TROLL 9500 Operator's Manual - Geotech Environmental Equipment

Section 15: Ammonium16. The final screen of the Calibration Wizard shows the sensorslope and offset calculated during the calibration process. For athree-point bithermal calibration, the calculated isopotential pointis shown. If a single-point calibration has been performed, theisopotential point is the one calculated during the last three-pointbithermal calibration.17. Select Finish to program the sensor with the newly calculatedcalibration coefficients.Usage Recommendations and CautionsAmmonium SensorOperating TemperaturePressure RatingpH range up to 8.5-5°C to 40°C (23°F to104°F) continuoustemperature; can tolerate up to 50°C(122°F) intermittently20 psi (14 m, 46 ft)Do not submerge the ammonium sensor deeper than 46 ft(14 m). Do not use in the basic pH range (8.5 or higher).pHThe sensor’s pH range is that range over which a change in pH willnot cause a significant change in the measured voltage. It is theplateau on a graph of pH against mV at constant concentration of thedetected ion. Outside this range, a change in pH may cause a significantchange in the measured mV.TemperatureThe ammonium sensor is now calibrated and ready to use.TIP: You can look at the calibration report right aftercalibrating, or at any time. See “Calibration History” inSection 10 for details.Options for storing sensors:The ammonium sensor should calibrated immediately before use. Ifstorage is necessary, remove the sensor from the instrument and immersein 14 ppm N solution, for later use in the low ammonium range,or 140 ppm N solution, for use in the high range.Sensor Slope and OffsetThe expected slope for a new sensor is about 56 (± 2) mV per decadeof concentration (ppm). The calibration curve begins to deviate fromlinear at about 1 ppm. The sensor’s zero offset is recalculated witheach single-point calibration.Units and Calculated MeasurementsAmmonium ion concentration is reported in ppm (equivalent to mg/L).No calculated measurements are currently available.17The higher the temperature, the shorter the lifetime of the electrode.1°C difference in temperature causes a 2% error at 10 ppm, unless abithermal calibration is performed.ConductivityIn saline waters (conductivities of 1,000 µS/cm or higher), the presenceof interfering ions such as sodium or potassium may limit theusability of the ammonium sensor.Potential InterferencesThe following table lists concentrations of possible interfering ions thatcause 10% error at various levels of NH 4 + .Ion 100 ppm NH 4+10 ppm NH 4+1 ppm NH 4+Cs + 100 10 1K + 270 27 2.7Tl + 3100 310 31H + pH 1.6 pH 2.6 pH 3.6Ag + 270,000 27,000 2700Li + 35,000 3500 350Na + 11,100 1,100 110TROLL 9500 Operator’s Manual 1080095110 rev. 007 01/09