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X-ray emission method for sulfur or chlorine |
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|  MIL-L- 24131C(SH)
(c)
Add in turn to a 50 milliliter (ml) volumetric flask the dissolved melt, 3 ml of 6N nitric acid, 2
ml each of reagents 1 and 2 and water to 50 ml, mixing thoroughly at each addition. Then read
15 minutes after preparation. The reference solution shall be water.
(d)
Reagents. Reagents, including water, shall be of suitable analytical grade. Reagent solutions
shall have the following composition:
(1)
99.7 grams of Fe2 (SO4)3 (NH4)2SO4 24H2O per liter dissolved in 6N nitric acid.
Store in a brown bottle for 24 hours before use.
(2)
7.5 grams of Hg (SCN)2 dissolved in 500 ml methyl alcohol, mixed at least 1 hour with a
magnetic stirrer and filtered through Whatman No. 41 paper, or equal.
4.3.4.3.4 X-ray emission method for sulfur or chlorine.
(a)
Apparatus. An X-ray emission spectrograph with provision for vacuum or helium operation,
pulse height selection, a thin window (i.e. 1/4 mil mylar or thin formvar with P-10 gas of 1
mil nonporous beryllium, if sealed), proportional counter tube and a crystal with a 2 d (lattice
spacing) greater than 5.6 (Angstrom) shall be used. For most efficient operation on chlorine
or sulfur in the ppm range, an optimum high voltage, a chromium target tube and a wide (about
20 mil) collimator, shall be used.
(b)
Standards. Matrix material shall be colloidal graphite powder with the content of the
element(s) being determined sufficiently low so that the additional count rate due to the
element is less than 10 percent of the background. Standards covering the concentration range
expected shall be made by adding a uniform dispersion of known amounts of the element as
salts. The standards shall be compacted with a flat surface large enough to cover the aperture
in the specimen holder. The net count rate shall increase linearly with concentration.
(c)
Specimen. Evaporate the isopropanol from a quantity of lubricant sufficient to yield 2-3 grams
of solid graphite. Compress the powder into a pellet one inch in diameter.
(d)
Procedure.
(1)
Spectrographic operating conditions, including line angle, background angle, pulse height
adjustment and alignment, shall be established on a standard containing about 10 percent
of the element (chlorine or sulfur) to be determined.
(2)
Counting time for the specimen and for standards shall be adequate to determine the net
count rate (count at line angle less count at background angle) with the desired precision.
(3)
The specimen and standards bracketing the concentration range of the specimen are
counted using identical procedures, and the element concentration is read from a plot of
net count rate against the element concentrations of the standard.
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