MIL-PRF-23236D
c. Immerse the titration electrodes into the solution, start the stirrer, and set the pH meter to indicate readings
on the acid scale. If the pH meter shows an apparent pH reading of greater than 1.5, add more HNO3, until a reading
of 0 to 1.5 is obtained. Next, titrate the bromides with 0.05N AgN03, making a record of apparent pH versus
milliliter AgN03 added. From a plot of the record of the data, determine the appropriate inflection points, and
calculate the quantities of bromine using the formulas below.
g Br = 0.003996B
Or
= 0.3025B(1+0.00065(tF-60))
g Br/gal at 15.6 °C (60 °F)
= 0.3025B(1+0.00065(l.8 tC-281))
Where:
B = mL 0.05N AgN03 required to titrate bromide, and
tF = temperature (°F) of gasoline when sampled
tC = temperature (°C) of gasoline when sampled
Bromine shall be as specified in 3.13.5.
NOTES:
1.
A heavy-gauge silver wire attached directly to the calomel jack of the pH meter may be used. The portion that
dips into the liquid shall be cleaned by rubbing lightly with fine emery paper and rinsing with ASTM D1193
(any type) distilled water.
2.
Use a lecture bottle as the source of ammonia. From such a container, gaseous ammonia may be introduced
into the flask with virtually complete condensation at rates up to 2 grams per minute. The quantity of
ammonia being added can be followed by periodic weighing of the lecture bottle. Steps involving the
charging and evaporation of ammonia should be carried out in a hood.
3.
Pre-cool the sample by placing it in a flask surrounded by dry ice before introducing it into the sodium liquid
ammonia mixture. In such cases, care should be taken to protect the sample from moisture and dissolving
carbon dioxide. After adding a pre-cooled sample to the reaction mixture, rinse the cooling vessel with
10 milliliters of room temperature isooctane. This rinsing may be added directly to the reaction mixture.
4.
By using a slightly larger amount of ammonia (about 20 grams), pre-cooling is not necessary. Under these
conditions, a 50-milliliter sample of gasoline (at room temperature) may be added directly to the reaction
mixture without causing excessive boiling of the ammonia, provided the addition is as slow as from a pipette.
5.
If indicating Drierite or equal is used, evolution of ammonia is evidenced by a color change.
6.
During this period, it is important that the solution remain alkaline. Since sulfuric acid is one of the
decomposition products of ammonium persulfate, the solution should be checked occasionally to assure
alkalinity. This is done by using either litmus paper as an external indicator or methyl orange as an internal
indicator. In the majority of cases, the 2 grams of sodium hydroxide specified will be entirely sufficient.
However, if the solution is becoming acidic, more sodium hydroxide should be used.
7.
In some cases, a reddish solid or a dark solution may form during the oxidation step. Such behavior shall not
affect the analyses.
8.
At this point, the solution may contain a precipitate. This is of no consequence and the precipitate will usually
redissolve on further acidification in the next step.
4.5.5 Volatile organic content (VOC). VOC for all types, classes, and grades shall be determined in accordance
with 40 CFR 60 ch.1, part 60, Appendix A, Method 24. Solvent content shall be as specified in 3.2.2.2.
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