Application Notes: Reflectometry – Ascorbic Acid in Juices

Reflectometric determination after reaction with molybdophosphoric acid to phosphomolybdenum blue

Reagents:

Cat.No. 116981 Reflectoquant® Ascorbic Acid Test
Cat.No. 117246 Reflectometer RQflex® 20

This application note pertains to RQflex® 20 and all  discontinued instruments (RQflex® 10, RQflex® plus)


Sample preparation:

The sample can be analyzed in its original form.


Analysis:

Press the reflectometer START key and simultaneously dip the test strip into the sample (5 - 30 °C) for ca. 2 seconds, ensuring that both reaction zones are immersed. Allow excess liquid to run off via the long edge of the strip on to an absorbent paper towel.

Wait 15 seconds and then measure the strip in the reflectometer. The value [mg/l] will be stored automatically. (Please refer to the RQflex® operating instructions and the package insert of the Reflectoquant® Ascorbic Acid Test.)


Note:

Without sample preparation strongly red-colored juices produce ascorbic acid results which are too high (Please refer to the application note: Ascorbic Acid in Red Colored Juices). This is also the case with apple juice samples containing reducing substances.


Results - comparison with enzymatic method:

Sample Reflectoquant® [mg/L] Enzymatic [mg/L]
Orange juice 1 309 292
Orange juice 2 553 511
Orange-maracuja juice 340 316
Orange lemonade 220 219


Results - comparison with photometric method:

Sample Reflectoquant® [mg/L] Photometry [mg/L]
Orange juice 1 414 420
Orange juice 2 374 358
Orange juice 3 421 440
Orange juice 4 436 415
Grapefruit nectar 264 255
Pineapple juice 299 288

 Materials

     
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