Malcolm Dole (March 4, 1903 – November 29, 1990) was an American chemist known for the Dole Effect in which he proved that the atomic weight of oxygen in air is greater than that of oxygen in water[1] and for his work on electrospray ionization, polymer chemistry, and electrochemistry.

[2][3] The Dole effect is the inequality in the ratio of heavy oxygen isotope 18O to the more abundant 16O in the Earth's atmosphere and in seawater.

[4][5] The effect is due to slightly different reaction rates for the two isotopes in respiration in plants and in animals which tends to retain the lighter 16O, which increases the relative concentration of 18O in the atmosphere.

The effect has also been linked to hydrologic processes, such as the enrichment of the lighter 16O as water vapor is transported poleward.

Dole in 1968 was the first to use electrospray ionization with mass spectrometry.