pH in Liquid and Soil
SW-846 Method 9040 (Liquid) and SW-846 Method 9045 (Soil)
Table 1. Summary of Holding' Times and. Preservation for liquid and soil pH
Analytical
Parameter
Technical and Contract Holding Times
Preservation
pH (Liquid
and Soil)
Analyze pH immediately upon sample receipt
by the laboratory
Cool to 4C
2  C
For soil samples:
In addition to the procedure outlined in Section 7.2 of SW-846 method 9045C,
For noncalcareous soils:
1.	Weigh 20 grams of soil in a 50 mL beaker. Add 20 mL of Type II
water. Stir the resulting suspension several times during the
next 30 minutes.
2.	Let the suspension to stand undisturbed for about 1 hour to allow
most of the suspended clay to settle out
For calcareous soils:
1.	Weigh 10 grams of soil in a 50 mL beaker. Add 20 mL of 0.01M
CaCl2. Stir the resulting suspension several times during the
next 30 minutes.
2.	Let the suspension to stand undisturbed for about 1 hour to allow
most of the suspended clay to settle out.
Data Calculations and Reporting Units:
Read pH meter results directly in pH units and solution temperature in C.
Report pH results to the nearest 0.1 pH unit and temperature to the nearest
C. Report the results for noncalcareous soils as "soil pH measured in water"
and for calcareous soils, report the results as "soil pH measured in 0.01M
CaCl2".
For rounding results, adhere to the following rules:
a)	If the number following those to be retained is less than 5, round down;
b)	If the number following those to be retained is greater than 5, round
up; or
c)	If the number following the last digit to be retained is equal to 5,
round down if the digit is even, or round up if the digit is odd.
All records of analysis must be legible and sufficient to validate all sample
and QC analyses.
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Table 2. Summary of Calibration Procedures for pH by SW-846 Method. 9040 (Liquids) and
SW-846 Method 9045 (Soil)
Calibration
Element
Frequency
Acceptance Criteria
Corrective Action
Meter
Standardization
Initially
Refer to manufacture's instructions
Refer to manufacture's instructions
concerning standardization and
electrode(s) care
Calibration
Daily,
prior to
sample
analysis
A minimum of 2 primary or secondary
standard buffers must be used;
Buffers must bracket expected pH of
sample;
Buffers must be 3 or more pH units
apart;
Buffer readings must be within 0.05
pH units of buffer's true value
1.	Allow buffer temperatures to
reach equilibrium
2.	Repeat measurement with
successive volumes of fresh
buffer until acceptance criteria
are met
3.	Replace electrode(s) (follow
manufacture's instructions)
Buffer pH Check
Check a
calibration
buffer
solution
after every
10 samples
(minimum)
<0.1 pH unit difference
1.	Repeat measurement with
successive volumes of fresh
buffer until acceptance criteria
is met before continuing
analysis
2.	Recalibrate meter and reanalyze
samples
NOTE: Electrode(s) must be cleaned after each sample analysis by thoroughly rinsing and gently wiping.
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Table 3. Summary of Internal Quality Control Procedures for pH by SW-846 Method. 9040 (Liquids) and
SW-846 Method 9045 (Soil)
QC Element
Frequency
Acceptance
Criteria
Corrective Action
Sample
Temperatures
Every sample
<2 C
difference
from buffer
Refer to manufacture's instructions concerning
the pH meter temperature compensating function
Duplicate
Sample (DUP)
One per batch or SDG
(1 per 20 samples
minimum)a
<0.1 pH unit
difference
1.	Allow sample temperatures to reach
equilibrium
2.	Perform buffer pH check (See Calibration
Procedure)
3.	Clean electrode (See Calibration Procedure
Note)
a SDG - Sample Delivery Group - each case of field samples received; or each 20 field samples within a
case; or each 14 calendar day period during which field samples in a case are received.
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