Application Notes: Reflectometry – Magnesium in Cheese

Reflectometric determination after reaction with phthalein purple


Cat. No. 116124 Reflectoquant® Magnesium Test
Cat. No. 117246 Reflectometer RQflex® 20
Cat. No. 109461 Buffer solution ready for use pH 9.00
Cat. No. 100807 Trichloroacetic acid
Folded filter

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

Sample preparation:

Grind exactly 2 g of the cheese sample with approx. 10 ml of distilled water (adjusted to approx. 50 °C) and 1 ml of trichloroacetic acid 20 % (20 g dissolved in 100 ml distilled water) in a mortar to obtain a homogenous paste. Transfer the paste to a 50-ml volumetric flask using approx. 25 - 30 ml distilled water (approx. 50 °C), swirl frequently and heat the mixture until it starts to boil. Allow to cool down and make up to 50 ml by adding distilled water. Filter through a folded filter.

Take 5 ml of the filtrate and add 5 ml of buffer solution pH 9.00 and mix thoroughly (pH of the sample solution should be in the range 7.5 - 8.5).

block of cheese

Press the reflectometer START key and simultaneously dip the test strip into the sample solution (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 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® Magnesium Test.)


Magnesium content [mg/kg] = Measured value [mg/l] x 50

Results - comparison with complexometric titration:

Sample Reflectoquant® [mg/kg] Titration [mg/kg]  
1 400 400
1 550 500


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