Mass Parts Per Million (Mass PPM) is a term commonly used in analytical chemistry to express the concentration of a particular substance dissolved or present in a solution. However, there are several synonymous terms used interchangeably with Mass PPM. One such term is "Milligrams per Kilogram" (mg/kg), which signifies the mass of a substance in milligrams per kilogram of a solution or sample. Another synonym for Mass PPM is "Micrograms per Gram" (µg/g), which represents the concentration of a substance in micrograms per gram of a sample. Both mg/kg and µg/g provide alternative units to express concentration precisely and accurately. In summary, Mass PPM can be conveyed as mg/kg or µg/g, signifying the mass of the substance in milligrams or micrograms per kilogram or gram, respectively.