Mercury—
Mercury Detection Instrument and Aeration Apparatus—
Proceed as directed for the section
Method IIa and Method IIb under
Mercury 
261
.
Nitric acid solution 1—
Carefully add 50 mL of nitric acid to 450 mL of water, and mix.
Nitric acid solution 2—
Carefully add 10 mL of nitric acid to 490 mL of water, and mix.
Hydrochloric acid–nitric acid solution—
Carefully add three volumes of concentrated hydrochloric acid to one volume of concentrated nitric acid. [NOTE—Prepare immediately before use.]
Stannous sulfate solution—
Add 25 g of stannous sulfate to 250 mL of 0.5 N sulfuric acid. [NOTE—The mixture is a suspension and should be stirred continuously during use.]
Sodium chloride–hydroxylamine sulfate solution—
Dissolve 12 g of sodium chloride and 12 g of hydroxylamine sulfate in water, dilute with water to 100 mL, and mix.
Potassium permanganate solution—
Dissolve 5 g of potassium permanganate in 100 mL of water, and mix.
Standard stock mercury solution—
Dissolve 0.1354 g of mercuric chloride in Nitric acid solution 1 to obtain a solution having a concentration of about 1.0 mg of mercury per mL. [NOTE—Use of a commercially prepared mercury standard is recommended.]
Standard working mercury solution—
Quantitatively dilute an accurately measured volume of the Standard stock mercury solution with Nitric acid solution 2 to obtain a solution having a known concentration of about 0.5 µg of mercury per mL.
Standard solutions—
Transfer 1-, 2-, 3-, and 4-mL aliquots of
Standard stock mercury solution to four separate 300-mL biological oxygen-demand (BOD) bottles. To each bottle, add 5 mL of water and 5 mL of
Hydrochloric acid–nitric acid solution. Heat the sample for 2 minutes in a water bath at 95
. Cool, and add 50 mL of water and 15 mL of
Potassium permanganate solution. Mix thoroughly, and place in a water bath for 30 minutes at 95
. Cool, add 5 mL of
Sodium chloride–hydroxylamine sulfate solution, dilute with water to 200 mL, and mix. These solutions contain the equivalents of 2.5, 5, 7.5, and 10 ng of mercury per mL, respectively.
Blank solution—
To a 300-mL BOD bottle, add 5 mL of water and 5 mL of
Hydrochloric acid–nitric acid solution. Heat the solution for 2 minutes in a water bath at 95
. Cool, and add 50 mL of water and 15 mL of
Potassium permanganate solution. Mix thoroughly, and place in a water bath for 30 minutes at 95
. Cool, add 5 mL of
Sodium chloride–hydroxylamine sulfate solution, dilute with water to 200 mL, and mix.
Test solution—
Transfer about 2.0 g of Zinc Oxide Neutral, accurately weighed, to a 300-mL BOD bottle. To the bottle, add 5 mL of water and 5 mL of
Hydrochloric acid–nitric acid solution. Heat the sample in a water bath for 2 minutes at 95
. Cool, and add 50 mL of water and 15 mL of
Potassium permanganate solution. Mix thoroughly, and place in a water bath for 30 minutes at 95
. Cool, add 5 mL of
Sodium chloride–hydroxylamine sulfate solution, dilute with water to 200 mL, and mix.
Procedure—
Add 5 mL of Stannous sulfate solution to a Standard solution, and immediately insert the bottle into the Aeration Apparatus. Obtain the absorbance of the Standard solution. Repeat with the remaining Standard solutions, Test solution, and Blank solution. Perform a blank determination, and make any necessary corrections. Plot the absorbances of the Standard solutions versus concentrations, in µg per mL, and draw the straight line best fitting the plotted points. From the graph so obtained, determine the concentration, in µg per g of mercury, in the Test solution: not more than 1 µg per g is found.
Content of magnesium oxide—
Nitric acid solution—
Carefully add 10 mL of concentrated nitric acid to 490 mL of water, and mix.
Standard solution—
Prepare a solution in
Nitric acid solution having a concentration of about 25 µg of magnesium per mL.
[Note—Use of a commercially prepared magnesium–inductively coupled plasma standard solution is recommended.
]
Test solution—
Transfer 200 mg of Zinc Oxide Neutral, accurately weighed, to a 50-mL volumetric flask. Dissolve in and dilute with Nitric acid solution to volume.
Procedure—
Set up an inductively coupled plasma–atomic emission spectrometer with a wavelength of 279.1 nm, RF power of about 1.2 KW, argon torch flow of about 17 L per minute, argon nebulizer flow of about 1.0 L per minute, and argon auxiliary flow of about 1.4 L per minute. Analyze the
Standard solution and
Test solution, using
Nitric acid solution as the blank. Calculate the percentage of magnesium oxide in the portion of Zinc Oxide Neutral taken by the formula:
5F(C/W)
in which
F is the conversion factor for conversion of magnesium to magnesium oxide (1.658);
C is the concentration, in µg per mL, of magnesium found in the
Test solution, determined from the instrument; and
W is the weight, in mg, of the portion of Zinc Oxide Neutral taken to prepare the
Test solution: not more than 0.7% is found.
Assay—
Dissolve about 1.5 g of freshly ignited Zinc Oxide Neutral, accurately weighed, and 2.5 g of ammonium chloride in 50.0 mL of 1 N sulfuric acid VS, with the aid of gentle heat, if necessary. When dissolution is complete, add
methyl orange TS, and titrate the excess sulfuric acid with 1 N sodium hydroxide VS. Each mL of 1 N sulfuric acid is equivalent to 40.69 mg of ZnO.
USP29
