USP辅料标准

Talc

?

Talc is a powdered, selected, natural, hydrated magnesium silicate. Pure

talc has the formula Mg

3

Si

4

O

10

(OH)

2< /p>

. It may contain variable amounts of

associated minerals among which chlorites (hydrated aluminum and

magnesium silicates), magnesite (magnesium carbonate), calcite (calcium

carbonate), and dolomite (calcium and magnesium carbonate) are

predominant.

Labeling

—

The label states, where applicable, that the substance is suitable for oral

or topical administration. The certificate of analysis states the absence of asbestos. It

also indicates which method specified under the test for

Absence of asbestos

was

used for analysis.

Identification

—

A:

The IR spectrum of a potassium bromide dispersion of it exhibits maxima at 3677 ±

2 cm

–

1

, at 1018 ±

2 cm

–

1

, and at 669 ±

2 cm

–

1

.

B:

Mix about 200 mg of anhydrous sodium carbonate with 2 g of anhydrous

potassium carbonate, and melt in a platinum crucible. To the melt add 100 mg of the

substance under test, and continue heating until fusion is complete. Cool, and transfer

the fused mixture to a dish or beaker with the aid of about 50 mL of hot water. Add

hydrochloric acid to the liquid until effervescence ceases, then add 10 mL more of the

acid, and evaporate the mixture on a steam bath to dryness. Cool, add 20 mL of water,

boil, and filter the mixture: [

NOTE

—

Save the insoluble residue for use in

Identification

test

C.

] To 5 mL of the filtrate add 1 mL of 6 N ammonium hydroxide and 1 mL of

ammonium chloride TS

. Filter, if necessary, and add 1 mL of

dibasic sodium

phosphate TS

to the filtrate: a white crystalline precipitate of magnesium ammonium

phosphate is formed.

C:

In a lead or platinum crucible and using a copper wire, mix about 100 mg of the

insoluble residue as obtained in

Identification

test

B

with about 10 mg of sodium

fluoride and a few drops of sulfuric acid to give a thin slurry. Cover the crucible with a

thin transparent plate of plastic under which a drop of water is suspended, and warm

gently. Within a short time, a white ring is rapidly formed around the drop of water.

Microbial limits

61

—

If intended for topical administration, the total aerobic

microbial count does not exceed 100 cfu per g, and the total combined molds and

yeasts count does not exceed 50 cfu per g. If intended for oral administration, the total

aerobic microbial count does not exceed 1000 cfu per g, and the total combined

molds and yeasts count does not exceed 100 cfu per g.

Acidity and alkalinity

—

Boil 2.5 g of Talc with 50 mL of carbon dioxide-free water

under reflux. Filter under vaccum. To 10 mL of the filtrate, add 0.1 mL of

bromothymol blue TS

. Not more than 0.4 mL of 0.01 N hydrochloric acid is required to

change the color of the indicator. To 10 mL of the filtrate, add 0.1 mL of

phenolphthalein TS: not more than 0.3 mL of 0.01 N sodium hydroxide is required to

change the color of the indicator to pink.

Loss on ignition

733

—

Weigh accurately about 1 g and ignite at 1075 ±

25

to

constant weight: it loses not more than 7.0% of its weight.

Water- soluble substances

—

To 10.0 g add 50 mL of carbon dioxide-free water, heat

to boiling, and boil under a reflux condenser for 30 minutes. Allow to cool, filter, and

dilute with carbon dioxide-free water to 50.0 mL: the filtrate is neutral to litmus paper.

Evaporate 25.0 mL of the filtrate to dryness, and dry at 105

for 1 hour: the weight of

the residue does not exceed 5 mg (0.1%).

Limit of iron

—

Test stock solution

—

Weigh 10.0 g of Talc into a conical flask fitted with a reflux

condenser, gradually add 50 mL of 0.5 N hydrochloric acid while stirring, and heat on

a water bath for 30 minutes. Allow to cool. Transfer the mixture to a beaker, and allow

the undissolved material to settle. Filter the supernatant into a 100-mL volumetric

flask, retaining as much as possible of the insoluble material in the beaker. Wash the

residue and the beaker with three 10-mL portions of hot water. Wash the filter with 15

mL of hot water, allow the filtrate to cool, and dilute with water to 100.0 mL.

Test solution

—

Transfer 2.5 mL of the

Test stock solution

to a 100-mL volumetric flask,

add 50.0 mL of 0.5 N hydrochloric acid, and dilute with water to volume.

Standard iron stock solution

—

Transfer 863.4 mg of ferric ammonium sulfate to a

100-mL volumetric flask, dissolve in water, add 10 mL of 2 N sulfuric acid, and dilute

with water to volume. Pipet 25 mL of this solution into a 100-mL volumetric flask, add

10 mL of 2 N sulfuric acid, dilute with water to volume, and mix. This solution contains

the equivalent of 250 ?

g of iron per mL.

Standard iron solutions

—

Into four 100-mL volumetric flasks, each containing 50.0 mL

of 0.5 N hydrochloric acid, transfer respectively 2.0, 2.5, 3.0, and 4.0 mL of the

Standard iron stock solution,

and dilute each flask with water to volume.

Procedure

—

Concomitantly determine the absorbance of the

Test solution

and the

Standard iron solutions

at the iron emission line of 248.3 nm with an atomic

absorption spectrophotometer (see

Spectrophotometry and Light-Scattering

851

)

equipped with an iron hollow-cathode lamp and an air

–

acetylene flame. Make any

correction using a deuterium lamp: not more than 0.25% of iron is found.

Limit of lead

—

Test solution

—

Use the

Test stock solution,

prepared as directed in the test for

Limit

of iron.

Lead standard stock solution

—

Dissolve 160 mg of lead nitrate in 100 mL water that

contains 1 mL of nitric acid, and dilute with water to 1000 mL. Pipet 10 mL of this

solution into a 100-mL volumetric flask, dilute with water to volume, and mix. This

solution contains the equivalent of 10 ?

g of lead per mL.

Standard lead solutions

—

Into four identical 100-mL volumetric flasks, each

containing 50.0 mL of 0.5 N hydrochloric acid transfer respectively 5.0, 7.5, 10.0, and

12.5 mL of

Lead standard stock solution,

and dilute with water to volume.

Procedure

—

Concomitantly determine the absorbance of the

Test solution

and the

Standard lead solutions

at the lead emission line of 217.0 nm with an atomic

absorption spectrophotometer (see

Spectrophotometry and Light-Scattering

851

)

equipped with a lead hollow-cathode lamp and an air

–

acetylene flame: not more than

0.001% of lead is found.

Limit of calcium

—

Cesium chloride solution

—

Dissolve 2.53 g of cesium chloride in 100 mL of water, and

mix.

Lanthanum chloride solution

—

To 5.9 g of lanthanum oxide slowly add 10 mL of

hydrochloric acid, and heat to boiling. Allow to cool, and dilute with water to 100 mL.

Test stock solution

—

[

Cautio n

—

Perchlorates mixed with heavy metals are known to

be explosive. Take proper precautions while performing this procedure.

] Weigh 500

mg of Talc in a 100-mL polytetrafluoroethylene dish, add 5 mL of hydrochloric acid, 5

mL of lead-free nitric acid, and 5 mL of perchloric acid. Stir gently, then add 35 mL of

hydrofluoric acid, and evaporate slowly on a hot plate to moist dryness (until about 0.5

mL remains). To the residue, add 5 mL of hydrochloric acid, cover with a watch glass,

heat to boiling, and allow to cool. Rinse the watch glass and the dish with water, and

transfer into a 50-mL volumetric flask containing 5 mL of the

Cesium chloride solution.

Rinse the dish again with water, and dilute with water to volume.

Test solution

—

Transfer 5.0 mL of the

Test stock solution

to a 100-mL volumetric flask,

add 10.0 mL of hydrochloric acid and 10 mL of

Lanthanum chloride solution,

and

dilute with water to volume.

Calcium standard stock solution

—

Dissolve 3.67 g of calcium chloride dihydrate in

diluted hydrochloric acid, and dilute with the same solvent to 1000 mL. Immediately

before use, pipet 10 mL of this solution into a 100-mL volumetric flask, dilute with

water to volume, and mix. This solution contains the equivalent of 100 ?

g of calcium

per mL.

Standard calcium solutions

—

Into four identical 100-mL volumetric flasks, each

containing 10.0 mL of hydrochloric acid and 10 mL of

Lanthanum chloride solution,

transfer respectively 1.0, 2.0, 3.0, and 4.0 mL of

Calcium standard stock solution,

and

dilute each flask with water to volume.

Procedure

—

Concomitantly determine the absorbance of the

Test solution

and the

Standard calcium solutions

at the calcium emission line of 422.7 nm with an atomic

absorption spectrophotometer (see

Spectrophotometry and Light-Scattering

851

)

equipped with a calcium hollow-cathode lamp and a nitrous oxide

–

acetylene flame:

not more than 0.9% of calcium is found.

Limit of aluminum

—

Cesium chloride solution

and

Test stock solution

—

Proceed as directed in the test for

Limit of calcium.

Test solution

—

Transfer 5.0 mL of the

Test stock solution

to a 100-mL volumetric flask,

add 10 mL of the

Cesium chloride solution

and 10.0 mL of hydrochloric acid, and

dilute with water to volume.

Aluminum standard stock solution

—

Dissolve 8.947 g of aluminum chloride in water,

and dilute with water to 1000 mL. Immediately before use, pipet 10 mL of this solution

into a 100-mL volumetric flask, dilute with water to volume, and mix. This solution

contains the equivalent of 100 ?

g of aluminum per mL.

Standard aluminum solutions

—

Into four identical 100-mL volumetric flasks, each

containing 10.0 mL of hydrochloric acid and 10 mL of

Cesium chloride solution,

transfer respectively 5.0, 10.0, 15.0, and 20.0 mL of

Aluminum standard stock solution,

and dilute with water to volume.

Procedure

—

Concomitantly determine the absorbance of the

Test solution

and the

Standard aluminum solutions

at the aluminum emission line of 309.3 nm with an

atomic absorption spectrophotometer (see

Spectrophotometry and Light-Scattering

851

) equipped with an aluminum hollow-cathode lamp and a nitrous

oxide

–

acetylene flame: not more than 2.0% of aluminum is found.

Absence of asbestos

—

[

NOTE

—

Suppliers of Talc may use one of the following

methods to determine the absence of asbestos.] Proceed as directed for test

A

or test

B.

If either test is positive, perform test

C.

A:

The IR absorption spectrum of a potassium bromide dispersion of it at the

absorption band at 758 ±

1 cm

–

1

, using scale expansion, may indicate the presence of

tremolite or of chlorite. If the absorption band remains after ignition of the substance at

850

for at least 30 minutes, it indicates the presence of the tremolite. In the range

600 cm

–

1

to 650 cm

–

1

using scale expansion, any absorption band or shoulder may

indicate the presence of serpentines.

B:

X-ray diffraction

941

employing the following conditions: Cu K

monochromatic 40 kV radiation, 24 mA to 30 mA; the incident slit is set at 1

; the

detection slit is set at 0.2

; the goniometer speed is 1/10

2

per minute; the

scanning range is 10

to 13

2

and 24

to 26

2

; the sample is not oriented.

Prepare a random sample, and place on the sample holder. Pack and smooth its

surface with a polished glass microscope slide. Record the diffractograms: the

presence of amphiboles is detected by a diffraction peak at 10.5 ±

0.1

2

, and the

presence of serpentines is detected by diffraction peaks at 24.3 ±

0.1

2

to 12.1 ±

0.1

2

.

C:

The presence of asbestos (see

Optical Microscopy

776

) is shown if there is a

range of length to width ratios of 20:1 to 100:1, or higher for fibers longer than 5 ?

m; if

there is a capability of splitting into very thin fibrils; and if there are two or more of the

following four criteria: (1) parallel fibers occurring in bundles, (2) fiber bundles

displaying frayed ends, (3) fibers in the form of thin needles, or (4) matted masses of

individual fibers and/or fibers showing curvature.

Content of magnesium

—

Lanthanum chloride solution

and

Test stock solution

—

Prepare as directed in the test

for

Limit of calcium.

Test solution

—

Dilute 0.5 mL of

Test stock solution

with water to 100.0 mL. Transfer

4.0 mL of this solution to a 100-mL volumetric flask, add 10.0 mL of hydrochloric acid

and 10 mL of

Lanthanum chloride solution,

and dilute with water to volume.

Magnesium standard stock solution

—

Dissolve 8.365 g of magnesium chloride in

diluted hydrochloric acid, and dilute with the same solvent to 1000 mL. Pipet 5 mL of

this solution into a 500-mL volumetric flask, dilute with water to volume, and mix. This

solution contains the equivalent of 10 ?

g of magnesium per mL.

Standard magnesium solutions

—

Into four identical 100-mL volumetric flasks, each

containing 10.0 mL of hydrochloric acid and 10 mL of

Lanthanum chloride solution,

transfer respectively 2.5, 3.0, 4.0, and 5.0 mL of

Magnesium standard stock solution,

and dilute with water to volume.

Procedure

—

Concomitantly determine the absorbance of the

Test solution

and the

Standard magnesium solutions

at the magnesium emission line of 285.2 nm with an

atomic absorption spectrophotometer (see

Spectrophotometry and Light-Scattering

851

) equipped with a magnesium hollow-cathode lamp and an air

–

acetylene flame:

between 17.0% to 19.5% of magnesium is found.

Residual solvents

467

:

meets the requirements.

(Official January 1, 2007)

Auxiliary Information

—

Staff Liaison

:

Catherine Sheehan, ., Scientist

Expert Committee

: (EM105) Excipient Monographs 1

USP29

–

NF24

Page 2054

Pharmacopeial Forum

: Volume No. 30(5) Page 1857

Phone Number

: 1-301-816-8262

Anhydrous Lactose

?

Anhydrous Lactose is primarily beta lactose or a mixture of alpha and beta

lactose.

Labeling

—

Where the labeling indicates the relative quantities of alpha and beta

lactose, determine compliance using

Content of alpha and beta anomers

.

USP Reference standards

11

—

USP Anhydrous Lactose RS

.

USP Sucrose RS

.

USP Fructose RS

.

USP Dextrose RS

.

Identification

—

A:

Infrared Absorption

197K

.

B:

Proceed as directed in

Identification

test

B

under

Lactose Monohydrate

, except to

use

USP Anhydrous Lactose RS

instead of

USP Lactose Monohydrate RS

in

Standard solution A

and

B

and to use Anhydrous Lactose in the

Test solution

.

C:

Proceed as directed in

Identification

test

C

under Lactose Monohydrate.

Loss on drying

731

—

Dry it at 80

for 2 hours: it loses not more than 0.5% of its

weight.

Water,

Method I

921

: not more than 1.0%, determined on a preparation

containing anhydrous lactose in a mixture of methanol and formamide (2:1).

Heavy metals,

Method II

231

: 5 ?

g per g.

Content of alpha and beta anomers

—

Silylation reagent

—

Prepare a mixture of pyridine and trimethylsilylimidazole (72:28).

Resolution mixture

—

Prepare a mixture of alpha lactose monohydrate and beta

lactose having an anomeric ratio of about 1:1 based on the labeled anomeric contents

of the alpha lactose monohydrate and the beta lactose.

Chromatographic system

(see

Chromatography

621

)

—

The gas chromatograph is

equipped with a flame-ionization detector and a 4-mm ×

0.9-m glass column packed

with 3% liquid phase G19 on support S1A. The column temperature is maintained at

about 215

, and the injection port and the detector temperatures are maintained at

about 275

. The carrier gas is helium, flowing at a rate of about 40 mL per minute.

Derivatization procedure

—

Transfer about 1 mg of Anhydrous Lactose to a 5-mL

reaction vial equipped with a screw cap, add 0.45 mL of dimethyl sulfoxide, seal the

vial tightly with a screw cap, and mix on a vortex mixer to dissolve. Add 1.8 mL of

Silylation reagent

, seal the vial tightly with a screw cap, and mix gently. Transfer about

1 mg of

Resolution mixture

to a second 5-mL reaction vial equipped with a screw cap,

add 0.45 mL of dimethyl sulfoxide, seal the vial tightly with a screw cap, and mix on a

vortex mixer to dissolve. Add 1.8 mL of

Silylation reagent

, seal the vial tightly with a

screw cap, and mix gently. Maintain both vials at room temperature for 20 minutes

before using.

Procedure

—

Inject a 2.0-?

L portion of the derivatized

Resolution mixture

into the

chromatograph, and record the peak areas for the major peaks: the relative retention

times are about 0.7 for the silyl derivative of alpha lactose and 1.0 for the silyl

derivative of beta lactose, and the resolution,

R,

between the two peaks is not less

than 3.0. Similarly inject a 2.0-?

L portion of the derivatized Anhydrous Lactose into the

chromatograph, and record the peak areas for the major peaks. Determine the

percentage of alpha anomer in the Anhydrous Lactose by the formula:

100

r

a

/ (

r

a

+

r

b

),

in which

r

a

is the response of the alpha anomer silyl derivative peak and

r

b

is the

response of the beta anomer silyl derivative peak. Determine the percentage of beta

anomer in the Anhydrous Lactose by the formula:

100

r

b

/ (

r

a

+

r

b

).

Residual solvents

467

:

meets the requirements.

(Official January 1, 2007)

Other requirements

—

It meets the requirements for

Packaging and storage

,

Labeling

,

Clarity and color of solution

,

Specific rotation

781

,

Microbial limits

61

,

Acidity or alkalinity, Residue on ignition

281

, and

Protein and light-absorbing

impurities

under

Lactose Monohydrate

.

Auxiliary Information

—

Staff Liaison

:

Catherine Sheehan, ., Scientist

Expert Committee

: (EM105) Excipient Monographs 1

USP29

–

NF24

Page 3357

Phone Number

: 1-301-816-8262

Lactose Monohydrate

?

Lactose Monohydrate is a natural disaccharide, obtained from milk, which

consists of one glucose and one galactose moiety. [

NOTE

—

Lactose

Monohydrate may be modified as to its physical characteristics. It may

contain varying proportions of amorphous lactose.]

Packaging and storage

—

Preserve in tight containers.

Labeling

—

Where the labeling states the particle size distribution, it also indicates the

d

10

, d

50

, and d

90

values and the range for each. For modified Lactose Monohydrate,

also label it to indicate the method of modification.

USP Reference standards

11

—

USP Lactose Monohydrate RS

.

USP Sucrose

RS

.

USP Fructose RS

.

USP Dextrose RS

.

Clarity and color of solution

—

A solution of 1 g in 10 mL of boiling water is clear and

nearly colorless. Determine the absorbance of this solution at a wavelength of 400 nm.

The absorbance divided by the path length in centimeters is not more than 0.04.

Identification

—

A:

Infrared Absorption

197K

.

B:

Diluent

—

Prepare a mixture of methanol and water (3:2).

Developing solvent

—

Prepare a solution consisting of a mixture of ethylene dichloride,

glacial acetic acid, methanol, and water (50:25:15:10).

Standard solution A

—

Prepare a solution of

USP Lactose Monohydrate RS

in

Diluent

having a known concentration of 0.5 mg per mL.

Standard solution B

—

Prepare a solution of

USP Dextrose RS

,

USP Lactose

Monohydrate RS

,

USP Fructose RS

, and

USP Sucrose RS

in

Diluent

having a known

concentration of 0.5 mg per mL for each Reference Standard.

Test solution

—

Transfer about 25 mg of Lactose Monohydrate to a 50-mL volumetric

flask, dissolve in and dilute with

Diluent

to volume, and mix.

Procedure

—

Apply separately 2 ?

L each of

Standard solution A

,

Standard solution B

,

and the

Test solution

to a thin-layer chromatographic plate (see

Chromatography

621

) coated with a 0.25-mm layer of chromatographic silica gel. Allow the spots to

dry, and develop the plate in a paper-lined chromatographic chamber equilibrated with

Developing solvent

for about 1 hour prior to use. Allow the chromatogram to develop

until the solvent front has moved about three-quarters of the length of the plate.

Remove the plate from the chamber, dry in a current of warm air, and redevelop the

plate in fresh

Developing solvent.

Remove the plate from the chamber, mark the

solvent front, and dry the plate in a current of warm air. Spray the plate evenly with a

solution containing 0.5 g of thymol in a mixture of 95 mL of alcohol and 5 mL of

sulfuric acid. Heat the plate at 130

for 10 minutes: the principal spot obtained from

the

Test solution

corresponds in appearance and

R

F

value to that obtained from

Standard solution A.

The test is not valid unless the chromatogram obtained with

Standard solution B

shows four clearly discernible spots, disregarding any spots at

the origin.

C:

Dissolve 250 mg in 5 mL of water. Add 3 mL of ammonium hydroxide, and heat in a

water bath at 80

for 10 minutes: a red color develops.

Specific rotation

781

—

Dissolve 10 g by heating in 80 mL of water to 50

. Allow

to cool, and add 0.2 mL of 6 N ammonium hydroxide. Allow to stand for 30 minutes,

and dilute with water to 100 mL: the specific rotation, calculated on the anhydrous

basis, determined at 20

, is between +54.4

and +55.9

.

Microbial limits

61

—

The total aerobic microbial count does not exceed 100 cfu

per g, the total combined molds and yeasts count does not exceed 50 cfu per g, and it

meets the requirements of the test for absence of

Escherichia coli

.

Acidity or alkalinity

—

Dissolve 6 g by heating in 25 mL of carbon dioxide-free water,

cool, and add 0.3 mL of phenolphthalein TS: the solution is colorless, and not more

than 0.4 mL of 0.1 N sodium hydroxide is required to produce a red color.

Loss on drying

731

—

Dry it at 80

for 2 hours: the monohydrate form loses not

more than 0.5% of its weight, and the modified monohydrate form loses not more than

1.0% of its weight.

Water,

Method I

921

: between 4.5% and 5.5%, determined on a preparation

containing lactose monohydrate in a mixture of methanol and formamide (2:1).

Residue on ignition

281

: not more than 0.1%, determined on a specimen ignited

at a temperature of 600 ±

25

.

Heavy metals

231

—

Dissolve 4 g in 20 mL of warm water, add 1 mL of 0.1 N

hydrochloric acid, and dilute with water to 25 mL: the limit is 5 ?

g per g.

Protein and light- absorbing impurities

851

—

Measure the light absorption of a

1% (w/v) solution in the range of 210 to 300 nm. The absorbance divided by the path

length in centimeters is not more than 0.25 in the range of 210 to 220 nm and is not

more than 0.07 in the range of 270 to 300 nm.

Residual solvents

467

:

meets the requirements.

(Official January 1, 2007)

Auxiliary Information

—

Staff Liaison

:

Catherine Sheehan, ., Scientist

Expert Committee

: (EM105) Excipient Monographs 1

USP29

–

NF24

Page 3357

Phone Number

: 1-301-816-8262

Corn Starch

?

Corn Starch consists of the starch granules separated from the mature

grain of corn [

Zea mays

Linné

(Fam. Gramineae)].

Packaging and storage

—

Preserve in well- closed containers. No storage

requirements specified.

Labeling

—

Where Corn Starch is intended for use in preparing Absorbable Dusting

Powder, it is so labeled, and the label states that it must be subjected to further

processing during the preparation of Absorbable Dusting Powder.

Identification

—

A:

Under a microscope, using not less than 20×

magnification and using a mixture of

glycerin and water (1:1) as a mounting agent, it appears either as angular polyhedral

granules of irregular sizes with diameters ranging from about 2 ?

m to about 23 ?

m, or

as rounded or spheroidal granules of irregular sizes with diameters ranging from

about 25 ?

m to about 35 ?

m. The central hilum consists of a distinct cavity or two- to

five-rayed cleft, and there are no concentric striations. Between crossed nicol prisms,

the starch granules show a distinct black cross intersecting at the hilum.

B:

Suspend 1 g of it in 50 mL of water, boil for 1 minute, and cool: a thin, cloudy

mucilage is formed.

C:

To 1 mL of the mucilage obtained in

Identification

test

B,

add 0.05 mL of iodine and

potassium iodide TS 2: an orange-red to dark blue color is produced, which

disappears on heating.

Microbial limits

61

—

The total aerobic microbial count does not exceed 1000 cfu

per g, the total combined molds and yeasts count does not exceed 100 cfu per g, and

it meets the requirements of the test for the absence of

Escherichia coli.

Where it is

intended for use in preparing Absorbable Dusting Powder, it also meets the

requirements of the tests for absence of

Staphylococcus aureus

and

Pseudomonas

aeruginosa.

pH

791

—

Prepare a slurry by weighing 5.0 g of Corn Starch, transferring to a

suitable nonmetallic container, and adding 25.0 mL of freshly boiled and cooled water.

Agitate continuously at a moderate rate for 1 minute. Stop the agitation, and allow to

stand for 15 minutes. Determine the pH to the nearest 0.1 unit: the pH, determined

potentiometrically, is between 4.0 and 7.0.

Loss on drying

731

—

Dry about 1 g, accurately weighed, at 130

for 90 minutes:

it loses not more than 15.0% of its weight.

Residue on ignition

281

:

not more than 0.6%, determined on a 1.0-g test

specimen.

Limit of iron

—

Shake 1.5 g of Corn Starch with 15 mL of 2 N hydrochloric acid, and

filter. Transfer 10 mL of the filtrate to a test tube, add 2 mL of citric acid solution (2 in

10), 0.1 mL of thioglycolic acid, and mix. Add 10 N ammonium hydroxide until the

solution is distinctly alkaline to litmus, dilute with water to 20 mL, and mix

(Test

solution).

Prepare a

Standard Iron Solution

containing the equivalent of 10 ?

g of iron

per mL as directed under

Iron

241

. Immediately before use, quantitatively dilute

an accurately measured volume of this solution with water to obtain a diluted

Standard

Iron Solution

containing the equivalent of 1 ?

g of iron per mL. Prepare the

Standard

solution

by transferring 10 mL of the diluted

Standard Iron Solution

to a test tube and

proceeding in the same manner as directed for the preparation of the

Test solution,

beginning with ―add 2 mL of citric acid solution (2 in 10).‖ After 5 minutes, any pink

color in the

Test solution

is not more intense than that in the

Standard solution,

corresponding to a limit of 10 ?

g of iron per g.

Limit of oxidizing substances

—

Transfer 4.0 g to a glass-stoppered, 125-mL

conical flask, and add 50.0 mL of water. Insert the stopper, and swirl for 5 minutes.

Transfer to a glass-stoppered, 50-mL centrifuge tube, and centrifuge to clarify.

Transfer 30.0 mL of the clear supernatant to a glass-stoppered, 125-mL conical flask.

Add 1 mL of glacial acetic acid and 0.5 g to 1.0 g of potassium iodide. Insert the

stopper, swirl, and allow to stand for 25 to 30 minutes in the dark. Add 1 mL of starch

TS, and titrate with 0.002 N sodium thiosulfate VS to the disappearance of the

starch

–

iodine color. Perform a blank determination, and make any necessary

correction. Each mL of 0.002 N sodium thiosulfate is equivalent to 34 ?

g of oxidant,

calculated as hydrogen peroxide. Not more than 1.4 mL of 0.002 N sodium thiosulfate

is required (20 ?

g per g, calculated as H

2

O

2

).

Limit of sulfur dioxide:

not more than 50 ?

g per g.

REAGENTS

—

Carbon dioxide

—

Use carbon dioxide, with a flow regulator that will maintain a flow of

100 ±

10 mL per minute.

Bromophenol blue indicator solution

—

Dissolve 100 mg of bromophenol blue in 100

mL of dilute alcohol (1 in 5), and filter if necessary.

Hydrogen peroxide solution

—

Dilute 30 percent hydrogen peroxide with water to

obtain a 3% solution. Just before use, add 3 drops of

Bromophenol blue indicator

solution,

and neutralize to a violet-blue endpoint with 0.01 N sodium hydroxide. Do not

exceed the endpoint.

APPARATUS

—

In this test, the sulfur dioxide is released from the test specimen in a

boiling acid medium and is removed by a stream of carbon dioxide. The separated

gas is collected in a dilute hydrogen peroxide solution where the sulfur dioxide is

oxidized to sulfuric acid and titrated with standard alkali. The apparatus consists

essentially of a 500-mL three- neck, round-bottom boiling flask, a separatory funnel

having a capacity of 100 mL or greater, a gas inlet tube of sufficient length to permit

introduction of the carbon dioxide within 2.5 cm of the bottom of the boiling flask, a

reflux condenser having a jacket length of 200 mm, and a delivery tube connecting the

upper end of the reflux condenser to the bottom of a receiving test tube. Apply a thin

film of stopcock grease to the sealing surfaces of all of the joints except the joint

between the separatory funnel and the boiling flask, and clamp the joints to ensure

tightness.

PROCEDURE

—

Add 150 mL of water to the boiling flask. Close the stopcock of the

separatory funnel, and begin the flow of carbon dioxide at a rate of 100 ±

5 mL per

minute through the

Apparatus.

Start the condenser coolant flow. Add 10 mL of

Hydrogen peroxide solution

to a receiving test tube. After 15 minutes, without

interrupting the flow of carbon dioxide, remove the separatory funnel from the boiling

flask, and transfer 25.0 g of test specimen into the boiling flask with the aid of 100 mL

of water. Apply stopcock grease to the outer joint of the separatory funnel, and

replace the separatory funnel in the boiling flask. Close the stopcock of the separatory

funnel, and add 80 mL of 2 N hydrochloric acid to the separatory funnel. Open the

stopcock of the separatory funnel to permit the hydrochloric acid solution to flow into

the boiling flask, guarding against the escape of sulfur dioxide into the separatory

funnel by closing the stopcock before the last few mL of hydrochloric acid drain out.

Boil the mixture for 1 hour. Remove the receiving test tube, and transfer its contents to

a 200-mL wide-necked, conical flask. Rinse the receiving test tube with a small portion

of water, add the rinsing to the 200-mL conical flask, and mix. Heat on a water bath for

15 minutes, and allow to cool. Add 0.1 mL of

Bromophenol blue indicator solution,

and

titrate the contents with 0.1 N sodium hydroxide VS until the color changes from

yellow to violet-blue, with the color change lasting for at least 20 seconds. Perform a

blank determination, and make any necessary correction (see

Titrimetry

541

).

Calculate the content, in ?

g per g, of sulfur dioxide in the test specimen taken by the

formula: