Bus and train operator National Express announced that its finance chief was quitting to join speciality chemicals group Croda International.National Express said Jez Maiden, its group finance director since 2008, had resigned to take up the equivalent role at Croda early in the New Year.The group said Maiden had agreed to stay with the group for the time being to ensure an orderly handover and the board had begun a search process for his replacement involving both internal and external candidates.It has appointed the finance director of its UK bus business and former group financial controller Matthew Ashley as interim group finance director, who will work alongside Jez in the coming months as part of the handover.Maiden has already worked in chemicals as finance boss at British Vita and at Hickson International, both listed speciality chemical companies. He has also served since 2007 as a non-executive director of FTSE 250 speciality chemical company Synthomer.He replaces Sean Christie at Croda, who announced in June that he would step down from the role in 2015 after nine years and will leave Croda in April 2015.Chief executive Dean Finch thanked Maiden, adding: "We understand the reasons behind his decision and wish him every success." Maiden said: "I have had a hugely enjoyable and rewarding time at National Express and will be sad to leave. I am looking forward to my new opportunity at Croda, in an industry where I began my plc career."Maiden has already worked in chemicals as finance boss at British Vita and at Hickson International, both listed speciality chemical companies. He has also served since 2007 as a non-executive director of FTSE 250 speciality chemical company Synthomer.