How to check your pH electrode slope
1) Select the millivolt (mV) mode of your pH meter
2) Using a pH electrode, obtain mV readings of two fresh
calibration buffers (i.e., pH 4.0 and pH 7.0 are best)
3) Determine the net mV change
4) Determine the net mV change per pH unit change and
compare using the chart at right
>102
102%
101%
100%
99%
98%
97%
96%
95%
94%
93%
92%
<92
1pH unit
>59.3
59.3
58.8
58.2
57.6
57.0
56.4
55.8
55.3
57.0
54.1
53.5
<53.5
at 25°C
3pH units
>178.0
178.0
176.3
174.5
172.8
171.0
169.3
167.5
165.8
171.0
162.3
160.5
<160.5
1pH unit
3pH units
>60.3
60.3
59.8
59.2
58.6
58.0
57.4
56.8
56.2
58.0
55.0
54.4
<54.4
>181.0
181.0
179.3
177.5
175.7
173.9
172.2
170.4
168.6
173.9
165.1
163.3
<163.3
Status
Poor
OK
Very Good
Ideal
Very Good
Very Good
Very Good
Very Good
Very Good
OK
OK
OK
Poor
Care and
Maintenance of Electrodes
• Calibrate regularly with fresh buffers
• Rinse electrode tip well between readings
• On refillable electrodes be sure to check your fill level and open the fill
hole before calibration or measurement
• Never rub the bulb to dry it; a static charge can develop!
• Store your electrode with fill-hole closed in electrode storage solution
(Never store in deionized water!)
• Special electrode cleaning solutions (13-642-583) help with
tough samples that coat your electrode bulb—proteins,
bacteria, oils, and more
• Record temperature along with your
pH value
For example, at 25°C: pH 4
= 170.5mV, pH 7 = -3.4mV:
Net change = 170.5mV (-3.4mV) = 173.9mV. Since
pH 4 and pH 7 are 3 pH units
apart, using the chart,
98% = Very Good
electrochemistry 101
with Dr. Seymour Blue
Need Help? Call
00
•Organic Oil/Grease Films—liquid dish soap and warm water are best.
Isopropyl alcohol can be used on most electrodes if additional cleaning is
needed. NOTE: Solvents such as acetone will damage plastic body electrodes!
•Inorganic Salt Deposits—soak probe in 0.1M HCl as needed
•Proteins—Use a protein-cleaning solution (13-642-584)
If you have a refillable probe, drain the chamber and refill with correct reference filling
solution. Rinse the probe tip with distilled or deionized water and condition the
probe in storage solution before using again.
w
Te
0
7
l: 1
6
-800-76
w
w
m
a
.
o
f
x:
i
c
6
shersci.
6
1-8
1
1
0 0- 9 2 6
for your accumet specialist!
Buffers should be at
the same temperature
as your sample.
pH Scale
0
0
1
Battery
Battery Acid
Acid
2
Lemon
LemonJuice
Juice
1
Increasing
Acidity
Neutral
pH Values of Buffers at Various Temperatures
F
1.67
1.67
1.67
1.67
1.68
1.68
1.69
1.71
1.72
1.74
1.77
1.79
4.00
4.00
4.00
4.00
4.01
4.02
4.04
4.06
4.09
4.13
4.16
4.21
6.98
6.95
6.92
6.87
6.86
6.85
6.84
6.83
6.84
6.85
6.86
6.88
7.11
7.08
7.06
7.01
7.00
6.98
6.97
6.97
6.97
6.99
7.03
7.08
9.46
9.40
9.33
9.23
9.18
9.14
9.07
9.01
8.96
8.92
8.89
8.85
10.32
10.25
10.18
10.06
10.01
9.97
9.89
9.83
9.79
9.78
9.78
9.80
3
3
Vinegar
Vinegar
Orange Juice
4
Increasing 4
Acidity
55
(per NIST)
Standardized Buffers
0°C
5°C
10°C
20°C
25°C
30°C
40°C
50°C
60°C
70°C
80°C
90°C
2
Acid Rain
Cleaning Probes
Cleaning a dirty, clogged or coated electrode can restore proper electrode
performance and prolong the useful life of the electrode. Here are some
cleaning suggestions:
888-358-4706
Did you know?
12.79
12.73
12.67
12.52
12.46
12.36
12.17
11.96
11.73
11.47
11.19
10.89
Neutral
66
77
Milk
Milk
Distilled Water
88
Increasing 99
Alkalinity
10
10
Increasing
Alkalinity
11
11
12
12
13
13
14
14
Baking Soda
Soda
Baking
Sea Water
Sea Water
Milk of
of Magnesia
Magnesia
Milk
Ammonia
Ammonia
Lye
Lye
Acid Rain
©2009 Thermo Fisher Scientific Inc. All rights reserved. Litho in U.S.A DC/MA 7/09 09_2129 BN0720094
Slope
at 20°C