MIL-DTL-98B
concentration of MeOH in the ACN is determined by measuring the weight of the MeOH and the
weight of the total internal standard solution. The actual water content of the internal standard is
determined by coulometric Karl Fischer (KF) analysis using a Brinkman 756 (KF) coulometric
titroprocessor. The response factor between water and MeOH is calculated at the beginning of
each shift and is determined by analyzing the internal standard solution with KF coulometric
analysis and by gas chromatography. The DPA sample is solvated in the internal standard
solution, analyzed by gas chromatography and total water content of solvent and sample is
determined. The water content of the DPA sample is calculated by subtracting the water content
of the internal standard solution from the total water content.
4.2.4.1.1 Procedure for making the methanol/water internal standard. Weigh 650.0 grams
of dried acetonitrile (ACN) into a 16 oz. amber bottle using a 2-place balance. Using a- 4-place
balance and appropriate weight of water to the bottle to make an approximate 500 ppm water in
ACN solution(weight of water = 0.0005 * weight of ACN) Using a 4-place balance and
appropriate weight of methanol (MeOH) to the bottle to make an approximate 1000 ppm MeOH
in ACN solution (weight of MeOH = 0.001 * weight of ACN). Record the exact weight of
MeOH in the bottle. Determine the actual concentration of MeOH in the solvent as follows:
Wt. of M eOH in grams * (106
Actual MeOH concentration ppm =
Wt. of ACN M eOH water in grams
4.2.4.1.2 Method for determination of moisture by gas chromatography. Place ½ oz.
bottles and autoinjector vials in a 65o C heated vacuum dessicator to warm. Place the DPA
sample in a 100o C convection oven to melt. Prepare an internal standard solution (ISTD) as
described to be used for water calculation. Inject 5 µ l of the ISTD in duplicate into a gas
chromatograph fitted with a thermal conductivity detector. Duplicates shall match within 20 ppm
for methanol. Record average heights of water peaks and average heights of the MeOH peaks for
use in determination of response factor. Analyze the water content of the ISTD in duplicate. Pull
up 1 ml of ISTD into a gas tight 1 ml syringe. Zero the syringe on a 4-place balance. Inject 1ml
of the ISTD into a coulometric Karl Fisher (KF) titroprocessor. Reweigh the syringe and enter
the weight into the titroprocessor. Record the average water content of the duplicate analyses for
use in determination of the response factor. The response factor is determined at the beginning of
every shift. DPA water analysis shall be in accordance with Figure 3.
Response factor = (peak height of water (ISTD) * (ppm of MeOH (ISTD))
(ppm of water from coulometric KF analysis * (peak height of MeOH (ISTD))
For DPA moisture determination weigh 2.0 g of molten sample into a heated ½ oz. bottle. Add
2.0 g of the ISTD. Cap the bottle. Mix well and immediately fill an autoinjector vial with the
same and cap the vial. Autoinject into the gas chromatograph and start the integrator. Order of
elution is air, water and methanol. The integrator will print out the peak heights to be used in the
calculation as follows:
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