ASTM D5015-95
(Test Method)Standard Test Method for pH of Atmospheric Wet Deposition Samples by Electrometric Determination
Standard Test Method for pH of Atmospheric Wet Deposition Samples by Electrometric Determination
SCOPE
1.1 This test method is applicable to the determination of pH in atmospheric wet deposition samples by electrometric measurement using either a pH half cell with a reference probe or a combination electrode as the sensor.
1.2 This standard does not purport to address all of the safety concerns, 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.
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Designation: D 5015 – 95
Standard Test Method for
pH of Atmospheric Wet Deposition Samples by
Electrometric Determination
This standard is issued under the fixed designation D 5015; 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.
1. Scope 4. Summary of Test Method
1.1 This test method is applicable to the determination of 4.1 The pH meter and the associated electrodes are cali-
pH in atmospheric wet deposition samples by electrometric brated with two reference buffer solutions that bracket the
measurement using either a pH half cell with a reference probe anticipated sample pH. The pH of the wet deposition sample is
or a combination electrode as the sensor. determined from this calibration and a quality control standard.
1.2 This standard does not purport to address all of the The quality control standard is necessary in this application to
safety concerns, if any, associated with its use. It is the evaluate the bias due to residual liquid junction potentials and
responsibility of the user of this standard to establish appro- to correct for this bias.
priate safety and health practices and determine the applica- 4.2 The pH of a solution is related to the EMF (millivolts)
bility of regulatory limitations prior to use. of a pH electrode system according to the operational definition
for a two-point calibration:
2. Referenced Documents
E 2 E
X S
pH X 5 pH S 1 pH S 2 pH S (1)
2.1 ASTM Standards: ~ ! ~ ! @ ~ ! ~ !#
1 2 1
E 2 E
S S
2 1
D 1129 Terminology Relating to Water
D 1193 Specification for Reagent Water
D 2777 Practice for Determination of Precision and Bias of where:
pH(X) = pH of an unknown sample,
Applicable Methods of Committee D-19 on Water
pH (S ) = pH of a Standard Solution 1,
D 5012 Guide for Preparation of Materials Used for the 1
pH (S ) = pH of a Standard Solution 2,
Collection and Preservation of Atmospheric Wet Deposi-
E = EMF (mV) measured in an unknown sample,
X
tion
E = EMF (mV) measured in Standard Solution 1,
S
D 5111 Guide for Choosing Locations and Sampling Meth-
and
ods to Monitor Atmospheric Deposition at Non-Urban
E = EMF (mV) measured in Standard Solution 2.
S
Locations
E 1 Specification for ASTM Thermometers
5. Significance and Use
E 380 Practice for Use of the International System of Units
5.1 The accurate measurement of pH in atmospheric wet
(SI) (the Modernized Metric System)
deposition is an essential and critically important component in
the monitoring of atmospheric wet deposition for trends in the
3. Terminology
acidity and overall air quality. Atmospheric wet deposition is,
3.1 Definitions:
in general, a low ionic strength, unbuffered solution. Special
3.1.1 pH—the negative logarithm to the base ten of the
precautions, as detailed in this test method, are necessary to
conventional hydrogen ion activity.
ensure accurate pH measurements (1). Special emphasis must
3.1.2 For definitions of other terms used in this test method,
be placed on minimizing the effect of the residual liquid
refer to Terminology D 1129. For an explanation of the metric
junction potential bias.
system including units, symbols, and conversion factors, see
5.2 This test method is applicable only to the measurement
Practice E 380.
of pH in atmospheric wet deposition. Its use in other applica-
tions may result in inaccuracies.
This test method is under the jurisdiction of ASTM Committee D-22 on
5.3 Fig. 1 provides a frequency distribution of precipitation
Sampling and Analysis of Atmospheresand is the direct responsibility of Subcom-
pH values measured in conjunction with a national monitoring
mittee D22.06on Atmospheric Deposition.
Current edition approved Jan. 15, 1995. Published March 1995. Originally program within the United States. These data are an indication
published as D 5015 – 89. Last previous edition D 5015 – 89.
Annual Book of ASTM Standards, Vol 11.01.
Annual Book of ASTM Standards, Vol 11.03.
4 6
Annual Book of ASTM Standards, Vol 14.03. The boldface numbers in parentheses refer to the list of references at the end of
Annual Book of ASTM Standards, Vol 14.02. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 5015
6.5.1 Eliminate the errors associated with residual stream-
ing potentials by agitating all calibration standards and wet
deposition samples thoroughly to speed electrode equilibration
and then allowing each aliquot to become quiescent before
taking a pH reading.
6.5.2 If magnetic stirring is used, take care not to contami-
nate the sample when inserting the stirring bar. Maintain an air
space between the surface of the stirring motor and the sample
container to prevent heating the wet deposition sample.
6.6 Laboratories used for the measurements of pH should be
free from gaseous and particulate contaminants that may affect
the true solution pH. Fumes from mineral acids such as
hydrochloric acid, sulfuric acid, and nitric acid should be kept
FIG. 1 Frequency Distribution of Measured Laboratory pH of
isolated from areas where pH measurements are made as well
Atmospheric Wet Deposition From the 1984 National
as alkaline fumes from solutions such as ammonia.
Atmospheric Deposition Program (NADP)/National Trends
Network (NTN)
7. Apparatus and Equipment
of the range of pH values common to atmospheric wet
7.1 Laboratory pH Meter—The meter may have either an
deposition.
analog or digital display with a readability of at least 0.01 pH
units. A meter that has separate calibration and slope adjust-
6. Interferences
ment features and is electrically shielded to avoid interferences
6.1 The pH meter and the associated electrodes reliably
from stray currents or static charge is necessary. It may be
measure pH in nearly all aqueous solutions and in general are
powered by battery or 110 V ac line; if battery powered, the
not subject to solution interferences from color, turbidity,
meter must have a battery check feature. A temperature
oxidants, or reductants.
compensator control for measurements at temperatures other
6.2 The pH of an aqueous solution is affected by the
than 25°C is desirable.
temperature. The electromotive force (EMF) between the glass
7.2 Sensing Electrode—Select a general purpose glass elec-
and the reference electrode is a function of temperature as well
trode that meets the performance criteria described in 12.2.
as pH. Temperature effects can be approximately compensated
This electrode type is characterized by a quick response, and
for automatically or manually depending on the pH meter
has a useful range from 2 to 11 pH units. This electrode should
selected.
be used exclusively for atmospheric wet deposition measure-
6.3 Organic materials dispersed in water appear to poison
ments.
the glass electrode, particularly when analyzing low ionic
7.3 Reference Electrode—The reference electrode recom-
strength solutions. Difficulty encountered when standardizing
mended for wet deposition analysis is one equipped with a
the electrode(s), erratic readings, or slow response times may
ceramic junction with controlled leakage of the internal elec-
be an indication of contamination of the glass bulb or the liquid
trolyte fill solution. The ceramic construction minimizes dif-
junction of the reference electrode. To remove these coatings,
ferences in potential between high ionic strength buffers and
refer to the manual accompanying the probe for the manufac-
low ionic strength samples thus reducing errors from residual
turer’s recommendations.
junction potential (1). Table 1 lists three possibilities for
6.4 When analyzing samples that have low ionic strengths,
suitable reference electrodes that have been found to be
such as wet deposition, an effect known as “residual junction
satisfactory. Other electrodes having similar characteristics are
potential” can lead to errors as large as 0.3 pH units. This error
also suitable. This electrode should be used exclusively for
occurs when the junction potential of the sample differs greatly
atmospheric wet deposition measurements.
from that of the standard. These conditions are frequently met
7.4 Combination Electrode—The combination electrode
in wet deposition analyses when the electrodes are calibrated
combines the indicating and reference elements in a single unit.
with high ionic strength standard reference buffers. In many
A ceramic reference junction is recommended (see 7.3). Since
cases, this error has been reduced by using a reference
sample volume requirements are a consideration when analyz-
electrode with a ceramic junction (2,3).
ing wet deposition samples, combination electrodes are more
6.5 To speed electrode equilibration, the sample should be
convenient than separate glass and reference electrodes. This
agitated prior to measurement. Care must be taken, however, to
electrode should be used exclusively for atmospheric wet
avoid introducing a source of error known as “residual stream-
ing potential’’ that can result in a significant difference
TABLE 1 Suitable pH Reference Electrodes for the Analysis of
between the stirred and unstirred pH of the sample (4). The
Wet Deposition Samples
magnitude of the streaming potential is dependent on the
Model
electrodes and on the stirring rate. Differences in pH for stirred
Manufacturer Electrode Type
Number
and unstirred wet deposition samples when the electrode
Beckman 39417 glass bodied with ceramic junction (calomel)
assembly has been calibrated only with quiescent reference
Corning 476109 glass bodied with ceramic junction (calomel)
standards average 0.05 pH units at a stirring rate of four
Orion (Ross) 800500 glass bodied reference half cell with ceramic junction
revolutions per second.
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 5015
deposition measurements and must meet the criteria stated in and Technology (NIST) number. Store the reference buffer
12.2 . solutions in polyethylene or chemical-resistant glass bottles
and replace after one year or sooner if a visible change such as
the development of colloidal or particulate materials is ob-
TABLE 2 National Institute of Standards and Technology (NIST)
Salts for Reference Buffer Solutions
served. Follow the directions on the Certificate of Analysis for
preparing solutions of known pH (5).
NIST Standard
A
Buffer Salt pH at 25°C
Sample Designation
8.4 Quality Control Sample (QCS) —Quality control
186-Ie potassium dihydrogen phosphate, 0.025 M 6.865
samples of verified pH in an atmospheric wet deposition matrix
186-IIe disodium hydrogen phosphate, 0.025 M
are to be used. Internally formulated quality control samples
185g potassium hydrogen phthalate 4.003
(see 8.4.1) may be prepared by dilutions of strong acids with
A
These buffer salts can be purchased from the Office of Standard Reference
water. The pH of such samples must be verified by comparison
Materials, National Institute of Standards and Technology, Gaithersburg, MD
20899. with SRM 2694a or other NIST traceable low-ionic strength
solutions of known pH.
−5
8.4.1 Dilute Nitric Acid (5.0 3 10 mol/L HNO )—Add
7.5 Temperature Control—Use either a constant tempera- 3
1.0 mL of concentrated nitric acid (HNO , sp gr 1.42) to 0.5 L
ture water bath, a temperature compensator, or a thermometer 3
water, dilute to 1 L and mix well. Dilute 3.2 mL of this stock
(see Specification E 1) to verify that all standards and samples
solution to 1 L with water. The resulting solution has a pH of
are maintained at temperatures within 6 1°C of one another. If
4.306 0.10 at 25°C. Store at room temperature in a high-
a thermometer is used, select one capable of being read to the
density polyethylene or polypropylene container. Various fac-
nearest 1°C and covering the range from 0 to 40°C.
tors may affect the stability of this solution. Verify the pH of
7.6 Stirring Device (Optional)—Electric or water-driven. If
this solution with a NIST traceable standard at monthly
an electric stirrer is selected, leave an air gap or place an
intervals.
insulating pad between the stirrer surface and the solution
container to minimize heating of the sample. Use a
9. Safety Hazards
fluorocarbon-coated stirring bar.
9.1 The reference buffer solutions, sample types, and most
7.7 Storage of Electrodes—When not in use, soak the
reagents used in this test method pose no hazard to the analyst
electrodes in a solution that is 0.1 mol/L of potassium chloride
as used in this test method. Use a fume hood, protective
and 0.1 mmol/L of hydrochloric acid. Do not store the
clothing, and safety glasses when handling concentrated nitric
electrodes in buffers, concentrated acids, concentrated potas-
acid.
sium chloride, basic solutions, or distilled water. Some manu-
9.2 Follow American Chemical Society guidelines regard-
facturers recommend dry storage for specific types of elec-
ing the safe handling of chemicals used in this test method (6).
trodes. If the electrode is of this specific type, store dry. Use
these electrodes exclusively for atmospheric wet deposition
10. Sample Collection, Preservation, and Storage
measurements.
10.1 Collect samples in high-density polyethylene (HDPE)
8. Reagents and Materials
containers that have been thoroughly rinsed with water. Do not
use strong mineral acids or alkaline detergent solutions for
8.1 Purity of Reagents—Use reagent or higher grade chemi-
cleaning collection vessels. Residual acids may remain in the
cals for all solutions. All reagents shall conform minimally to
polyethylene matrix and slowly leach back into the sample.
the specifications of the Committee on Analytical Reagents of
Alkaline detergents may also leave residues that may affect the
the American Chemical Society (ACS) where such specifica-
sample chemistry. Cap collection containers after cleaning to
tions are available.
prevent contamination from airborne contaminants; air dry
8.2 Purity of Water—Use water conforming to Specification
collection containers in a laminar flow clean air work station
D 1193, Type II. Point of use 0.2 μm filters are recommended
and wrap in polyethylene bags prior to use. If a laminar flow
for all faucets supplying ASTM Type II water to prevent the
work station is not available, pour out any resi
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