FED-STD-791D
Insert spiral reflux condenser in mouth of flask,connect condenser to cold water line,
place flask on hot plate, adjust heat so that contents boil gently and continue refluxing for
16 h.
6.13 Recovery of acid-Transfer contents of flask to crystallizing dish, rinse flask
3 or 4 times with 15 mL water and add washing to dish. Take to complete dryness on
steam bath, , add 15 mL water to dish.and warm to dissolve salts. Transfer solution to
separatory funnel, rinse dish 3 or 4 times with 15 mL water and add washings to funnel.
Place funnel in Ice bath, add 50 mL of cold dilute hydrochloric acid (1:1),cool for 10 min
and swirl to complete mixing of contents. Add 50 mL of ethyl ether, shake vigorously for
2 min,venting frequently to relieve pressure. Let phase separate completely and run the
lower (water) phase into a second separatory funnel. Run the upper (ether) layer into a
300 mL glass stoppered Erlenmeyer flask. Add 50 mL of ethyl ether to the second funnel
and re-extract the water layer as above, adding the ether layer to the 300-mL flask
.Repeat the ether extraction of the water layer twice more in individual funnels, collecting
the ether layers inthe300mL flask. Discard the water layer. Add 35-40 g of sodium sulfate
to the ether extract, shake and let stand a few hours or probably overnight. Filter the ether
solution through 10-m filter membrane (using stainless filter and funnel)in to a 300mL
Erlenmeyer flask with tapered joint. Rinse filter and funnel a few times with ethyl ether
to ensure complete removal of acids from sodium sulfate.Add 6-10 granules of silicon
carbide into the flask to avoid superheating, connect to Vigreux column and distill off the
ether in a hot water bath until the remaining solution is 20-25 mL stopper flask and retain
for essay. Conduct recovery of acids under hood.
6.14 Preparation of chromatograms- Using standard acid mixture and the
recovered acids, prepare chromatograms in the following manner: Inject 1 L of the
standard acid mixture into the chromatograph, mark for reference on recorder chart paper
where recorder pen was located at the time of injection, and complete chromatogram.
Examine chromatogram for peak heights of the acids. If the greatest peak height is
approximately three quarters of the chart width, the dosage and attenuator settings are
satisfactory. If not, adjust dosage and attenuator until the desired peak height is attained
A flash evaporator may be used as an alternate for removal of the water and alcohol.
In a similar manner inject 1L of the recovered acid, obtain chromatogram and proceed
as above until the peak height of the scan is satisfactory.
Identification and quantitative determination of recovered acids.
6.15 Identification of the acids recovered from the sample- On the chromatogram
of the standard acid mixture, assign C4 acid to first peak from reference mark on chart,
designate next peak as is -C5 acid, then the successive peaks to -C5 through C10 acids in
numerical order. Measure in mm the distances from reference mark to each peak and
record each distance against the corresponding acid. These values are designed as the
retention times of the acids. On the chromatogram of the recovered acids, measure
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