Sigma-Aldrich, headquartered in St Louis in the US, is already the world's largest supplier of biochemicals and organic chemicals to research laboratories, clocking up sales of $2.7 billion last year.

According to the Associated Press, Merck CEO Karl-Ludwig Kley said the firm had a “clear commitment” to St. Louis, Missouri, where Sigma-Aldrich is based. According to the news report, “he said it was ...