Hach-Lange ISENa38103 - Manual (Page 14)

Message or symptom Possible cause Action
Out of range Measurement value is outside of range Make sure that the sample is within the range of
the probe.
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 probe 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.
Check probe response
To check the probe response, measure the probe potential (in mV) of two Sodium
Standard Solutions one decade apart in concentration that are above and below the
expected sample concentration. For example, use 10 and 100 mg/L Sodium Standard
Solutions. The two solutions should have potentials (difference in mV readings) that are
59 mV (±3 mV) apart at 25 °C. Both solutions should be above 1.4 mg/L Na
+ .
Check accuracy of sample reading
To check the accuracy of the sample reading, add a spike of Standard Sodium Solution
with the volumetric pipet. Refer to
Table 4 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 4 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
Percent recovery
Use the following formulas to calculate the percent recovery when the sample volume is
25 mL.
E = (C x V
1
) / V
2
R = (A / (E + S)) x 100
Where:
• S = mg/L of Na + in sample (before spike)
• C = concentration of standard used for spiking (mg/L)
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