Rebekah Livesley, 2008 Analysis of Vitamin C in Fruit Juices Instrument Metrohm Polarograph

Vitamin C (Ascorbic Acid) formula weight g Water Soluble melting point ° C, unstable in solutions containing oxygen as it is readily oxidized

Why is Vitamin C important? It is involved in over 300 biological processes in the body for example  Antioxidant  Collagen manufacture & neurotransmitters  Immune function It is a Nutrient not synthesized by the body Complete deficiency results in scurvy Deficiency symptoms  Bleeding gums  Joint pain  Bruising & wounds that don’t heal  Fatigue & muscular weaknesses

Recommended Daily intake is 30-60mg The RDI is what you need to consume to prevent a deficiency 100ml (which is less than ½ a cup) of the Popper Juice orange Juice is all you would need to consume excess vitamin C is usually eliminated through the urine An excess of Vitamin C can cause diarrhea as water is pulled into the colon from the circulatory system

Fruit Juices Expected concentrations of Vitamin C in Fruit Juices

Samples Popper Juice Apple and Blackcurrant Popper Juice Orange Juice Popper Juice Apple Juice Popper Juice Apple And Mango Juice WESTCLIFF Apple Juice And V8 Vegetable Juice

Metrohm Polarograph Photographed by Shay

Procedures Differential Pulse Polarography Standard Addition Method Dilute sample accurately to approximate concentration of 40mg/L Place in sample cell with water and buffer solution Run scan -0.4 to +0.1 V 3 standard additions Normal Calibration Method Prepare 0, 5, 10, 25mg/L standard solutions in buffer solution Dilute sample accurately to an approximate concentration of 10mg/L in buffer Runs scans as above

Differential Pulse Polarography Standard Addition Results SampleWESTCLIFF Apple Juice200mg/L standard Solution of Ascorbic acid Average concentration 263 mg/L235 mg/L Recovery Check % recovery Standard Deviation 68%51% Relative Error 17%

Differential Pulse Polarography Normal Calibration Results SampleAverage concentration (mg/L) Recovery Check (% recovery) Standard Deviation WESTCLIFF Apple Juice % JUST JUICE Apple Juice POPPER JUICE – Orange Juice POPPER JUICE – Apple and Blackcurrant Juice POPPER JUICE – Apple and Mango Juice POPPER JUICE – Apple Juice662-- V8 – Vegetable Juice

Concentration Range of Vitamin C

Choice of method normal calibration  simpler for sample delivery (no pipetting required)  more consistent results  better RC values

What went wrong Standard Addition Method Lack of precision in the results obtained Caused by Micropipettes Human error 3 aliquots to be transferred to sample cell per run

What went wrong Normal Calibration Method  An aliquot of the V8 vegetable juice could not be taken by pipette as the juice was so viscous  Had to weigh a mass and do a density calculation before diluting the juice JUST JUICE – Apple Juice concentration was outside the concentration range of the standards used in the calibration graph Easily fixed – just recalibrate

Polarography Disadvantages Not time efficient Must use a buffer solution

Conclusion The normal Calibration polarographic method for the analysis of vitamin C is better than the standard addition method All sample analyzed had considerably more vitamin C than specified on the packet except Just Juice apple juice which had about a 1/5