Emergency services - including British Transport Police, the ambulance service and South Yorkshire Fire and Rescue - rushed to the station just after rush hour on Friday.
Police are investigating the incident after revealing the substance was hydrochloric acid, which is extremely corrosive to the eyes and skin.
A spokesperson for the British Transport Police said: “A 36-year-old woman was arrested by officers in London yesterday on suspicion of possessing a corrosive substance in a public place.
“It follows an incident at Barnsley station last Friday.
“She remains in custody assisting detectives with their enquiries.”
Dan Jarvis, Barnsley Central MP and Sheffield City Mayor, condemned the incident over the weekend.
He told the Chronicle: “I was deeply concerned by the incident involving a flask of acid being left at the station, which clearly posed a considerable risk to the travelling public.”