If you do not intend to seperate the mixture, but still obtain mass composition, I have an alternate method.
assumption: salt is NaCl
1. dissolve the mixture in water
2. add excess aqueous silver nitrate to the solution
3. filter the solution to obtain silver chloride
4. measure the mass of the silver chloride
from the mass of silver chloride, you can deduce the mass of NaCl in the mixture.
eg. u dissolved 100g of the mixture in 500ml of water, and you obtain 50g of AgCl.
number of moles of AgCl = 50/(107.9+35.5) = 0.349moles
NaCl(aq) + AgNO3 (aq) -> AgCl(s) + NaNO3 (aq)
from the stoichiometric ratio of the above reaction,
number of moles of NaCl in mixture = number of moles of AgCl formed = 0.349moles
mass of NaCl in mixture = 0.349 x molar mass of NaCl = 20.4g
mass of sugar in mixture = 100 - 20.4 = 79.6g
percentage mass composition = 20.4% salt and 79.6% sugar