[scribus] OT: Online preflight or pay-per file?

[Ralf-Diether Ebel]

Hello Scribus-Users,
does anyone know a preflight-service when I can check my Scribus 
generated pdf-files that they only contain cmyk colors and not rgb 
anymore?
I think instead of buying the expensive Acrobat there must be cheaper 
solutions, so for ex. an online-service?
Greetings
Ralf