One embodiment includes a method for correlating external references to a Web Page with conversions performed by one or more visitors to the Web Page. Said internal standard is prepared by reaction of an authentic sample of said carboxylic acid with a stable isotope labeled reagent, and is added to a sample containing said carboxylic acid. The avatar based video message apparatus and method displays information that corresponds to input user speech. The central server manages the call request received from the call server.