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Appendix B
5/20/2009
13
9.7.
General Operation
9.7.1.
To assure optimal operation and analytical results, it is advisable to
track the stability of the instrument. Of primary importance is the
precision and repeatability of standard and blank values during the
course of a day of operation. Thus, a standard (as an unknown) should
be inserted approximately every twenty runs. Try to use different
standards for QA in order to assure the validity of the calibration values
over the entire operating range of the instrument.
10. CALIBRATION, STANDARDIZATION and CALCULATIONS
10.1.1. Calibration - Daily calibration procedures must be performed and evaluated
before sample analysis may begin. Single point calibration is used with the Exeter
Model 440 Analyzer.
10.1.2. Establish single calibration factors (K) for each element (carbon, hydrogen, and
nitrogen) by analyzing three weighed portions of calibration standard
(acetanilide). The mass of the calibration standard should provide a response
within 20% of the response expected for the samples being analyzed. Calculate
the (K) for each element using the following formula:
Where:
RN = Instrument response to standard (µv)
ZN = Instrument zero response (µv)
BN = Instrument blank response (µv)
M = Mass of standard matter in µg
T = Theoretical % C, N, or H in the standard. For acetanilide %C =
71.09, %N = 10.36 and %H = 6.71.
10.2.
The detector generates a signal directly proportional to the compound of
interest in the sample. The following formula is used to calculate carbon, nitrogen
and hydrogen concentrations in unknown samples.
Where
K = calibration factor for the 440 instrument
W = sample weight
R = read signal of sample gas
Z = zero reading or base line of instrument
B = blank signal generated by instrument itself, including ladle and
capsules
All the calculations are done by the PC computer but the operator decides
which values to enter into the computer memory.
10.3.
The K-factor is established by running samples of a known standard. The
default value is for acetanilide, which we will use for our standard: