ASTM D8294-21

Standard Practice for Estimating pH to Verify Status of Aqueous Samples

SIGNIFICANCE AND USE
5.1 This practice is intended for use by samplers, technicians, or analysts to verify that samples are preserved or at the proper pH specified in analytical procedures.  
5.2 The pH is indicated within about 1 pH unit for wide-range paper and within 0.5 pH units for narrow-range paper.  
5.3 Unless stated otherwise in the test method, a wide-range paper estimating pH within 1 unit is suitable.  
5.4 A narrow-range pH paperstrip may be used for test methods with tighter pH requirements; however, accuracy better than ±0.5 pH units of the estimate should not be implied.  
5.5 Rapid pH tests allow users to make spot determinations directly without auxiliary equipment.
SCOPE
1.1 This practice provides information on verifying the pH of aqueous samples before analysis. This practice is not intended to be used for non-aqueous samples like oil or grease.  
1.2 This practice may also be used in adjusting pH of samples during various analytical steps.  
1.3 Wide-range pH papers/strips are used for a rapid indication of pH to within about 1 pH unit, and narrow-range pH papers/strips are used to indicate pH within about 0.5 pH units.  
1.4 In some instances, a universal liquid indicator may be used.  
1.5 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.6 This practice offers a set of instructions for performing one or more specific operations. This document cannot replace education or experience and should be used in conjunction with professional judgment. Not all aspects of this practice may be applicable in all circumstances. This ASTM International standard is not intended to represent or replace the standard of care by which the adequacy of a given professional service must be judged, nor should this document be applied without consideration of a project’s many unique aspects. The word “Standard” in the title means only that the document has been approved through the ASTM consensus process.  
1.7 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Sep-2021
• ICS: 13.060.01 - Water quality in general
• Technical Committee: D19 - Water
• Drafting Committee: D19.05 - Inorganic Constituents in Water

Relations

• Refers: ASTM D1293-12 - Standard Test Methods for pH of Water
• Effective Date: 01-Jan-2012
• Refers: ASTM D1293-99(2005) - Standard Test Methods for pH of Water
• Effective Date: 01-Jan-2005
• Refers: ASTM D1293-99 - Standard Test Methods for pH of Water
• Effective Date: 10-Dec-1999

Overview

ASTM D8294-21: Standard Practice for Estimating pH to Verify Status of Aqueous Samples is a key ASTM International standard that provides guidelines for verifying the pH of water-based samples before analytical testing. Designed for use by samplers, technicians, and analysts, this practice helps confirm that samples are appropriately preserved or conditioned to the required pH specified in laboratory procedures. It plays an essential role in water testing, environmental monitoring, and laboratory quality control where rapid and accurate pH verification is crucial.

Key Topics

• Scope of Practice: The standard is applicable to aqueous samples only, excluding substances such as oil or grease. It is used for both rapid verification before analysis and for pH adjustment during analytical procedures.

• pH Estimation Methods:

  • Wide-range pH papers/strips: Indicate pH within ±1 unit, suitable for most routine screening where strict accuracy is not mandatory.
  • Narrow-range pH papers/strips: Indicate pH within ±0.5 units, recommended when procedures require tighter pH controls.
  • Universal pH indicator solutions: Can also be used, especially when sample clarity allows visual comparison.

• Precision and Suitability:

  • Wide-range papers are generally precise to ±1 pH unit.
  • Narrow-range papers offer ±0.5 pH unit precision.
  • Spot checks using indicator papers/strips allow for rapid determinations without additional equipment.

• Quality Control: Guidance is given for proper training using buffer solutions, regular verification of products, and storage recommendations to maintain accuracy.

• Limitations and Safety: Not suitable for very weakly buffered or non-aqueous solutions, samples that mask color, or in circumstances requiring higher precision. Users are responsible for safety protocols and regulatory compliance.

Applications

The practice outlined in ASTM D8294-21 is widely used in sectors requiring fast, reliable pH verification of aqueous (water-based) samples, including:

• Drinking Water Testing: Ensuring compliance with preservation requirements prior to chemical or microbiological analysis.
• Environmental Monitoring: Rapid field verification of surface water, groundwater, and wastewater pH during collection or on-site assessments.
• Laboratory Sample Handling: Checking or adjusting pH during various stages of analytical procedures, especially for tests sensitive to pH fluctuations.
• Industrial Water Quality Control: Spot-checking cooling water, process water, or effluents to maintain regulatory and operational standards.
• Academic and Research Laboratories: Convenient for screening analyses, method development, or student training in water analysis.

Related Standards

• ASTM D1293 – Test Methods for pH of Water: Provides standardized procedures for precise pH measurement using pH meters.
• ASTM Water Standards: A broad set of standards by ASTM Committee D19 on Water, which address analytical methods, sampling, and preservation requirements for water and wastewater.
• International Principles: Developed according to the World Trade Organization's technical barriers to trade (TBT) principles, ensuring global applicability.

Keywords: pH verification, aqueous sample, pH paper, pH strips, water testing, sample preservation, laboratory quality control, rapid pH estimate, ASTM D8294-21, environmental monitoring.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D8294 − 21
Standard Practice for
Estimating pH to Verify Status of Aqueous Samples
This standard is issued under the fixed designation D8294; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
1.1 This practice provides information on verifying the pH 2.1 ASTM Standards:
of aqueous samples before analysis. This practice is not D1293 Test Methods for pH of Water
intended to be used for non-aqueous samples like oil or grease.
3. Terminology
1.2 This practice may also be used in adjusting pH of
3.1 Definitions:
samples during various analytical steps.
3.1.1 pH paper, n—piecesofpaperusuallysuppliedassmall
1.3 Wide-range pH papers/strips are used for a rapid indi-
rolls that change color depending on the pH.
cation of pH to within about 1 pH unit, and narrow-range pH
3.1.1.1 Discussion—pH paper is an inexpensive, robust, and
papers/strips are used to indicate pH within about 0.5 pH units.
relatively accurate way of estimating the pH of an aqueous
1.4 In some instances, a universal liquid indicator may be
liquid. A strip of filter paper is soaked with different pH
used.
indicators, or a mixture of indicators (universal indicator), and
allowed to dry. Touching solution to the paper or dipping the
1.5 Units—The values stated in SI units are to be regarded
paper in an aliquot of solution causes the color of the indicator
as standard. No other units of measurement are included in this
on the paper to change according to the pH. The color and
standard.
relativeintensityofthecoloriscomparedtoachartfromwhich
1.6 This practice offers a set of instructions for performing
pH is estimated. Using only one indicator per paper enables a
one or more specific operations. This document cannot replace
better estimate of a narrow pH range.
educationorexperienceandshouldbeusedinconjunctionwith
3.1.2 pH paper/strip, n—throughout this practice, the term
professional judgment. Not all aspects of this practice may be
is used as a reference to both, pH paper and pH strip.
applicable in all circumstances. This ASTM International
standard is not intended to represent or replace the standard of 3.1.3 pH strips, n—strips of plastic with one or more
care by which the adequacy of a given professional service squares or rectangles of pH paper fastened to one end.
must be judged, nor should this document be applied without 3.1.3.1 Discussion—pH strips are more rugged than pH
consideration of a project’s many unique aspects. The word paper. They consist of one or more (usually up to four) small
“Standard” in the title means only that the document has been squares or rectangles of pH paper attached to one end that are
approved through the ASTM consensus process. dipped into an aliquot of the sample. In contrast to indicator
papers described in 3.1.1, pH strips typically have the indicator
1.7 This standard does not purport to address all of the
chemically bound or fixed to the paper to prevent it from
safety concerns, if any, associated with its use. It is the
leaching into the sample. However, products that contain
responsibility of the user of this standard to establish appro-
impregnated filter papers on test strips are also available and
priate safety, health, and environmental practices and deter-
these may release indicator into the sample. When necessary,
mine the applicability of regulatory limitations prior to use.
the type can be checked by putting a test strip “face down” on
1.8 This international standard was developed in accor-
absorbent paper. Each square features a different pH indicator
dance with internationally recognized principles on standard-
resulting in different colors and intensity in relation to the pH.
ization established in the Decision on Principles for the
The color and intensity of each square is compared to a chart
Development of International Standards, Guides and Recom-
from which pH is estimated. The different indicators/colors of
mendations issued by the World Trade Organization Technical
each square provide users with greater confidence in their
Barriers to Trade (TBT) Committee.
estimation of the pH.
This practice is under the jurisdiction of ASTM Committee D19 on Water and
is the direct responsibility of Subcommittee D19.05 on Inorganic Constituents in For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Water. contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Current edition approved Oct. 1, 2021. Published November 2021. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D8294-21. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D8294 − 21
3.1.4 screening analysis, n—preliminary qualitative or papers/strips in which the indicator is chemically bound to the
semi-quantitative test designed to give the user specific infor- fiber (3.1.1) when the pH paper/strip is left in the sample until
mation before conducting quantitative chemical analysis. the color no longer changes (5–10 min). Very weakly buffered
solutions (as in accordance with 3.1.6) are not suitable for pH
3.1.5 universal pH indicator, n—pH indicator composed of
paper/strip testing.
a solution of several compounds that exhibits several smooth
6.1.1 Specifically, do not use for high-performance liquid
color changes over a pH value range from 0 to 14.
chromatography (HPLC) eluents or deionized water.
3.1.5.1 Discussion—There are several commercially avail-
able universal pH indicators. A universal indicator solution is
6.2 The degree of dissociation by pH indicators is influ-
typicallycomposedofwater,phenolthalein,methylred,methyl
enced by neutral salts, proteins, colloids, and organic solvents.
orange, bromothymol blue, thymol blue, and thymolphthalein
Salt error is specific to each indicator; however, generally the
among other ingredients and stabilizers. A clear liquid can be
higher concentrations of neutral salts tend to shift indicator
added to an indicator solution. For non-clear samples, it is best
acids to read too low and indicator bases to read too high.
to use pH papers/strips.
6.3 Materials that mask the pH paper/strip, for example,
3.1.6 very weakly buffered solution, n—in the context of pH
oils, grease, paint, syrup, and so forth may cause the visual
paper/striptesting,averyweaklybufferedsolutionisasolution
estimation of color on the pH paper/strip to be difficult.
that does not meet one of the following criteria: (1) the
6.4 Oxidizers can bleach the pH paper/strip. Dechlorinate
+ -4
H -concentration is >10 mol/L (pH < 4), (2) the OH-
samples with the test-method-required reagent first before
-4
concentration is >10 mol/L (pH > 10), and (3) the concen-
adjusting and checking pH.
-4
tration of a buffer active in the respective pH-range is >10
6.5 Indicator papers (3.1.1) may “bleed” indicator into the
mol/L.
sample solution. Most pH strips (3.1.3) do not, but this needs
3.1.6.1 Discussion—For example, rainwater and desalted
to be verified for the brand used when necessary.
water are typically considered very weakly buffered solutions.
6.6 Some test methods, such as volatile organics, may
3.1.7 weakly buffered solution, n—in the context of pH
paper/strip testing, a weakly buffered solution is a solution that require verification of pH after the analysis is completed.
+
does not meet one of the following criteria: (1) the H -
6.7 This practice may not be suitable for color blind
-3
concentration is >10 mol/L (pH < 3), (2) the OH- concentra-
technicians.
-3
tion is >10 mol/L (pH > 11), and (3) the concentration of a
-3 6.8 Measurement in colored solutions
...