Identification—
A:
Gently add 1 g to the top of 100 mL of water in a beaker, and allow to disperse over the surface, tapping the top of the container to ensure an even dispersion of the test specimen. Allow the beaker to stand until the specimen becomes transparent and mucilaginous (about 5 hours), and swirl the beaker to wet the remaining substance, add a stirring bar, and stir until solution is complete: the mixture remains stable when an equal volume of 1 N sodium hydroxide or 1 N hydrochloric acid is added.
B:
Heat a few mL of the solution prepared for
Identification test
A: the solution becomes cloudy and a flaky precipitate, which redissolves as the solution cools, appears.
C:
Pour a few mL of the solution prepared for
Identification test
A onto a glass plate, and allow the water to evaporate: a thin, self-sustaining film results.
Apparent viscosity—
Place a quantity, accurately weighed and equivalent to 2 g of solids on the dried basis, in a tared, wide-mouth 250-mL centrifuge bottle, and add 98 g of water previously heated to 80
to 90
. Stir with a propeller-type stirrer for 10 minutes, place the bottle in an ice-bath, continue the stirring, and allow to remain in the ice-bath for 40 minutes to ensure that hydration and solution are complete. Adjust the weight of the solution to 100 g, if necessary, and centrifuge the solution to expel any entrapped air. Adjust the temperature of the solution to 20 ± 0.1
, and determine the viscosity in a suitable viscosimeter of the Ubbelohde type as directed for
Procedure for Cellulose Derivatives under
Viscosity 
911
. Its viscosity is not less than 80.0% and not more than 120.0% of that stated on the label for viscosity types of 100 centipoises or less, and not less than 75.0% and not more than 140.0% of that stated on the label for viscosity types higher than 100 centipoises.
Assay—
[
Caution—Perform all steps involving hydriodic acid carefully,
in a well-ventilated hood. Use goggles,
acid-resistant gloves,
and other appropriate safety equipment. Be exceedingly careful when handling the hot vials,
since they are under pressure. In the event of hydriodic exposure,
wash with copious amounts of water,
and seek medical attention at once.]
Hydriodic acid—
Use a reagent having a specific gravity of at least 1.69, equivalent to 55% HI.
Internal standard solution—
Transfer about 2.5 g of toluene, accurately weighed, to a 100-mL volumetric flask containing 10 mL of o-xylene, dilute with o-xylene to volume, and mix.
Standard preparation—
Into a suitable serum vial weigh about 135 mg of adipic acid, add 4.0 mL of Hydriodic acid, then pipet 4 mL of Internal standard solution into the vial, and close the vial securely with a suitable septum stopper. Weigh the vial and contents accurately, add 90 µL of methyl iodide with a syringe through the septum, again weigh, and calculate the weight of methyl iodide added, by difference. Shake, and allow the layers to separate.
Assay preparation—
Transfer about 0.065 g of dried Methylcellulose, accurately weighed, to a 5-mL thick-walled reaction vial equipped with a pressure-tight septum closure, add an amount of adipic acid equal to the weight of the test specimen, and pipet 2 mL of
Internal standard solution into the vial. Cautiously pipet 2 mL of
Hydriodic acid into the mixture, immediately secure the closure, and weigh it accurately. Shake the vial for 30 seconds, heat at 150
for 20 minutes, using a heating block or a protective wrapping, remove it from the source of heat, shake it again, using extreme caution, and heat it as before at 150
for an additional 40 minutes. Allow the vial to cool for about 45 minutes, and again weigh it. If the weight loss is greater than 10 mg, discard the mixture, and prepare another
Assay preparation.
Chromatographic system—
Use a gas chromatograph equipped with a thermal conductivity detector. Under typical conditions, the instrument contains a 1.8-m × 4-mm glass column packed with 10% liquid phase G1 on 100- to 120-mesh support S1A, the column is maintained at 100
, the injection port and the detector are maintained at 200
, and helium is used as the carrier gas at a flow rate of 20 mL per minute.
Calibration—
Inject about 2 µL of the upper layer of the
Standard preparation into the gas chromatograph, and record the chromatogram. The retention times for methyl iodide, toluene, and
o-xylene are approximately 3, 7, and 13 minutes, respectively. Calculate the relative response factor,
Fmi, of equal weights of toluene and methyl iodide taken by the formula:
Qsmi / Asmi,
in which
Qsmi is the quantity ratio of methyl iodide to toluene in the
Standard preparation, and
Asmi is the peak area ratio of the methyl iodide to toluene obtained from the
Standard preparation.
Procedure—
Inject about 2 µL of the upper layer of the
Assay preparation into the gas chromatograph, and record the chromatogram. Calculate the percentage of methoxy in the Methylcellulose taken by the formula:
2(31 / 142)Fmi Aumi (Wt / Wu),
in which 31/142 is the ratio of the formula weights of methoxy and methyl iodide;
Fmi is defined under
Calibration,
Aumi is the ratio of the area of the methyl iodide peak to that of the toluene peak obtained from the
Assay preparation;
Wt is the weight, in g, of toluene in the
Internal standard solution; and
Wu is the weight, in g, of Methylcellulose taken for the
Assay.
