Application Notes: Reflectometry – Nitrate in Hops

Reflectometric determination after reduction to nitrite and reaction with Griess reagent

Reagents:

Cat. No. 116971 Reflectoquant® Nitrate Test
Cat. No. 116995 Reflectoquant® Nitrate Test
Cat. No. 117246 Reflectometer RQflex® 20
Folded filter (nitrate-free)

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


Sample preparation:

Weigh 5 g raw hops or hop pellets in a closeable vessel. Add 100 ml distilled water. Stir at a temperature of 50 °C for 60 minutes. Then filter through nitrate-free folded filter to remove undissolved particles. Dilute filtrate with distilled water in a ratio 1+24.

glass of beer with hops

Analysis:
Press the reflectometer START key and simultaneously dip thel test strip into the sample (15 - 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 60 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® Nitrate Test.)


Calculation:

Nitrate content [mg/kg] Measured value [mg/l] x 100 ml x 25
Weight of sample [g]
Nitrate content [%] = Measured value [mg/l]
20


Results - comparison with enzymatic method:

Sample Reflectoquant® Enzymatic
  measured value[mg/l]   Nitrate content[%] measured value [mg/l]  Nitrate content[%]
Raw Hops 1 2 0.10 2.8 0.14
Raw Hops 2 23 1.15 20.8 1.04
Raw Hops 3 24 1.20 20.1 1.01
Raw Hops 4 26 1.30 21.2 1.06
 
Hops pellets 1 20 1.00 18.4 0.92
Hops pellets 2 21 1.05 22.7 1.14
Hops pellets 3 20 1.00 18.4 0.92

 Materials

     
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