Thermo Fisher Scientific CyberScan pH/Ion 510 - Manual (Page 30)

Instruction Manual pH 510/ Ion 510
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8 ADDITIONAL INFORMATION
8.1
pH and Temperature
Automatic Temperature Compensation (ATC) compensates for temperature changes. Some solutions show an increase
while others a decrease in pH with the same temperature change. Record the solution temperature along with the pH
value, or the measurement may be meaningless. Temperature changes also affect the signal the pH electrode sends to
the meter and causes a loss of accuracy for the reading. To limit the loss of accuracy during calibration, make the
temperature of the pH buffer calibrating solutions and the sample solution the same.
8.2 Use of Standard pH Buffers
Use standard buffer solutions to calibrate a pH meter before you measure the pH of a sample. They serve as reference
standards for basis of comparison between measurements. The most common USA standard buffers are the pH 1.68,
pH 4.01, pH 7.00, pH 10.01 and pH 12.45 and the NIST standard buffers are pH 1.68, 4.01, pH 6.86 pH 9.18 and pH
12.45. For 1-point calibration, use a standard buffer of pH 7.00 or a standard buffer whose pH value is close to that of the
sample. Use 2-point calibration when you know the sample is acidic (low pH) or basic (high pH). For acidic samples, use
standard buffers of pH 7.00 and pH 4.01. For basic samples, use standards of pH 7.00 and pH 10.01. Use a 5-point
calibration when the sample pH is completely unknown. Use all pH 1.68, pH 7.00, pH 4.01, pH 10.1 and pH 12.45
calibration solutions (using a low sodium error electrode).
8.3
Standard pH Buffers
The following table shows the various pH values at different temperature of the solution during calibration. The table also
illustrates why a calibration value may be different from the buffer value at 25
o
C.
USA Buffer NIST Buffer Temperature
( o C)
pH 1.68 pH 4.01 pH 7.00 pH 10.01 pH 12.45 pH 1.68 pH 4.01 pH 6.86 pH 9.18 pH 12.45
0 1.67 4.01 7.12 10.32 13.43 1.67 4.01 6.98 9.46 13.43
5 1.67 4.01 7.09 10.25 13.21 1.67 4.01 6.95 9.40 13.21
10
1.67
4.01 7.06 10.18 13.00
1.67
4.01 6.92 9.33 13.00
15 1.67 4.00 7.04 10.12 12.81 1.67 4.00 6.90 9.28 12.81
20 1.68 4.00 7.02 10.06 12.63 1.68 4.00 6.87 9.23 12.63
25 1.68 4.01 7.00 10.01 12.45 1.68 4.01 6.86 9.18 12.45
30 1.69 4.01 6.99 9.97 12.29 1.69 4.01 6.85 9.14 12.29
35 1.69 4.02 6.98 9.93 12.13 1.69 4.02 6.84 9.11 12.13
40 1.70 4.03 6.97 9.89 11.99 1.70 4.03 6.84 9.07 11.99
45 1.70 4.04 6.97 9.86 11.84
1.70
4.04 6.83 9.04 11.84
50 1.71 4.06 6.97 9.83 11.70 1.71 4.06 6.83 9.01 11.70
55 1.72 4.08 6.97 9.81 11.58 1.72 4.08 6.83 8.99 11.58
60 1.73 4.10 6.98 9.79 11.45 1.73 4.10 6.84 8.96 11.45
65 1.73 4.11 6.98 9.77 11.45 1.73 4.11 6.84 8.94 11.45
70 1.74 4.12 6.99 9.76 11.45 1.74 4.12 6.85 8.92 11.45
75 1.75 4.14 6.99 9.75 11.45 1.75 4.14 6.85 8.91 11.45
80 1.77 4.16 7.00 9.74 11.45 1.77 4.16 6.86 8.89 11.45
85 1.78 4.18 7.01 9.73 11.45 1.78 4.18 6.87 8.87 11.45
90 1.80 4.23 7.02 9.73 11.45 1.80 4.23 6.88 8.85 11.45
95 1.81 4.23 7.03 9.74 11.45 1.81 4.23 6.88 8.85 11.45
100 1.81 4.23 7.03 9.74 11.45 1.81 4.23 6.88 8.85 11.45