The pH of water is a critical parameter affecting the solubility of trace minerals, the ability of the water to form scale or to cause metallic corrosion, and the suitability of the water to sustain living organisms. It is a defined scale, based on a system of buffer solutions with assigned values. In pure water at 25°C, pH 7.0 is the neutral point, but this varies with temperature and the ionic strength of the sample. Pure water in equilibrium with air has a pH of about 5.5, and most natural uncontaminated waters range between pH 6 and pH 9.

1. Scope

1.1 These test methods cover the determination of pH by electrometric measurement using the glass electrode as the sensor. Two test methods are given as follows:

1.2 Test Method A covers the precise measurement of pH in water utilizing at least two of seven standard reference buffer solutions for instrument standardization.

1.3 Test Method B covers the routine measurement of pH in water and is especially useful for continuous monitoring. Two buffers are used to standardize the instrument under controlled parameters, but the conditions are somewhat less restrictive than those in Test Method A. For on-line measurement, also see Test Method D6569 which provides more detail.

1.4 Both test methods are based on the pH scale established by NIST (formerly NBS) Standard Reference Materials.

1.5 Neither test method is considered to be adequate for measurement of pH in water whose conductivity is less than about 5 μS/cm. Refer to Test Methods D5128 and D5464.

1.6 Precision and bias data were obtained using buffer solutions only. It is the user's responsibility to assure the validity of these test methods for untested types of water.

1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.8 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.

2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.

ASTM Standards

D1066 Practice for Sampling Steam

D1067 Test Methods for Acidity or Alkalinity of Water

D1129 Terminology Relating to Water

D1192 Guide for Equipment for Sampling Water and Steam in Closed Conduits

D1193 Specification for Reagent Water

D2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water

D3370 Practices for Sampling Water from Closed Conduits

D5128 Test Method for On-Line pH Measurement of Water of Low Conductivity

D5464 Test Method for pH Measurement of Water of Low Conductivity

D6569 Test Method for On-Line Measurement of pH

E70 Test Method for pH of Aqueous Solutions With the Glass Electrode

Keywords

hydrogen ion concentration; pH; pH buffer solution; Routine measurement (of pH) method; Water quality monitoring; Acidity, alkalinity, pH--water; Buffer solutions; Continuous measurement/monitoring; Field testing--water; Glass electrodes; Hydrogen ion concentration; Instrumental measurement--water; pH--glass electrode; pH--water; Precise laboratory measurement (of pH) method; Process pH measurements; Reference buffer solutions; Remote pH measurements

ICS Code

ICS Number Code 13.060.50 (Examination of water for chemical substances)

Citing ASTM Standards

[Back to Top]