Measuring the content of Vitamin C in fruit juice

Página 1

Independent: fruit juice

Dependent: Vol. juice decolourise 1cm3 of DCPIP

Control:

Temp.

Conc. DCPIP solution (1%)

Shake tube same number times

Same end point colour (until blue colour

of DCPIP disappears)

Method:

Pipette 1cm3 blue DCPIP

into test tube.

Using burette/ accurate

pipette/syringe, add 1% vitamin C solution drop by drop, while shaking tube

gently after each drop, until blue colour just disappears.

Record volume solution needed to

decolourise the DCPIP.

Repeat further 2 times &

calculate mean result.

Repeat procedure with different juices.

Calculation:

1cm3 of

1% vitamin solution contains 10mg Vitamin C,

mass 1cm3 = 10mg x

volume of 1% vitamin C decolourise 1cm3 of DCPIP.

Mass sample =

mass vitamin C decolourise 1cm3 DCPIP/ volume sample to decolourise 1cm3 DCPIP

Evaluation issues:

Difficult control temp.

Amount shaking (too much adds O2, slightly restore DCPIP blue)

End point difficult judge when blue colour disappears especially in high coloured juices.

Method