Thermo Fisher Scientific Ion Selective Electrodes Lead User Manual
Page 22

Low Slope or
standards contaminated
prepare fresh standards
No Slope
or incorrectly made
standard used as ISA
use ISA
ISA not used
use recommended ISA
membrane dirty
polish membrane; use
or oxidized
methanol-formaldehyde solution
air bubble on
remove bubble by
membrane
re-dipping probe
"Incorrect Answer"
incorrect scaling
plot millivolts on the linear axis. On
(but calibration
of semi-log paper
the log axis, be sure concentration
curve is good)
numbers within each decade are
increasing with increasing
concentration
incorrect sign
be sure to note sign
of millivolt reading correctly
incorrect standards
prepare fresh standards
wrong units used
apply correct conversion factor:
10
-3
M = 207 ppm Pb
+2
= 96 ppm SO
4
-2
complexing agents
check section entitled
in sample
Precipitation and Complexation
;
use titration method