substances is best performed with a fairly precise voltage or electrical potential applied to the coupon 31 that may be adjusted or optimized the actual electrical potential applied is influenced by on varying factors such as ph of the sample temperature of the sample and other factors and the inputted electrical charge on the coupon 31 may be adjusted to obtain the precise surface potential to draw the target substance to the surface the voltage adjustment will be explained below the coupon 31 may be a specimen of any material that is the target of the analysis or test and may be for example a piece of metal of the kind used in the pipeline 5 or storage tank if the residual chemical monitoring system is deployed to provide monitoring for a storage tank other suitable materials may also be used that are sufficiently active for chemical monitoring cost effective and would have an acceptable service life in the field suitable materials may include gold silver and copper the coupon 31 is preferably planar and may present substantially any shape the coupon 31 also includes some features that enhance the attractiveness of the target substance or target substances to the surface the coupon 31 is preferably an electrically conductive but non corrosive or corrosion resistant material in the preferred embodiment a nickel copper alloy is used that is commonly called monel the surface of the nickel copper alloy is polished and cleaned and provided with a precious metal layer such as gold silver or copper gold is preferred and is applied by an electrochemical.