Assay of gadolinium.

Limit:

1 ml of the product should have 74.6 - 82.4 mg (95-105%) of gadolinium.

The assay is performed by atom absorption spectroscopy.

Reagents:

65% (w/w) nitric acid, Suprapur (Merck) or similar;

30% (w/w) hydrochloric acid, Suprapur (Merck) or similar;

Water with ≤50 µS conductivity;

10% (w/v) cesium chloride

Dissolve 10.00 g of cesium chloride Suprapur (Merck) in water with ≤50 µS conductivity contained in 100 ml volumetric flask and dilute to volume with the same solvent;

Gadolinium (III) oxide solution working standard; 10000 mg Gd per liter

Methods:

Preparation of test solution:

Expose 1.00 ml of product (v) in porcelain pot to 0.2 ml of 65% (w/w) nitric acid, evaporate on a hot stove, dry, ignite at approximately 500°C, then burn in muffle furnace at 800°C till black particles disappear (approximately 1 hour).  Then leave the residue to cool to room temperature on fire-resistant surface.  Dissolve the white residue at heating in 1.0 ml of water and 1.0 ml of 30% (w/w) hydrochloric acid, Suprapur (Merck) or similar.  Put the solution quantitatively to 100 ml volumetric flask, add 10 ml of 10% (w/v) cesium chloride solution, dilute to volume with water with ≤50 µS conductivity.

Preparation of gadolinium stock standard solution:

Dissolve the weighting of 11.5260 g of gadolinium (III) oxide working standard (accurately weighted) (MR) in 25 ml of 30% (w/w) hydrochloric acid Suprapur (Merck) or similar in 1000 ml volumetric flask, then dilute to volume with water with ≤50 µS conductivity (C=~10 mg of gadolinium per ml).

Preparation of gadolinium standard solutions 1, 2 and 3:

Put 3.0 ml, 4.0 ml and 5.0 ml of gadolinium stock standard solution into individual 50 ml volumetric flasks, add 5.0 ml of 10% (w/v) cesium chloride solution and 0.5 ml of 30% (w/w) of hydrochloric acid, Suprapur (Merck) or similar, then dilute to volume with water with ≤50 µS conductivity (corresponds to 600 mg of gadolinium per liter, 800 mg gadolinium per liter and 1000 mg of gadolinium per liter respectively).

Control test:

Put 10.0 ml of 10% (w/v) cesium chloride solution into 100 ml volumetric flask, add 1.0 ml of 30% (w/w) hydrochloric acid, Suprapur (Merck) or similar and then dilute to volume with water ≤50 µS with conductivity.

Chromatographic conditions:

Methods:

Perform three quantifications of test solution and standard solutions 1, 2 and 3.  Use average value of three quantifications for the calculation.