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ASTM International - ASTM D5128-14

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

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Organization: ASTM International
Publication Date: 1 January 2014
Status: active
Page Count: 11
ICS Code (Physicochemical methods of analysis): 71.040.50
significance And Use:

5.1 Continuous pH measurements in low conductivity samples are sometimes required in pure water treatment using multiple pass reverse osmosis processes. Membrane rejection efficiency for several... View More

scope:

1.1 This test method covers the precise on-line determination of pH in water samples of conductivity lower than 100 μS/cm (see Table 1 and Table 2) over the pH range of 3 to 11 (see Fig. 1), under field operating conditions. pH measurements of water of low conductivity are problematic for conventional pH electrodes, methods, and related measurement apparatus.

TABLE 1 Calculated Conductivity and pH Values at 25°C of Low Concentrations of NaOH in Pure Water ANote 1-This table tabulates the theoretical conductivity and pH values of low levels of NaOH in pure water as calculated from available thermodynamic data. Note 2-To illustrate the high sensitivity of the sample pH at these low concentrations to contaminants, the last column lists errors that would result if the sample were contaminated with an additional 1 mg/L through sample or equipment handling errors.

Sample
Concentration,
mg/L
Sample
Conductivity,
μS/cm
Sample
pH
Δ pH Error from Additional 1 mg/L NaOH Contaminate
0.001  0.055  7.05 Δ 2.35
0.010  0.082  7.45 Δ 1.95
0.100  0.625  8.40 Δ 1.03
1.0  6.229  9.40 Δ 0.30
8.0 49.830 10.30 Δ 0.05

A Data courtesy of Ref (1).B This data developed from algorithms originally published in Ref (2).B The boldface numbers in parentheses refer to a list of references at the end of this standard.TABLE 2 Calculated Conductivity and pH Values at 25°C of Low Concentrations of HCl in Pure Water ANote 1-This table tabulates the theoretical conductivity and pH values of low levels of HCl in pure water as calculated from available thermodynamic data Note 2-To illustrate the high sensitivity of the sample pH at these low concentrations to contaminants, the last column lists errors that would result if the sample were contaminated with an additional 1 mg/L through sample or equipment handling errors.

Sample
Concentration,
mg/L
Sample
Conductivity,
μS/cm
Sample
pH
Δ pH Error from Additional 1 mg/L HCl Contaminate
0.001  0.060 6.94 Δ2.38
0.010  0.134 6.51 Δ 1.95
0.100  1.166 5.56 Δ 1.03
1.0 11.645 4.56 Δ 0.30
8.0 93.163 3.66 Δ 0.05

A Data courtesy of Ref (1). This data developed from algorithms originally published in Ref (2).
FIG. 1 Restrictions Imposed by the Conductivity pH Relationship

1.2 This test method includes the procedures and equipment required for the continuous pH measurement of low conductivity water sample streams including the requirements for the control of sample stream pressure, flow rate, and temperature. For off-line pH measurements in low conductivity samples, refer to Test Method D5464.

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

1.4 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.

Document History

ASTM D5128-14
January 1, 2014
Standard Test Method for On-Line pH Measurement of Water of Low Conductivity
1.1 This test method covers the precise on-line determination of pH in water samples of conductivity lower than 100 μS/cm (see Table 1 and Table 2) over the pH range of 3 to 11 (see Fig. 1), under...
October 1, 2009
Standard Test Method for On-Line pH Measurement of Water of Low Conductivity
1.1 This test method covers the precise on-line determination of pH in water samples of conductivity lower than 100 μS/cm (see Table 1 and Table 2) over the pH range of 3 to 11 (see Fig. 1), under...
January 1, 2005
Standard Test Method for On-Line pH Measurement of Water of Low Conductivity
pH measurements are typically made in solutions that contain relatively large amounts of acid, base, or dissolved salts. Under these conditions, pH determinations may be made quickly and precisely....
June 10, 1999
Standard Test Method for On-Line pH Measurement of Water of Low Conductivity
1.1 This test method covers the precise on-line determination of pH in water samples of conductivity lower than 100 [mu]S/cm (see Tables 1 and 2) over the pH range of 3 to 11 (see Fig. 1), under...
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