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:
Device | Atomic absorption flame spectrophotometer |
Measurement type | Absorption with background compensation |
Light source | Gadolinium hollow cathode lamp |
Conditioning time | 15 minutes |
Measured wavelength | 368.4 nm |
Opening width | 0.2 nm |
Fuel gas | Acetylene > 99.6% (v/v) free from solvent |
Oxidant | Nitrous oxide >99.8% (v/v) |
Burner type | Nitrous oxide burner |
Calibration method | Linear |
Methods:
Perform three quantifications of test solution and standard solutions 1, 2 and 3. Use average value of three quantifications for the calculation.