Units aside, say you actually want 10 microlitres per ml. How many microlitres are in 1ml? Subtract 10, pipette the difference of hexane, add 10microlitres of hydrocarbon, mix. If you want ten times the volume, multiply everything by 10.
If you need to mix all 5 hydrocarbons into the same stock at 10ul/ml each, use 50ul minus 1ml hexane, then add 10ul of each hydrocarbon, mix.
Overall, you need to check your units, and we don't know if you need to make 5 separate stocks, or 1 stock with all 5.