Identification—
A:
Gently add 1 g of Hypromellose 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 substance. Allow the beaker to stand until the substance becomes transparent and mucilaginous (about 5 hours), and then 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:
Add 1 g of Hypromellose to 100 mL of boiling water, and stir the mixture: a slurry is formed, but the powdered material does not dissolve. Cool the slurry to 20
, and stir: the resulting liquid is a clear or opalescent mucilaginous colloidal mixture.
C:
Pour a few mL of the mixture prepared for
Identification test
B onto a glass plate, and allow the water to evaporate: a thin, self-sustaining film results.
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 apparent 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—Hydriodic acid and its reaction byproducts are highly toxic. Perform all steps of the Assay preparation and the Standard preparation in a properly functioning hood. Specific safety practices to be followed are to be identified to the analyst performing this test.
]
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 and 4.0 mL of Hydriodic acid, 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 30 µL of isopropyl iodide through the septum with a syringe, again weigh, and calculate the weight of isopropyl iodide added, by difference. Add 90 µL of methyl iodide similarly, 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 Hypromellose, accurately weighed, to a 5-mL thick-walled reaction vial equipped with a pressure-tight septum-type closure, add an amount of adipic acid equal to the weight of the test specimen, and pipet 2 mL of
Internal standard into the vial. Cautiously pipet 2 mL of
Hydriodic acid into the mixture, immediately cap the vial tightly, and weigh accurately. Mix the contents of the vial continuously, while heating at 150
for 60 minutes. Allow the vial to cool for about 45 minutes, and again weigh. If the weight loss is greater than 10 mg, discard the mixture, and prepare another
Assay preparation.
Chromatographic system
(see
Chromatography 621)—The gas chromatograph is equipped with a thermal conductivity detector and a 4-mm × 1.8-m glass column packed with 20% liquid phase G28 on 100- to 120-mesh support S1C that is not silanized. Helium is used as the carrier gas and the temperature of the column is maintained at 130
. Chromatograph the
Standard preparation, and record the peak responses as directed for
Procedure: the relative retention times are about 1.0, 2.2, 3.6, and 8.0 for methyl iodide, isopropyl iodide, toluene, and
o-xylene, respectively; and the resolution,
R, between toluene and isopropyl iodide is not less than 2.0.
Calibration—
Inject about 2 µL of the upper layer of the
Standard preparation into the gas chromatograph, and record the chromatogram. Calculate the relative response factor,
FM, of equal weights of toluene and methyl iodide taken by the formula:
QM / RSM,
in which
QM is the quantity ratio of methyl iodide to toluene in the
Standard preparation, and
RSM is the peak area ratio of methyl iodide to toluene obtained from the
Standard preparation. Similarly, calculate the relative response factor,
FI, of equal weights of toluene and isopropyl iodide taken by the formula:
QI / RSI,
in which
QI is the quantity ratio of isopropyl iodide to toluene in the
Standard preparation, and
RSI is the peak area ratio of isopropyl 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 (–OCH
3) in the Hypromellose taken by the formula:
2(31 / 142)FM RUM (WT / WU),
in which 31/142 is the ratio of the formula weights of methoxy and methyl iodide;
FM is defined under
Calibration; RUM 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 Hypromellose taken for the
Assay. Similarly, calculate the percentage of hydroxypropoxy (–OCH
2CHOHCH
3) in the Hypromellose taken by the formula:
2(75 / 170)FI RUI (WT / WU),
in which 75/170 is the ratio of the formula weights of hydroxypropoxy and isopropyl iodide;
FI is defined under
Calibration; RUI is the ratio of the area of the isopropyl 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 Hypromellose taken for the
Assay.
