7
VIIVII
VIIVII
VII.
General GuidelinesGeneral Guidelines
General GuidelinesGeneral Guidelines
General Guidelines
• Calibration standards and sample solutions should
have the same ionic strength. ISA should be added to
both samples and standards immediately before tak-
ing measurements.
• Calibration standards and sample solutions should be
stirred at the same rate using identical sized stir bars.
Stir thoroughly and continuously.
• Calibration standards and sample solutions should be
at the same temperature. Thermally insulate solution
vessel from magnetic stirrer with cork or other insulat-
ing medium.
• Wait until sensor value has stabilized before taking
reading (at least 5 minutes when going from more
dilute to more concentrated samples, longer when the
order is reversed).
• Surface coating on the PTFE membrane will effect the
response. Inspect sensor before using. Wash off with a
jet of deionized water or mild detergent to remove
film.
• Replace PTFE membrane if damage is evident or a
droplet of internal electrolyte is seen.
• Rinse electrode with distilled or deionized water be-
tween samples and dab dry with lab wipe or other soft
disposable absorbent toweling.
• Check calibration every 1-2 hours. Recalibrate if nec-
essary.
• Position sensors at an angle of approximately 20° to
30° from verticle to reduce possibility of trapping gas
bubbles on on the membrane cap. Gas bubbles also
form from solution out-gassing due to temperature
change. Gently tap body of sensor to dislodge them.
• Close container with plastic wrap or use HI 4000-71
gas sensor test vessel to prevent gas from leaving.
• If electrode was left out in air for a prolonged period,
gently pulling cable will permit an exchange of fill
solution at the membrane surface. Re-Calibration is
required.
