BUCHI DuMaster D-480 - Manual (Page 56)

Operation Manual D-480 ©BÜCH Labortechnik AG
4 - Understanding the instrument and planning its use 56
Computing calibration coefficients
Once the absolute element contents have been computed and the peak areas have been measured
for the respective sample, the pairs of values (absolute content / peak area) are transferred into a
coordinate system where they form the calibration curve. By means of an algorithm, the calibration
coefficients a - e are computed which, entered in a polynomial, constitute the calibration curve.
Absolute element content is computed according to this formula:
where:
y = absolute element content in [mg]
a...e = calibration coefficients
x = peak area
Computing the quality factor for polynomials of the 1st degree
In order to assess how well the calibration curve described by the polynomial follows the actual
development of the pairs of values, the softare computes a quality factor for each calibration process.
For a polynomial of the 1st degree (linear equation), this quality factor corresponds to the correlation
coefficient. The closer the correlation coefficient tends to 1, the better the fit.
The correlation coefficient is computed according to this formula:
where:
r 2 = correlation coefficient
x
i
= peak area of the corresponding sample
y
i
= absolute content of the corresponding
sample
n = number of samples
i = index from 1 to n
Computing the quality factor for polynomials of a higher degree
In order to assess how well the calibration curve described by the polynomial follows the actual
development of the pairs of values, the softare computes a quality factor for each calibration process.
For a polynomial of a higher degree, this quality factor corresponds to the sum of the error squares.
The closer the sum of error squares tends to 0, the better the fit.
The sum of error squares is computed with these formulae:
where:
q = quality
ssq = sum of error squares
act
i
= actual absolute content computed respectively
theo
i
= theoretical absolute content respectively
n = number of samples
i = index from 1 to n
Routine measuring work
Definitions
Routine measuring work comprises the following activities:
 Determination of instrument blank values.
 Instrument conditioning with conditioning samples.
 Determination of daily factors.