MIL-DTL-10958G
7. Sample recovery curve:
a. Weigh 10.00 grams of sample into each of six 250-ml beakers, add 0, 5, 10, 12, 15, and 17
ml of calcium EDTA standard solution B from a buret. Dilute to 100 ml with distilled water.
b. Add to each beaker 4.0 grams of filter aid and 2.0 grams of barium carbonate. Mix with a
stirring rod and heat almost to boiling on a hot plate with continuous stirring.
c. Transfer the samples to the steam bath and digest for one-half hour with stirring at 10
minute intervals.
d. Remove the beakers from the steam bath, cool to room temperature in a cold water bath
and filter on a Buchner funnel catching the filtrate in a clean beaker. (The filter should be
prepared using a 9.0 cm Whatman No. 3 or equivalent paper and 2.0 grams of filter aid added as
a slurry and pulled down under full vacuum). Wash the contents of the funnel by adding four
successive 25-ml portions of water to the original beaker, policing down the sides with the first
wash and pouring into the funnel.
e. To the filtrate from 7d add 3.0 ml of 5N hydrochloric acid and 10 ml of magnesium
chloride solution (3d). Adjust the resulting solution to a pH of 9.0 with concentrated
ammonium hydroxide and add 0.5 ml in excess. Add 5.0 ml of phosphoric acid (3f) to the
solution while stirring vigorously.
f. Transfer the filtrate to a 250-ml volumetric flask, rinse the beaker with distilled water,
transfer into the flask, make to volume and mix thoroughly.
g. Filter 75-100 ml of the solutions, after allowing them to stand for at least one hour,
through a dry fine porosity filtering crucible or a dry 42 Whatman filter paper. Discard the first
25 ml of filtrate collecting the remaining filtrate in a clean dry beaker.
h. Prepare a 50-ml volumetric flask as in (5a) for each sample. Also prepare another 50-ml
volumetric flask for each sample to be used as a color blank (do not add zirconium to the sample-
color reagent blank). Pipet a 25.0 ml aliquot into the second prepared volumetric flasks to be
used as a sample color reagent blank. Dilute each flask to volume and mix well. Proceed with
the determination as in (5c). Determine the absorbance of each sample using its color blank as
the reference standard. Read the micrograms of calcium EDTA from the standard curve.
Calculation of results:
ppm calcium EDTA = micrograms of calcium EDTA found
grams of sample x aliquot
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