Im very confused with this question

The purity of citric acid was tested

Step 1- A sample of 0.48g of citric acid was dissolves in 50cm3 of distilled water
Step 2- drops of phenolphthalein indicator was added
step 3- It was the titrated with a solution of NaOH (0.50 mol/dm3)

Complete:
Final burette reading/cm3: 14.60
First burette reading/cm3: 0.20
Volume of NaOH(aq) added/cm3:

Pcm3 of NAOH (aq) containing 0.50 moles in 1000cm3 were used.

Number of moles NaOH used= 0.5/1000 x P= Q=___________
Number of moles of citric acid in sample= Q/3=R=__________
Relative formula mass of citric acid=_______________
Mass of citric acid in sample=RxMr=S=__________
Percentage purity of sample=S/0.48 x 100=__________%

How can the sample of citric acid be purified further?