6.4.8 Calculating the Concentration of Glucose in Urine

Steps to Calculate Glucose Concentration in Urine:

1. Prepare a series of glucose standards:

• Create a set of solutions with known glucose concentrations (e.g., 0.1, 0.2, 0.3 mol dm⁻³).

2. Add Benedict's reagent to each solution:

• Mix equal volumes of Benedict's reagent and glucose solutions.

3. Heat the solutions:

• Heat the mixtures in a water bath at 95°C for 5 minutes.
• A coloured precipitate forms depending on the glucose concentration (e.g., blue for none, green/yellow for low, brick red for high).

4. Use a colorimeter to measure absorbance:

• Filter the solutions to remove the precipitate.
• Place each solution into a cuvette and use a colorimeter to measure light absorbance.

5. Plot a calibration curve:

• Plot a graph of absorbance (y-axis) against glucose concentration (x-axis).

6. Test the urine sample:

• Repeat steps 2-4 for the urine sample.
• Use the calibration curve to determine the glucose concentration by matching the absorbance of the urine sample to a point on the graph.

Key Notes:

• The presence of glucose in urine indicates that blood glucose levels have exceeded the renal threshold, which could be a sign of diabetes.
• Use the same conditions (e.g., temperature, volume, equipment) for all solutions to ensure accuracy.