Thermo Fisher Scientific Ion Selective Electrodes Lead - 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