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INSTRUMENTS
PHILIPS
PW2440 4kW automated XRF
spectrometer system with a Rhodium 60kV end window x-ray tube,
five x-ray detectors, four primary beam filters, eight analysing crystals, two
fixed channels for simultaneous measurement of Na and F, and PW2540 168 sample
X-Y autochanger.
AFT 6000/C
automated fusion preparation system. HERZOG HTP 40 Pelletizing Press
SAMPLE PREPARATION
The Major Elements
Si Ti Al Fe Mn Mg Ca Na K P
and the trace elements Ba Ce Co
Cr Cu Ni Sc V
Zn are analysed using 32mm diameter fused beads prepared from a 1:5 sample:
Lithium Tetraborate mixture.
Other trace
elements, from Fluorine to Uranium, are determined by analysing
40mm diameter
pressed pellets prepared at a pressure of 20 tons from a mixture of 10g sample powder with 2g
Hoechst Wax C Micropowder.
CALIBRATION
Calibration lines are prepared using between 15 to 40 International Standard
Reference Materials (Geostandards Newsletter, XVIII, Special Issue, July 1994).
MASS ABSORPTION CORRECTIONS
All concentration values are corrected for mass absorption effects by using a
combination of alpha
coefficients and/or Compton scatter (in cases where the concentration is less
than 1000ppm, etc.).
ACCURACY
The accuracy
for Silica is within 0.5%. For the other major elements it is within 1%. For
trace elements the accuracy
is within 5%. The limiting factor for accuracy is the degree of scatter of
analyses from which the
consensus values are determined (Geostandards Newsletter, XVIII,2, 1994,
p 256, see values for Nb as an example).
PRECISION
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