Determination of Turbidity (Opalescence)
The determination of turbidity may be performed by visual comparison (Procedure A
), or instrumentally using a suitable ratio turbidimeter (Procedure B
). For a discussion of turbidimetry, see Spectrophotometry and Light-Scattering 851
. Instrumental assessment of clarity provides a more discriminatory test that does not depend on the visual acuity of the analyst.
Hydrazine Sulfate Solution
Dissolve 1.0 g of hydrazine sulfate, in water and dilute with water to 100.0 mL. Allow to stand for 4 to 6 hours.
Dissolve 2.5 g of hexmethylenetetramine in 25.0 mL of water in a 100 mL glassstoppered flask.
Opalescence Stock Suspension
Add 25.0 mL of Hydrazine Sulfate Solution to the Hexamethylenetetramine Solution in the flask. Mix, and allow to stand for 24 hours. This suspension is stable for 2 months, provided it is stored in a glass container free from surface defects. The suspension must not adhere to the glass and must be well mixed before use.
Opalescence Standard Suspension
Prepare a suspension by diluting 15.0 mL of the Opalescence Stock Suspension with water to 1000.0 mL. Opalescence Standard Suspension is stable for about 24 hours after preparation.
Prepare according to Table 2
. Mix and shake before use. [note
Stabilized formazin suspensions that can be used to prepare stable, diluted turbidity standards are available commercially and may be used after comparison with the standards prepared as described.]
||Reference Suspension A
||Reference Suspension B
||Reference Suspension C
||Reference Suspension D
|Standard of Opalescence
|Nephelometric turbidity units
Procedure A: Visual Comparison
Use identical test tubes made of colorless, transparent, neutral glass with a flat base and an internal diameter of 15 to 25 mm. Fill one tube to a depth of 40 mm with Solution S,
one tube to the same depth with water, and four others to the same depth with Reference Suspensions A, B, C,
. Compare the solutions in diffuse daylight 5 minutes after preparation of the Reference Suspensions,
viewing vertically against a black background. The light conditions shall be such that Reference Suspension A
can be readily distinguished from water and that Reference Suspension B
can be readily distinguished from Reference Suspension A
is not more opalescent than Reference Suspension B
for Type I closures, and not more opalescent than Reference Suspension C
for Type II closures. Solution S
is considered clear if its clarity is the same as that of water when examined as described above, or if its opalescence is not more pronounced than that of Reference Suspension A
(refer to Table 3
Procedure B: Instrumental Comparison
Measure the turbidity of the Reference Suspensions
in a suitable calibrated turbidimeter (see Spectrophotometry and Light Scattering 851
). The blank should be run and the results corrected for the blank. Reference Suspensions A, B, C,
represent 3, 6, 18 and 30 Nephelometric Turbidity Units (NTU), respectively. Measure the turbidity of Solution S
using the calibrated turbidimeter.
The turbidity of Solution S
is not greater than that for Reference Suspension B
(6 NTU FTU) for Type I closures, and is not greater than that for Reference Suspension C
(18 NTU FTU) for Type II closures (refer to Table 3
||Procedure A (Visual)
||Procedure B (Instrumental)
|Type I closures
||no more opalescent that Suspension B
||no more than 6 NTU
|Type II closures
||no more opalescent than Suspension C
||no more than 18 NTU
Determination of Color
Prepare a solution by diluting 3.0 mL of Matching Fluid O
(see Color and Achromicity 631
) with 97.0 mL of diluted hydrochloric acid.
Use identical tubes made of colorless, transparent, neutral glass with a flat base and an internal diameter of 15 to 25 mm. Fill one tube to a depth of 40 mm with Solution S, and the second with Color Standard. Compare the liquids in diffuse daylight, viewing vertically against a white background.
Solution S is not more intensely colored than the Color Standard.