multi N/C 2100S (duo, pharma)
Function and design
33
c
TOC
= c
TC
– c
TIC
The parameters appear in the TIC and TC analysis channels in the method.
The TC and TIC parameters can be calibrated simultaneously. The use of mixed standard
solutions such as carbonate/hydrogen carbonate and potassium hydrogen phtalate or
sucrose is recommended for this.
The TIC and TC channels can also be calibrated consecutively with separate standard so-
lutions. This is useful if different ranges are to be calibrated for the TC and TIC channels.
NPOC plus
The calibration of the NPOC plus method is the same as the calibration of the TOC (Diff)
method. Before analysis, the TIC must be sufficiently purged for the use of the differen-
tial method to be practical.
Method process:
¡
Separate calibration of TIC and TC channels
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Measurement of samples and calculation of the analysis results via the software
– Purging of the acidified sample (3 to 5 min)
– Determination of the remaining TIC with the calibration curve
– Determination of the TC with the calibration curve
– Calculation of the TOC from the difference of TC and TIC
The matrix-dependent calibration is as close to real samples as possible. To do this, add
carbonate to the standard solutions until you get a TIC content similar to that of the
samples.
TNb
The TN channel is calibrated. The following applies for the determined calibration func-
tion: c
TN
= f(I
TN
).
The calculated parameters appear in the method in the TN analysis channel.
3.6.4
Method characteristics
Remaining standard deviation
The remaining standard deviation (remaining variance) expresses the dispersion of the
integral values around the regression function (regression precision).
Method standard deviation
The standard deviation of the method describes the quality of the calibration in a non-
ambiguous and generally applicable way. For the non-ambiguous evaluation of the
quality, the standard deviation of the method must be used.
Method variation coefficient
The variation coefficient of the method (relative standard deviation of the method) is
used for the comparison of different calibrations with different calibration ranges.
Correlation coefficient
The correlation coefficient compares the dispersion of the calibration measuring points
of the regression function with the total dispersion of the calibration. If all calibration
measuring points are on the calculated regression function, the correlation coefficient is
+1 or -1. With a positive correlation coefficient, the regression function is increasing,
with a negative coefficient it is decreasing.
Coefficient of determination
The square of the correlation coefficient is called the coefficient of determination.
Limit of verification
The verification limit of the calibration specifies the lowest concentration that can be
differentiated qualitatively from the zero point with a given probability. The verification
limit should always be smaller than the lowest calibration measuring point.
