Hach-Lange ISENH418103 User Manual - Manual (Page 12)

Message or symptom Possible cause Action
Out of limits
Check standard value is outside of
limits set in the current method Make sure that the standard is within the limits of the
current method.
Make another method that expands the acceptable
limits.
Measurement value is outside of
measurement limits set in the
current method. Make sure that the sample is within the limits of the
current method.
Make a new method with an expanded range.
Temperature out of range
Calibration temperature value is
outside of range Make sure that the sample temperature is within the
range of the probe.
Make sure that the temperature sensor is working
correctly.
Measured temperature is outside
the range of the electrode. Make sure that the standard temperature is within
the range of the probe.
Make sure that the temperature sensor is working
correctly.
Check standard temperature value
is outside of range Make sure that the check standard temperature is
within the range of the probe.
Below detection limit
Measurement is not quantifiable
with current saved calibration
(based on IUPAC-defined practical
detection limit). Perform a new calibration. Check that sample
concentration is bracketed between two standard
solution values (if within linear range).
Re-run calibration and measurement, optimizing
meter settings for slope acceptance and stabilization
criteria for expected sample concentration.
Re-run calibration and sample measurement with
the tips for low-level measurement.
Measurement value is outside of
range. Make sure sample is within the range of the probe.
Check probe response
To make sure there is a probe response, measure the probe potential (in mV) of two
Ammonium Standard Solutions that are above and below the expected sample
concentration. For example, use 10 and 100 mg/L Ammonium Standard Solutions. The
two solutions should have potentials (difference in mV readings) that are 57 mV apart at
25 ºC (within the slope limits of the method is acceptable). Both solutions should be
above 1.8 mg/L Ammonium.
Check accuracy of sample reading
To make sure the sample measurement is accurate, add a spike of Ammonium Standard
Solution with the volumetric pipet. Refer to
Table 3 and formulas to calculate the percent
of recovery.
Typically a percent of recovery of 100% ±5% is a good indication that the instrument,
technique and the sample do not contribute to measurement errors.
Table 3 Spike reference
Measured sample concentration Volume of standard at add Concentration of standard
1 to 2 mg/L 0.5 mL 100 mg/L
3 to 6 mg/L 1.0 mL 100 mg/L
7 to 15 mg/L 0.3 mL 1000 mg/L
15 to 30 mg/L 0.5 mL 1000 mg/L
30 to 60 mg/L 1.0 mL 1000 mg/L
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