Folch also studied blood glucose and lactic acid metabolism under the direction of the man he considered his scientific mentor, Professor Rosend Carrasco Formiguera.
[3][5] In 1936, just before the Spanish Civil War broke out, he was accepted as a research fellow at the Rockefeller Institute in New York, and he took the post.
The following year he obtained a formal position as an assistant and later as an associate on the scientific staff of the Hospital of the Rockefeller Institute for Medical Research in Donald Van Slyke’s department.
He then devised a procedure that involved precipitation of lipids and proteins with colloidal iron and removal of most of the non-lipid components with water, which solved the contamination problem.
[7] During these first investigations he co-signed a paper with Donald Van Slyke on an improved manometric method for carbon analysis.
Using this newly developed method, he characterized the isolated "cephalin" fraction from brain tissue that after Johannes Thudichum (the nineteenth-century founder of the field of structural neurochemistry) was considered as pure phosphatidyl ethanolamine.
[3] In 1947 he was joined by Marjorie Lees, together[8] they developed mild procedures for quantitative extraction of brain lipids leading to the classic method using a chloroform-methanol mixture and a phase partition with water which resulted in quantitative extraction of tissue lipids and removal of water-soluble contaminants.
[9] The technique he developed for purifying the brain lipids is still referred to as "Folching" and is one of the most cited papers in the history of biochemistry.
After his retirement in 1977, he was Professor of Neurochemistry Emeritus and continued to be active as honorary biochemist at McLean Hospital until his death.
When he moved to America and married, he decided to hyphenate his paternal and maternal last names, so that his children would bear his full family heritage: "Folch-Pi".
In 1945, Folch married Willa Babcock, a manuscript curator at the Francis Countway Medical Library, and would later become the academic dean of Tufts University.