When converting a substance’s mass from milligrams/kilograms (mg/kg) to parts per million (ppm), the ratio is 1:1, and no conversion is required. Because 1 milligramme is equal to 0.001 grammes and 1 kilogramme is equal to 1,000 grammes, 1 mg/kg is the same as 1 ppm. When you divide 0.001 by 1,000, you get 0.000001, or a millionth of a gramme, which is the same as 1 part per million.
This logic only applies to large-scale conversions. If you’re converting mg/kg of volume or moles to ppm, the compounds you’re using will affect the result. The formula c/s is used to calculate ppm for both volume and moles, where “c” is the volume or moles of the compound divided by “s,” which is the volume or moles of the solution.
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