Two-Point Calibration - GE Sievers InnovOx Operation And Maintenance Manual

Chapter 5: Calibration and Verification
In a single-point calibration, the calibration constant is the slope of the line shown in Figure 14, and the response
of the Analyzer is assumed to pass through the origin.
Certain recommendations can be made about the use of single-point calibrations:
• Reagent water (TOC or IC concentration of zero) may not be used as the single point.
• If the highest accuracy is sought, calibrate using at least two points.
• The concentration of the calibration point in a single-point calibration should be greater than the
expected concentration of the samples, but not exceed them by too much.
• Because Auto Dilution contributes some uncertainty to the calibration, single-point calibrations using
Auto Dilution normally are not recommended.
• If you plan to use the Auto Range feature, calibration of the 50,000 ppm range is important because the
preliminary measurement used to determine the appropriate analysis range is performed in this range.
For best performance of the Auto Range feature, it is recommended that the 50,000 ppm range be
calibrated using a six-point, point-to-point calibration (see page 96). The recommended points are:
Reagent Water, 100 ppm, 1,000 ppm, 5,000 ppm, 20,000 ppm and 50,000 ppm.

Two-Point Calibration

The concentrations of the two points should be selected to bracket the range of concentrations expected in the
samples that will be subsequently analyzed.
As in all calibrations involving more than a single point, the point having the lowest concentration is measured
first. In most cases the Analyzer will be used to analyze samples containing substantial TOC concentrations.
However, if the Analyzer will be used to measure samples having very low TOC concentrations, then Point 1 may
have to be reagent water (TOC  0.1 ppm) in order to bracket the concentrations of the samples.
When you plan on measuring TOC(TC-IC) in your samples, it is recommended that the first calibration point for
the TC and IC portions be reagent water. This will ensure that the best linear response will be achieved for both
TC and IC regardless of the variability of the individual concentrations.
Figure 15 depicts a two-point calibration in which point 1 is not reagent water. The concentrations of both points
are entered into the calibration protocol.
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