Method Statement pH
@(#) Uncontrolled Document pH.html Version 1.4 Last
Revised on 11/20/02
Contents
Introduction
Principle
Performance
Characteristics
Range
of Application
Limit of
Detection
Analytical
Quality Control
References
Introduction
The performance of this method is validated in accordance with
internationally recognised procedures.
The measurement of pH is a simple and rapid process yet it
provides valuable information. An anomalously low or high pH value
in a sample of soil or water indicates the presence of contamination.
Furthermore, groundwater of low pH dissolves contaminants more
effectively than that of a higher value. Hence, the measurement of
pH is important in the field of contaminated land assessment.
The pH is used in conjunction with the sulphate concentration
ascertain the optimal chemical composition (type and quantity of
cement) for a concrete mix in building developments.
Principle
The hydrogen ion activity of a solution is determined from the
measurement of the electrochemical potential of a galvanic cell. The
cell contains two electrodes, an indicator electrode and the
reference electrode. When the electrodes are immersed in a solution,
a the potential developed is dependent on both electrodes. Ideal
measuring conditions exist when only the potential of the indicator
electrode changes in response to varying pH, while the potential of
the reference electrode remains constant.
The equipment is calibrated using buffer solutions of known pH.
Performance
Characteristics
Substances Determined
Log10(Hydrogen ion activity) pH.
Range of Application
Limit of Detection
Soil samples n/a
Aqueous samples n/a
Analytical Quality
Control
Analytical quality control is maintained by a number of measures:
Multi-point calibration with
authentic standards (with defined minimum performance
characteristics)
Analysis of control samples within
each analytical batch, such as independent standards, matrix spikes
or reference materials
Analysis of reagent/method blanks
within each analytical batch
Ongoing quality assured by the use
of control charts in conjunction with warning and action limits for
the QC sample data
Participation in external
proficiency testing and interlaboratory schemes such as LGC CONTEST,
HSE WASP, CSL FAPAS
References
BS:1377: Part 3:1990.
“The Measurement of Electrical Conductivity and the
Laboratory Determination of pH Value of Natural, Treated and Waste
Waters, 1978”. DOE Methods For The Examination of Waters and
Associated Materials, published by HMSO.
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