Murexide or ammonium purpurate

Murexide or ammonium purpurate or MX, is the ammonium salt of purpuric acid. This metallochromic indicator undergoes a color change in the presence of calcium. Murexide is used in analytical chemistry as a complexometric indicator for complexometric titrations, most often of calcium ions, but also for copper, nickel, cobalt, thorium and rare-earth metals.

General Properties and Specifications of Murexide or Ammonium Purpurat:
Appearance: Dark red to purple powder.
Assay: 98%
pH: 5 at 20C, 1 g/L in water.
Sulfated ash: 1% maximum.
Loss on drying at 105C: 2% maximum.
Relative density: 1.72 Hydrate.
Melting point: >300C.
Solubility: Slightly soluble in water.
Storage: Room temperature.

Murexide Analytical Reagent Grade Specifications:
5,5'-Nitrilobarbituric Acid Monoammonium Salt
C8H8N6O6 Formula Weight 284.20
C8H8N6O6-H2O Formula Weight 302.22
CAS Number 3051-09-0 anhydrous and 6032-80-0monohydrate
NOTE. This material is available in anhydrous and monohydrate forms. The tests are identical for both forms.

Suitability as Complexometric Indicator: Dissolve 0.1 g in 100 mL of water. Add 1 mL to 100 mL of water, then add 10 mL of pH 10 ammoniacal buffer, and divide into 2 equal portions, A and B. Titrate A with nickel standard solution (0.01 mg Ni/mL) until the blue component of the color is discharged. The color of the solution changes from purple to red. Use portion B as a control. The purple color is restored by adding 0.1 mL of 0.1 M EDTA. Portion A matches portion B.