B) Sample: 0.5 g of calcium citrate

Analysis: ignite completely the sample at low a temperature as possible, cool and dissolve the residue in dilute glacial acetic acid (1:10). filter and add 10 ml of ammonium oxalate TS to the filtrate.

Acceptance criteria: a voluminous white precipitate that is soluble in hydrochloric acid is formed.

Acceptance criteria: NMT 3 ppm

Acceptance criteria: NMT 20ppm

Standard stock solution: 1000 µg/ml of fluoride ion from USP sodium fluoride WS in water.

Standard solution: 5µg/ml of  fluoride ion from standard stock solution          ( NOTE- Prepare on the day of use)

Linearity solution A: transfer 1.0 of the standard solution to a 250 ml plastic beaker. Add 50 ml of water, 5 ml of 1 N hydrochloric acid, 10 ml of 1M sodium citrate, and 10 ml of 0.2 M edetate disodium if necessary adjust with 1 N sodium hydroxide or 1 M hydrochloric acid to pH-5.5. Transfer to 100 ml volumetric flask and dilute with water to volume. This solution contains 0.05 µg/ml of fluoride.

Linearity solution B: transfer 5.0 ml of the standard solution to a 250 ml plastic beaker and proceed as directed for linearity solution A beginning with adds 50 ml of water. This solution contains 0.50 µg*/ml of fluoride.

Linearity solution C: Transfer 10.0 ml of the standard solution to a 250 ml plastic beaker and proceed as directed for linearity solution A beginning with add 50 ml of water, this solution contains 0.50µg/ml of the fluoride.

Sample solution: transfer 1.0 g of calcium citrate to a 100 ml beaker. Add 10 ml of water and, while titrating, 10 ml of 1N hydrochloric acid. When dissolved, boil rapidly for 1 min, transfer the solution to a 250 ml plastic beaker, and cool in ice water. add 15 ml of 1.0 M  sodium citrate and 10.0 ml of 0.2 M edetate disodium, and adjust with 1N sodium hydroxide or 1 M hydrochloric acid to a pH of 5.5. Transfer this solution to a100 ml volumetric flask, and dilute with water to volume.

Electrode system:   use afluoride specific, ion indicating electrode and a silver – silver chloride reference electrode connected to a pH meter capable of measuring potentials with a minimum reproducibility of ± 0.2 Mv.

Analysis

Samples: linearity solution A,  linearity solution B,  linearity solution C,  and sample solution

Transfer 50 ml of each linearity solution A, linearity solution B, and linearity solution C to separate 250 ml plastic beakers, and measure the potential of each  solution with the electrode system. Between each reading wash the electrode with water and absorb any residual water by blotting the electrodes dry. plot the logarithms of the fluoride concentrations (0.05, 0.25, and 0.50µg/ml, respectively) versus potential to obtain a standard response line.

Transfer 50 ml of the sample solution to a 250 ml plastic beaker, and measure the potential with the electrode system. from the measured potential and the standard response line determine the concentration, C, in µg/ml,  of fluoride ion in the sample solution. calculate the percentage of fluoride in the specimen taken by multiplying C by 0.01.

Acceptance criteria: NMT 0.003%.

Analysis: filter wash and dry at 105º for 2 h the residue so obtained.

Acceptance criteria:  The weight of the residue is NMT 10mg (2.0%).

Sample solution: dissolve 350 mg of calcium citrate previously dried at 150º to constant weight, in 12 ml of 0.5 M hydrochloric acid, and dilute with water to about 100 ml.

Analysis: while stirring the sample solution, add 30ml of 0.05 M disodium edetate VS from a 50 ml burette. Add 15 ml of 1 M sodium hydroxide add 300 mg of hydroxy naphthol blue, and continue the titration to a blue endpoint. each ml of 0.05 M  disodium edetate is equivalent to 8.307 mg calcium citrate.

Calculation                                             Limit 97.5 – 100.5% (on dried basis)

  Volume x 8.307 x M x 100

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0.05 x wt of spl