oEWV
United States
Environmental Protection
Agency
Method 150.3: Determination of pH in Drinking Water

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Questions concerning this document should be addressed to:
William A. Adams. PhD
U.S. EPA, Office of Ground Water and Drinking Water, Standards and Risk Management Division,
Technical Support Center, 26 W. Martin Luther King Dr. Cincinnati, OH 45268
Phone:(513) 569-7656
adams.william@epa.gov
Office of Water (MS-140)
EPA 815-B-17-001
February 2017
Version 1.0
Authors
William A. Adams, PhD, U.S. EPA (Cincinnati, OH)
Steven C. Wendelken, PhD, U.S. EPA (Cincinnati, OH)
Glynda A. Smith, PhD, U.S. EPA (Cincinnati, OH)
Acknowledgements
The following people are acknowledged for their support in development of this method:
Alejandra Beier, Cincinnati Water Works
Brad Baker, Pennsylvania Department of Environmental Protection
Cathy Port, Pennsylvania Department of Environmental Protection
Craig Corder, Arkansas Department of Health
Ed Chescattie, Pennsylvania Department of Environmental Protection
Jeff Vogt, Cincinnati Water Works
Justin Blashaw, Pennsylvania Department of Environmental Protection
Nancy Feagin, Washington State Department of Health
Rick Lieberman, U.S. EPA
Steve Deem, Washington State Department of Health
Tom Waters, U.S. EPA
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Contents
1	SCOPE AND APPLICATION	1
2	SUMMARY OF METHOD	1
3	DEFINITIONS	1
4	INTERFERENCES	2
5	SAFETY	2
6	EQUIPMENT AND SUPPLIES	2
7	REAGENTS AND STANDARDS	3
8	SAMPLE COLLECTION, PRESERVATION, AND STORAGE	4
9	QUALITY CONTROL	4
10	CALIBRATION	6
11	PROCEDURE	7
12	DATA ANALYSIS AND CALCULATION	9
13	POLLUTION PREVENTION	9
14	WASTE MANAGEMENT	9
15	REFERENCES	9
16	TABLES AND FLOWCHARTS	11
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1 SCOPE AND APPLICATION
1.1	Method
This method is to be used when obtaining pH measurements from drinking water. It applies to
measurements of grab samples via bench-top and portable pH meters, and also to continuous pH
measurement of drinking water via continuous pH monitoring instrumentation. This method is to be
utilized when pH measurements are being submitted for compliance with daily monitoring requirements.
Analysts should be skilled in the operation of the instrumentation and interpretation of the associated
data. This method allows the use of any type of bench-top, portable, or continuous monitoring pH meter
for compliance monitoring, and allows for the use of different technologies that conform to the
constraints outlined in this method. Non-glass probes may be used provided method quality control (QC)
parameters are met. This method is intended to measure drinking water pH with a resolution of 0.1 pH
unit.
1.2	Means of Calibration and Calibration Verification
Calibration and calibration verification can be performed directly using a bench-top, portable, or
continuous monitoring pH meter and reference pH buffers, or indirectly using a grab sample and
calibrated bench-top or portable pH meter.
2 SUMMARY 01 MtfHOD
A bench-top, portable, or continuous monitoring pH meter is used to measure the pH of drinking water
using pH probes that include, but are not limited to, glass electrodes in combination with a reference
potential, ion-selective field-effect transistor (ISFET) electrodes in combination with a reference potential,
combination electrodes, and molecular sensors. Calibration and calibration verification can be performed
directly or indirectly. Direct calibration and calibration verification involve measurement of reference pH
buffers with the instrumentation. Alternatively, continuous monitoring pH meters may be calibrated or
verified indirectly by using a grab sample from the sample stream and measuring the pH of the grab
sample with a calibrated bench-top or portable pH meter. The continuous monitoring analyzer accuracy is
verified or adjusted based on results from grab sample analyses.
3 DEFINITIONS
Calibration Verification - A process using a sample of known pH to verify pH meter calibration accuracy
through the use of reference pH buffers or grab sample checks of continuous monitoring pH meters.
Portable pH Meter - A pH meter capable of being routinely transported to sampling sites for measuring
sample pH to a resolution of 0.1 pH unit. Portable (also referred to as field pH meters) must be capable of
user calibration or have a record of a pre-installed manufacturer calibration. Portable pH meters must be
able to compensate for temperature manually or automatically.
Grab Sample - A discreet sample taken from the sample stream for measurement. Grab samples can also
be used in the calibration verification and pH adjustment of continuous monitoring pH meters. The grab
sample should be sampled near the continuous monitoring meter, must be measured as soon as possible,
and must represent the conditions of the sample stream.
Bench-top pH Meter - A stand-alone pH meter capable of measuring sample pH to a resolution of 0.1 pH
units. Bench (also referred to as laboratory) pH meters are typically user calibrated and must be able to
1

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compensate for temperature manually or automatically.
Continuous Monitoring pH Meter - A pH meter directly connected to the sample stream and capable of
measuring pH to a resolution of 0.1 pH unit. The system may use a flow-through, pipe mounted, or
immersion electrode.
pH Probe - The electrode or sensor portion of the pH meter. The type of electrode can include, but are not
limited to, glass electrodes in combination with a reference potential electrode, ion-selective field-effect
transistor (ISFET) electrodes in combination with a reference potential electrode, combination measuring
and reference electrodes, and molecular sensors.
Reference pH Buffer - A solution of known pH used to calibrate pH meters. This method requires the use
of at least three reference pH buffers in meter calibration.
Safety Data Sheet (SDS) - Written information provided by vendors concerning a chemical's toxicity,
health hazards, physical properties, fire-fighting measures and reactivity data including storage, spill, and
handling precautions.
4 INTERFERENCES
4.1	Manufacturer Recommendations for Probes
Refer to manufacturer recommendations regarding interferences specific to the probes used during
analysis.
4.2	Probe Fouling
Periodically inspect the conditions of probes for fouling. Clean and maintain the probes according to
manufacturer recommendations.
4.3	Temperature Effects
Temperature can affect the electrometric measurement of pH in two ways. The first is the change in
electrode output at various temperatures. This interference can be controlled with instruments having
temperature compensation. The second is the change of pH inherent in the sample at various
temperatures. This is sample dependent and cannot be controlled. It should therefore be noted by
reporting both the pH and temperature at the time of analysis.
5 SAFETY
The toxicity or carcinogenicity of each reagent used in this method has not been precisely identified; each
chemical compound should be treated as a potential health hazard unless otherwise determined, and
exposure to these chemicals should be minimized. The laboratory or water system is responsible for
maintaining documentation of OSHA regulations regarding the safe handling of the chemicals specified in
this method. A reference file of Safety Data Sheets (SDS) should also be made available to all personnel
1-4
involved in the chemical analysis. Additional references to laboratory safety are available.
6 EQUIPMENT AND SUPPLIES
6.1 pH Meter
A bench-top, portable, or continuous monitoring pH meter may be used. A wide variety of instruments are
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commercially available with various specifications and optional equipment. Meters must be capable of
user calibration or have documentation of initial calibration from the manufacturer. Meters must be
capable of automatic or manual temperature compensation. Results must be reported to the nearest 0.1
pH unit.
6.1.1 Continuous Monitoring pH Meter Special Considerations
6.1.1.1	Meter Adjustment and Grab Sample Location
Analysts must be capable of adjusting the continuous monitoring pH meter readout when comparing
readings to stream grab sample results from a bench-top or portable pH meter during calibration or
calibration verification. Grab sample location should be as near as possible to the continuous monitoring
pH meter probe location.
6.1.1.2	Recording Readout
The meter must have a readout at its installation location and the readings must be continually recorded
(hard copy chart or electronic data). For remote installations, the meter should also have the capability for
transmission of the output to a centralized location.
6.1.1.3	Meter Alarm
The continuous monitoring pH meter should have the capability to activate an alarm when the pH is
outside the normal operating range.
6.2 pH Probes
The pH probes include, but are not limited to, glass electrodes in combination with a reference potential
electrode, ion-selective field-effect transistor (ISFET) electrodes in combination with a reference potential
electrode, combination measuring and reference electrodes, and molecular sensors. Refer to
manufacturer's recommendations regarding application.
6.2.1	Reference Potential Electrode
A calomel, silver-silver chloride or other reference electrode of constant potential may be used.
6.2.2	Continuous Monitoring Mounting Type
For continuous monitoring, electrode mounting may be flow-through, pipe mounted, or immersion.
Probes should be installed so that they are in constant contact with the sample stream, even when not in
use. Probes should also be installed as near the sampling point as possible.
7 REAGENTS AND STANDARDS
7.1 Reference pH Buffer Solutions
Reference buffers used in the calibration and calibration verification of pH meters are commercially
available as liquids or in powder packets (powder packets require preparation; follow vendor's
instructions). Typical pH buffer solutions have pH values near 4, 7, and 10. Buffer solution pH values are
dependent upon temperature. Refer to the manufacturer specifications for each buffer used and adhere
to the specified expiration dates. If using the same aliquots of pH reference solutions for multiple
calibrations and calibration verifications, users should change out solutions weekly to prevent
contamination and potential changes to reference pH.
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8 SAMPLE COLLECTION, PRESERVATION, AND STORAGE
8.1	Representative Samples
Samples should be analyzed immediately after collection in order to best represent conditions at the
sample collection location. If using a grab sample, the grab sample collection point should be as close as
possible to the location where the sample enters the continuous monitoring pH meter. A sample line may
be equipped with a valve that allows for intermittent grab sampling with minimal disruption of flow to the
meter. Grab samples must be representative of conditions where the sample stream enters the
continuous monitoring pH meter.
8.2	Sample Collection
Collect approximately 100 mL of sample in a clean plastic or glass container. Minimize sample aeration and
the presence of air bubbles, which can interfere with analysis. Do not store samples.
Note: The use of temperature compensation with off-line or continuous monitoring pH meters will
compensate for Nernst equation-related differences in pH between measurements of samples at different
temperatures. However, temperature directly impacts dissociation and sample hydrogen ion
concentration, which cannot be compensated for in samples. Therefore, the temperature should always
be recorded at the time of sampling, and analysts should not allow the temperature of the sample after
collection to change by more than 5 C before analysis.
TROL
Quality control (QC) procedures are incorporated into analytical methods in order to demonstrate that the
results are valid and within the accuracy and precision ranges needed for protection of public health. The
following sections detail the QC procedures that are required for bench-top, portable, and continuous
monitoring pH meters. The Initial Demonstration of Capability (IDC) and ongoing QC criteria are
summarized in Section 16, Tables 1 and 2. The laboratory or water system is required to maintain
performance records that define the quality of data generated. For regulatory drinking water monitoring
applications, additional QC and documentation may be specified by the associated primacy agency.
9.1 Bench-top and Portable pH Meter Initial Demonstration of Capability (IDC)
9.1.1	IDC frequency
An IDC must be successfully performed by each analyst prior to analyzing field samples and following any
instrument maintenance. Calibrate as described in Section 10 prior to conducting the IDC.
9.1.2	Demonstration of Precision
Analyze four separate aliquots of a reference buffer of known pH. Samples should be continuously and
gently stirred to minimize the presence of air bubbles. If mechanical stirring is not available, the sample
should be gently swirled. Allow for the measurement to stabilize. Calculate the standard deviation of the
replicates. The standard deviation must be <0.1 pH units.
9.1.3	Demonstration of Accuracy
Using the four replicates from the Demonstration of Precision, calculate the average measured pH. The
result must be within 0.1 pH units of the true pH value.
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9,2 Bench-top and Portable pH Meter Ongoing QC
9.2.1 Bench-top or Portable pH Meter Calibration Verification
A single reference buffer of known pH must be analyzed at least daily or at the time of measurement for
systems that monitor less frequently. The sample should be continuously and gently stirred to minimize
the presence of air bubbles. If mechanical stirring is not available, the sample should be gently swirled.
Allow the measurement to stabilize. The calibration verification reference buffer sample measurement
must be within 0.1 pH units of the true pH value. If the calibration verification fails, the instrument must
be recalibrated (Section 10.1). If the calibration verification continues to fail, the pH meter or electrode
may need maintenance or replacement.
9.3	Continuous Monitoring pH Meter QC using a Removable Probe
9.3.1 IDC and On-going QC
Follow the IDC and Ongoing QC procedures as discussed in Sections 9.1 and 9.2 by removing the probe
from the sample stream and placing the probe in separate containers of the reference buffer solution.
Rinse the probe with distilled water in between placement.
9.4	Continuous Monitoring pH Meter QC usin	pie
9.4.1	IDC and On-going QC
The bench-top or portable pH meter used in the grab sample analysis must meet the IDC and Ongoing QC
as described in Sections 9.1 and 9.2.
9.4.2	Continuous Monitoring pH Meter Calibration Verification
When using continuous monitoring pH meters, grab samples may be collected following the procedure in
Section 8 and measured using a bench-top or portable pH meter. The sample should be continuously and
gently stirred to minimize the presence of air bubbles. If mechanical stirring is not available, the sample
should be gently swirled. Allow for the measurement to stabilize. Compare the result obtained from the
bench-top or portable pH meter to the readout of the continuous monitoring pH meter. The results must
not deviate by more than 0.2 pH units. If the verification check fails, refer to Section 10.3 for calibration.
9.4.3	Verification Frequency
A grab sample must be verified daily or at the time of measurement for systems that monitor less
frequently.
9.4.4	Optional Grab Sample Duplicate
Analysis of duplicate grab samples (two samples collected at the same time) provides an estimate of the
precision of the grab sample analyses that are used to verify the accuracy of the continuous monitoring pH
meter. Poor grab sample precision can cause problems in the analyzer adjustment. Analysis of grab sample
duplicates is suggested when there are difficulties in adjusting the continuous monitoring meter to agree
with the grab sample measurement. Results from grab sample duplicates should be within 0.2 pH units. If
the Sample and the Sample Duplicate result falls outside the designated range, analyze two aliquots of a
reference buffer with the bench-top or portable pH meter to verify that the grab sample method is in
control.
9.5	Additional QC
Laboratories and water systems are encouraged to institute additional QC practices to meet their specific
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needs.
10 CALIBRATION
Because of the wide variety of pH meters and accessories, detailed operating procedures cannot be
incorporated into this method. Each analyst must be acquainted with the operation of each system and
familiar with all instrument functions. Special attention to care for the probes is required as prescribed by
the manufacturer. The analyst should refer to the particular manufacturer's instructions.
10.1	Bench-top and Portable pH Meter Calibration
10.1.1	Calibration Guidelines
If a pH meter is capable of user calibration, then it must be calibrated using the following guidelines.
Follow the manufacturer's instructions. Calibrate each meter at a minimum of two pH levels that bracket
the expected pH of the samples and are approximately three pH units or more apart. Typically, for drinking
water, 2-point calibrations are performed using the pH 7.0 and pH 10.0 buffers. The buffers should be
continuously and gently stirred to minimize the presence of bubbles. Allow for the measurement to
stabilize.
10.1.2	pH Buffer Verification
Following calibration, analyze another reference pH buffer (e.g., pH 4 buffer) for calibration verification.
The result must be within 0.1 pH units of the true pH value.
10.1.3	Calibration Frequency
Calibration must be carried out at least weekly or at the time of measurement for systems that monitor
less frequently and must be performed if the daily calibration verification sample (Section 9.2.1) does not
meet QC.
10.1.4	Factory Calibration Documentation
If a pH meter uses a pre-installed factory calibration, documentation must be provided by the
manufacturer that the meter was initially calibrated and that the meter requires no further user
calibration. Calibration must be verified as described in Section 9.2.1.
10.2	Continuous Monitoring pH Meter Calibration using a Removable Probe
10.2.1	User Calibration Capability
The continuous monitoring meter must be capable of user calibration in order to perform the steps
described in Sections 10.2.2 - 10.2.4.
10.2.2	Calibration Guidelines
Calibrate the electrode at a minimum of two pH levels that bracket the expected pH of the water and are
approximately three pH units or more apart. Typically, for drinking water, 2-point calibrations are
performed using the pH 7.0 and pH 10.0 buffers. The buffers should be continuously and gently stirred to
minimize the presence of bubbles. If mechanical stirring is not available, the sample should be gently
swirled. Allow for the measurement to stabilize.
10.2.3	pH Buffer Verification
Following calibration, analyze another reference pH buffer. The result must be within 0.1 pH units of the
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true pH value.
10.2.4 Calibration Frequency
Calibration must be carried out at least weekly or at the time of measurement for systems that monitor
less frequently and must be carried out if the daily calibration verification sample (Section 9.3.1) does not
meet QC.
10,3 Continuous Monitoring pH Meter Calibration using a Grab Sample
10.3.1	Calibration Guidelines
The bench-top or portable pH meter must be calibrated prior to use against at least two buffers and
calibration must be verified with another buffer as outlined in Section 10.1, unless a factory calibration is
used (Section 10.1.4). It is not necessary that reference pH buffers be at the same temperature as the
sample stream for temperatures typically observed in drinking water sample lines.
10.3.2	Initial Calibration
The continuous monitoring pH meter system should be initially calibrated by the manufacturer (with
documentation) or against two reference buffers as outlined in Section 10.2 before being placed into
service.
10.3.3	Grab Sample Adjustment
Collect a grab sample of the flowing stream from a point as close to the meter as possible. A sample line
may be equipped with a valve that allows for intermittent grab sampling with minimal disruption of flow
to the meter. Separate sampling lines are acceptable as long as samples are representative of where the
sample stream enters the continuous monitoring pH meter. Measure the pH of this grab sample as quickly
as possible with a bench-top or portable pH meter. The sample should be continuously and gently stirred
to minimize the presence of bubbles. If mechanical stirring is not available, the sample should be gently
swirled. Allow for the measurement to stabilize. Adjust the calibration control of the continuous
monitoring pH meter to the reading obtained.
10.3.4	Temperature Effects
The temperature and condition of the grab sample must remain constant (5 C) until its pH has been
measured by the bench-top or portable pH meter. The temperature of the sample should be measured
and recorded. The pH meter should compensate for any Nernst equation-related differences in
temperature, but it is recommended that the analyst acclimate the probe to the sample temperature prior
to measurement.
11 PROCEDURE
11.1 Bench-top and Portable pH Meters
11.1.1	Meter Installation, Operation, and Maintenance
Follow the manufacturer's instructions for installation, operation, and maintenance of the bench-top pH
meter. Refer the manufacturer's instructions for operation and maintenance of the portable pH meter.
11.1.2	Calibration Frequency
The bench-top or portable pH meter must be calibrated weekly as outlined in Section 10.1.
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11.1.3 Verification Frequency
Between calibrations, the bench-top or portable pH meter calibration must be verified daily as described
in Section 9.2.
11.1.4	Sample Collection
Place no more than 100 mL of sample in an appropriately sized container for the analysis, since larger
volumes of sample can lead to longer equilibration times. Be sure to pre-rinse the container with a small
volume of the sample and discard prior to filling the container with the sample that will be measured.
11.1.5	Rinsing Probe
Rinse the sensor or electrode with distilled water and insert the sensor or electrode into the container
ensuring the probe is in complete contact with the sample.
11.1.5.1 Portable pH Meters and Temperature
Portable pH meters may be used in more extreme temperature conditions than where bench-top pH
meters are used. Portable meters must be capable of automatic or manual temperature compensation. To
mitigate other temperature effects, it is recommended that the pH probe be allowed to reach sample
temperature by placing the probe in the sample for several minutes prior to analysis.
11.1.6	Sample Stirring
During pH analysis, samples should be stirred using a magnetic stirrer. If magnetic stirring is unavailable,
the sample should be swirled with care to not let the probe touch the sides of the container. Care should
also be taken to not promote bubble formation.
11.1.7	Measurement
Measure the pH of the sample to the nearest 0.1 pH unit and record the temperature of the sample in C.
11.1.8	Probe Care
Maintain, store, and clean probes or portable meters as needed according to the manufacturer's
instructions.
11.2 Continuous Monitoring pH Meter
11.2.1	Meter Installation, Operation, and Maintenance
Follow the manufacturer's instructions for installation, operation, and maintenance of the continuous
monitoring pH meter.
11.2.2	Calibration Frequency
The continuous monitoring pH meter must be calibrated weekly if using removable electrodes as outlined
in Section 10.2 and initially before use if using a grab sample as described in Section 10.3.
11.2.3	Verification Frequency
After calibration, the continuous monitoring pH meter calibration must be verified daily as described in
Sections 9.3 and 9.4.
11.2.4	Stream Contact
Ensure there is proper flow through the continuous monitoring pH meter and that the probe or sensor is in
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complete contact with the sample stream.
11.2.5 Measurement
Measure the pH of the sample to the nearest 0.1 pH unit and record the temperature of the sample in C.
12	DAI A ANALYSIS AND CAkNHl A1 ION
Meters read directly in pH units. Report pH to the nearest 0.1 pH unit and temperature to the nearest C.
13	1	ON PREVENTION
Pollution prevention encompasses any technique that reduces or eliminates the quantity or toxicity of
waste at the point of generation. Numerous opportunities for pollution prevention exist in laboratory
operation. EPA has established a preferred hierarchy of environmental management techniques that
places pollution prevention as the waste management option of first choice. Whenever feasible,
laboratory personnel should use pollution prevention techniques to address their waste generation. When
wastes cannot be feasibly reduced at the source, the Agency recommends recycling as the next best
option.
Quantity of a chemical purchased should be based on expected usage during its shelf-life, disposal cost,
and environmental impact of unused material. Actual reagent preparation volumes should reflect
anticipated usage and reagent stability.
For information about pollution prevention that may be applicable to laboratory operations, consult
Prudent Practices in the Laboratory: Handling and Management of Chemical Hazards.~
14 WASTE MANAGEMENT
The analytical procedures described in this method generate relatively small amounts of waste since only
small amounts of reagents are used. The matrixes of concern are drinking water. However, the Agency
requires that waste management practices be conducted consistent with all applicable rules and
regulations, and that the air, water, and land are protected by minimizing and controlling all releases from
bench operations. Also, compliance is required with any sewage discharge permits and regulations,
particularly the hazardous waste identification rules and land disposal restrictions.
15 REFERENCES
1.	Safety in Academic Chemistry Laboratories. Vol 1. 7th Edition. American Chemical Society
Publication, Committee on Chemical Safety, Washington DC, 2003.
rd
2.	Chemical Safety Manual for Small Businesses. 3 Edition. American Chemical Society, Committee
on Chemical Safety, Washington DC, 2009.
3.	Occupational Safety and Health Administration (OSHA), Hazard Communication, 29 CFR
1910.1200.
4.	Occupational Safety and Health Administration (OSHA), Occupational Exposure to Hazardous
Chemicals in Laboratories, 29 CFR 1910.1450.
5.	Prudent Practices in the Laboratory: Handling and Management of Chemical Hazards: Updated
Version, National Academies Press, Washington, D.C., 2011.
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6.	USEPA. 1982. Method 150.1. In Methods for Chemical Analysis of Water and Wastes, EPA/600/4-
79/020.
7.	USEPA. 1982. Method 150.2. In Methods for Chemical Analysis of Water and Wastes, EPA/600/4-
79/020.
8.	Standard Method for the Examination of Water and Wastewater, 22nd Edition, American Public
Health Association, Washington, D.C., 2012
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1 \\ ' AN ^ -o\u s
3 1A. Bench-top or Portable pH Meter Initial Demonstration of Capability (IDC) Quality
Control Requirements
Type of pH Meter
Method Reference
Requirement
Specification
Acceptance Criteria
Bench-top or
10.1
Calibration
Calibrate using two
Following
Portable pH Meter


reference pH
calibration, the



buffers that bracket
third reference pH



the expected pH of
buffer must be



the samples.
within 0.1 pH units



Analyze a third
of the true pH



reference pH buffer
value.



following the two-




point calibration.




Calibrate weekly or
Note: Meters with



at the time of
pre-installed factory



measurement for
calibrations may be



systems that
used with proper



monitor less
documentation and



frequently.
must be verified




using the discussed




procedures.
Bench-top or
9.1.2
Demonstration of
Analyze four
The standard
Portable pH Meter

Precision
replicate reference
deviation must be



pH buffers.
<0.1 pH units.



Calculate the




standard deviation




of the replicates.

Bench-top or
9.1.3
Demonstration of
Analyze four
The mean measured
Portable pH Meter

Accuracy
replicate reference
pH must be within



pH buffers.
0.1 pH units of the



Calculate the mean
true pH value.



measured pH.

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* e IB. Continuous Monitoring (Removable Electrode) pH Meter Initial Demonstration of
Capability (IDC) Quality Control Requirements
Type of pH Meter
Method Reference
Requirement
Specification
Acceptance Criteria
Continuous
10.2
Calibration
Calibrate using two
Following
monitoring pH


reference pH
calibration, the
Meter (Using


buffers that bracket
third reference pH
Removable


the expected pH of
buffer must be
Electrode)


the samples.
within 0.1 pH units



Analyze a third
of the true pH



reference pH buffer
value.



following the two-




point calibration.




Calibrate weekly or




at the time of




measurement for




systems that




monitor less




frequently.

Continuous
9.3.1
Demonstration of
Analyze four
The standard
monitoring pH

Precision
replicate reference
deviation must be
Meter (Using


pH buffers.
<0.1 pH units.
Removable


Calculate the

Electrode)


standard deviation




of the replicates.

Continuous
9.3.1
Demonstration of
Analyze four
The mean measured
monitoring pH

Accuracy
replicate reference
pH must be within
Meter (Using


pH buffers.
0.1 pH units of the
Removable


Calculate the mean
true pH value.
Electrode)


measured pH.

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* e 1C. Continuous Monitoring u" v ^ Sample) pH Meter Initial Demonstration of Capability
(IDC) Quality Control Requirements
Type of pH Meter
Method Reference
Requirement
Specification
Acceptance Criteria
Continuous
10.3
Calibration
Initial Calibration by
Calibration control
monitoring pH


manufacturer with
must be adjusted
Meter (Using Grab


documentation or
when comparison
Sample)


calibrated according
results is >0.2 pH



to Section 10.3.
units.



Calibration control




adjusted based on




comparison




between bench-top




or portable pH




meter and




continuous




monitoring pH




meter. Compare




daily or at the time




of measurement for




systems that




monitor less




frequently.

Continuous
9.4.1
Demonstration of
The bench-top or
For bench-top or
monitoring pH

Precision,
portable pH meter
portable pH meter
Meter (Using Grab

Demonstration of
used in the grab
IDC, see Sections
Sample)

Accuracy
sample analysis
9.1.2 and 9.1.3.



must meet the IDC




as described in




Section 9.1.

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* e 2. Ongoing Quality Control Requirements
Type of pH Meter
Method Reference
Requirement
Specification
Acceptance Criteria
Bench-top or
Portable pH Meter
9.2
Calibration
Verification
A single reference
pH buffer analyzed
daily or at the time
of measurement for
systems that
monitor less
frequently.
The calibration
verification sample
must be within
0.1 pH units of the
true pH value.
Continuous
monitoring pH
Meter (Using
Removable
Electrode)
9.3
Calibration
Verification
A single reference
pH buffer analyzed
daily or at the time
of measurement for
systems that
monitor less
frequently.
The calibration
verification sample
must be within
0.1 pH units of the
true pH value.
Continuous
monitoring pH
Meter (Using Grab
Sample)
9.4
Calibration
Verification
Daily or at the time
of measurement for
systems that
monitor less
frequently analyze a
grab sample from
the stream and
compare with a
bench-top or
portable pH meter.
The laboratory pH
meter used in the
grab sample
analysis must meet
the on-going QC as
described in Section
9.2.
The compared
results must not
deviate by more
than 0.2 pH units.
Continuous
monitoring pH
Meter (Using Grab
Sample)
9.4.4
Optional Grab
Sample Duplicate
Analyze duplicate
grab samples to
verify the accuracy
of the continuous
monitoring pH
meter.
Results from grab
sample duplicates
should be within
0.2 pH units.
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