Heavy metals 
231
—
Transfer to a suitable vessel a volume, in mL, of Injection, calculated to two significant figures by the formula:
0.2/[(GKLK) + (GSLS)],
in which
GK and
GS are the labeled amounts, in g, of potassium chloride and sodium chloride, respectively, in each 100 mL of Injection, and
LK and
LS are the limits, in percentage, for
Heavy metals specified under
Potassium Chloride and
Sodium Chloride, respectively. Adjust the volume by evaporation or addition of water to 25 mL, as necessary: it passes the test.
Assay for potassium and sodium—
Internal standard solution—
Transfer 1.04 g of lithium nitrate to a 1000-mL volumetric flask, add a suitable nonionic surfactant, then add water to volume, and mix.
Potassium stock solution—
Transfer 18.64 g of potassium chloride, previously dried at 105
for 2 hours and accurately weighed, to a 250-mL volumetric flask, add water to volume, and mix. Each mL of this stock solution contains 39.10 mg (1 mEq) of potassium.
Sodium stock solution—
Transfer 14.61 g of sodium chloride, previously dried at 105
for 2 hours and accurately weighed, to a 250-mL volumetric flask, add water to volume, and mix.
Stock standard preparation—
Transfer 0.1J mL of Potassium stock solution and 0.1J¢ mL of Sodium stock solution to a 100-mL volumetric flask, J and J¢ being the labeled amounts, in mEq per liter, of potassium and sodium, respectively, in the Injection. Dilute with water to volume, and mix. Each mL of this solution contains 0.0391J mg of potassium (K) and 0.02299J¢ mg of sodium (Na).
Standard preparation—
Transfer 5.0 mL of Stock standard preparation to a 500-mL volumetric flask, dilute with Internal standard solution to volume, and mix.
Assay preparation—
Transfer 5.0 mL of Injection to a 500-mL volumetric flask, dilute with Internal standard solution to volume, and mix.
Procedure—
Using a suitable flame photometer, adjusted to read zero with
Internal standard solution, concomitantly determine the flame emission readings for the
Standard preparation and the
Assay preparation at the wavelengths of maximum emission for potassium, sodium, and lithium (766 nm, 589 nm, and 671 nm, respectively). Calculate the quantity, in mg, of K in each mL of the Injection taken by the formula:
C(RU,766 / RU,671)(RS,671 / RS,766),
in which
C is the concentration, in mg per mL, of potassium in the
Stock standard preparation,
RU,766 and
RU,671 are the emission readings at the wavelengths identified by the subscript numbers obtained from the
Assay preparation, and
RS,671 and
RS,766 are the emission readings at the wavelengths identified by the subscript numbers obtained from the
Standard preparation. Each mg of potassium is equivalent to 0.02558 mEq of potassium. Calculate the quantity, in mg, of Na in each mL of the Injection taken by the formula:
C(RU,589 / RU,671)(RS,671 / RS,589),
in which
C is the concentration, in mg per mL, of sodium in the
Stock standard preparation,
RU,589 and
RU,671 are the emission readings at the wavelengths identified by the subscript numbers obtained for the
Assay preparation, and
RS,671 and
RS,589 are the emission readings at the wavelengths identified by the subscript numbers obtained from the
Standard preparation. Each mg of sodium is equivalent to 0.04350 mEq of sodium.
Assay for chloride—
Transfer an accurately measured volume of Injection, equivalent to about 55 mg of chloride, to a conical flask, and add 10 mL of glacial acetic acid, 75 mL of methanol, and 3 drops of
eosin Y TS. Titrate, with shaking, with 0.1 N silver nitrate VS to a pink endpoint. Each mL of 0.1 N silver nitrate is equivalent to 3.545 mg of Cl. Each mg of chloride is equivalent to 0.0282 mEq of Cl.
