Thermo Scientific Orion Versa Star Pro, Руководство пользователя

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Appendix A

Channel Specific Settings and Features
134

Orion Versa Star Pro Meter User Manual Thermo Scientific
The meter evaluates the relationships between the three potentials E
1
, E
2
and E
3
and the three
concentrations C
1
, C
2
and C
3
. If the relationships indicate that blank correction is desired, a
blank will automatically be calculated and the non-linearity will be corrected for in a Nernstian
manner. If the appropriate conditions are not met, the blank is set at zero and each segment of
the multi-point calibration is treated independently.
When all three of the following conditions are met, blank correction is invoked.
1. The concentration of the first standard is zero, or the slope of the electrode between the
first and second standards is less than the slope between the second and third.
2. Potential differences between points are significant. For example, E
3
- E
1
> 10 mV
3. The blank correction algorithm converges at reasonable blank and slope values.
Conditions in steps 1 and 2 prevent failure to converge in most situations. However, the
slope will attain any value necessary for convergence to a calculated blank value of 3 x C
3
.
When blank correction is implemented, the slope value for the electrode may be outside the
range of values normally considered acceptable during an ordinary calibration. For best results,
calibration standards should be close in range to the expected sample concentrations and
should bracket the expected sample concentration. When conditions 1, 2 and 3 are not met, the
calibration data is handled by the multi-point calibration method described earlier.
In calibrations with more than three points, a combination of methods is utilized. Automatic
blank correction is used if the lowest three points satisfy the criteria and multi-point calibration is
used for the other points. The slope calculated in the automatic blank correction algorithm and
the slopes for each additional segment are used to calculate the average slope.
Low Level Stability
Versa Star Pro meters with a pH/ISE module offer the option to use the low level stability
feature when calibrating ion selective electrodes. The low level stability feature improves the
accuracy of low concentration ISE measurements by adjusting the timing for calibration points
of low level standards, allowing a longer stabilization time for the electrode in the calibration
standards. The stabilization time is typically extended to about three to five minutes per
calibration point, but will vary based on the actual readings from the electrode during
calibration.