By following the link you could find the summary of ingredients that are present in Liqua e-liquids currently sold in European Union with full compliance to the requirements of European Tobacco Products Directive 2014/40/EU (TPD)
General List of Ingredients and Maximum Concentration Limits
Limit of detection is 0.0001%. The actual content and concentration of each substance depends on the type of liquid, local country legislation and chemical legislation, such as REACH, and each liquid goes through the TPD notification process before being introduced for sales.