTE 2).

7.3  Calculate bicarbonate

HC03 (mg/L) =  1000    x [(mLa at ep near pH 4.5) 
                mLs   -2(mLa at ep near pH 8.3)] x 1.0
(See NOTE 2).

where mLs = volume of sample in mL mLa = volume of titrant 
(surfuric acid standard solution) added in mL ep = endpoint 
determined by 7.lA or 7.lB

NOTE 2: If the sulfuric acid standard solution has normality 
different from 0.01639N, compute new multiplying factors as 

For C03 Factor = 0.9835 x Acid Normality 

For HC03 Factor = 1.00 x Acid Normality 

7.4  Calculate carbonate alkalinity

Carbonate Alkalinity (mg/L as CaC03) = 

8. Report

Report carbonate (99445), bicarbonate (99440), and carbonate 
alkalinity (99430) as follows: less than 1000 mg/L, whole 
numbers: 1000 mg/L and above, three significant figures.

9. Precision 

The precision of this method in the field has not been 


Barnes, Ivan. 1964. Field measurement of alkalinity and pH. 
U.S. Geological Survey Water-Supply Paper 1535-H, p. 17.

Hem, John D. 1970. Study and interpretation of the chemical 
characteristics of natural water. U.S. Geological Survey 
Water-Supply Paper 1473, second edition, p. 363.

Skougstad, M., Fishman M., Friedman, L.C., Erdman, D.E. and 
Durran, S.S. (editors) 1979. Methods for determination of 
inorganic substances in water and fluvial sediments. 
Techniques of Water-Resources Investigations of the United 
States Geological Survey, book 5, chapter Al, p. 626.

Wood, Warren W. 1976. Guidelines for collection and field 
analysis of groundwater samples for selected unstable 
constituents. Techniques of WaterResources Investigations of 
the United States Geological Survey, Book 1, chapter D2, 
p. 24.