Analytical Method: Determination of Sugar Solution Color at pH 7.0 by the MOPS Buffer Method (According to ICUMSA Method GS9/1/2/3-8)

Materials and Reagents:
Cat.No. 1.16754.9010  Water for analysis EMSURE® or distilled water
Cat.No. 475898-100     MOPS, free acid, ULTROL® Grade, Calbiochem®
Cat.No. 1.09137.1000  Sodium hydroxide solution 1 mol/l Titripur®

Cat.No. 1.14946.0001  Rectangular cells 10 mm or
Cat.No. 1.14947.0001  Rectangular cells 20 mm or
Cat.No. 1.14944.0001  Rectangular cells 50 mm

Cat.No. 1.73016.0001 Spectroquant® VIS Spectrophotometer Prove 100 or
Cat.No. 1.73017.0001 Spectroquant® UV/VIS Spectrophotometer Prove 300 or
Cat.No. 1.73018.0001 Spectroquant® UV/VIS Spectrophotometer Prove 600

Membrane filters Millex-HA, pore size 0.45 µm, diameter 25 mm, Luer-Lok inlet
Membrane pre-filter unit, pore size 0.80 µm, diameter 25 mm, Luer-Lok inlet
Plastic syringes 10 – 50 ml, Luer-Lok outlet
Volumetric flasks 100 ml and 1000 ml
Beaker 100 ml
pH meter
Ultrasonic bath

Spectrophotometric Color Determination at 420 nm

Measuring range:
Method No. 2551
0 – 20 000 IU7.0

Working instructions:

MOPS buffer solution
Dissolve 41.8 g of MOPS in 800 ml water (Water for analysis EMSURE® is recommended), adjust the solution pH to 7.00 ± 0.01 by adding Sodium hydroxide solution Titripur® 1 mol/l. Transfer the solution to a 1000 ml volumetric flask and make up to the mark with distilled water.

Reference solution
Transfer 10.0 ml MOPS buffer solution to a 100 ml volumetric flask and make up to the mark with distilled water (Water for analysis EMSURE® is recommended).

Sample preparation
Mix the sample thoroughly.
Weigh the quantity of sample as shown in “Table 1” and make a note of the sample weight.
Transfer the sample with distilled water or water for analysis into a 100-ml volumetric flask.
Dissolve the sample by swirling at room temperature. Add 10.0 ml of MOPS buffer and make up the contents of the volumetric flask to the mark with distilled water or water for analysis and mix.

Fill the syringe with 10 – 20 ml of the sample solution. Connect a pre-filter unit to the syringe and connect the Millex-HA filter unit to the pre-filter unit.
Filter the sample solution into a clean and dry beaker.
Degas the solution for 3 minutes in the ultrasonic bath.

Table 1
Aliquots of sample and recommended cell length   


Cell length ICUMSA Color Sample
[mm] Range [IU7.0] [g]
  0 - 1000 20.0 + 0.1
50 200 - 2000 10.0 + 0.1
  400 - 4000 5.0 + 0.1
  250 - 2500 20.0 + 0.1
20 500 - 5000 10.0 + 0.1
  1000 - 10000 5.0 + 0.1
  500 - 5000 20.0 + 0.1
10 1000 - 10000 10.0 + 0.1
  2000 - 20000 5.0 + 0.1


Zero adjustment
For each measurement series, a zero adjustment is required.
It is recommended to use the same cell for zero adjustment and for sample measurement.
The zeroing procedure for the measurement series is automatically prompted by the instrument after entering the sample weight.
For zero adjustment fill a corresponding rectangular cell with reference solution.
After prompting, place the rectangular cell filled with reference solution in the cell compartment, the zero adjustment is executed automatically.
Confirm the implementation of zero adjustment with OK.
The zero adjustment is valid for the entire measurement series.

Measurement procedure
Select the method (2551, "ICUMSA Color GS9/1/2/3-8") from the method list of the Spectroquant® Prove. 
Enter the sample weight in g. Confirm with OK.
Press START to start the measurement mode.
Perform a zero adjustment (procedure see “Zero adjustment”) with reference solution.
Transfer the sample solution into a corresponding cell. Place the cell into the cell compartment. The measurement is performed automatically.
Confirm measurement with OK. The IU7.0 value is shown in the display.

Press START to start the measurement procedure for the next sample. The system does not prompt a repeat of the zero adjustment.



According to ICUMSA Method GS9/1/2/3-8 the method checks automatically if the measured absorption is below 2.500 A. If the absorption is not in this range, a pop-up message appears: “Condition not met – Absorbance > 2.5”.
In these cases, the sample preparation needs to be adjusted. Use an appropriate cell length, sample and water weight according to recommendations of Table 1.


The result is calculated according to ICUMSA GS9/1/2/3-8(2011) chapter 8.1.
Individual ICUMSA methods or references are available online within 48 h: under “Methods book”.


Short measuring procedures on Spectroquant® Prove instruments are described in the Analytical Procedures and Appendices, available online on our website



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