Can be classified based on their location:

Interstial Fluid
  • Bicarbonate
  • Phosphates
Blood
  • Bicarbonate
  • Haemoglobin
  • Plasma protein
Intercellular Fluid
  • Cell proteins
  • Phosphates
Urine
  • Phosphate
  • Ammonia
Bone
  • Mineral phosphates & carbonate