[OfficialAnu]

For example, to separate two similarly polar molecules such as water and 1-pentanol, why is the mixture in a ratio (ex. 70:30)? How does this create more visible separation?

[jeffmoonchop]

Water is way more polar than pentanol. Not sure what you're asking about the ratios though. With HPLC, you can calculate the quantity of each in a mixture. So if it's 70:30, then its because someone made a mixture of 70:30 water: pentanol. I should also note that pentanol is not miscible with water so you actually wouldn't be able to make a mixture without some additives.