Analytical Method for Determining the Solution Color of Raw Sugars, Brown Sugars and Colored Syrups at pH 7.0

Measuring solution color in sugar manufacturing is important for grading product concentration and quality. When refining sugar, each processing step removes color from the solution. This method for evaluating sugar quality uses a spectrophotometer to measure color at 420 nm.

Materials and Reagents Required

Water for analysis (Product No. 1.16754.9010) EMSURE^® or distilled water
Hydrochloric acid 0.1 mol/l Titripur^® (Product No. 1.09060.1000)
Sodium hydroxide solution 0.1 mol/l Titripur^® (Product No. 1.09141.1000)

Rectangular cells 10 mm (Product No. 1.14946.0001) or
Rectangular cells 20 mm (Product No. 1.14947.0001) or
Rectangular cells 50 mm (Product No. 1.14944.0001)

Spectroquant^® VIS Spectrophotometer Prove 100 (Product No. 1.73016.0001) or
Spectroquant^® UV/VIS Spectrophotometer Prove 300 (Product No. 1.73017.0001) or
Spectroquant^® UV/VIS Spectrophotometer Prove 600 (Product No. 1.73018.0001)

Membrane filters, cellulose nitrate, pore size 0.45 µm, diameter 50 mm
Conical flasks 250 mL
Volumetric flask 500 mL
pH meter
Ultrasonic bath
Refractometer

Method

Spectrophotometric Color Determination at 420 nm

Measuring Range

Method No. 2548
0 – 50 000 IU_7.0

Sample Preparation

1. Mix the sample thoroughly.
2. Weigh quantities of sample and water as shown in Table 1 below into a 250 mL conical flask.
3. Dissolve the sample by swirling at room temperature.
4. Adjust the pH of the prepared solution to 7.0 ± 0.1 with Hydrochloric acid 0.1 mol/L Titripur^® or, respectively, sodium hydroxide solution 0.1 mol/L Titripur^® as required.
5. Vacuum-filter the pretreated solution over a membrane filter into a clean and dry conical flask.
6. Filter the sample solution under vacuum through a membrane filter into a dry conical flask.
7. Degas the solution for 3 minutes in the ultrasonic bath.
8. Measure the % RDS (refractometric dry substance) of the solution to an accuracy of ± 0.1 g/100g (according to ICUMSA Method GS4/3-13).

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 %RDS value.

For zero adjustment fill a corresponding rectangular cell with distilled water or water for analysis. After prompting, place the rectangular cell filled with water 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

1. Select the method (2548, "ICUMSA Color GS1/3-7") from the method list of the Spectroquant^® Prove.
2. Enter the RDS value in %. Confirm with OK.
3. Press START to start the measurement mode.
4. Perform a zero adjustment (procedure see “Zero adjustment”).
5. Transfer the sample solution into a corresponding cell. Place the cell into the cell compartment. The measurement is performed automatically.
6. Confirm measurement with OK. The IU_7.0 value is shown in the display.
7. Press START to start the measurement procedure for the next sample. The system does not prompt a repeat of the zero adjustment.

Note:
The result is calculated according to ICUMSA GS1/3-7(2011) chapter 8.1 and ICUMSA SPS-4 table B (Sucrose; 20°C).
Individual ICUMSA methods or references are available online within 48 h: www.icumsa.org under “Methods book”.